[R.O. 2017 § 405.510; Ord. No. 02-19, 10-15-2002; Ord. No. 10-13 §§ 1 — 3, 7-20-2010; Ord.
No. 24-04, 2-6-2024]
A.
Definitions And Policies.
1.
ALLEY
ARTERIAL STREET (PRIMARY)
ARTERIAL STREET (SECONDARY)
BENCHMARK
BLOCK
BRIDGE
CITY OF BATTLEFIELD STANDARD GENERAL CONDITIONS AND TECHNICAL
SPECIFICATIONS FOR PUBLIC IMPROVEMENTS
COLLECTOR STREET
CONSULTANT
CORNER
CROSSWALK
CUL-DE-SAC or DEAD-END STREET
CULVERT
CURB RETURN
DRIVEWAY
DRIVEWAY APPROACH
EASEMENT
EXPRESSWAY
FREEWAY
GUTTER
IMPROVED STREET
INTERSECTION
JOINT DRIVEWAY
LOCAL STREET
LOT
OWNER
PARKWAY
PRELIMINARY PLAT
PROPERTY DESCRIPTION
PROPERTY LINE
PUBLIC IMPROVEMENTS
REFERENCE POINTS
RIGHT-OF-WAY
RIGHT-OF-WAY LINE or STREET RIGHT-OF-WAY LINE
ROADWAY
SERVICE ROAD
SHALL, MAY
SIDEWALK
SIGHT DISTANCE TRIANGLE
STORMWATER DETENTION FACILITY
STREETS
SUBDIVISION
SUBGRADE
SURVEYING
TENDERING
UNIMPROVED STREET
VEHICLE
Definition Of Terms, Phrases, And Words. The definitions of this Subsection apply specifically to Section 405.510 (design standards for public improvements). These definitions shall take priority in Section 405.510 over differing definitions in other Sections of Title IV, Land Use (Ch. 400, Zoning Code, Ch. 405, Subdivision Regulations, or Ch. 410, Floodplain Management).
A minor way which is used primarily for vehicular service
access to the back or the side of properties otherwise abutting a
street.
A street or highway primarily intended to provide for high
volume, moderate speed, and extended trip length traffic movement
between major activity centers, with access to abutting property subordinate
to major traffic movement.
A street which interconnects with and augments the major
arterial system. The secondary arterial is primarily intended to provide
for moderate volume, moderate speed, and short to moderate trip length
while providing partially controlled access to abutting property.
A permanent object of known elevation and location that is
in an area where disturbance is unlikely.
A piece or parcel of land entirely surrounded by public highways,
streets, streams, railroad rights-of-way, parks, or a combination
thereof.
A structure having a clear span greater than twenty (20)
feet or a multiple span structure where the total length of the span
is in excess of twenty (20) feet.
The official General Conditions and Technical Specifications
used on public City improvements within the City of Battlefield, Missouri.
This document contains data for public improvements from the advertising
stage of a project through the actual construction and acceptance
of the project.
A street which collects and distributes traffic to and from
local and arterial street systems. The collector is primarily intended
to provide for low to moderate volume, low speed, and short length
trips while providing access to abutting property.
An individual, firm, association, partnership, corporation,
or other legal entity registered in the State of Missouri and engaged
in the practice of engineering or architecture.
A point of intersection of lines of two (2) street curb faces
extended into street intersection.
A right-of-way, dedicated to or set aside for public use,
which cuts across a block or street to facilitate pedestrian access
to adjacent streets and properties.
A minor street with only one (1) one outlet.
A structure not classified as a bridge, which provides a
conduit for drainage.
The portion of curb at the beginning of a driveway approach,
which serves as a transition from the height of the curb to the level
of the approach.
An area intended for the operation of automobiles and other
vehicles from the street right-of-way line to a garage, parking area,
building entrance, structure, or approved use located on the property.
Any dimensions relating to the width of a driveway or driveway surface
shall be measured at the right-of-way line.
An area intended for the operation of automobiles and other
vehicles giving access between a roadway and abutting property. The
driveway approach includes the sum of the curb returns on each side
of the driving surface, plus the driving surface.
A grant by the property owner to the public, a corporation,
or persons of the use of land for specific purposes.
A street or highway with limited and partially controlled
points of access at arterial system intersections. The expressway
is primarily intended to provide for high-volume, moderate to high-speed
extended intra-City traffic between major activity centers with minimal
impairment to movement.
A divided highway with fully controlled access limited to
grade-separated interchanges constructed at major thoroughfares. A
freeway is primarily intended to provide for high-volume, high-speed
inter-City traffic movements.
That portion of the driving surface of an improved street,
driveway, approach, or other public way, which abuts the curb and
provides for the runoff of surface drainage.
A public street having concrete curbs, or curb and gutters,
or other such equivalent physical features, which serve to establish
a permanent street grade.
The general area where two (2) or more roadways meet, join,
or cross at a common point establishing an area within which vehicles
traveling different roadways may come in conflict.
A driveway which provides access to a public street for more
than one (1) parcel of land.
A street primarily providing direct access to abutting property
and designed to accommodate low-volume, low-speed traffic.
An undivided tract or parcel of land under one (1) ownership
having access to a street, whether occupied or to be occupied by a
building or building group together with accessory buildings, which
parcel of land is designated as a separate and distinct tract and
is identified by a tract or lot number or symbol in a duly approved
subdivision plat filed of record.
The City of Battlefield, Missouri, its agents, employees,
and representatives, with whom contractor has entered into the agreement
and for whom the work is to be performed.
That portion of the street right-of-way between the edges
of the roadway and the adjacent property line, or lines, on the same
side of the street except any portion used for sidewalks.
The preliminary map, drawing, or chart indicating the proposed
layout of the subdivision initially required in the subdivision process.
Description of a lot, tract, or parcel by metes and bounds,
by reference to a plat or by reference to government survey.
The boundary between two (2) or more parcels of land.
Those things that are constructed, installed, or performed
on public land, or on land that is to become public in the subdivision
process, including, but not limited to, street and alley pavement,
curbs, storm drainage facilities, sidewalks, and sanitary sewers,
and including the grading of such land.
Points of reference located by a survey of the project. The
points are to be tied or referenced to at least three (3) identifiable
features.
A general term denoting public ownership or interest in land,
usually in a strip, which has been acquired for or devoted to the
use of a street or alley.
The boundary between any public street or alley and one (1)
or more parcels of private property.
That area of a street intended and used for vehicular travel.
A minor street which is parallel and adjacent to an arterial
street, and which provides access to abutting properties and protection
from through traffic.
The word "shall" shall be deemed as mandatory. The word "may"
shall be deemed as permissive.
That paved portion of a parkway intended for the use of pedestrians.
A triangular-shaped area of street right-of-way, generally
acquired at major intersections to ensure adequate sight distance.
A drainage facility designed and constructed for the purpose
of detaining stormwater runoff to reduce downstream flows and/or reduce
stormwater pollutant levels.
"Street" is a way for vehicular traffic, whether designated
as a street, highway, thoroughfare, parkway, throughway, road, avenue,
boulevard, lane, place, or however otherwise designated.
The division of land into two (2) or more lots, tracts, or
parcels for the purpose of transfer of ownership or building development,
or, if a new street or easement of access is involved, any division
of a parcel of land. The term includes resubdivision and, when appropriate
to the context, shall relate to the process of subdividing or to the
land subdivided.
The surface of a street on which a base course or riding
surface is to be placed.
The act of determining the positions of points on the earth's
surface by means of measurement of distance, direction, and elevation.
The legal transfer of ownership and maintenance responsibility
of a public improvement to the City of Battlefield.
A street not having concrete curbs, or curbs and gutters,
or other such equivalent physical features which serve to establish
a permanent street grade.
Every device in, upon, or by which any person or property
is, or may be transported, or drawn upon a street, except devices
used exclusively upon stationary rails or tracks.
2.
Policies.
a.
Minimum Standards For Design. The City Administrator or designee
must approve all plans for public improvements within the City of
Battlefield. This approval is a conceptual approval only and does
not give detail approval to any particular design item or data shown
on the plans, nor does it give approval for any deviation from City
specifications unless that deviation is shown on the plans by a general
note. The engineer who sealed the plans is responsible for all lines
and grades, field data, constructability of the design, and all other
items affecting the project, including compliance with the City specifications.
b.
Variance From Minimum Standards.
(1)
All design requirements will be strictly adhered
to unless written justification for a design variance, sealed by a
professional engineer is presented and approved. This justification
should be submitted along with the preliminary plat and variance applications
which will be reviewed by the Planning and Zoning Commission and Board
of Aldermen.
(2)
Should a request for a design variance occur after
preliminary plat approval, the sealed justification for a design variance,
variance application and any required amendment to the preliminary
plat must be resubmitted to the Planning and Zoning Commission and
Board of Aldermen for approval. Substantial changes would require
a new preliminary plat.
c.
Acceptance Of Public Improvements. No streets, alleys, sanitary
sewers, storm sewers, or other public improvements will be accepted
or approved by either the Board of Aldermen, the City Administrator,
or designee unless the improvements were constructed in accordance
with plans, special provisions, and technical specifications on record
with the City.
d.
Utility Location Policies.
(1)
General.
(a)
The following criteria has been established for
the uniform treatment of the location or relocation of utility facilities
within the right-of-way of the public street system in order to preserve
the traffic-carrying capacity of the street and to minimize interference
with normal maintenance operations. These requirements apply to all
public and private utilities, including power transmission, telephone,
cable television, telegraph, water, gas, oil petroleum products, pipelines,
and any other utility facilities (excluding sanitary sewers). The
requirements apply to underground, surface, or overhead facilities
located within or crossing street rights-of-way. Exceptions to the
requirements set forth will be considered when major utility extensions
are proposed or when improvements by their size necessitate special
consideration. All utilities installing any facilities in a public
right-of-way must meet the requirements of the City and shall receive
advance approval from the City Administrator or designee prior to
commencing construction on a public right-of-way. In order to receive
approval, an engineering drawing detailing the installation shall
be required. This engineering drawing shall depict adequate data to
determine location and impact on other facilities located in the public
right-of-way.
(b)
In the case of reconstruction or rehabilitation
where location of existing utilities will not be relocated and where
breaks or normal maintenance is needed, the requirement for an engineering
drawing shall be waived.
(2)
New Subdivisions - Residential. Parallel installations
of overhead facilities within the street right-of-way are to be located
within one (1) foot of the right-of-way line when proposed for construction
on the same side of the street that sidewalks are constructed. Streetlights
and poles used to support transverse crossings of the right-of-way
shall not be located closer than two (2) feet of the curb or edge
of roadway or paved shoulder. Poles, guys, anchors, braces, and other
appurtenances for overhead facilities shall not encroach into sidewalk
or streets. Parallel installation of overhead facilities and underground
facilities, including meters, valves, and other appurtenances, within
the street right-of-way, are to be located within a seven-foot area
adjacent to the right-of-way line where no sidewalks exist. In no
case will the City allow the facility to be constructed within the
street pavement area except for valves necessary for tapping existing
facilities, nor will it be allowed to conflict with the street drainage.
Careful consideration must be given to the location of valves, meter
boxes, and other appurtenances, so that interference with the sidewalk
and street curb is held to a minimum. Minimum cover for all underground
facilities shall be twenty-four (24) inches.
(3)
New Subdivisions - Non-residential. Parallel overhead
and underground facilities are to be located within seven (7) feet
of the right-of-way line. Streetlights and poles used to support transverse
crossings of the right-of-way shall not be located closer than two
(2) feet of the curb or edge of roadway or paved shoulder. Poles,
guys, anchors, braces, and other appurtenances for overhead facilities
shall not encroach into sidewalks or streets. Parallel installation
of the underground facilities, including meters, valves, and other
appurtenances, within the street right-of-way, are to be located within
seven (7) feet of the right-of-way line. In no case will the City
allow the facility to be constructed within the street pavement area
except for valves necessary for tapping existing facilities, nor will
it be allowed to conflict with the street drainage. Careful consideration
must be given to the location of valves, meter boxes, and other appurtenances,
so that interference with the sidewalk and curb is held to a minimum.
The minimum cover shall be twenty-four (24) inches or conforming to
Federal, State, or local agency requirements, whichever is greater.
(4)
Existing Subdivisions - Residential And Non-Residential. Plans developed for new underground or overhead facilities must be designed to take into account existing utilities, as well as possible future utilities. Where possible, corridors outlined in Subsection (A)(2)(d)(2) and (3) are to be adhered to. Due to existing facilities, this may be impractical. Design based upon remaining corridor is encouraged, but it is understood local, State, and Federal codes may make this impossible. Since existing conditions must be taken into account, deviation from the corridor requirements in Subsection (A)(2)(d)(2) and (3). will be accepted in existing subdivisions.
e.
Permits.
(1)
City-Maintained Streets. All utility work and property
improvements to be performed within the City right-of-way limits will
require an excavation permit from the City Administrator or designee
prior to the work being done by the contractor. In emergency situations
where necessary repairs to an existing utility facility must be made
immediately in order to protect the public health, safety, and welfare,
a permit must be obtained as soon as possible once emergency repairs
commences.
(2)
State-Maintained Streets And Highways. All utility
work to be performed on State-maintained facilities will require a
permit from the Missouri Highway and Transportation Commission. All
requirements of the State must be met.
(3)
Open Cutting Or Boring Of City Streets.
(a)
As a general policy, no open cutting of the pavement
will be permitted on the City's streets except special permission
to open cut a street may be given when the street has not yet been
constructed to the ultimate design or major maintenance or rehabilitation
of the street surface is programmed within three (3) years of the
open cut. Boring or other tunneling methods will be allowed on all
City-maintained streets. In cases where a break, leak, or malfunction
occurs in an existing facility, or when spot lowerings or connections
are made in rehabilitation, open cutting will be allowed as necessary
to repair or rehabilitate the facility.
(b)
As additional streets are constructed or improved
to ultimate standards, open cutting will not be permitted on these
facilities except where maintenance or repairs occur.
(4)
Backfilling And Repair Of Utility Cuts. When open
cutting of an existing or proposed street is approved, aggregate backfill
conforming to City standards must be placed for the full trench depth
and compacted in six-inch layers across the street to within two (2)
feet of the outside of the street curbs, as well as under all sidewalks,
driveways, and other structures or pavements. Any damage to existing
curbs, sidewalks, and other public improvements shall be repaired
and/or replaced by the utility forces or contractor at their expense.
Details for backfill and pavement repair for concrete pavement and
asphalt pavement can be found in Figure ST-13 and Figure ST-13A.[1]
[1]
Editor's Note: These figures are included as an attachment to this chapter.
(5)
Utilities Constructed Through Sanitary Or Storm
Sewer Structures. Any utility found in a sanitary or storm sewer structure
during the course of that structure's rehabilitation or reconstruction
shall be relocated outside of the structure. Further, any new utility
will be prohibited from passing through any storm sewer structure
regardless of the age of the structure, and regardless of the fact
that there are existing utilities in the structure. Relocation expenses
will be incurred by the utility in the sewer structure.
(6)
Reimbursement To Public Utilities.
(a)
On Public Works' projects constructed either
by contract or by City maintenance forces where conflicts occur with
existing utilities, the utility company shall be required to relocate
their existing utilities in accordance with the policies set forth
in these Design Standards. Where the utility is privately owned, all
costs related to the relocation will be borne by the utility.
(b)
Both the designer and the utility must make a good
faith effort and agree on the approximate location of the utility.
Disclaimer clauses will not be accepted as good faith effort. Charges
for reimbursement must include credits for all salvageable materials
and must not include costs for betterment.
B.
Plan Preparation.
1.
Drawing Standards.
a.
General. Drawings for all submissions shall be submitted electronically.
Final approved drawings will be stamped and filed electronically and
will be available for download after all requirements have been met
and fees are paid. After filing, the original drawings shall become
the property of the City of Battlefield. Drawings to comply with latest
electronic document submittal standards.
(1)
Utilities. All utilities must be coordinated as
necessary by the applicant.
(2)
State Highways. Projects involving State highways
will require the approval of the Missouri Highway and Transportation
Department.
(3)
File Type Standards.
(a)
Only searchable PDF files are accepted for calculations,
reports and other supporting documentation (non-drawing files).
(b)
Both vector PDF and Design Web Format (DWF) files
will be accepted for drawing files. Since AutoCAD software is commonly
used to create drawing files, converting a DWG to DWF file print ready
is the preferred secured file format. Files must be 2D DWF file print
ready, i.e., setup properly for printing with title block, no extra
data outside the print page area, etc. The DWF must be saved as AutoCAD
Version 10 or lower format.
(c)
If you choose to create PDF files, you will need
to convert your AutoCAD files to a vector PDF by using Auto Desk Vector
Graphic Converter "DWG to PDF.pc3 Plotter Driver."
(4)
Electronic Stamps And Signature.
(a)
All files must be electronically stamped with signature
per Missouri Statues and Missouri Administrative Code. There are specific
provisions for electronic signatures within the Rules and Regulations.
Architects and engineers are responsible for compliance with these
rules.
(b)
Electronic stamps and signatures must be inserted
images on DWG files.
(c)
Confer with the City Administrator or designee
for electronic document submittal standards.
b.
Drawing Scale. Engineering plan and profiles shall be prepared
on a scale of 1" = 40' horizontal and 1" = 4' vertical.
When requirements for detail necessitates a larger scale, a horizontal
scale of 1" = 20' and 1" = 4' vertical may be used. Drainage
area maps, construction details, cross sections, and contour maps
shall be drawn to a scale suitable to show complete detail.
c.
Elevation Datum. Elevations shown on plans shall be in the North
American Vertical Datum of 1988. At least one (1) National Geodetic
Survey (NGS) or City of Battlefield benchmark shall be used to establish
the project datum. At least one (1) project benchmark shall be established
on-site or near the site. The project benchmark will be semi-permanent
in nature and not easily disturbed. The NGS or City of Battlefield
benchmark used, and the project benchmark established, shall be noted
on the first plan sheet of each project, and their location and elevation
shall be clearly defined.
d.
Stationing And North Arrow.
e.
Topography.
(1)
When more than one (1) drawing sheet is required
for a project, an overlap of not less than one hundred (100) feet
shall be provided.
(2)
Each project shall show at least one hundred (100)
feet of topography on each side. Subdivision plans shall show at least
one hundred (100) feet of topography outside the plat limits. All
existing topography and any proposed changes, including utilities,
telephone installations, etc., shall be shown on both the plan and
profile portion of the drawing.
f.
Revisions To Drawings. Revisions to filed drawings shall be
clearly noted and shown within a revision cloud on the plan and noted
within a revision block showing the nature of the revision and the
date made.
g.
Symbols. Typical symbols shall be used in the preparation of
engineering drawings. Topography for which symbols have not been standardized
shall be indicated and named on the plan and profile sheet. In utilizing
the standard symbols for engineering plans, all existing utilities,
telephone installations, sanitary and storm sewers, pavements, curbs,
inlets, and culverts, etc., shall be shown with a broken line; proposed
facilities with a solid line; land, lot, and property lines to be
shown with a slightly lighter solid line. All easements must be shown,
as well as the book and page number, if recorded.
h.
Minimum Requirements. It shall be understood that the requirements
outlined in these standards are minimum requirements and shall be
applied when conditions, design criteria, and materials conform to
the City specifications. When unusual subsoil or drainage conditions
are encountered, an investigation should be made, and a special design
prepared in conformance with good engineering practices.
i.
Owner's Name. The title sheet must indicate the owner's
name and address for whom the improvements are to be constructed.
j.
Dimensions. Lot lines, dimensions, and subdivision name shall
be shown where applicable.
k.
Cover Sheet. All plans shall have a cover sheet showing the
general location of the project in relation to the Battlefield City
Street system. The cover sheet shall show the complete project area
to a scale of 1" = 100' or an appropriate scale for small projects.
l.
Box Culvert Design. When standard box culvert designs are referenced,
the engineer shall show and label in the drawings the size, spacing,
and shape of the reinforcing and the dimensions of the structure.
Box culverts should be designed for HS-20 loading at a minimum.
2.
Preconstruction Requirements.
a.
Fees. After plans have been approved and filed by the City,
it is the developer's responsibility to pay all necessary fees
prior to construction.
b.
Copy Of Contract. A detailed copy of the construction bid, showing
unit costs for all items included in the contract, and showing the
total contract value, must accompany the fee.
c.
Start Of Construction. No construction of public facilities
shall be permitted prior to approval and filing of the plans and/or
paying of fees. In addition, twenty-four-hour notification must be
given to the City prior to the commencement of any work on public
facilities. No street construction will be permitted prior to completion
of construction of all private and/or public utilities within the
street right-of-way.
d.
Easements. All easements required for construction, which are
not included on the plan, shall be recorded and filed with the City
prior to filing of original plan sheets.
C.
Survey Requirements.
1.
Horizontal Control. Establish accurate horizontal control on
the proposed work site. Physical monuments such as large nails, iron
pins, or other durable materials must be set, and accurate horizontal
positions established on them. A positional tolerance error between
any two (2) points in the control network will not exceed five hundredths
(0.05) feet. A positional tolerance error between adjacent pairs of
control monuments will not exceed two hundredths (0.02) feet.
2.
Vertical Control. Establish accurate vertical control on the
proposed work site. The North American Vertical Datum of 1988 will
be used, propagated from NGS or City of Battlefield benchmarks. The
benchmark used to establish vertical control will be listed on the
plans. Elevations will be established on the same monuments used for
horizontal control as well as two (2) temporary benchmarks located
in areas where they will not be disturbed by construction. A vertical
tolerance error between adjacent pairs of control monuments will not
exceed one hundredths (0.01) feet. Overall, the error shall not exceed
five hundredths (0.05) feet in five thousand (5,000) feet. Some form
of differential leveling with a spirit level will be used; trigonometric
leveling or GPS derived elevations are not acceptable for establishing
elevations on control monuments.
3.
Topography. Topography shall include all surface features within
the limits of the project such as buildings, curbs, trees, water valves,
walls, etc. This may also include painted markings for subsurface
utilities as well as utilities that are exposed by excavation for
more accurate locations. Sizes of pipes, culverts, and conduits shall
be noted. Elevations and horizontal positions of critical topographic
features such as flow lines of box culverts, flow lines of sewer manholes,
curbs and other hard surfaces must be accurate to within five hundredths
(0.05) feet or better.
4.
Contours. The vertical accuracy of contours shown on plans will
be +/- five tenths (0.50) feet for contour intervals of one (1) foot
or more. The vertical accuracy of contours of less than one-foot intervals
will be +/- one-half (1/2) the contour interval.
5.
Boundary And Right-of-Way. All work relating to property corners,
boundary lines, right-of-way lines, and calculated property lines
will be done under the direct supervision of a professional land surveyor
licensed in the State of Missouri. The land surveyor will use the
current City of Battlefield Subdivision Regulations for any boundary
survey work related to design surveys.
D.
Earthworks.
1.
Embankment Construction. All embankments required for construction
of public streets and alleys must be compacted. The method of compaction
and densities are as required in the latest revision of the City of
Springfield, Missouri, Standard General Conditions and Technical Specifications
for Public Works Construction. All embankment construction shall have
a minimum 4:1 (H:V) forward and back slopes. All trees, shrubs, and
plants designated to remain within the public right-of-way shall be
shown and clearly noted on the plans. The plans shall require that
the public right-of-way be left in a finished and neat appearing condition.
2.
Subgrade Compaction. The plans shall require that the street
subgrade for both public and private improvements be compacted as
required in the latest revision of the City of Springfield, Missouri,
Standard General Conditions and Technical Specifications. All street
subgrades shall have at least four (4) inches of compacted aggregate
(meeting Type 1, Type 5 or Type 7 aggregate base requirements) base.
Aggregate should extend one (1) foot zero (0) inches outside the limits
of the curb and gutter.
E.
Sanitary Sewers.
1.
General.
a.
Materials. All materials used in the construction of sanitary
sewers shall conform to the latest revision of the City of Springfield,
Missouri, Standard General Conditions and Technical Specifications
for Public Improvements unless specifically designated otherwise by
special provision drawings and prior approval is obtained.
b.
Discrepancies. Where discrepancies between standard details,
drawings and/or special provisions occur, the special provisions shall
govern.
c.
Structures. Whenever possible, structures shall be constructed
as shown in the standard details. Structures other than those shown
in the standard details shall be considered to be special structures
and must be designed and detailed by the design engineer.
d.
Construction On Fill. Where a sewer must be constructed on fill,
a profile of the original undisturbed ground line along sewer centerline
shall be shown. All sewers to be constructed on fill must have a special
design approved by the City of Battlefield Administrator or his/her
designate.
2.
Sanitary Sewer Design.
a.
Design Period. Sanitary sewer systems must be designed for the
estimated ultimate tributary population. Consideration should be given
to the maximum anticipated capacity of institutions and industries.
c.
Design Basis.
(1)
Per Capita Flow.
(a)
Sewer systems shall be designed based on the maximum
hourly flow tributary to the proposed improvement determined using
an average daily flow of one hundred (100) gallons per capita plus
wastewater flow from industrial, major institutional, and commercial
facilities, multiplied by a peaking factor derived from the following
formula:
|
Peaking Factor (PF) =
 Where P = population expressed in thousands
|
(b)
Wastewater flow from industrial, major institutional,
and commercial facilities can be converted to population equivalent
by dividing the flow by one hundred (100) gallons per capita per day.
The one hundred (100) gallons per capita figure is assumed to cover
normal infiltration, but an additional allowance should be made where
ground conditions are known to be unfavorable.
(2)
Alternative Method. When deviations from the foregoing
per capita rates are warranted, a brief description of the proposed
procedure to be used for the sewer design shall be included. It is
recommended that 2,500 to 3,000 GPD per acre for single-family gross
area exclusive of sewage or other waste from industrial plants.
d.
Design Details.
(1)
Minimum Size. No public sewer shall be less than
eight (8) inches in diameter.
(2)
Location. Sewers shall be placed in street rights-of-way
where feasible. Plans shall show the stationing of all in-line tees.
(3)
Depth. Sewers shall be designed deep enough to
prevent freezing, and to allow house connections to cross under water
mains at such an elevation that the bottom of the water main is at
least eighteen (18) inches above the top of the sewer line. If the
proposed sewer is parallel to a water main, it shall be designed to
provide a minimum eighteen-inch vertical clearance or a minimum ten-foot
horizontal clearance from the water main. Unless approved by the City
Administrator, no sewer shall be designed and/or constructed that
will not provide a minimum depth of four (4) feet to top of pipe.
All standard PVC sewer mains up to twelve (12) feet deep shall be
SDR 21, Class two hundred (200) pipe. All sewers over twelve (12)
feet deep shall have a minimum of twelve (12) inches of aggregate
bedding material over the top of the pipe. The engineer shall perform
calculations to select pipe type and material for sewers exceeding
twenty (20) feet in depth.
(4)
Slope. All sewers shall be designed and constructed
to give mean velocities, when flowing full, of not less than two (2.0)
feet per second, based on the Manning formula using an "n" value of
0.013.
(5)
Slope Calculations And Detailing.
(a)
The slope on all sewer lines shall be calculated
from inside wall of manhole to inside wall of manhole.
(b)
The following are the minimum slopes, which should
be provided; however, slopes steeper than these are desirable.
|
Sewer Size
(inches)
|
Minimum Slope in Feet
per 100 Feet
|
|---|---|
|
8
|
0.50
|
|
10
|
0.35
|
|
12
|
0.30
|
|
14
|
0.17
|
|
15
|
0.15
|
|
16
|
0.14
|
|
18
|
0.12
|
|
21
|
0.10
|
|
24
|
0.08
|
(c)
Designers are not allowed to increase the size
of sewer pipes only to take advantage of flatter slopes.
(d)
Sewers shall be laid with uniform slope between
manholes. The maximum slope for all main line sewer pipes shall be
thirty-five percent (35%). The minimum slope for all laterals shall
be one-eighths (1/8) inch per foot, unless otherwise approved.
(6)
Loading. All sewers shall be designed to prevent
damage from superimposed loads. Proper allowance for loads on the
sewer shall be made because of the width and depth of trench. Details
for backfilling gravity and forced sanitary mains are shown in Figures
SAN-28 and SAN-29.
(7)
Grade Through Manholes. A drop of two tenths (0.2)
feet shall be shown through manholes. A drop of five tenths (0.5)
feet minimum shall be shown through manholes where a Z-lok is required
[pipe slope greater than ten percent (10%)]. The flow line of new
sewer lines coming into a main sewer manhole should be at least one-half
(1/2) the diameter of the trunk sewer above the flow line of the trunk
sewer.
(8)
Increasing Size. When a smaller sewer joins a larger
one (1), the invert of the larger sewer should be lowered sufficiently
to maintain the same energy gradient.
(9)
Alignment.
i.
Sewers in streets should be placed in or near the
center of the driving lane where possible. Sewers located at back
property lines should be about three (3) feet to one (1) side of the
property line and on the opposite side from pole lines or other utilities.
The ends of sewer lines should extend at least fifteen (15) feet beyond
the property line of the last lot served, to provide room for the
house connection with a tee below the manhole. Cutting corners and
running diagonally across streets is not allowed.
ii.
A minimum permanent easement according to the table
below is required.
|
Size of Pipe (Diameter)
(inches)
|
Depth to Flowline
(feet)
|
Overall Width of Permanent Easement (pipe in center of easement)
(feet)
|
|---|---|---|
|
8 to 24
|
0 to 12.0
|
15
|
|
12.1 to 20.0
|
20
| |
|
> 20.0
|
ES approval req.
| |
|
Greater than 24
|
Any depth
|
ES approval req.
|
iii.
A temporary construction easement shall be provided,
as necessary. All crossing and/or cutting of streets must be backfilled
with granular material. All sewers with a trench wall within two (2)
feet of the back of the street curb shall be backfilled with granular
material.
(10)
Non-Typical Connections. Connections for recreational
vehicles (RVs) and/or food trucks shall be a typical four-inch diameter
cleanout placed within six (6) inches to twelve (12) inches above
grade with removable cap. Approximately twelve (12) inches under the
removable cap shall be a cross bar to prevent RV or food truck sewer
hoses from falling into the public sewer line. A connection is required
at every RV or food truck stall.
e.
Relation To Water Mains Or Storm Sewers.
(1)
Horizontal Separation. Wherever possible, sewers
should be laid at least ten (10) feet, horizontally, from any existing
water main or storm sewer. Should local conditions prevent a lateral
separation of ten (10) feet, a sewer may be laid closer than ten (10)
feet to a water main or storm sewer if:
(a)
It is laid in a separate trench; or
(b)
It is laid in the same trench with the water mains
or storm sewer located at one (1) side on a bench of undisturbed earth;
and
(c)
In either case the elevation of the top (crown)
of the sewer is at least eighteen (18) inches below the bottom (invert)
of the water main or storm sewer.
(2)
Vertical Separation.
(a)
Whenever sanitary sewers must cross under water
mains or storm sewers, the sanitary sewer shall be laid at such an
elevation that the top of the sanitary sewer is at least eighteen
(18) inches below the bottom of the water main or storm sewer. When
the elevation of the sanitary sewer cannot be varied to meet the above
requirement, the water main or storm sewer shall be relocated to provide
this separation.
(b)
When it is not feasible to obtain proper vertical
separation as stipulated above, the sewer must be constructed of SDR
21, Class 200 pressure water line pipe and must be pressure tested
to water pipe standards at a pressure not less than one hundred fifty
(150) pounds per square inch to assure water tightness. The sewer
pipe may be required to be installed in a steel casing or by bridging
(SAN-33). A manhole must be located at each end of the pressure pipe;
and the near side of the manholes can be no closer than ten (10) feet
from the water main.
(c)
No water line shall pass through or come into contact
with any part of a sanitary sewer manhole.
f.
Manholes.
(1)
Location. Manholes shall be installed at all changes
in grade, size, or alignment, at all intersections, and at intervals
of not more than four hundred (400) feet for all sewers. Manholes
shall not be placed in existing or proposed sidewalks without prior
approval from the City Administrator or designee. Standard Four-Foot
Diameter is shown in Figure SAN-3 and New Manhole on Existing Sewer
Line is shown in Figure SAN-4.[2]
[2]
Editor's Note: These figures are included as an attachment to this chapter.
(2)
Drop Type. A drop pipe shall be provided for a
sewer entering a manhole at an elevation of twenty-four (24) inches
or more above the manhole invert. Where the difference in elevation
between the incoming sewer and the manhole invert is less than twenty-four
(24) inches, the invert shall be filleted to prevent solids deposition;
manholes, where the difference in elevation between the incoming sewer
and the manhole invert is greater than twenty-four (24) inches but
less than thirty-six (36) inches will not be allowed. See Figure SAN-6.[3] Special design is required for connection to manholes
with interior linings.
[3]
Editor's Note: This figure is included as an attachment to this chapter.
(3)
Diameter. The minimum diameter of manholes shall
be forty-eight (48) inches [four (4) feet] and shall conform to the
latest revision of the City of Battlefield Standard General Conditions
and Technical Specifications. All inside drop manholes shall have
a minimum diameter of sixty (60) inches [five (5) feet].
(4)
Manhole Covers. All sanitary sewer manhole covers
shall be Type "A," non-rocking. See Figure SAN-1[4] unless located within floodplain or prone to submersion.
If located within floodplain or prone to submersion, use water-tight,
hinged Pamrex, EJ twenty-four (24) inches ERGO No. EJ001040013L01,
or R-1743-LM (NF-1743915) lid and frame or approved equal. See Figure
SAN-2.[5]
[4]
Editor’s Note: This figure is included as an attachment to this chapter.
[5]
Editor's Note: This figure is included as an attachment to this chapter.
(5)
Stationing And Elevation. Stationing and elevations
should be shown at all M.H. locations and at the ends of casings.
g.
Lamp Holes. Lamp holes may be permitted upon the approval of
the City Administrator or designee. Lamp holes will be permitted only
in cases where the slope of the land will not permit a future extension
of the sewer beyond the proposed lamp hole. The maximum length to
the nearest manhole shall not be greater than one hundred fifty (150)
feet. Lamp holes will not be permitted within street surfaces. Tees
not to be located within five (5) feet of the lamp hole riser. Lamp
hole standard drawing is shown in Figure SAN-13.[6]
[6]
Editor's Note: This figure is included as an attachment to this chapter.
3.
Drawings And Documents To Be Submitted.
a.
Sewer Drawings. Sewer drawings shall be prepared on plans separate
from other utilities. District, section, and public improvements file
numbers shall be obtained from the City.
(1)
Plan. The plan shall be at the top of the drawing.
Standard symbols shall be used. A standard north arrow shall be located
on each sheet (pointing up or to the left).
(2)
Profile. The profile shall be shown under the plan.
(a)
Scale. Scale shall be 1" = 4' vertical, and
1" = 40' horizontal for undeveloped areas and 1" = 20' for
developed areas.
(b)
Grades. Established elevations of existing manholes
shall be obtained from field surveys. Existing ground and proposed
pavement over sewer shall be shown and labeled. Existing or proposed
building floor elevations or sufficient ground elevations one hundred
(100) feet either side of centerline shall be shown to determine required
depth and slope of service lines.
(3)
Utilities. Existing and proposed utilities shall
be accurately and clearly shown in the plan and profile. Elevations
of existing utilities shall be obtained where the possibility of conflict
exists.
(4)
Location And Design Information. A cover sheet shall be Sheet No. 1 of the drawings, indicating the entire area to be served by the proposed sewers and indicating the sheet number on which each segment of sewer line is drawn. The scale shall be 1" = 100'. When this cannot be done without attaching an extra drawing, then the scale will be 1" = 200'. Proposed district boundaries shall be shown with sufficient data that a written district boundary description may be described from it, and a written boundary shall be attached to the drawing. Also, all lots, blocks, and the location of proposed sewer lines shall be known. When the cover sheet will not show at least two (2) well-known streets or routes, a small location map shall be added to the cover sheet showing the location of the project. Benchmarks based on USGS datum shall be shown on the drawings as per the survey requirements included in Subsection (C) of these Design Standards. The City will review the plans to determine its compatibility with the entire drainage area. The developer or owner's name shall be shown on the cover sheet along with the subdivision name.
b.
Plan Review Checklist For Sanitary Sewers.
Note: The following checklist is presented for developer's
convenience and is not all encompassing of the City's Design
Standards.
|
General Information:
| ||||
|---|---|---|---|---|
|
Yes
|
No
|
N/A
| ||
 |
|
|
Copy of the replat, lot split, or Council-approved preliminary
plat conditions has been provided which includes public improvement
requirements.
| |
|
|
|
|
Plans sealed, signed, and dated by professional engineer.
| |
|
|
|
|
City logo on all sheets.
| |
|
|
|
|
Revisions noted.
| |
|
|
|
|
Mains sized for drainage basin.
| |
|
|
|
|
Off-site sewer easements provided (list book and page on plans).
| |
|
|
|
|
Minimum finished floor elevations shown on the cover sheet and
plan sheet and are based on:
| |
|
1.
|
Minimal lateral connection flow line elevation at main spring-line
[four (4) inches above line of an eight (8) inch main].
| |||
|
2.
|
Minimum lateral slope of one-eighth (1/8) inch per foot.
| |||
|
3.
|
Maintain eighteen (18) inches of cover over top of lateral.
| |||
|
4.
|
Serve the entire lot based on existing and/or proposed contours.
| |||
|
|
|
|
Note: All minimum finished floor elevations must be shown on
the final plat.
| |
|
|
|
|
Obtained State approval (if in State ROW).
| |
|
|
|
|
Obtained appropriate permit to build within a floodplain. If
manholes are located in floodplain, specify waterproof lids.
| |
|
|
|
|
Submitted a sinkhole report and received a sinkhole permit in
accordance with the sinkhole ordinance.
| |
|
|
|
|
Submitted plans for land disturbance permit.
| |
|
|
|
|
Checked for proximity to brownfields or hazardous material.
| |
|
|
|
|
If crossing a street or concrete ditch, will the street or storm
sewer department allow the structure to be cut or will it need to
be bored, appropriate details shown on the plans.
| |
|
|
|
|
Are there special connection fees to be paid with the engineering
and inspection fees.
| |
|
|
|
|
Install two-way clean-out at R/W or edge of easement with tracer
wire full length of lateral within R/W or easement.
| |
|
Title Sheet:
| |||||
|---|---|---|---|---|---|
|
Yes
|
No
|
N/A
| |||
|
|
|
|
Name of subdivision/improvement shown.
| ||
|
|
|
|
Name, address, and zip code of developer/owner shown.
| ||
|
|
|
|
Location sketch shown:
| ||
|
|
|
|
1.
|
Scale shown.
| |
|
|
|
|
2.
|
North arrow shown.
| |
|
|
|
|
3.
|
Two major streets shown.
| |
|
|
|
|
Site plan shown:
| ||
|
|
|
|
1.
|
Legal description given (subdivision and/or sewer district boundary).
| |
|
|
|
|
a.
|
Reference made to land tie, existing subdivision or other known
point.
| |
|
|
|
|
b.
|
Bearings and distances shown on plan and in written form.
| |
|
|
|
|
c.
|
Elevation contours shown over the entire sewer district.
| |
|
|
|
|
d.
|
Lot lines and dimension shown.
| |
|
|
|
|
2.
|
Two City benchmarks referenced.
| |
|
|
|
|
3.
|
North arrow shown.
| |
|
|
|
|
4.
|
Correct scale shown (1" = 40' or other appropriate).
| |
|
|
|
|
Neighboring subdivision name and lot numbers shown if affected
by sewer or needed for boundary description information.
| ||
|
|
|
|
Consultant's name, address, zip code, and phone number
shown.
| ||
|
|
|
|
Manholes on title sheet labeled.
| ||
|
|
|
|
Sections of the main indexed by sheet number.
| ||
|
|
|
|
All applicable standard construction notes shown.
| ||
|
|
|
|
The "One Call" stamp and phone number shown.
| ||
|
Plan and Profile Sheets Plan:
| |||
|---|---|---|---|
|
Yes
|
No
|
N/A
| |
|
|
|
|
Scale shown (1" = 40' horizontal, 1" = 4' vertical
for undeveloped areas, 1" = 20' horizontal, 1" = 4' vertical
for developed areas).
|
|
|
|
|
North arrows shown.
|
|
|
|
|
Line types defined (if not in standards).
|
|
|
|
|
Easements shown with book/page numbers.
|
|
|
|
|
Names shown of all landowners affected by project.
|
|
|
|
|
Manholes not shown in detention. If detention is necessary,
specify manhole above detention rim and grading around manhole.
|
|
|
|
|
New easements dimensioned and properly described.
|
|
|
|
|
Length of sewer main is to be measured from inside wall of manholes
(not center to center of manholes).
|
|
|
|
|
Stationing of manholes and casing ends shown.
|
|
|
|
|
All other existing and proposed utilities and structures appear
to be shown.
|
|
|
|
|
Stationing in fifty-foot intervals.
|
|
|
|
|
Main placed in center of parkway where possible, otherwise is within an easement or right-of-way. Easements should conform to Subsection (E)(2)(d)(9).
|
|
|
|
|
Manholes shown to not be within existing or proposed sidewalks
unless approved by City of Battlefield.
|
|
|
|
|
State plane coordinates on manholes and angles at manholes shown
with bearing reference.
|
|
|
|
|
Station, size, and length of service lateral and tee shown.
Tee and lateral shown to be perpendicular to main within easement
or R/W.
|
|
|
|
|
All end-of-line manholes shown to be fifteen (15) feet past
property line.
|
|
|
|
|
If adding manhole to existing sewer, the immediate upstream
and downstream manhole elevations shown as shot in field, and any
service laterals shown.
|
|
Profile:
| |||
|---|---|---|---|
|
Yes
|
No
|
N/A
| |
|
|
|
|
Stationing shown.
|
|
|
|
|
Scale shown (1" = 40', 1" = 4' for undeveloped areas,
1" = 20', 1" = 4' developed areas).
|
|
|
|
|
Stationing and elevation of manholes and casing ends shown.
|
|
|
|
|
All other existing and proposed utilities and structures to
be shown.
|
|
|
|
|
Pipe slope, material, and size is shown.
|
|
|
|
|
Z-Lok connection specified where incoming or outgoing pipe grade
is greater than ten percent (10%) and manhole should have five tenths
(0.5) feet of fall through invert.
|
|
|
|
|
Four (4) feet of cover maintained over all mains.
|
|
|
|
|
Plot minimum finished floor elevation at station shown on plan
and show Lot number, size, and length of lateral.
|
|
|
|
|
SDR 21 PVC pipe used if less than eighteen (18) inches clearance
between top of sanitary sewer and bottom of storm sewer. Sewer pipe
may be required to be installed in steel casing or by bridging (SAN-33).
|
|
|
|
|
SDR 21 PVC pipe present from MH to MH if sanitary sewer less than eighteen (18) inches vertical clearance of a water main. Also, note the special testing procedures shown. [See Subsection (E)(2)(e)(2).]
|
|
|
|
|
Sewer main in steel casing if ground cover of eighteen (18)
inches impossible to attain; concrete encasement acceptable at creek
crossings.
|
|
|
|
|
Note to place fill prior to sewer installation shown where fill
proposed to attain four (4) feet of cover.
|
|
|
|
|
Distance between manholes centers less than four hundred (400)
feet.
|
|
|
|
|
Minimum slope for eight (8) inch main five-tenths percent (0.5%).
|
|
|
|
|
Concrete anchors along main shown if slope exceeds fifteen percent
(15%) (see SAN-32[7]).
|
|
|
|
|
Trench seal specified on both sides of creek crossings (see
SAN-21[8]).
|
|
|
|
|
Bank and channel protection specified at creek crossing.
|
|
|
|
|
Casing and boring details shown with a minimum boring slope
of one percent (1%).
|
|
|
|
|
If utilizing existing sewer, all existing and proposed service
connections are shown, and all manhole lid and flow line elevations
are given.
|
[7]
Editor's Note: This figure is included as an attachment to this chapter.
[8]
Editor's Note: This figure is included as an attachment to this chapter.
4.
Sewage Pumping Stations (Lift Stations).
a.
General.
(1)
A sewage pumping station shall consist of a wet
well, sewage pumps, control systems, electrical systems (normal and
emergency), superstructures, site security systems, grading, and access.
(2)
The purpose and goal of a sewage pumping station
is to serve as a sewage collection point for development and to pump
that sewage to a gravity sewer line serving the area using the most
cost effective and reliable design for maintenance and operation.
(3)
Sewage pumping stations will only be considered
when a ten-year life cycle cost-effective analysis comparing the construction,
operation, and maintenance costs between proposed sewage pumping station
and a reasonable gravity sewer alternative clearly indicates that
gravity sewers are not economically feasible.
b.
Buildings And Grounds.
(1)
Flooding. Sewage pumping stations shall not be
subject to flooding due to stormwater runoff. Structures and electrical
and mechanical equipment shall be protected from physical damage by
the 100-year flood and remain fully operational and accessible during
the twenty-five-year flood.
(2)
Fencing. A fence surrounding the pump station site
shall be provided. The fence shall be eight (8) feet high (minimum)
with a fourteen-foot wide, double-leaf gate. The fence shall be located
to provide ten (10) feet clearance between all pump station components
and the fence perimeter. Fencing shall be galvanized chain-link except
where subdivision rules require wooden privacy fence. The gate shall
be located so that entranceway does not go over manholes. The pump
station and emergency generator unit shall be easily accessible for
maintenance from the entranceway. The gate shall be set back at least
twenty-five (25) feet from the edge of public street.
(a)
Sign.
i.
A sign containing the following wording shall be
securely attached to the fence at a location clearly visible from
the pump station access road:
|
Station Name & I.D. No. (Obtain from City)
Sewage Pumping Station
City of Battlefield
No Trespassing
In Case of Emergency or Alarm
Please Call (417) 883-5840 or 911
|
ii.
Wording shall be centered horizontally and vertically
on the sign. The sign panel shall be standard gauge aluminum sheet,
minimum thirty (30) inches by thirty (30) inches, with black letters
on white background. Top four (4) lines shall be minimum two-inch-high
letters and bottom two (2) lines shall be minimum one-inch-high letters.
(3)
Surfacing of Sewage Pumping, Lift Station Area.
(a)
The area inside the fence must be constructed of
six (6) inches of Type 1 aggregate, compacted according to City Specifications
on a medium weight, non-woven geotextile, permeable vegetation barrier
placed over the entire enclosed area.
(b)
Subgrade shall be graded to provide positive drainage
away from building and structures. Maintain finished grade/surfacing
a minimum of six (6) inches below face of exposed concrete at locations
around the perimeter of all structures. Slope subgrade and surfacing
for adequate drainage. For all sidewalks, running slope is not to
exceed five percent (5%) and cross slope is not to exceed two percent
(2%) in any direction. Embankment and drainage channels shall have
a maximum slope of 4:1.
(4)
Accessibility To Site. The pump station must be
accessible by an acceptable all-weather, hard-surface road meeting
the same requirements as other roads in development. The road shall
have a minimum driving surface width of twelve (12) feet and maximum
grade of ten percent (10%). Enough room shall be provided at the site
to permit turning vehicles around. The junction of pump station road
and public street shall have a minimum sixteen-foot long culvert of
acceptable diameter in ditch if applicable.
(5)
Exterior Lighting. A weatherproof, pole- or building-mounted,
exterior LED area lighting fixture with dusk-to-dawn operation shall
be provided. The fixture shall be dimmable with the capability to
provide an average range of illumination of one (1) foot-candle over
the entire site for security purposes and fifteen (15) foot-candles
over the wet well and equipment areas for maintenance purposes.
(6)
Control Building. All electrical switch gear and
controls shall be mounted inside a weatherproof building with four
(4) feet (minimum) clearance at front of electrical enclosures and
a minimum ceiling height of eight (8) feet. The building may be masonry,
pre-engineered metal, or pre-engineered fiberglass reinforced plastic
(FRP) construction, as required by the City of Battlefield. The building
shall be securely anchored to a minimum six-inch-thick steel reinforced
concrete floor designed to support applied loads. Buildings shall
be provided with appropriate heating and ventilation equipment. Buildings
for permanent stations shall also be provided with restroom facilities
and shop sink with hot- and cold-water supply. Construction details
and technical specifications for the building shall be incorporated
into the plans and special provisions specific to that project.
c.
Design. The following items should be given consideration in
the design of sewage pumping stations:
(1)
Type. Sewage pumping stations shall be non-clog,
solids handling, suction type or submersible type. Grinder pumps will
be considered by the City only in special cases if sufficient information
is presented to justify their use. Built-in-place dry well/wet well-type
stations may be acceptable for large stations and will be considered
by the City on a case-by-case basis when one (1) pump is 700 GPM or
greater.
(2)
Structures. Pump station wet well, and valve vault
shall be constructed of either precast or poured-in-place reinforced
concrete. Precast structures shall conform with ASTM C478 and ASTM
C890. Poured-in-place structures shall conform with Chapter 6 of the
General Conditions and Technical Specifications.
(a)
Buoyancy. Where high groundwater conditions are
anticipated, buoyancy of the pump station structures shall be considered
and, if necessary, adequate provisions shall be made for protection.
(b)
Separation. Wet and dry wells, including their
superstructure, shall be completely separated. Common wall construction
between wet and dry wells may be permitted, provided there is no interconnection
between the wet well and dry well atmospheres.
(c)
Pump Removal. Provision
shall be made to facilitate removing pumps, motors, and other mechanical
and electrical equipment.
i.
Submersible pump stations shall have a quick-disconnect
connection and guide rail lifting system for each pump. A stainless-steel
lifting chain, with one (1) end permanently attached to the pump-lifting
bail and the other end secured to a stainless-steel hook at grade
level, shall be provided for each pump.
ii.
Dry well/wet well stations shall have a hoist and
trolley system to lift and move the pumps to the access opening. System
shall have a minimum lifting capacity equal to one hundred fifty percent
(150%) of the maximum combined pump and motor weight.
iii.
Suction lift stations shall have a lifting arm
for removing motor and pump from base.
iv.
Where pump station is enclosed in a building, the
hoist and trolley system described above shall be capable of moving
pumps and motors to the access doorway.
(d)
Access. Suitable and safe means of access shall
be provided to dry wells of pump stations and shall be provided to
wet wells containing either bar screens or mechanical equipment requiring
inspection and maintenance. Stairways or ladders shall have rest landings
at vertical intervals not exceeding ten (10) feet. Such stairways
and ladders shall be OSHA compliant.
(3)
Pumps.
(a)
Design. Pumps shall be designed so that it is not
necessary to disconnect piping, valves, electrical circuits, and other
appurtenances in the wet well when the pumps are removed for service
or replacement.
(b)
Multiple Units. At least two (2) pumps shall be
provided. If only two (2) units are provided, they must have the same
capacity. Each pump shall be capable of handling the design peak hourly
flow. Where more than two (2) units are provided, each unit must be
of such capacity that with any one (1) unit out of service the remaining
units will have capacity to handle the design peak hourly flow.
(c)
Protection Against Clogging. Where the size of
the lift station is seven hundred (700) gpm or greater, a trash rack
located below floor level shall be provided. Where screens are located
below ground, facilities must be provided for handling screenings.
(d)
Pump Openings. Pumps shall be capable of passing
spheres of at least three (3) inches in diameter. Pump suction and
discharge openings shall be at least four (4) inches in diameter.
(e)
Priming. The pump shall be so placed that under
normal operating conditions it will operate under a positive suction
head except as specified for suction-lift stations. Each suction lift
pump shall have a priming system independent from other pumps.
(f)
Intake. Each pump shall have an individual intake.
Wet well design shall be such as to avoid turbulence near the intake.
(g)
Dry Well Dewatering. A separate sump pump shall
be provided in the dry well to remove leakage or drainage with the
discharge above the overflow level of the wet well. The sump pump
discharge line shall be provided with dual check valves and coupling
to facilitate sump pump removal for maintenance. Water ejectors connected
to a potable water supply will not be approved. All floor and walkways
surfaces shall have an adequate slope to a point of drainage.
(h)
Submersible Pump Seals. Tandem mechanical seals
are required on submersible pumps. Seal faces shall be tungsten carbide.
(4)
Piping And Valves.
(a)
Station piping shall be at least four (4) inches
in diameter. A shut-off valve shall be placed on the discharge line
of each submersible pump. For dry pit stations, shut-off valves shall
also be placed on the suction line and discharge line of each pump.
(b)
A check valve with external spring (or weight)
and lever shall be placed on each discharge line between the shut-off
valve and the pump. Each check valve shall be equipped with a lever-operated
micro switch for common alarm telemetering purposes. Valves on the
discharge side of each pump shall be provided with instrument ports.
(c)
For submersible stations, these valves shall be
located inside a valve vault separate from the wet well and shall
be readily accessible for repairs. Dismantling joint fittings should
be provided adjacent to valves to facilitate installation or removal
of valves.
(5)
Wet Wells.
(a)
Sizing. The design fill time and minimum pump cycle time shall be considered in sizing the wet well. The effective volume of the wet well shall be based on the design average daily flow determined in accordance with Subsection (E)(2)(c)(1) of these Design Standards and a filling time not to exceed thirty (30) minutes unless the facility is designed to provide flow equalization. The pump manufacturer's duty cycle recommendations shall be utilized in selecting the minimum cycle time. For constant speed pumps the minimum cycle volume shall be based on the following formula:
|
Vrmin = (T x Q) ÷ (4)
| ||
|
Where:
| ||
|
Vrmin
|
=
|
Required minimum pump cycle volume between pump-on and pump-off,
gallons
|
|
T
|
=
|
Required time between pump starts, minutes
|
|
Q
|
=
|
Pump discharge capacity, gallons per minute
|
(b)
Grit. Where it may be necessary to pump sewage
prior to grit removal, the design of the wet well should receive special
attention and the discharge piping shall be designed to prevent grit
settling in pump discharge lines of pumps not operating.
(c)
Divided Wells. Where continuity of pumping station
operation is required, consideration shall be given to dividing the
wet well into two sections, properly interconnected, to facilitate
repairs and cleaning.
(d)
Sump. Wet well sump design shall provide for proper
approach flow to the pumps and prevent accumulation of sediments.
The wet well floor shall be sloped to direct flow toward the pump
inlets with a minimum of localized swirl and air-entraining vortices
and include fillets or benching to prevent sedimentation. For larger
wet wells, a properly placed baffle wall close to the inlet should
be considered to reduce the potential for localized swirl and vorticity.
Water levels during pump cycling must be great enough suppress surface
vortices yet lowered as much as possible at intervals to increase
velocity and turbulence.
(6)
Ventilation. Adequate ventilation shall be provided
for all pump stations. For submersible type stations, passive ventilation
of the wet well will be adequate and shall consist of a four-inch
stainless steel or aluminum vent pipe extending at least eighteen
(18) inches above top of wet well with a return bend and stainless-steel
insect screen. In dry well/wet well stations, mechanical ventilation
of the dry well is required. Mechanical ventilation of the wet well
is also required when screens or other mechanical equipment requiring
maintenance or inspection is located in the wet well. There shall
be no interconnection between the wet well and dry well ventilation
systems. In pits over fifteen (15) feet deep, multiple inlets and
outlets are required. Dampers shall not be used on exhaust or fresh
air ducts, and fine screens or other obstructions in air ducts shall
be avoided to prevent clogging. Switches for operation of ventilation
equipment shall be marked and located at grade level. Ventilation
equipment and lighting shall be energized when access cover is open
on dry well type stations. The fan wheel shall be fabricated from
non-sparking material. Automatic heating and dehumidification equipment
is required when station is located below grade level.
(a)
Wet Wells. Ventilation may be either continuous
or intermittent. Ventilation, if continuous, shall provide at least
twelve (12) complete air changes per hour; if intermittent, at least
thirty (30) complete air changes per hour. Such ventilation shall
be accomplished by the introduction of fresh air into the wet well
by mechanical means.
(b)
Dry Wells. Ventilation may be either continuous
or intermittent. Ventilation, if continuous, shall provide at least
six (6) complete air changes per hour; if intermittent, at least thirty
(30) complete air changes per hour.
(7)
Water Supply. Potable water shall be supplied;
however, there shall be no physical connection between the potable
water supply and a sewage pumping station. Potable water supply lines
shall not be smaller than one (1) inch. A freeze-proof hydrant with
hose bib and vacuum breaker shall be located within ten (10) feet
of pumping station but not in the traffic path. The water supply to
the pump station site shall be protected by a reduced pressure type
backflow preventer. Backflow preventer piping shall be provided with
unions and isolation valves to allow removal for maintenance.
(8)
Dry Well, Wet Well And Valve Vault Access. Suitable
and safe means of access shall be provided to pump station dry wells,
wet wells, and valve vaults. Access covers and frames shall be aluminum
construction and sized to provide adequate clearance for removal of
pumps, motors, and other equipment. Access cover frames shall be extruded
aluminum angle frame with concrete anchors around the perimeter. Door
leaves shall be 1/4-inch aluminum diamond pattern plate, reinforced
to support a minimum live load of three hundred (300) psf. Doors shall
open to ninety degrees (90°) and automatically lock with an aluminum
or stainless steel hold open arm with release handle. Doors shall
close flush with frame and be equipped with a flush drop handle for
lifting and a non-corrosive locking bar. Hinges and all fastening
hardware shall be stainless steel. Factory finish shall be mill finish
aluminum. An alkali-resistant bitumastic coating shall be applied
to the frame exterior where it will contact concrete.
(a)
Fall Through Prevention System. Access openings
shall be provided with a hinged safety grate system. Grate shall be
aluminum construction, designed to support a minimum live load of
three hundred (300) psf. Grate openings shall be four (4) inches by
six (6) inches to allow for visual inspection and limited accessibility
for maintenance purposes when the grate is closed. Grate shall open
to ninety degrees (90°) and automatically lock with an aluminum
or stainless steel hold open arm with release handle. Hinges and all
fastening hardware shall be aluminum or stainless steel. Grate shall
have an OSHA safety yellow finish to increase visual awareness of
the safety hazard.
(9)
Spare Parts. Pump stations are to be provided with
two (2) mechanical seals and two (2) gasket kits to install with seals.
If seal filters are used, six (6) spares are to be included. Two (2)
complete sets of contacts and coils if equipped with full voltage
starters, or one (1) RVSS/VFD if so equipped, and one (1) spare alternator
relay or timer shall also be furnished.
(10)
Force Main Interface. A force main interface consisting
of piping, a forty-five degree (45°) "Y," forty-five degree (45°)
elbow, and flanged plug valve, and male cam-lock coupling shall be
provided.
(a)
All pipe and fittings shall be the same diameter
and be the same material as the pump station piping.
(b)
The interface shall be constructed within a four-foot
diameter, flat top manhole of required depth located external from
but adjacent to the pump station.
(c)
A thirty-inch by thirty-inch aluminum access hatch and fall prevention system as described in Subsection (E)(4)(c)(8) of these Standards shall be provided.
(d)
Special Requirements
for Suction-Lift Pump Stations. In addition to the previously mentioned
requirements for suction-lift stations, the following shall apply:
i.
Priming. Suction-lift pumps shall have a reliable
record of satisfactory operation and be installed with a single piece
suction line braced to the side of wet well. Priming shall be by dual
vacuum systems independent of each other.
ii.
Capacity. Approval will be restricted to installations
where total suction-lift does not exceed fifteen (15) feet.
(11)
General Electrical Requirements. All electrical
equipment and wiring shall comply with the latest revision of the
National Electrical Code (NEC). Particular attention shall be given
to electrical equipment enclosed in places where gas may accumulate
(hazardous areas). Submersible pumps are considered to be in a hazardous
area and shall be rated for use in NEC Class 1, Division 1, Group
C and D hazardous locations. This rating shall include pumps, removal
systems, and controls. Vacuum-primed pump controls systems must be
operated through intrinsically safe relays for hazardous locations.
All conduits shall be of galvanized rigid type and shall be installed
below grade wherever possible. Dry-type transformers for 110-Volt
utility service and control systems power shall be provided.
(a)
Service And Distribution.
The primary power to the station shall be 480 volt, 3 phase, and shall
be provided by connection to a commercial utility service.
i.
A service entrance disconnect switch acceptable
to the utility provider shall be provided between the pump station
and the utility. Service entrance equipment, when installed, shall
be provided with maximum available fault current labeling in accordance
with NEC guidelines. The field labeling shall include the date the
fault current calculation was performed and be of sufficient durability
to withstand the environment involved.
ii.
3-phase power distribution and 1-phase branch circuit
panel boards shall be provided as necessary.
iii.
A dry-type transformer for 120/240-volt single
phase utility service and control system power shall be provided.
iv.
Equipment shall have a withstand and closing rating
in RMS symmetrical amperes greater than the available fault current
at the site and be provided with field or factory arc flash labeling
in accordance with NEC guidelines.
v.
All conduit, fittings, and conduit bodies shall
be galvanized rigid steel, PVC coated externally, and urethane coated
internally, equal to OCAL or Robroy and shall be installed below grade
wherever possible. Conduit passing from a hazardous area into a non-hazardous
area shall be provided with a sealing fitting which shall be located
at the boundary in accordance with NEC.
vi.
Types, sizes, ratings, and electrical characteristics
of service and distribution equipment and accessories shall be indicated
on the plans and special provisions.
(b)
Emergency Operation. Provision of an emergency
power supply for pumping stations shall be made and may be accomplished
by connection of the station to a second independent public utility
source or by provision of a stationary engine generator rated at one
hundred twenty-five percent (125%) of total combined load of all pumps
and auxiliary loads.
(12)
Controls. Control system shall automatically operate
the pumps in a pump down, lead/lag, common off, mode of operation.
Control of pumps shall be by the use of a conductance relay level
sensing system equal to Multitrode level sensor, three (3) meters
in length, with a MTIC controller. The controller shall have a minimum
of four (4) switches used to indicate "PUMPS OFF," "LEAD PUMP ON,"
"LAG PUMP ON," and "HIGH LEVEL ALARM." The control panel shall include
automatic pump alternation to equalize operating time on all duplex
components and provisions to prevent simultaneous starting of pumps.
Provisions shall be made to bypass the alternator in the event that
either pump is out of service for maintenance. On larger sewage pumping
station installations other control systems may be required. One (1)
hand-off-auto switch and elapsed time meter shall be provided for
each pump and be operable through the control panel door. Elapsed
time meters shall be calibrated in one-tenth (0.1) hour increments
on all pumps.
(13)
Alarm And Monitoring Systems. Alarm systems shall
be provided for all pumping stations. Equipment shall be a Mission
Communications MyDro 150. All necessary equipment shall be provided
to monitor and transmit the following conditions: 1. Pump No. 1 running;
2. Pump No. 2 running; 3. Pump No. 3 (if applicable); 4. High wet
well level; 5. Control power failure; 6. Transfer to emergency power
source; 7. Generator running; 8. Common alarm. Other alarm conditions
may be required based upon pump station configuration and design such
as grinder failure, dry well sump pump failure, or any cause of pump
station malfunction.
(a)
Flow Metering. All sewage pumping stations shall be provided with flow metering. The flow meter shall be of the electromagnetic type and provide for transmitting of flow in full pipes. The flow tube shall be installed on the force main between two (2) pipe flanges having the same nominal diameter as the flow meter end connections. A standard four-foot diameter manhole with removable flat top, and hinged frame and cover shall be installed around the force main and flow tube. The associated flow meter transmitter shall be installed in the control building housing the electrical switchgear. The transmitter shall contain all necessary circuitry to utilize the signal from the flow tube and display flow in gallons per minute and totalized flow in gallons. The transmitter shall include analog outputs to interface with the alarm and monitoring system specified in Subsection (E)(4)(c)(13) above.
(14)
Emergency Power Supply. Provision of an emergency
power supply for pumping stations shall be made and may be accomplished
by connection of the station to at least two (2) independent public
utility sources, or by provision of in-place internal combustion engine
equipment which will generate electrical energy unless a fail-safe
gravity relief system can be incorporated into the wet well.
(a)
General.
i.
The power module shall consist of an engine, generator, and control panel assembly, all mounted with antivibration mounts onto a fabricated steel skid base with an integral weather/sound enclosure and, if applicable, a subbase fuel tank. An automatic transfer switch (Refer to Subsection (E)(4)(c)(14)(d) of these Design Standards) shall be provided to automatically switch to emergency power in the event of commercial power failure. The engine generator shall be sized for starting all pumps and all auxiliary loads, with an additional twenty-five percent (25%) overload capacity at site altitude within the following parameters:
(i)
Minimum genset load allowed, thirty percent (30%)
of rated capacity.
(ii)
Maximum genset load allowed, seventy-five percent
(75%) of rated capacity.
(iii)
Maximum allowable voltage dip, twenty-five percent
(25%).
(iv)
Maximum allowable frequency dip, ten percent (10%).
(v)
Site temperature, fifty degrees Celsius (50°
C.).
(vi)
Maximum allowable temperature rise, one hundred
twenty-five degrees Celsius (125° C.), Class H.
(vii)
Emissions, EPA Stationary Emergency Application.
ii.
The complete power module shall be factory assembled
and factory tested to ensure that all controls and protective devices
are in proper working order. The motor starting capability shall be
tested by a simulation of the exact operating load, with certified
test results provided. The power module must be coordinated with the
starting characteristics of the pump motors plus axillary loads.
(b)
Engine. The engine
shall be multi-cylinder, 4-cycle, one thousand eight hundred (1,800)
RPM, water-cooled, equipped to operate on natural gas for units rated
up to and including 100 kw, natural gas or diesel at City's discretion
for units rated 100 kw to 150 kw, diesel for units rated over 150
kw, and include the following features and accessories:
i.
Electronic governor to provide automatic engine-generator
set frequency regulation of five percent (5%) from steady state no
load to steady state full load.
ii.
Unit-mounted closed loop radiator system to properly
cool the engine when generator set is delivering full rated load with
fifty degrees Celsius (50° C.) inlet air and provide protection
to minus twenty degrees Fahrenheit (-20° F.) Guard rotating parts
from accidental contact.
iii.
Low oil pressure, high water temperature, over-crank,
and automatic over-speed shutdown devices.
iv.
Electric starter capable of three (3) complete
cranking attempts without overheating.
v.
Positive displacement, mechanical, full pressure,
lubrication oil pump.
vi.
Full flow lubrication oil filters with replaceable
spin-on cannister elements, dipstick oil level indicator and oil drain.
vii.
Replaceable dry element air cleaner for heavy-duty
application.
viii.
Engine-mounted battery charging alternator with
solid-state voltage regulator.
(c)
Alternator. The alternator
shall be a full 3-phase, 4-pole, self-excited, brushless, revolving
field type with static exciter. It shall be self-regulated and designed
specifically for motor starting application. The alternator shall
be directly connected to the engine flywheel housing and driven through
a semi-flexible driving flange to ensure permanent alignment. It shall
have drip-proof construction. Voltage regulation shall be within plus
or minus five percent (5%) of rated voltage from no load to full load.
Insulation shall be Class H with a one hundred twenty degrees Celsius
(120° C.) maximum temperature rise. A completely wired and assembled
generator control panel shall be furnished. It shall contain the following
items:
(d)
Automatic Transfer Switch. The automatic transfer
switch shall be a mechanically held, double throw, open transition
or break before making switch. The transfer action must be completely
electrical and not rely on springs or counterweights. Operating coils
must be momentarily energized from the source to which the load is
being transferred. The switch must be interlocked both mechanically
and electrically to prevent both sources from feeding the load at
the same time. Electrical operation must not allow a neutral position.
The main contacts of the transfer switch shall meet with a rolling
and wiping action. They shall be copper with cadmium plating up to
and including one hundred (100) amps and silver plating on all sizes
above one hundred (100) amps. They shall be rated for all classes
of load to 480-volt AC and equipped with blowout coils and arc chutes.
They shall have air inrush current rating of twenty (20) times rated
current and an interrupting capacity of one and five tenths (1.5)
times rated current. The transfer switch shall include auxiliary contacts
to provide connection to the alarm system. It shall also have three
(3) voltage-sensitive relays with adjustable dropout of seventy percent
(70%) to eighty percent (80%) and adjustable pickup of ninety percent
(90%) to one hundred percent (100%). Upon sensing of under-voltage
condition, the generator startup and transfer sequence shall be initiated
automatically. Provision shall also be made to manually initiate the
sequence. A programmable exerciser timer shall be provided to set
week, day, time, and duration of generator set exercise period.
(e)
Engine Control Panel. The engine control panel
is to include five (5) ten-second-on/10-second-off cranking cycles,
a switch for testing the automatic operation, a switch for deactivating
the automatic operation, and a microprocessor-based controller with
an LCD display that will indicate oil pressure, coolant temperature,
battery charging voltage, elapsed time meter, fail-to-start, line-power-on,
and standby-power-on, protective shut-down, engine overspeed, low
oil pressure, overload, high coolant temperature, manual start-run-stop
switch, 0-60-second time delay on transfer Normal to Emergency, 0-30-minute
time delay on transfer Emergency to Normal, 0-5-minute time delay
after transfer to normal for engine cool down, contacts to signal
emergency power on, contact to signal fail-to-start, and contact to
signal protective shut-down and fail-to-start.
(f)
Placement. The unit shall be bolted in place. Facilities
shall be provided for unit removal for purposes of major repair or
routine maintenance.
(g)
Engine Location. The unit internal combustion engine
shall be located above grade with exhaust muffler and outlet located
inside of weatherproof housing. The muffler system shall be residential
type or better.
(h)
Engine Cooling Ventilation. Engine housing shall
have adequate ventilation to maintain a safe equipment operating temperature.
(i)
Emergency Power Generation. All emergency power
generation equipment shall be provided with instructions indicating
the essentiality of routinely and regularly starting and running each
unit at full load.
(j)
Spare parts were discussed to be added with no
verbiage.
d.
Acceptance Of Sewage Pumping Station.
(1)
Shop Drawings. Shop drawings shall be submitted
on sewage pumping stations, stand-by power source, and structures,
and be approved prior to installation. One (1) electronic copy in
portable document format (.pdf). Two (2) reviewed print copies will
be returned to the contractor.
(2)
Testing.
(a)
Prior to acceptance of sewage pumping stations
by the City, testing of each equipment item shall be required in the
presence of the contractor, a City representative, and the equipment
manufacturer's representative. Final acceptance will not be made
until all deficiencies are corrected and retesting is performed.
(b)
Diesel fueled generator units are to be run with
site loads when NFPA testing results are supplied by the manufacturer.
Natural/propane gas units to be run with a two-hour load bank, one
(1) hour at eighty percent (80%) load and one (1) hour at one hundred
percent (100%) load to test gas supply.
(3)
As-Builts. Prior to acceptance of operation of
sewage pumping station, generator units, and other related appurtenances
by the City, one (1) electronic copy of "as-builts" in AutoCAD and
portable document format (.pdf) and one (1) set of prints of "as-builts"
shall be submitted.
(4)
Operation And Maintenance Manuals. Four (4) complete
sets plus an electronic copy in portable document format (.pdf) of
operational instructions shall be provided to include emergency procedures,
maintenance schedules, maintenance manuals, and service manuals on
all equipment. Special tools and such spare parts as may be necessary
should be provided to the City for the facilities to be accepted.
Such tools and spare parts shall be provided in duplicate pairs.
5.
Force Mains.
a.
Velocity. Force main pipe diameter shall be sized to provide
a minimum velocity of two (2) feet per second with one (1) pump operating
and a maximum velocity of eight (8) feet per second with multiple
pumps operating.
b.
Sewage Combination Air Valve. A single body sewage combination
air valve equal to APCO Series 440 shall be placed at high points
in the force main to automatically exhaust large quantities of air
during pipeline filling at system startup, automatically allow air
to reenter the pipeline to protect the pipeline against negative pressures
during draining, and automatically release small pockets of air from
the pipeline while system is operating under pressure to prevent air
locking. A standard four-foot-diameter manhole with removable flat
top, hinged frame and cover, and interior corrosion protection per
Figure SAN-31[9] shall be installed around force main and relief valve
for maintenance access to valve.
[9]
Editor's Note: This figure is included as an attachment to this chapter.
c.
Connection To Gravity System. The force main shall connect to the gravity sewer system at a point not more than two (2) feet above the flow line of the receiving manhole in a manner that provides a smooth transition of flow and minimizes turbulence. Corrosion protection for the interior of the receiving manhole, upstream manhole, and two (2) downstream manholes shall be provided. At the City's discretion, corrosion protection may also be required for additional upstream and downstream manholes, depending on the potential for sulfide generation as discussed in Subsection (E)(3)(b). Corrosion protection of new manholes shall be accomplished by the monolithic spray-application of a high-build, solvent-free epoxy resin coating system. Surface preparation and product application and film thickness shall conform to the coating system manufacturer's recommendations. Rehabilitation of existing manholes to repair voids and restore structural integrity may be required prior to applying corrosion protection system. If required, rehabilitation of existing manholes shall be completed.
d.
Design Pressure. The force main pipe and fittings shall be designed
to withstand normal pressure and pressure surges (water hammer).
(1)
Design Friction Losses. Friction losses through
force mains shall be based on the Hazen-Williams Formula or other
acceptable method. A C-factor of one hundred twenty (120) shall be
used for computation of force main friction losses. When initially
installed, force mains will have a significantly higher C-factor.
Higher C-factors should only be considered in calculating maximum
power requirements.
e.
Thrust Blocks. Concrete thrust blocking shall be provided at
all bends, tees, plugs, fittings, or other significant changes in
direction. Thrust block locations shall be noted on both plan and
profile views of the construction plans. Mechanical joint restraint
devices should be considered in addition to concrete thrust blocks.
See Concrete Thrust Block and Anchor Details Figure SAN-30 and Figure
SAN-32.[10]
[10]
Editor's Note: These figures are included as an attachment to this chapter.
f.
Force Main Pipe. All force main pipe shall be PVC conforming
to AWWA C900 and have minimum pressure rating of two hundred (200)
psi (DR21) HDPE pipe will be considered by the City only in special
cases, provided sufficient information is presented to justify its
use. If approved, material and installation requirements shall be
addressed in the plans and special provisions for the project.
g.
Trace Wire And Detectable Marking Tape.
(1)
A trace wire shall be installed the entire length
of the force main. Trace wire shall be accessible from the surface
at intervals not to exceed one thousand (1,000) feet of developed
pipe length apart, at each end of roadway crossings, and adjacent
to all air valve vaults. Terminal/access boxes shall be at grade level,
in-ground type specifically manufactured for such applications. Terminal
boxes shall be installed flush with finished grade and centered in
grade level reinforced concrete pad, minimum eighteen (18) inches
by eighteen (18) inches by six (6) inches thick, at locations approved
by engineer.
(2)
In addition to trace wire, a detectable marking
tape specifically manufactured for marking and locating underground
utilities shall be installed the entire length of the force main.
Marking tape shall be installed directly over force main at a depth
of twelve (12) inches to eighteen (18) inches below finished grade.
(3)
A tracer wire is also required for all laterals.
Tracer wire shall be installed in accordance with Figure SAN-25.[11]
[11]
Editor's Note: This figure is included as an attachment to this chapter.
h.
Depth. Force main pipe shall be designed and so constructed
to provide a minimum depth of three (3) feet of cover over the top
of the pipe.
i.
Steel Casing. Force mains designed to cross public streets must
be encased in steel casing conforming to ASTM A53 with a minimum yield
strength of thirty-five thousand (35,000) psi and a minimum wall thickness
of twenty-five hundredths (0.25) inch. The casing inside diameter
shall be at least eight (8) inches greater than the nominal diameter
of the force main. Casing spacers shall be provided to permanently
position the force main inside the casing and prevent any lateral
or vertical movement. Force main joints inside casing shall be restrained
to allow multiple pipe segments to be pushed or pulled without compressing
or separating the assembled joints. Casing ends seals shall also be
provided. See Figure SAN-15[12] for details casing spacers and ends seals.
[12]
Editor's Note: This figure is included as an attachment to this chapter.
j.
Testing. Testing of the force main is required in accordance
with the requirements of AWWA C-600. Testing pressure shall be: Total
Design Head x 0.433 x 1.5, but not less than one-hundred fifty (150)
psi. (Note: This must be shown on the plans.)
F.
Storm Sewers.
1.
General.
a.
Scope. These design standards set forth the minimum requirements
for design of storm drainage facilities on public rights-of-way and
private property in the City of Battlefield, Missouri. These standards
shall apply to all subdivisions for which preliminary plats approved
after the date of passage by the City of Battlefield, or building
permit submittals, or grading permit applications which are received
after the date of passage by the City of Battlefield.
b.
Coordination With Other Jurisdictions. Where proposed storm
drainage facilities are located on property adjoining other local
government jurisdictions, design of storm drainage facilities shall
include provisions to receive or discharge stormwater in accordance
with the requirements of the adjoining jurisdiction, in addition to
meeting City of Battlefield requirements. In these cases, two (2)
additional sets of plans shall be submitted and will be forwarded
to the adjoining jurisdiction for review and comment.
c.
Coordination With Transportation Facilities And Utilities. Planning
and design of proposed storm drainage facilities must be compatible
with proposed or existing utilities, highways, streets, roads, railroads,
and other public facilities. Where other public facilities may be
affected by proposed storm drainage facilities, plans for storm drainage
facilities shall be forwarded to the appropriate agency for review
and comment. No grading or construction of storm drainage facilities
may commence without prior notification of the Missouri One Call utility
warning system at 811 as required by State law.
d.
Ownership And Maintenance.
(1)
Improvements On Public Road Rights-Of-Way. Storm
drainage improvements on public rights-of-way shall, upon acceptance
of the improvements by the City of Battlefield, become the property
of the City of Battlefield and shall be maintained by the City of
Battlefield.
(2)
Improvements On Private Property. Storm drainage
improvements on private property shall be maintained by the owner
of the lot upon which the improvements are located, or by the subdivision
homeowners' association for improvements located in common areas.
2.
Plan Submittal And Inspections.
a.
General. This Subsection defines the minimum plan submittal
and inspection requirements for private and public stormwater improvements.
b.
Stormwater Construction Plans.
(1)
Stormwater construction plans shall include a title
sheet, site plan, grading plan, detention and/or water quality stormwater
control measure (SCM) plan, storm drain plan, details plan and an
erosion and sediment control plan. Submitting a complete set of stormwater
construction plans will help reduce permit review time and is essential
to effectively communicate to contractors what the engineer intends
to be constructed. Often, poor construction plans or poorly constructed
stormwater improvements result in ineffective stormwater systems and
flooding problems.
(2)
Stormwater improvement projects will require the
submittal of stormwater improvement plans which must be designed to:
(b)
Protect all structures from inundation and provide
two (2) feet of freeboard below any finished floor for the 100-year
peak flow.
(c)
Protect public streets from flooding, worsen flooding
or cause the street to not meet the City's stormwater drainage
criteria.
(d)
Adequately discharge both on-site and off-site
peak flows to a public right-of-way, drainage easement, or certified
natural surface water channel.
c.
Stormwater Report. A supplemental stormwater report that includes
detailed drainage design computations must be submitted with stormwater
construction plans. The stormwater report must include all details
of the stormwater system, including detention and water quality calculations
and any other relevant hydraulic calculations required to ensure that
the proposed stormwater system is designed in accordance with all
City regulations. Stormwater calculations for predevelopment and post-development
conditions must be submitted for the 1-, 10- and 100-year storm events
to show that post development runoff peaks will not exceed predevelopment
runoff peaks. All details of the routing procedure must be submitted
with the report.
(1)
Project Description And Background. Provide the
development name, address, and location along with any other relevant
information to identify the specific location of said development
such as nearest intersection or known landmark. State the type of
development (i.e., commercial, residential, etc.), the overall size
of the development, and if there are any plans for future development.
State if there is any concentrated off-site stormwater runoff crossing
the development and, if so, how the off-site runoff will be conveyed
through the site. State if work is to be performed on a State or County
right-of-way and provide written approvals from said agencies. State
if site contains a sinkhole or is located in a sinkhole watershed.
If so, provide a sinkhole evaluation report in accordance with this
manual. State if the development is located in the FEMA floodway or
one percent (1%) annual floodplain and provide name of the receiving
water body. A floodplain development permit will be required from
the Building Department in accordance with the City's Floodplain
Management Ordinance[13] for any work in a FEMA floodplain. A jurisdictional determination
and permit may also be required from the United States Army Corps
of Engineers.
(2)
Detention Summary. State the existing and proposed
percentage of impervious surfacing for the site. If there is an increase
in impervious surfacing, state which method the development will use
to meet the City's stormwater flood control regulations (i.e.,
existing detention, stormwater detention buyout, or stormwater detention
construction).
(a)
Existing Detention. If an existing stormwater detention
facility was previously constructed to serve a development, it must
be shown that the proposed development is in conformance with the
original design criteria of the existing detention facility. Runoff
from the proposed development must drain directly to the existing
detention facility or drain through drainage easements and/or street
rights-of-way to the detention facility. If runoff from the proposed
development exceeds the existing detention facility design criteria,
additional detention must be provided in accordance with current stormwater
regulations.
(b)
Stormwater Detention Construction. If constructing
a stormwater detention facility, provide a description of the facility
(i.e., dry, wet) along with the facility location and the maximum
amount of impervious surfacing the facility is designed to handle.
State the design method used to size the detention facility and provide
a summary of the proposed stormwater detention facility.
(c)
Emergency Overflow Spillway. An emergency overflow
spillway will usually be needed in a detention basin to convey flows
that exceed the primary outlet capacity or to direct overflows to
a specific location. The SCS Type II, twenty-four-hour storm event
shall be used to design the emergency overflow spillway. If an emergency
overflow spillway is needed, provide a summary of the spillway including
the location, type, size, and flow capacity.
(3)
Water Quality Summary. Proposed developments must comply with the water quality requirements in Subsection (F)(8), and developments draining to a sinkhole must also comply with the water quality requirements in Subsection (F)(9). All new impervious surfacing must convey runoff into the water quality facility. State what type of water quality stormwater control measures (SCMs), also known as "permanent BMPs," will be constructed along with the required water quality control volume.
(4)
Storm Drainage Collection And Conveyance System
Summary. State how the development will collect and convey stormwater
runoff. Provide a summary of the stormwater collection and conveyance
system, including the hydraulic method and design storm event used.
State where the storm drainage system will discharge concentrated
flows off-site (public right-of-way, drainage easement or certified
natural surface water channel). Whenever possible, connect private
drainage facilities to a public drainage system, which will require
a public improvement plan or an excavation permit.
d.
Detailed Drainage Analysis. Provide detailed hydrologic and hydraulic stormwater computations in accordance with Subsection (F)(3) through (11) of these standards showing that the proposed stormwater facilities meet current City stormwater regulations.
(1)
Calculation Of Runoff.
(a)
Stormwater runoff calculations shall be submitted in accordance with Subsection (F)(3) of this manual. Provide drainage area maps showing the overall drainage catchment areas for predevelopment and post-development conditions.
(b)
The stormwater system design for developments shall
consider runoff from off-site areas. For flood control planning and
modeling, effects of detention should be disregarded except for publicly
owned and maintained facilities with storage dedicated in perpetuity.
(2)
Streets, Inlets And Storm Drains. Street, inlet and storm drain designs shall be submitted in accordance with Subsection (F)(4) of this manual. Calculations shall be provided to show that the proposed storm drainage system will not exceed the allowable drainage encroachment within public streets, provides allowable types, sizes, and placement of inlets, and provides appropriate sizing and design of storm drains.
(a)
Streets. Provide drainage calculations showing
that the proposed stormwater collection system meets the two-year
and 100-year street inundation criteria and the twenty-five-year conveyance
and hydraulic grade line gutter criteria.
(b)
Inlets.
i.
State the design rainfall event and type of inlets
to be constructed. Provide a drainage area inlet map showing catchment
areas and peak flow for each inlet. Provide calculations showing that
the proposed drainage inlets will have the hydraulic capacity to capture
peak flows. Inlets must be located to limit gutter flows to no more
than five (5) cubic feet per second (cfs) for the two-year event and
meet spread limitations based on the street classification. Inlets
shall also be provided at all low points in the gutter grade or on
the upstream side of intersections and crosswalks.
ii.
Other types of inlets including trench drains may
be permissible if approved by the City. Private inlets may include
other proprietary designs. The effects of inlet clogging must be considered.
A fifty percent (50%) reduction in capacity shall be used for a single
grate inlet and a ten percent (10%) reduction shall be used for a
single curb opening inlet. A smaller reduction may be allowed in cases
where multiple inlet units are accepted.
(c)
Storm Drains. State the design rainfall event.
All public storm drains shall be designed to convey the twenty-five-year
storm event. Minimum and maximum velocities must be met in the two-year
and 100-year storm events. Provide pipe layouts and profiles showing
location, pipe materials and sizes, slopes, lengths, vertical alignments,
and crossings with other utilities. Storm sewer reports shall be submitted
showing pipe lengths, deflection angles, junction types, runoff coefficients,
intensities, inlet areas, flow rates, slopes, upstream and downstream
elevations, Manning's n values, minor losses, hydraulic and energy
grade lines, and velocities. If using the Rational Method to calculate
flow rates, antecedent moisture conditions shall be accounted for
in the twenty-five (25)- and 100-year storm events.
(3)
Culverts And Bridges. Culvert and bridge design shall be submitted in accordance with Subsection (B) of this manual.
(4)
Open Channels. Open Channel designs shall be submitted in accordance with Subsection (F)(6) of this manual. Provide type of channel (i.e., natural or engineered), detailed profile and cross section, design flow rates and velocities, slope, freeboard, sediment loading, channel lining, outfall, and buffer zone information.
(5)
Detention For Flood Control. Stormwater flood control shall be submitted in accordance with Subsection (F)(7) of this manual. Provide hydraulic detention design calculations.
(6)
Water Quality. Water quality calculations shall be submitted in accordance with Subsection (F)(8) of this manual. Provide calculations showing the required water quality control volume for the site and the design calculations for the stormwater control measures (SCMs) used to meet the water quality requirements.
e.
Submittal Requirements. This Subsection describes the requirements
for drawings and calculations for storm drainage facilities which
must be submitted and approved prior to filing of final plats for
subdivisions, issuance of commercial building permits or issuance
of grading permits.
Review and approval of drawings and calculations by the City
of Battlefield is conceptual in nature only and does not imply detailed
approval to any particular design item or data shown on the drawings,
nor does it give implied approval for any variance from any City of
Battlefield regulations or design standards. The design professional
whose seal appears on the plans is responsible for all lines and grades,
field data, and constructability of the design in compliance with
the City of Battlefield standards and regulations.
(1)
Subdivisions.
(a)
Submittal
Requirements.
i.
Construction plans for storm drainage improvements
required by the City of Battlefield Subdivision Regulations must be
completed and approved by the City of Battlefield before the final
plat can be filed or a grading permit can be issued for construction
of the improvements. Construction plans must be submitted to the City
of Battlefield. The following items must be submitted:
ii.
Incomplete submittals will be returned without
review.
(b)
Construction
Drawing Requirements.
i.
General.
(i)
Construction drawings for streets and storm drainage
improvements shall be submitted as a single set of construction drawings
titled as follows:
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Paving and Storm Drainage Improvements
for
(Name of Subdivision)
a Subdivision in the City of Battlefield, Missouri
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(ii)
Construction drawings shall be bound in a set
of consecutively numbered sheets. Each drawing must be signed by the
City of Battlefield before the drawings are approved for construction.
Construction drawings shall clearly show the location and, extent
of proposed construction in relation to existing and proposed property
lines, physical features, topography, and utilities, and shall include
all details necessary to properly construct the proposed facilities.
All construction drawings shall show the following:
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A)
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Title block, showing the name of the proposed project, drawing
title, and drawing number.
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B)
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Name, address, and telephone number of the consultant.
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C)
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Seal of responsible design professional.
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D)
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A scale for each plan or detail.
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E)
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A north arrow for all full or partial site plans and maps.
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F)
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The Missouri One Call utility locates symbol on all drawings
involving earthwork.
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ii.
Drawing Size. Unless otherwise approved in writing
by the City of Battlefield, original drawings shall be thirty-four
(34) inches wide by twenty-two (22) inches high with a one-half (1/2)
inch clear border on the top, bottom, and right sides of the drawing,
and a one and one-half (1 1/2) inch clear border on the left
side of the drawing. Lettering shall be in a size large enough to
allow reproduction of legible half-size drawings for use in the field.
iii.
Required Information. The following information
must be included in the construction drawings:
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A)
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General project information.
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B)
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Site boundary and dimensions.
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C)
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Grading plan.
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D)
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Plan of proposed storm drainage facilities.
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E)
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Sediment and erosion control plan (SECP).
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F)
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Profiles for storm drainage improvements.
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G)
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Details of stormwater facilities.
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It is not required that a separate drawing be prepared
for each item listed above. The required information may be shown
on the fewest number of drawings needed to present the information
clearly and legibly, depending upon the size of the project and complexity
of the proposed work.
iv.
Benchmarks. Benchmark references shall be noted
on the drawings. Two (2) benchmarks shall be referenced.
v.
General Project Information.
(i)
The following general information must be shown
on the first sheet of the construction drawings:
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A)
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Location map at a scale of 1" = 2,000' (one inch equals two
thousand feet), showing streets and roads of collector or greater
classification and municipal boundaries within one thousand (1,000)
feet of the site.
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B)
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General Notes. See Figure SS-2.[14]
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C)
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Name, address, and telephone number of developer.
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D)
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Index to drawings.
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E)
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Benchmark data.
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F)
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Legal description of property.
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G)
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Key to symbols used in the drawings.
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H)
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Location plan.
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[14]
Editor's Note: This figure is included as an attachment to this chapter.
(ii)
Where the proposed construction site consists
of a phase of an approved preliminary plat, a location plan shall
be shown on the first sheet, or the sheet immediately following the
cover sheet of the drawings. The location plan shall show the entire
area and boundary of the preliminary plat and the location and boundary
of the proposed phase within the preliminary plat. Location plan scale
shall not be smaller than one (1) inch equals two hundred (200) feet.
vi.
Site Boundary And Dimensions. The first or second
drawing of the set must include a plan showing the site boundary and
dimensions at a minimum scale of 1" = 100' (one inch equals one hundred
feet), and the following information:
(i)
North arrow and graphic scale.
(ii)
Site boundary with dimensions and bearings.
(iii)
Proposed rights-of-way and lot lines with dimensions
and bearings.
(iv)
Property lines and owners' names for all
properties adjoining the site [property lines for adjoining properties
need only extend one-inch actual scale, outside the site boundary].
(v)
Location and dimensions of existing and proposed
easements.
(vi)
Street names.
(vii)
Boundaries of cities and other political subdivisions.
vii.
Grading Plan. A grading plan for the entire site
must be included in the drawings. The site boundary and dimension
plan shall serve as the base for the grading plan. The grading plan
shall show the following:
(i)
Existing topographic contours at two (2) foot maximum
intervals. Each fifth contour shall be drawn as an index contour by
using a heavier line weight. Index contours must be labeled.
(ii)
Existing streets, transportation facilities, utilities,
and storm drainage facilities.
(iii)
Existing
physical features, including waterbodies and watercourses, sinkholes,
springs, and caves.
(iv)
Existing structures, pavements, sidewalks, tree
masses, pavements, and fences.
(v)
Proposed streets, transportation facilities, utilities,
and storm drainage facilities.
(vi)
Proposed structures, sidewalks, and pavements.
(vii)
Proposed
topographic contours. The line type used for proposed contours must
be heavier than that used for existing grades and must have a different
line type. Proposed contours shall be shown at two (2) foot maximum
intervals. Each fifth contour shall be drawn as an index contour by
using a heavier line weight. Index contours must be labeled.
viii.
Plan Of Proposed Storm Drainage Facilities. An
overall plan of the site showing all proposed storm drainage facilities
shall be provided. The site boundary and dimension plan shall serve
as the base for this plan. This plan may be superimposed upon the
site grading plan, depending upon the size and complexity of the project,
provided that clarity and legibility can be maintained. The plan of
storm drainage facilities shall show the location of the following
items:
(i)
Detention basins.
(ii)
Sediment
basins.
(iii)
Storm
drain piping.
(iv)
Inlets.
(v)
Junction structures.
(vi)
Open
channels and swales.
(vii)
Other
components of the storm drainage system.
(viii)
Horizontal location of all components of the storm drainage system,
dimensioned to easements, rights-of-way, or property lines. Where
all components of the system cannot be legibly dimensioned at the
scale of the overall plan, enlarged plans of these areas shall be
provided.
(ix)
Line
numbers and structure reference numbers, as described below:
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A)
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Beginning at each point of discharge from the site, the storm
drainage system shall be organized into a system of "lines" for identification
of profiles. Storm drainage lines shall be numbered in consecutive
order, beginning with the number one (1). Inlets, outlets, junction
structures, and other points of reference shall be designated by letters
beginning at the downstream-most point in each line with the line
number followed by the reference letter, beginning with the letter
"A"; i.e., 1-A, 1-B, etc. Each line shall extend from the downstream
point of discharge to the upstream-most element in the line, and shall
include "non-constructed" elements, such as natural channels.
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(x)
Overflow Routes Identified.
ix.
Sediment And Erosion Control Plan (SECP). An overall
plan of the site showing proposed sediment and erosion control measures
shall be included in the construction drawings. The sediment and erosion
control plan shall be superimposed upon the site dimension plan, grading
plan, and storm drainage facilities plan. The sediment and erosion
control plan shall also show the following:
(i)
General limits of the area stripped of vegetation
or disturbed by construction activities shall be shaded or otherwise
clearly delineated.
(ii)
A summary table showing the total site area and
the total area estimated to be disturbed.
(iii)
Location of temporary construction entrance(s).
(iv)
Proposed sediment containment measures: vegetative
filter areas, straw bale dikes, silt fences, temporary containment
berms, diversion berms, inlet protection, etc.
(v)
Site stabilization measures, showing the type of
surface stabilization to be provided in various areas of the site,
whether sod, erosion control blanket, mulch, riprap, concrete, etc.
If more than one (1) type of erosion control blanket or mulch, is
specified, the different areas should be distinguished by use of varying
shading or symbols.
(vi)
Seeding and mulching specifications, and allowable
seasons for temporary and permanent seeding.
(vii)
Temporary and permanent erosion control measures,
such as outlet protection, channel linings, riprap, or paved chutes,
etc.
(viii)
General
notes for sediment and erosion control. See Figure SS-3.[15]
[15]
Editor's Note: This figure is included as an attachment to this chapter.
x.
Profiles. Profiles for all storm drainage lines
shall be included in the construction drawings. Profiles may be drawn
at horizontal scales of 1" = 10' (one inch equals ten feet) to
1" = 50' (one inch equals fifty feet), depending upon the length of
line to be shown, and vertical scales of 1" = 2' (one inch equals
two feet)] to 1" = 5' (one inch equals five feet). Profiles shall
be stationed starting at the downstream end with Station 0+00. Profiles
shall be drawn continuously from the downstream to the upstream end,
with breaks only as needed when the profile exceeds the drawing width.
Profiles shall not be combined with street profiles. Wherever breaks
are made, equation stations and elevations shall be called out. Profiles
shall include the following:
(i)
Reference grid lines showing elevations along the
left or right vertical margin and stationing along the bottom margin.
(ii)
Existing grade at centerline with a dashed line,
labeled "Existing Grade at Centerline."
(iii)
Proposed grade at centerline with a solid line,
labeled "Proposed Grade at Centerline."
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A)
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Where the difference in grade between the centerline and the
edge of the easement in which the proposed improvement is located
is one (1) foot or more, additional existing grade and/or finish grade
profile lines may also be required along the easement lines. Additional
profile lines shall be labeled as to location.
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(iv)
Existing and proposed utility crossings, labeled
as to type, e.g., "Proposed 8," "sanitary sewer," etc.
(v)
Existing and proposed pavements, riprap, concrete
linings, structures, foundations, or other features which would affect
the grade of the proposed storm drain or channel. Both the top and
bottom surface of pavements, foundations, etc., must be shown, in
order that clearance is apparent. It is preferred that a shading or
pattern be used.
(vi)
Profile of the proposed storm drain or channel
invert, and the interior top of pipe or top of channel bank. For reinforced
concrete pipe and reinforced concrete box culverts, the exterior top
and bottom shall also be shown in the profile. The station and structure
number shall be called out at each structure. Stations shall also
be called out at each change of direction in the centerline, at points
of horizontal curvature and tangency, and at changes in grade.
(vii)
The pipe or channel length in feet, and pipe
or channel slope in percent.
(viii)
Invert elevations shall be called out for each
structure, and at points of horizontal curvature and tangency. Incoming
and outgoing invert elevations shall be shown.
(ix)
Incoming lines at structures and tees shall be
shown and invert elevations called out.
(x)
Where the vertical clearance is less than the minimum
required, the actual clearance dimension shall be shown.
(xi)
Hydraulic grade line must be shown wherever storm
drainage piping is under pressure flow conditions, and shall be labeled
along with the return frequency of the storm for which the hydraulic
grade line was calculated: e.g., "HGL25 for the twenty-five-year storm,"
etc.
xi.
Details. Enlarged plans and other details must
be shown wherever necessary to clearly describe the location, dimensions,
and grades for the proposed construction. Details shall be drawn in
accordance with generally prevailing drafting standards. Details shall
be drawn to conventional scales, unless noted as "Not to Scale." Any
scale distortions used for isometric or other views must be noted.
Standard details included in these Design Standards may be referenced
by note where available. The following details will typically be required:
(i)
Typical trench cross section for storm drains lines.
(ii)
Typical cross sections for drainage channels,
showing side slopes, design depth or water surface, freeboard, and
type of lining.
(iii)
Typical cross sections of retaining walls.
(iv)
Plan and sections for detention and sediment basin
outlet structures.
(v)
Enlarged plans of inlets or junction structures,
where incoming piping is thirty (30) inches or greater in diameter,
or connection is made at other than ninety degrees (90°).
(c)
Calculations.
i.
Supporting calculations for storm drainage facilities
must be included in the plan submittal. Supporting calculations shall
include the following:
(i)
Drainage area map meeting the requirements set
forth in the paragraph below.
(ii)
Summary table for inlet calculations.
(iii)
Summary table for storm sewer and channel design.
(iv)
Hydraulic data for drainage channels with uniform
flow.
(v)
Water surface profile computations for drainage
channels with gradually or rapidly varied flow.
(vi)
Calculations for detention facilities.
(vii)
Calculations for sediment basins and other sediment
and erosion control facilities specified on the sediment and erosion
control plan.
(viii)
Where required, calculations for directly connected
impervious area, water quality capture volume, and stormwater quality
best management practices (BMPs).
ii.
Drainage area maps must be provided for both on-site
areas and off-site areas. Due to the difference in area, it will typically
be necessary to provide a larger scale map for on-site drainage areas,
and a smaller scale map for off-site drainage areas. Off-site drainage
areas shall be shown on U.S.G.S. 7 1/2 minute quadrangle maps
at a minimum scale of 1" = 2,000' (one inch equals two thousand
feet). Where more detailed or more current topographic maps are available,
they must be used.
iii.
On-site drainage area maps shall be shown superimposed
upon the site plan, with existing and proposed topographic contours
shown. Drainage areas shall be clearly outlined on the map, and the
identifying designation clearly shown. Drainage areas shall be given
the same designation as the inlet or reference point to which they
are tributary (i.e., drainage area 1-A is tributary to inlet 1-A).
The schematic plan of the proposed storm drainage improvements shall
be shown on the drainage area map. Both pre- and post-development
drainage areas must be shown for each primary outfall from the site.
(d)
Revisions
To Drawings.
i.
Prior to approval of the drawings by the City of
Battlefield, drawings are considered preliminary, and revisions shall
not be noted. Revision notes made by the consultant for his own records
prior to plan approval must be made outside the drawing border along
the left margin of the drawing. Any use of the construction drawings
for bids or pricing which occurs prior to the plans being approved
by the City of Battlefield, is solely at the risk of the developer.
ii.
Revisions made after the plans are signed must
be noted in the revision block and must be replotted and signed by
the City of Battlefield. When revisions are made, two (2) copies of
the revised drawing must be submitted to the City of Battlefield for
review. After the revision is approved, two (2) copies of the revised
drawing shall be provided to the City of Battlefield. Revised areas
must be clearly identified by clouding and noting with a symbol showing
the revision number. The final revision noted shall be the as-built
drawings.
(e)
As-Built
Surveys And Drawings.
i.
When construction of the improvements is completed,
the engineer shall perform surveys to determine that the location,
dimension, and grade of the drainage improvements is in substantial
conformance with the approved plans. The location of improvements
shall be checked by field survey to ensure that the improvements are
completely located within the easements or rights-of-way which have
been provided. The location of improvements which vary more than six
(6) inches from the location shown on the approved plans, must be
approved in writing by the City of Battlefield prior to approval.
Elevations and grades shall be verified at the following locations:
(i)
Center of access manhole or grate for junction
structures and inlets.
(ii)
Inlet entry for side opening inlets (except curb
opening inlets).
(iii)
Pipe And Culvert Inverts. For box culverts greater
than five (5) feet wide, invert elevation shall be checked at each
side of the inlet and outlet.
(iv)
Detention basin and sediment basin outlet structures.
(v)
Maximum intervals of one hundred (100) feet and
at grade changes in drainage channels (excluding roadside borrow ditches).
(vi)
Detention and sediment basins.
ii.
Elevations differing by more than one-tenth (0.1)
of a foot from plan grades or five-hundredths (0.05) of a foot for
detention basin outlet structures, must be approved in writing by
the City of Battlefield prior to final approval. Dimensions must be
verified for the following:
(i)
Pipe diameter for circular pipe.
(ii)
Height and width for elliptical or arch pipe,
or box culverts.
(iii)
Drainage channel cross sections at maximum intervals
of two hundred (200) feet.
(iv)
Riprap or other erosion protection at pipe outlets.
(v)
Overflow spillways and outlet structures for detention
and sediment basins.
(vi)
Detention and sediment basin volume.
iii.
As-built information shall be shown on the approved
plans in the same manner that revisions are noted on the drawings.
As-built information shall be clouded and noted with a symbol showing
the revision number. Where the as-built dimension or elevation does
not differ from the plan, the plan dimension or elevation shall be
clouded to signify that it has been verified.
(2)
Commercial Building Permits.
(a)
Submittal
Requirements.
i.
Construction plans for storm drainage improvements
must be completed and approved by the City Engineer and Building Inspector
before the building permit can be issued. Storm drainage drawings
and calculations shall be submitted to the Building Department along
with the building plans. The following items must be submitted:
ii.
Incomplete submittals will be returned without
review.
(b)
Construction
Drawing Requirements.
i.
General. Construction drawings for storm drainage
improvements may be submitted as a separate set of construction drawings
or included in the building plans. Construction drawings shall clearly
show the location and extent of proposed construction in relation
to existing and proposed property lines, physical features, topography,
and utilities, and shall include all details necessary to properly
construct the proposed facilities. Linework and lettering shall be
neat and clear. Original copies of the drawings shall be free from
smudges, tears, folds, and other imperfections which affect the legibility
of the drawing. All construction drawings shall show the following:
(i)
Title block, showing the name of the proposed project,
drawing title, and drawing number.
(ii)
Name, address, telephone number of consultant.
(iii)
Seal of responsible design professional.
(iv)
A scale for each plan or detail.
(v)
A north arrow for all full or partial site plans
and maps.
(vi)
The Missouri One Call utility locates symbol on
all drawings showing plans or details involving earthwork.
(vii)
A block for approval signature by the City of
Battlefield, located in the lower right area of each drawing.
ii.
Drawing Size - Commercial Building Permits. Unless
otherwise approved in writing by the City of Battlefield, original
drawings shall be thirty-four (34) inches wide by twenty-two (22)
inches high. Drawings shall have a one-half (1/2) inch clear border
on the top, bottom, and right sides of the drawing, and a one and
one-half (1 1/2) inch clear border on the left side of the drawing.
Lettering shall be of a large enough size to allow reproduction of
legible half-size drawings for use in the field.
iii.
Required Information — Commercial Building
Permits.
(i)
The following information must be included in the
construction drawings:
|
A)
|
General project information.
|
|
B)
|
Site boundary and dimensions.
|
|
C)
|
Grading plan.
|
|
D)
|
Plan of proposed storm drainage facilities.
|
|
E)
|
Sediment and erosion control plan (SECP).
|
|
F)
|
Profiles for storm drainage improvements.
|
|
G)
|
Details of stormwater facilities.
|
(ii)
It is not required that a separate drawing be
prepared for each item listed above. The required information may
be shown on the fewest number of drawings required to present the
information clearly and legibly, depending upon the size of the project
and complexity of the proposed work.
iv.
Benchmarks - Commercial Building Permits. For sites
within the Springfield Urban Services Area, it is preferred that the
City of Springfield benchmarks should be referenced. For sites outside
this area, it is preferred that U.S.G.S. benchmarks be referenced.
Assumed datum may be used, provided that it is based upon assumed
elevation of one hundred and zero-tenths (100.0), so as not to be
confused with actual elevations from mean sea level. Benchmark references
shall be noted on the drawings.
v.
General Project Information -Commercial Building
Permits. The following general information must be shown on the first
sheet of the construction drawings:
(i)
Location map at a scale of 1" = 2,000' (one
inch equals two thousand feet), showing streets and roads of collector
or greater classification and municipal boundaries, within one thousand
(1,000) feet of the site.
(ii)
General notes.
(iii)
Name, address, telephone number of owner or developer.
(iv)
Index to drawings.
(v)
Benchmark data.
(vi)
Legal description of property.
(vii)
Key to symbols used in the drawings.
vi.
Site Plan - Commercial Building Permits. The drawings
must include a plan showing the site boundary and dimensions, and
existing and proposed utilities and improvements at a minimum scale
of 1" = 100' (one inch equals one hundred feet), including the
following information:
(i)
North arrow and graphic scale.
(ii)
Site boundary with dimensions and bearings.
(iii)
Rights-of-way and names of streets adjoining
the site.
(iv)
Property lines and owners' names for all
properties adjoining the site [property lines for adjoining properties
need only extend one (1) inch, actual scale, outside the site boundary].
(v)
Location and dimensions of existing and proposed
easements.
(vi)
Boundaries of cities and other political subdivisions.
(vii)
Existing transportation facilities, utilities,
and storm drainage facilities.
(viii)
Existing
physical features, including waterbodies and watercourses, sinkholes,
springs, and caves.
(ix)
Existing structures, pavements, sidewalks, tree
masses, pavements, and fences.
(x)
Proposed transportation facilities, utilities,
and storm drainage facilities.
(xi)
Proposed buildings, incidental structures, structures
such as retaining walls, sidewalks, pavements, and other proposed
improvements.
vii.
Grading Plan - Commercial Building Permits. A
grading plan for the entire site must be included in the drawings.
The site plan shall serve as the base for the grading plan. The grading
plan shall show the following:
(i)
Existing topographic contours at two-foot maximum
intervals. Each fifth contour shall be drawn as an index contour by
using a heavier line weight. Index contours must be labeled.
(ii)
Proposed topographic contours. The line type used
for proposed contours must be heavier than that used for existing
grades and must have a different line type. Proposed contours shall
be shown at two-foot maximum intervals. Each fifth contour shall be
drawn as an index contour by using a heavier light weight. Index contours
must be labeled.
(c)
Revisions To Drawings. Revisions made after the
plans are signed must be noted in the revision block and must be initialed
by the City of Battlefield prior to approval. When revisions are made,
two (2) copies of the revised drawing must be submitted to the City
of Battlefield for review. After the revision is approved, two (2)
copies of the revised drawing shall be provided to the City of Battlefield.
Revised areas must be clearly identified by clouding and noting with
a symbol showing the revision number. The final revision noted shall
be the as-built drawings.
(d)
As-Built Surveys And Drawings. When construction
of the improvements is completed, the engineer shall perform surveys
to determine that the location, dimension, and grade of the drainage
improvements is in substantial conformance with the approved plans.
The location of improvements shall be checked by field survey to ensure
that the improvements are completely located within the easements
or rights-of-way which have been provided. The location of improvements
which vary more than six (6) inches from the location shown on the
approved plans must be approved in writing by the City of Battlefield
prior to approval. Elevations and grades, and location and dimensions
of improvements shall be verified and shown on as-built drawings.
As-built surveys must be approved prior to the final approval of the
building and issuance of a temporary or permanent occupancy permit.
(3)
Commercial Grading Permits. For sites upon which
only grading and construction of utilities and/or drainage improvements
are proposed, construction drawings and calculations shall be submitted
to the City of Battlefield. The following items must be submitted:
f.
Permits.
(1)
Land Disturbance Permit. A land disturbance permit
must be obtained from the Missouri Department of Natural Resources
(MDNR) for sites that disturb one (1) or more acres and for sites
that disturb less than one (1) acre when part of a larger common plan
of development or sale that will disturb a cumulative total of one
(1) or more acres over the life of the project. A land disturbance
permit must also be obtained from MDNR and included in the stormwater
pollution prevention plan (SWPPP). Upon approval of the SWPPP, the
applicant will be notified to submit the required security, agreement,
and permit fee. Prior to permit issuance, the applicant must schedule
a pre-permit meeting with the Division. Following this meeting, the
first phase of Best Management Practices (BMPs) can be installed.
No other work is to occur other than what is needed to install the
first phase of BMPs. The applicant must then schedule an initial Best
Management Practice (BMP) inspection with the Division. If the initial
BMP inspection is satisfactory, the permit is issued, and work may
begin. Termination of the permit requires seventy percent (70%) uniform
perennial grass growth, removal of all temporary BMPs, and removal
of all sources of pollution associated with construction. When the
site is ready for permit termination, the applicant must submit a
request for termination form and a release of securities application.
Staff will conduct a termination inspection. If the permit termination
inspection is satisfactory, the permit will be terminated, and the
security released.
(2)
Public Improvement Permit. Any stormwater improvement
project that serves multiple properties or routes stormwater runoff
from one (1) property across another is defined as a public stormwater
improvement project. Public stormwater improvement projects will require
the submittal and approval of public stormwater improvement plans
using City of Battlefield title block. Once the stormwater construction
plans have been reviewed and approved, the developer will be notified
to submit a signed, itemized bid for review. Upon approval of the
bid, the applicant will be notified of the amount of the engineering
and inspection permit fee. The engineering and inspection permit fee
is a percentage of the amount of the construction cost from the approved
bid. The engineering and inspection fee must be paid prior to the
stormwater permit approval. The fee shall be made to the "City of
Battlefield" and can be paid over the phone at (417)883-5840 or in
person at Battlefield City Hall, 5434 S. Tower Dr, 65619. After the
engineering and inspection fee is paid, plans will be stamped, and
construction may begin. The public stormwater improvements must be
constructed, inspected, approved and operational prior to filing a
final plat or issuance of a building permit. Alternatively, the final
plat may be filed and building permits issued prior to construction
of public stormwater improvements if an escrow is completed for the
public improvements and a temporary plan is submitted, approved, and
constructed that will provide for the conveyance and storage of stormwater
during construction of the development without impacting adjacent
properties. The escrow will not be returned until all public improvements
are constructed, inspected, and approved. An application to secure
public improvements must be submitted for review and approval.
(3)
Stormwater Permit.
(a)
A stormwater
(STM) permit is required for all private stormwater facilities, detention
buyouts, and any work within a sinkhole or sinkhole watershed. The
Building Inspector may require that certain stormwater improvements
be constructed prior to issuance of a building permit when necessary
to protect downstream properties from adverse stormwater impacts.
Adverse impacts are defined as erosion and/or flooding caused by an
increase in discharge, depth, or velocity or the discharge of pollutants,
including sediment, downstream. The decision to require certain stormwater
improvements to be constructed prior to issuance of the building permit
will be based on the following factors:
(b)
In the event that it is infeasible to install stormwater
improvements prior to issuance of the building permit, a phased approach
is also permissible whereby a temporary plan may be submitted, approved,
and constructed that will provide for the conveyance and/or storage
of stormwater during construction of the development without impacting
adjacent properties. Under this approach the building permit will
be issued after all temporary stormwater controls shown on the approved
plans are constructed and accepted. It may be permissible to issue
a foundation permit in conjunction with the installation of temporary
stormwater controls. No certificate of occupancy will be issued until
all permanent stormwater improvements are constructed, inspected,
approved, and operational.
(4)
Excavation Permit. An excavation permit is required
when excavating in the right-of-way or when connecting private stormwater
improvements to a public stormwater system and public stormwater improvements
are not required. An excavation permit must be obtained from the Building
Department prior to excavation.
(5)
Floodplain Permit. For any construction work in
a FEMA Floodplain, a floodplain (FLD) development permit is required
from the Building Department prior to approval of the stormwater construction
plans.
(6)
United States Army Corps Of Engineers Permit. A
United States Army Corps of Engineers (USACE) jurisdictional determination
may be required to determine if a Section 404 permit is needed for
work in a stream or waters of the United States.
g.
Easements.
(1)
Drainage Easement. Drainage easement criteria shall be met in accordance with Subsection (F)(10) of this manual. Drainage easements shall be provided when a private stormwater system is serving multiple properties or routes stormwater from one (1) property across another. Drainage easements shall be shown on the construction plans and shall be of adequate size to contain the 100-year peak flow rate. If existing drainage easements are no longer needed, an application for relinquishment of easement must be submitted to the Building Department and approved by the Battlefield Planning and Zoning Commission. Proposed drainage easements shall be submitted to the Battlefield Building Department for review and approval using the appropriate standard drainage easement form. Once the proposed drainage easements have been reviewed and approved, signatures may be obtained, and the documents returned to the City to be filed. All required drainage easements shall be obtained prior to construction.
(2)
Certified Natural Surface Drainage Channel. If
runoff is proposed to discharge to a natural watercourse, a signed
and sealed statement by a registered engineer must be made on the
plans certifying that runoff discharges to a natural watercourse as
defined by State law. This letter must be sent by the architect or
engineer of record and must be sealed, signed, and dated by that professional.
An example of an acceptable letter may be obtained from the Building
Department.
h.
Operation And Maintenance Plan And Agreement. A stormwater control
measure (SCM) operation and maintenance plan and agreement is required
as a condition of stormwater permitting for construction of SCMs required
to meet flood control detention requirements, water quality requirements,
or zoning conditions. The SCM operation and maintenance plan and agreement
must be prepared recorded with the Greene County Recorder of Deeds.
Long-term operation and maintenance self-inspections and submittal
of a self-inspection report is required annually. Self-inspections
and reporting shall be conducted and submitted to the Building Department.
i.
Construction Inspections. City staff will make periodic inspections
of the construction of stormwater improvements and SCMs throughout
the construction period and require that any non-conformities with
the plans be addressed. The contractor may be required to schedule
inspections at certain milestones to allow inspection of key aspects
of SCMs.
j.
As-Built Requirements. When construction of stormwater improvements
is completed, the professional engineer of record shall sign, seal,
and submit the following as-built information:
k.
Final Inspection And Approval Of Improvements. Upon receipt
of the required as-built information, City staff will review the same
for substantial conformity with the plans. The engineer of record
will be notified in writing of any deficiencies discovered during
review of the as-built information. Upon correction of the noted deficiencies,
the engineer shall notify the City. Final approval of the improvements
will be given upon approval of the as-built information.
3.
Calculation Of Runoff.
a.
General. This policy describes methods which can be used to
determine rates and volumes of stormwater runoff. It is important
to remember that the physical relationship between precipitation and
the rate and amount of runoff is very complex, and that computational
methods which have been developed are empirical. When applying any
hydrologic technique, the designer must be aware of its basic assumptions
and limitations. Experience and good judgement must be used to evaluate
the results.
b.
FULLY URBANIZED CONDITIONS
POST-PROJECT CONDITIONS
PRE-PROJECT CONDITIONS
Definitions. As used herein, the following definitions shall
apply:
The topography, surface cover, and other hydrologic conditions
in the watershed as they will be after all areas in the watershed
have been developed in accordance with current zoning designations,
as provided in the Greene County Comprehensive Plan, or as can otherwise
be reasonably anticipated.
The topography, surface cover, and other hydrologic conditions
in the watershed as they will be after construction of the proposed
development.
The topography, surface cover, and other hydrologic conditions
in the watershed being considered as they exist prior to the proposed
development.
c.
Precision In Reporting Runoff. Runoff computations are based
upon empirical methods and cannot be expected to give precise results.
Results should always be rounded off or shown with a limited number
of significant digits to avoid implying an accuracy greater than that
which can be expected. Runoff rates and volumes should be rounded
up to the nearest ten percent (10%) of the computed value.
d.
Precipitation Data. Precipitation data used for computing runoff
rates and volumes for use in the design of stormwater management facilities
in the City of Battlefield are derived from the National Oceanic and
Atmospheric Administration (NOAA) Atlas 14, Volume 8, Version 2, Precipitation-Frequency
Atlas of the United States, Midwest States. Tables 1 and 2 below provide
depth and intensity values for various rainfall durations and frequencies
in the Battlefield area.
|
Table 1: Rainfall Depth-Duration-Frequency Relationships from
NOAA Atlas 14 Volume 8 Version 2, Precipitation-Frequency Atlas of
the United States, Midwestern States.
| |||||||
|---|---|---|---|---|---|---|---|
|
Duration
|
Depth of Precipitation (in)
| ||||||
|
1-year
|
2-year
|
5-year
|
10-year
|
25-year
|
50-year
|
100-year
| |
|
5 min.
|
0.38
|
0.43
|
0.53
|
0.61
|
0.72
|
0.81
|
0.90
|
|
10 min.
|
0.55
|
0.63
|
0.77
|
0.89
|
1.05
|
1.18
|
1.31
|
|
15 min.
|
0.67
|
0.77
|
0.94
|
1.08
|
1.28
|
1.44
|
1.60
|
|
30 min.
|
0.98
|
1.14
|
1.39
|
1.60
|
1.89
|
2.12
|
2.33
|
|
1 hr.
|
1.29
|
1.50
|
1.84
|
2.14
|
2.55
|
2.88
|
3.21
|
|
2 hr.
|
1.60
|
1.86
|
2.30
|
2.67
|
3.21
|
3.64
|
4.08
|
|
3 hr.
|
1.79
|
2.08
|
2.58
|
3.01
|
3.63
|
4.14
|
4.67
|
|
6 hr.
|
2.19
|
2.51
|
3.09
|
3.60
|
4.35
|
4.97
|
5.64
|
|
12 hr.
|
2.67
|
3.02
|
3.65
|
4.22
|
5.06
|
5.77
|
6.52
|
|
24 hr.
|
3.16
|
3.60
|
4.35
|
5.01
|
5.98
|
6.77
|
7.60
|
|
48 hr.
|
3.65
|
4.23
|
5.19
|
6.00
|
7.14
|
8.04
|
8.95
|
|
72 hr.
|
4.01
|
4.63
|
5.65
|
6.51
|
7.70
|
8.64
|
9.59
|
|
Table 2: Rainfall Intensity-Duration-Frequency Relationships
from NOAA Atlas 14 Volume 8 Version 2, Precipitation-Frequency Atlas
of the United States, Midwestern States
| |||||||
|---|---|---|---|---|---|---|---|
|
Duration
|
Intensity of Precipitation (in/hr)
| ||||||
|
1-year
|
2-year
|
5-year
|
10-year
|
25-year
|
50-year
|
100-year
| |
|
5 min.
|
4.56
|
5.16
|
6.36
|
7.32
|
8.64
|
9.72
|
10.80
|
|
10 min.
|
3.30
|
3.78
|
4.62
|
5.34
|
6.30
|
7.08
|
7.86
|
|
15 min.
|
2.68
|
3.08
|
3.76
|
4.32
|
5.12
|
5.76
|
6.40
|
|
30 min.
|
1.96
|
2.28
|
2.78
|
3.20
|
3.78
|
4.24
|
4.68
|
|
1 hr.
|
1.29
|
1.50
|
1.84
|
2.14
|
2.55
|
2.88
|
3.21
|
|
2 hr.
|
0.80
|
0.93
|
1.15
|
1.34
|
1.61
|
1.82
|
2.04
|
|
3 hr.
|
0.60
|
0.69
|
0.86
|
1.00
|
1.21
|
1.38
|
1.56
|
|
6 hr.
|
0.37
|
0.42
|
0.52
|
0.60
|
0.73
|
0.83
|
0.94
|
|
12 hr.
|
0.22
|
0.25
|
0.30
|
0.35
|
0.42
|
0.48
|
0.54
|
|
24 hr.
|
0.13
|
0.15
|
0.18
|
0.21
|
0.25
|
0.28
|
0.32
|
|
48 hr.
|
0.08
|
0.09
|
0.11
|
0.13
|
0.15
|
0.17
|
0.19
|
|
72 hr.
|
0.06
|
0.06
|
0.08
|
0.09
|
0.11
|
0.12
|
0.13
|
(1)
Precipitation Distribution. When using the Kinematic
Wave Method or SCS Method for runoff computations, the Huff rainfall
distribution shall be used for the temporal distribution. The Huff
distribution is presented in Table 3 and is expressed as cumulative
percentages of total duration and total rainfall accumulation. Different
families of Huff distribution curves are applicable to different drainage
areas. Table 3 is applicable to drainage areas less than ten (10)
square miles. For larger drainage areas, refer to the Rainfall Frequency
Atlas of the Midwest (Huff and Angel 1992). Each family of curves
consists of four (4) storms (first quartile, second quartile, third
quartile, and fourth quartile) that correspond to the quartile within
the storm event when the bulk of the rainfall occurs. Storms with
durations of six (6) hours or less, six (6) hours to twelve (12) hours,
twelve (12) hours to twenty-four (24) hours, and greater than twenty-four
(24) hours tend to be associated with the first-, second-, third-,
and fourth-quartile storms, respectively (Huff and Angel 1992).
|
Table 3
Cumulative Storm Rainfall (%) for Given Storm Type
| ||||
|---|---|---|---|---|
|
Cumulative Storm Time
(%)
|
First Quartile
(Duration £ 6 hours)
|
Second Quartile
(6 < Duration £ 12 hours)
|
Third Quartile
(12 < Duration £24 hours)
|
Fourth Quartile (Duration > 24 hours)
|
|
0%
|
0%
|
0%
|
0%
|
0%
|
|
5%
|
16%
|
3%
|
3%
|
2%
|
|
10%
|
33%
|
8%
|
6%
|
5%
|
|
15%
|
43%
|
12%
|
9%
|
8%
|
|
20%
|
52%
|
16%
|
12%
|
10%
|
|
25%
|
60%
|
22%
|
15%
|
13%
|
|
30%
|
66%
|
29%
|
19%
|
16%
|
|
35%
|
71%
|
39%
|
23%
|
19%
|
|
40%
|
75%
|
51%
|
27%
|
22%
|
|
45%
|
79%
|
62%
|
32%
|
25%
|
|
50%
|
82%
|
70%
|
38%
|
28%
|
|
55%
|
84%
|
76%
|
45%
|
32%
|
|
60%
|
86%
|
81%
|
57%
|
35%
|
|
65%
|
88%
|
85%
|
70%
|
39%
|
|
70%
|
90%
|
88%
|
79%
|
45%
|
|
75%
|
92%
|
91%
|
85%
|
51%
|
|
80%
|
94%
|
93%
|
89%
|
59%
|
|
85%
|
96%
|
95%
|
92%
|
72%
|
|
90%
|
97%
|
97%
|
95%
|
84%
|
|
95%
|
98%
|
98%
|
97%
|
92%
|
|
100%
|
100%
|
100%
|
100%
|
100%
|
(2)
Minimum Rainfall Duration. The rainfall duration
should correspond to the maximum peak flow rate for the watershed
being analyzed. A critical duration analysis should involve applying
the hydrograph-based methods to events with durations ranging from
thirty (30) minutes to twenty-four (24) hours to determine the duration
that produces the largest peak runoff rate for the watershed. Guidelines
for the minimum recommended storm duration based on watershed size
are shown in Table 4 below. The guidelines are intended to preclude
the use of short duration events that typically do not cover the corresponding
watershed uniformly. The information in Table 4 should be considered
as guidance for the minimum storm duration to use when calculating
runoff and is not a replacement for a critical duration analysis.
|
Table 4
| |
|---|---|
|
Watershed Size
|
Minimum Recommended Duration
|
|
< 160 acres
|
30 min
|
|
160 acres to < 1 sq. mi.
|
1 hr.
|
|
1 sq. mi. to < 4 sq. mi.
|
2 hr.
|
|
4 sq. mil to < 8 sq. mi.
|
3 hr.
|
|
8 sq. mi. to < 16 sq. mi.
|
6 hr.
|
|
16 sq. mi. to < 32 sq. mi.
|
12 hr.
|
|
> 32 sq. mi.
|
24 hr.
|
e.
Topographic Data. Topographic data utilized in determining drainage
areas must be sufficiently detailed to allow computation of runoff
with a reasonable degree of accuracy.
(1)
On-Site Drainage Areas. Topographic maps with a
maximum contour interval of not more than one (1) foot must be utilized
for determining drainage areas within the development site. Topographic
maps must show existing and proposed drainage facilities such as storm
drains, culverts, road cuts, ditches and other physical features which
affect the patterns of runoff on the site.
(2)
Off-Site Drainage Areas. Maps published by the
U.S. Geological Survey having a maximum contour interval of ten (10)
feet will generally be considered sufficiently accurate for use in
determining drainage areas where no development has occurred. For
small drainage areas where U.S.G.S. maps do not have a sufficient
level of accuracy or where drainage patterns have been altered by
development, the best available data should be used.
|
NOTE: Topographic information (five-foot contour intervals)
is available for certain portions of the area around the City of Springfield
on the 1976 Springfield Planning Area maps. These maps should be used
in determining off-site drainage areas, where more detailed maps are
not available. Where no other topographic maps having sufficient detail
to determine the drainage area in question are available, aerial photo
maps available from the County Assessor's office should be used
with drainage area limits and paths of flow determined in the field.
|
|
Regardless of the data used, it is the designer's responsibility
to field verify that the drainage areas used are reasonably accurate.
|
f.
Peak Runoff Rates.
(1)
Drainage Areas Less Than One Hundred (100) Acres.
Where the tributary drainage area is less than one hundred (100) acres,
and only the peak runoff rate is needed, the Rational Method may be
used to compute the peak runoff rate as described below. Peak flow
rates for designing inlets and conveyance facilities (storm drains
and open channels) for most developments can be computed by this method.
(2)
Urban Drainage Areas Equal To Or Greater Than One-Hundred
(100) Acres. Where the tributary drainage area is one hundred (100)
acres or more, and only the peak flow rate is needed, the peak runoff
rate shall be computed by any of the following methods:
(a)
Kinematic Wave Method.
(b)
Soil Conservation Service TR-55, Graphical Peak Discharge Method. Hydrologic soil groups for soils listed in the Greene County soil survey are shown in the table in Subsection (F)(3)(i)(1).
(c)
Unit hydrograph methods.
(3)
Rural Drainage Areas Equal To Or Greater Than One
Hundred (100) Acres. Peak runoff rates for rural watersheds equal
to or greater than one hundred (100) acres shall be computed by any
of the following methods:
(a)
Soil
Conservation Service TR-55 Graphical Peak Discharge Method.
i.
NOTE: This method is limited to a maximum time of
concentration of ten (10) hours.
(b)
U.S. Geological Survey Technique for Estimating
the two- to 500-year Flood Discharges on Unregulated Streams in Rural
Missouri.
(c)
Unit hydrograph methods.
g.
Peak Runoff Volumes. Runoff volumes shall be computed using
Soil Conservation Service TR-55, or any of the unit hydrograph methods
listed below.
h.
Rational Method. The Rational Formula may be used to compute
peak runoff rates only for drainage areas less than one hundred (100)
acres. The Rational Method or variations of the Rational Method are
not reliable for use in determining runoff volumes. The formula for
the Rational Method is as follows:
|
Q = CIA, where:
| ||
|
Q
|
=
|
peak runoff rate for a design storm of recurrence interval,
T, in cubic feet per second (cfs)
|
|
C
|
=
|
dimensionless runoff coefficient; recommended runoff coefficient values are given in Subsection (F)(3)(h)(3). The value used shall be the composite value based upon the type of surface coverage in the drainage area for the runoff condition being considered.
|
|
I
|
=
|
average rainfall intensity for a storm of recurrence interval,
T, over a duration equal to or greater than the time of concentration
for the contributing drainage area.
|
|
A
|
=
|
tributary watershed area in acres
|
|
The time of concentration utilized shall be determined for conditions
under which the peak flow rate is calculated, i.e., pre-project conditions
for the pre-project peak flow rate and post-project conditions for
the post-project peak flow rate, etc.
| ||
|
The general procedure for Rational Method calculations for a
single watershed is as follows:
| ||
|
1.
|
Delineate the watershed boundary and calculate its area.
| |
|
2.
|
Define and measure the flow path from the upper-most portion
of the watershed to the design point.
| |
|
3.
|
Calculate the slope for the flow path.
| |
|
4.
|
Calculate time of concentration, tc.
| |
|
5.
|
Find the rainfall intensity, i, for the design storm using the
calculated tc as the duration.
| |
|
6.
|
Determine the runoff coefficient, C.
| |
|
7.
|
Calculate the peak flow rate from the watershed.
| |
(1)
Assumptions. The basic assumptions made when the
Rational Method is applied are:
(a)
The computed maximum rate of runoff to the design
point is a function of the average rainfall rate for a duration equal
to the time of concentration over the drainage area.
(b)
The depth of rainfall used is one (1) that occurs
from the start of the storm to the time of concentration. It has a
level distribution over the duration of the rainfall, meaning the
rainfall intensity is constant throughout the storm.
(c)
The maximum runoff rate occurs when the entire
area is contributing flow. However, this assumption often should be
modified when a more intensely developed portion of the watershed
with a shorter time of concentration produces a higher rate of maximum
runoff than the entire watershed with a longer time of concentration.
(2)
Time Of Concentration. The time of concentration
is defined as the travel time from the hydraulically most distant
point in the contributing drainage area to the point under study or
the rainfall intensity averaging time. Time of concentration for use
with the Rational Method may be computed by either of the two (2)
methods described below. The minimum time of concentration which shall
be used is five (5) minutes.
The Soil Conservation Service Method, or other methods for which
there is documentation in commonly accepted literature, shall be used
in computing peak runoff rates for other methods.
(a)
Kirpich Formula.
 | |||
|
where:
| |||
|
tc
|
=
|
time of concentration in minutes
| |
|
L
|
=
|
length of travel in feet
| |
|
S
|
=
|
slope of the flow path from the remote part of the basin to
the calculation point divided by the horizontal distance between the
two points (ft./ft.)
| |
|
The Kirpich equation is most applicable for undeveloped watersheds
with well-defined channels, bare-earth overland flow, or flow in mowed
channels. The following adjustment factors are recommended for other
conditions (Chow et al. 1988):
| |||
|
•
|
For flow in natural grassed channels, multiply by 2.
| ||
|
•
|
For overland flow on concrete or asphalt surfaces, multiply
by 0.4.
| ||
|
•
|
For concrete channels, multiply by 0.2.
| ||
 | |||
|
where:
| |||
|
Nk
|
=
|
coefficient of roughness, presented in Table 5 below
| |
|
L
|
=
|
overland flow length (ft), maximum of 100 feet for undeveloped
areas and 100 feet for developed areas
| |
|
S
|
=
|
average overland slope (ft/ft)
| |
|
Total time of concentration can be found using the following
equation:
| |||
 | |||
|
Table 5
| |
|---|---|
|
Surface Type
|
Nk
|
|
Smooth impervious surface
|
0.05
|
|
Smooth bare packed soil, free of stones
|
0.10
|
|
Poor grass, cultivated row crops, or moderately rough bare surfaces
|
0.20
|
|
Pasture or average grass cover
|
0.40
|
|
Deciduous timberland
|
0.60
|
|
Conifer timberland, deciduous timberland with deep forest litter,
or dense grass cover
|
0.80
|
(b)
Soil Conservation Method. This method given in
Chapter 3 of Soil Conservation Service TR-55 may be used to compute
times of concentration. In using this method, it must be remembered
that overland flow elements are limited to one hundred (100) feet
in rural areas, and generally to one hundred (100) feet in urban areas.
The designer must consider whether calculated runoff rates from directly
connected impervious areas having a shorter time of concentration
will exceed the runoff rate for the entire drainage area when pervious
areas are included.
(3)
Runoff Coefficient. The runoff coefficient, C,
represents the percentage of rainfall that becomes runoff. In a non-homogeneous
drainage area, C should be calculated as an area-weighted composite
of the different land uses in the watershed.
|
Table 6: Runoff Coefficients
| |
|---|---|
|
By Surface Type - Use as Basis for Computation of Composite
Runoff Coefficients
| |
|
Surface Type
|
Runoff Coefficients
|
|
Asphalt, concrete pavement, roofs
|
0.95 to 1.0
|
|
Gravel surfaces, compacted
|
0.85 to 0.95
|
|
Gravel surfaces, not compacted
|
0.50 to 0.70
|
|
Parks, golf courses, farms
|
0.10 to 0.20
|
|
Lawns, pastures, hayfields
| |
|
Flat (< 2% slopes)
|
0.10 to 0.15
|
|
Average (2% to 7% slopes)
|
0.15 to 0.20
|
|
Steep (> 7% slopes)
|
0.20 to 0.30
|
|
Woods
|
0.05 to 0.15
|
|
Composite Coefficients for Single-Family Residential Areas
| |||
|---|---|---|---|
|
Surface Type
|
Runoff Coefficients
| ||
|
Average lot size, 1/4 acre
|
Flat (<2% slopes)
0.35 to 0.45
|
Average (2% to 7% slopes)
0.40 to 0.50
|
Steep (>7% slopes)
0.45 to 0.55
|
|
Average lot size, 1/3 acre
|
Flat (<2% slopes)
0.30 to 0.40
|
Average (2% to 7% slopes)
0.33 to 0.43
|
Steep (>7% slopes)
0.40 to 0.50
|
|
Average lot size, 1/2 acre
|
Flat (<2% slopes)
0.25 to 0.35
|
Average (2% to 7% slopes)
0.30 to 0.40
|
Steep (>7% slopes)
0.36 to 0.46
|
|
Average lot size, 1 acre
|
Flat (<2% slopes)
0.20 to 0.25
|
Average (2% to 7% slopes)
0.25 to 0.30
|
Steep (>7% slopes)
0.60 to 0.38
|
|
Average lot size, 3 acres
|
Flat (<2% slopes)
0.10 to 0.20
|
Average (2% to 7% slopes)
0.13 to 0.24
|
Steep (>7% slopes)
0.25 to 0.33
|
|
Note: The ranges of C values presented in Table 6 above are
typical for return periods of two (2) years to ten (10) years and
assume average antecedent moisture conditions. Higher values are appropriate
for larger design storms.
|
|
Table 7: Multiplier for larger design storms
| |
|---|---|
|
Recurrence Interval (years)
|
Adjustment Multiplier
|
|
25
|
1.1
|
|
50
|
1.2
|
|
100
|
1.25
|
i.
Hydrograph Methods. When runoff rates must be known as a function
of time, such as for reservoir routing computations or when the limitations
of the methods listed above are exceeded, hydrograph methods must
be used. Commonly accepted hydrograph methods are as follows:
|
U.S. Army Corps of Engineers HEC-HMS Flood Hydrograph Package.
|
|
Soil Conservation Service TR-55 and TR-20
|
|
Kinematic Wave Method
|
|
Other methods may be used upon written approval of the City
of Battlefield, provided that they are documented in accepted engineering
literature and are used within the limitations stated. Methods used
for distribution of rainfall, determining precipitation losses, accounting
for channel and reservoir storage effects, etc., shall be as prescribed
in the literature for the selected method.
|
(1)
SCS Curve Number. The determination of the CN value
for a watershed is a function of soil characteristics, hydrologic
condition and cover, or land use. For watersheds with multiple soil
types or land uses, an area-weighted CN should be calculated.
|
Table 8: Curve Number based on Hydrologic Soil Group
| ||||
|---|---|---|---|---|
|
Cover Description
|
Curve numbers for hydrologic soil group
| |||
|
Cover type and hydrologic condition
|
A
|
B
|
C
|
D
|
|
Idle lands (not yet developed)
| ||||
|
Pasture, grassland, or range - continuous forage for grazing:
| ||||
|
Good condition (ground cover >75% and only occasionally grazed)
|
39
|
61
|
74
|
80
|
|
Meadow - continuous grass, protected from grazing, and generally
mowed for hay
|
30
|
58
|
71
|
78
|
|
Woods-grass (50%-50%) combination, orchard or tree farm Other
combinations can be calculated as composite of pasture and woods Good
condition
|
32
|
58
|
72
|
79
|
|
Woods
Good condition (i.e., woods are protected from grazing, and
litter and brush adequately cover the soil)
|
30
|
55
|
70
|
77
|
|
Farmsteads - buildings, lanes, driveways, and surrounding lots
|
59
|
74
|
82
|
86
|
|
Table 9: Weighted Curve Number for watersheds with multiple
soil types
| |||||
|---|---|---|---|---|---|
|
Cover Description
|
Curve numbers for hydrologic soil group
| ||||
|
Cover type and hydrologic condition
|
Average percent impervious area
|
A
|
B
|
C
|
D
|
|
Fully developed urban areas (vegetation established)
| |||||
|
Open space (lawns, parks, golf courses, cemeteries, etc.)
| |||||
|
Good condition (grass cover >75%)
|
39
|
61
|
74
|
80
| |
|
Fair condition (grass cover 50% to 75%)
|
49
|
69
|
79
|
84
| |
|
Poor condition (grass cover less than 50%)
|
68
|
79
|
86
|
89
| |
|
Impervious areas
| |||||
|
Paved parking lots, roofs, driveways, compacted
gravel, etc.
(excluding right-of-way)
|
98
|
98
|
98
|
98
| |
|
Small open spaces within development or ROW:
|
72
|
82
|
87
|
89
| |
|
Streets and roads:
| |||||
|
Paved; curbs and storm sewers (including right-of-way)
|
90
|
93
|
95
|
97
| |
|
Paved; open ditches (including right-of-way)
|
83
|
89
|
92
|
93
| |
|
Gravel (including right-of-way)
|
76
|
85
|
89
|
91
| |
|
Dirt (including right-of-way)
|
72
|
82
|
87
|
89
| |
|
Urban districts:
| |||||
|
Commercial and business
|
85%
|
89
|
92
|
94
|
95
|
|
Industrial
|
72%
|
81
|
88
|
91
|
93
|
|
Residential districts by average lot size:
| |||||
|
1/8 acre or less (townhouses)
|
65%
|
77
|
85
|
90
|
92
|
|
1/4 acre
|
38%
|
61
|
75
|
83
|
87
|
|
1/3 acre
|
30%
|
57
|
72
|
81
|
86
|
|
1/2 acre
|
25%
|
54
|
70
|
80
|
85
|
|
1 acre
|
20
|
51
|
68
|
79
|
84
|
|
2 acres
|
12%
|
46
|
65
|
77
|
82
|
|
Developing urban areas:
| |||||
|
Newly graded areas (pervious areas only, no vegetation)
|
77
|
86
|
91
|
94
| |
j.
USGS Regression Equations. For urban watersheds larger than
one hundred (100) acres, the engineer should compare the peak flow
rate determined from the critical duration analysis with the peak
flow rate calculated using the USGS regression equations in The Estimation
of the Magnitude and Frequency of Floods in Urban Basins in Missouri,
2010 (Southard 2010). These equations are summarized in Table 10 and
are applicable for urban areas within Missouri that have drainage
areas between 0.29 square miles and one hundred eighty-nine (189)
square miles and impervious areas between two and three-tenths percent
(2.3%) and forty-six percent (46%). These equations do not apply when
there is significant storage in the watershed. Although the resulting
peak flow rates typically have a relatively high coefficient of variation,
regression equations provide a useful reasonableness check for urban
watersheds.
|
Table 10: USGS Regression Equations
| |
|---|---|
|
Recurrence Interval
|
USGS Regression Equation
(Q = estimated peak flow rate [cfs], A = drainage area [mi2], I = impervious area in percent)
|
|
2-year
|
Q2= 188DRNAREA0.599100.014IMPLNLCD01
|
|
5-year
|
Q2= 352DRNAREA0.592100.011IMPLNLCD01
|
|
10-year
|
Q2= 484DRNAREA0.594100.010IMPLNLCD01
|
|
25-year
|
Q2= 671DRNAREA0.599100.008IMPLNLCD01
|
|
50-year
|
Q2= 826DRNAREA0.604100.008IMPLNLCD01
|
|
100-year
|
Q2= 991DRNAREA0.608100.007IMPLNLCD01
|
|
500-year
|
Q2= 1420DRNAREA0.619100.006IMPLNLCD01
|
k.
Off-Site And Adjacent Runoff. The design of a drainage system
should consider the runoff from off-site and adjacent areas, recognizing
their urban development potential. For hydrologic analysis, calculations
for off-site areas should assume these areas are completely developed,
even if they are undeveloped or have not yet reached their full development
potential. For the purposes of calculations and modeling, land use
for off-site areas should be based on City zoning and anticipated
land use for these areas. For flood control planning and modeling,
effects of detention should be disregarded except for publicly owned
and maintained facilities with storage dedicated for perpetuity, unless
otherwise approved by the City. Fully developed flows should be used
for facility sizing and design. The City may request additional modeling,
including the effects of detention in the watershed, especially where
timing of peak flow rates is a concern.
4.
Streets, Inlets, And Storm Drains.
a.
General. This Subsection contains design information and criteria
for the design of urban stormwater collection and conveyance systems.
This Subsection specifies criteria for: the allowable drainage encroachment
within public streets, allowable types, sizing, and placement of inlets,
and sizing and design of storm drains.
b.
Design Storms.
(1)
The stormwater system, at a minimum, shall commence
at the point where the two-year flow rate for fully developed conditions
equals or exceeds five (5) cubic feet per second (cfs) or street spread/depth
limitations are exceeded. The following criteria apply to the design
of streets, inlets, and storm drains:
(a)
The two-year flow rate shall be calculated for
the fully developed conditions to show that street inundation criteria
are met.
(b)
The hydraulic grade line (HGL) for the twenty-five-year
flow shall not exceed the elevation of the gutter for a pipe system
within public right-of-way or a drainage easement and shall not exceed
channel capacity with a freeboard of six (6) inches for an open channel.
(c)
All street storm drains and channels shall be designed
to convey the twenty-five-year flow with fully developed conditions.
(d)
Inlet, storm drain, and channel capacity shall
be designed so that the HGL from the 100-year flow under fully developed
conditions meets street inundation criteria and all runoff is directed
to the receiving detention basin or drainage system.
(e)
Inlets and storm drain within parking lots shall
be designed to limit ponding to twelve (12) inches for a 100-year
event.
(2)
In determining peak flow rates for design events
for the design of streets, inlets, and storm drains, the effects of
detention basins on adjacent properties may be accounted for if assurances
that detention will be provided for perpetuity and maintenance is
assured. Assurances must typically be provided through recorded documents
with land use restrictions and maintenance responsibilities properly
noted.
c.
Street Drainage.
(1)
Allowable Inundation Depth And Spread. The purpose
of limitations for inundation depth and spread is to ensure the safe
travel of the public and emergency vehicle access. These limitations
are based on the use classification of the street. The criteria used
for inundation limitations are the minor storm event (two-year) and
the major storm event (100-year). These criteria govern the design
of the longitudinal street slope, inlet size, and inlet spacing. Table
11 below presents City street inundation criteria. For collector and
arterial streets, no flow shall pass through an intersection for a
twenty-five-year or lesser event.
|
Table 11: City Street Inundation Criteria
| ||||
|---|---|---|---|---|
|
Street Classification
|
Minor Storm (2-year)
|
Major Storm (100-year)
| ||
|
Local
|
•
|
No flow from 1 side of street to another
|
•
|
No curb overtopping
|
|
•
|
No curb overtopping
| |||
|
•
|
Inlets spaced for a maximum spread of 8 feet from curb face
with 1 clear 10-foot travel lane
| |||
|
Collector
|
•
|
No flow from 1 side of street to another
|
•
|
No curb overtopping
|
|
•
|
No curb overtopping
| |||
|
•
|
Inlets spaced for a maximum spread of 8 feet from curb face
with on 12-foot travel lane clear for residential collectors, and
2 10-foot travel lanes clear for non-residential collectors
| |||
|
Arterial
|
•
|
No flow from 1 side of street to another
|
•
|
No curb overtopping
|
|
•
|
No curb overtopping
| |||
|
•
|
For secondary arterials, inlets spaced for a maximum 12-foot
spread with 2 12-foot travel lanes open
| |||
|
•
|
For other arterials, inlets spaced for a maximum 6-foot spread
with 1 full lane and 1 8-foot lane clear in both directions
| |||
(2)
Curb And Gutter Hydraulics. The required design
standard for public streets includes curbs and gutter. The minimum
allowable longitudinal slope for a public street is five-tenths percent
(0.5%). The maximum allowable longitudinal slope for a public street
range is from five percent (5%) to ten percent (10%), depending on
street classification. Standard gutter width is two (2) feet, with
a depth of two (2) inches, resulting in a gutter cross slope of 0.0833
foot per foot (ft/ft). The standard cross slope for a public street
is a one-fourth (1/4) inch per foot or approximately two and one-tenth
percent (2.1%). Gutter depression is one and five-tenths (1.5) inches
for typical Battlefield street sections. A greater longitudinal slope
results in higher velocities, less spread, and generally, higher inlet
efficiencies.
(a)
Gutter Flow And Spread. Gutter flow and spread
can be determined using Manning's Equation for open channel hydraulics.
Assuming the standard gutter and street cross-section found in the
Design Standards, gutter flow can be determined by using the figure
below.
 |
(3)
Roadside Swales. Battlefield's standard for public streets in new developments is a curb and gutter section with enclosed storm drains. Other street sections, such as roadside swale sections or other low-impact development (LID) designs, will be considered on a case-by-case basis. A subdivision variance will be required through the subdivision approval process, and generally, the developer or property owners' association will be required to maintain all street rights-of-way and LID components. Alternative designs shall take into consideration topography and the proposed development and must adhere to the principles of containing the 100-year flow within the right-of-way or drainage easement and preventing erosion. Refer to Subsection (F)(6), Open Channels, and Subsection (F)(8), Water Quality, for more information on open channel hydraulics, grass swales, and LID techniques.
d.
Inlets. Properly designed inlets are vital components of the
urban stormwater collection and conveyance system. Inlets collect
excess stormwater from the street, transition the flow into storm
drains, and can provide maintenance access to the storm drain system.
Inlets can be made of cast iron, steel, concrete, and/or precast concrete
and are installed on the edge of the street adjacent to the street
gutter or in the bottom of a swale.
Inlets shall not have a vertical opening greater than six (6)
inches. If a larger opening is used, a steel bar with a minimum diameter
of three-fourths (3/4) inch shall be placed in the opening so there
is no vertical opening greater than six (6) inches.
(1)
Inlet Locations. Inlets shall be provided at locations and intervals that shall have a minimum inflow capacity such that maximum flooding depths are not exceeded for the major or minor storm. Inlets shall be provided at all sump locations to prevent ponding of water. It is recommended that inlets be provided at street intersections upstream of pedestrian crosswalks. The spacing of inlets placed in addition to those required by geometric controls is governed by the allowable inundation criteria given in the table above in Subsection (F)(4)(c)(1).
(2)
Inlet Types.
(a)
Standard
Inlet Types.
i.
Curb Opening Inlets. The standard curb opening used
in Battlefield and Greene County has been very successful. However,
there has been a considerable amount of confusion over inlet nomenclature.
It is the intention of these standards to maintain commonly used terms
while clarifying inconsistencies and confusion. The following standard
curb inlet designations are recommended for use in City of Battlefield:
(i)
SS-5 Inlet (Figure SS-10).[16] The standard SS-5 curb opening inlet shall refer to a
shallow standard four-foot by eight-foot curb opening inlet with a
seven-foot long opening, located over a storm drain with a riser pipe
connecting the inlet with the storm drainpipe. Riser pipe capacities
for use with SS-5 inlets are shown in Figure SS-11.[17]
[16]
Editor's Note: This figure is included as an attachment to this chapter.
[17]
Editor's Note: This figure is included as an attachment to this chapter.
(ii)
SS-6 Inlet (Figure SS-12).[18] SS-6 inlet shall refer to a full depth standard four-foot
by eight-foot curb opening inlet with a seven-foot long opening, which
can also serve as a junction structure. Precast SS-6 inlets may be
provided with a six-inch precast top, known as an "SS-6 top," or an
eighteen-inch deep precast top, known as an SS-8 top. The largest
diameter pipe which can enter the short side of a SS-6 inlet is thirty
(30) inches.
[18]
Editor's Note: This figure is included as an attachment to this chapter.
(iii)
SS-6S Inlet. SS-6S inlet shall refer to a short
SS-6 inlet, i.e., a full depth inlet with a four-foot by four-foot
exterior dimension and a three-foot long opening, which can also serve
as a junction structure. SS-6S inlets are intended for use in sumps
serving small areas.
(iv)
SS-6G Inlet (Figure SS-14).[19] SS-6G inlet shall refer to an SS-6 inlet modified to include
a grate in the gutter. Grates used for SS-6G inlets shall be Deeter
2048L, Neenah R3076, or equal. Grates may not extend outward from
the curb any further than the width of the standard gutter, which
is two (2) feet. Vanes shall be oriented in the direction of gutter
flow.
[19]
Editor's Note: This figure is included as an attachment to this chapter.
(v)
Double Curb Inlets. Where necessary to meet allowable
flooding depth criteria, two (2) curb opening inlets may be placed
side by side. An opening shall be provided in the common walls between
the inlets to provide flow from one inlet to the other. The opening
shall be a minimum of eighteen (18) inches high and shall extend the
entire interior width of the inlet box.
(vi)
Special Inlet Box Designs. Where necessary to
accommodate large diameter pipes, curb opening inlets may be specially
designed. Details of concrete dimensions and reinforcement shall be
included in the drawings.
|
Curb opening inlets may be constructed of either precast or
cast-in-place concrete. Cast-in-place concrete construction shall
meet the requirements of Chapter VII of the City of Springfield Technical
Specifications or Public Works Construction.
|
ii.
Area Inlets.
(i)
Open-Side Drop Inlets, Type DI-1 (Figure SS-15).[20]
|
A)
|
Open side drop inlets are intended for use in locations where
open drainage channels, ditches, or swales terminate and flow enters
the storm drain system, and flows range from ten (10) cubic feet to
one hundred (100) cubic feet per second. These inlets are preferred
in order to minimize the risk of persons being swept into an open
storm drain entrance.
|
|
B)
|
This inlet has a four-foot by four-foot exterior dimension and
a maximum capacity of about eighteen (18) cfs per opening at a maximum
allowable depth of two (2) feet. The designer must stipulate on the
drawing the number of open sides to be provided, i.e., Type DI-1 w/2
sides open, etc. Interception capacity data for standard DI-1 inlets
are shown in Figure SS-16.[21]
|
|
C)
|
Where additional capacity is needed, larger inlet structures
can be used, provided dimensions are detailed on the drawings and
interception capacity calculations are submitted. The maximum allowable
opening height is six (6) inches. For greater opening heights, a horizontal
bar shall be placed across the opening at maximum six-inch intervals.
|
[20]
Editor's Note: This figure is included as an attachment to this chapter.
[21]
Editor's Note: This figure is included as an attachment to this chapter.
(ii)
Grated Area Inlets.
|
A)
|
Grated area inlets may be provided in parking lots and lawn
areas. The maximum ponding depth over grated inlets shall be twelve
(12) inches for the major (100-year) storm. Concrete dimensions and
reinforcement requirements for the inlet structure and the type of
grate and frame to be used shall be specified in the drawings. Gratings
shall be bicycle safe.
|
|
B)
|
It is recommended that a one-and-one-half-inch depression be
provided for area inlets in paved parking areas to minimize standing
water (see Figure SS-17[22]). It is also recommended that a reinforced concrete paving
apron be provided for two (2) feet around the inlet to prevent pavement
failure and subsequent water ponding around the inlet.
|
[22]
Editor's Note: This figure is included as an attachment to this chapter.
(b)
Types
of Inlets Allowed.
i.
Public Streets.
(i)
Curb Opening Inlets. Standard curb opening inlets
are required for use in public streets with curbs and gutter. Curb
openings are not permitted, except in situations where the drainage
area is one-half acre or less, and there is not sufficient grade to
permit installation of a storm drainpipe.
(ii)
Grated Inlets. In general, the use of grated inlets
will not be permitted in streets since these generally require adjustment
when streets are re-paved. Where conditions are such that curb inlets
cannot intercept the required rate of flow necessary to control street
flooding depth or to provide diversion of flow to detention, sedimentation,
or infiltration basins, combination grate and curb opening inlets
(Type SS-6G) may be used, provided that the width of the grate is
no greater than the gutter width. "Trench inlets" with vaned grates
may be specified with approval of the City of Battlefield. Use of
trench inlets will be permitted only when there is no practical alternative.
|
Other types of inlets will not be permitted unless approved
by the City of Battlefield.
|
ii.
Outside Of Public Right-Of-Way. The type of inlets
specified outside of public right-of-way is left to the discretion
of the designer provided the following criteria are met:
(i)
Maximum flooding depths for the major or minor storm as set forth in Subsection (F)(4)(c)(1), Table 11, are not exceeded.
(ii)
General safety requirements set forth in Subsection (F)(4)(d)(4) are met.
(3)
Inlet Interception.
(a)
Inlet
Interception Capacities.
i.
Inlet capacities shall be determined in accordance
with Federal Highway Administration HEC-12 or HEC-22. The gutter slope
to be used for design of curb opening inlets located on vertical curves
shall be the average gutter slope for twenty (20) feet upstream of
the inlet. See Figure SS-5 and Figure SS-6.[23]
[23]
Editor's Note: These figures are included as an attachment to this chapter.
ii.
Nomographs and methods presented in the Neenah
Inlet Grate Capacities report may also be used where applicable. The
use of commercial software utilizing the methods of HEC-12 or HEC-22
is acceptable.
(b)
Interception And Bypass Flow. It is generally not
practical for inlets on slopes to intercept one hundred percent (100%)
of the flow in gutters. Inlets must intercept sufficient flow to comply
with street flooding depth requirements. Bypass flows shall be considered
at each downstream inlet until all flow has entered approved storm
sewers or drainageways.
(c)
Clogging Factors.
i.
The inlet capacities determined as required in this
Subsection should be reduced as follows to account for partial blockage
of the inlet with debris. A clogging factor of 0.9 shall be used for
curb opening inlets, and a clogging factor of 0.5 shall be used for
grate inlets.
ii.
Inlet lengths or areas shall be increased as required
to account for clogging.
(4)
General Safety Requirements. All inlet openings
shall:
(a)
Provide for the safety of the public. The maximum
allowable opening for standard curb opening inlets and open side drop
inlets shall not exceed six (6) inches in height. The maximum bar
spacing for grated inlets shall be six (6) inches. Where the height
of the opening exceeds six (6) inches, a three-quarter (3/4) inch
diameter galvanized steel bar, or other approved restriction shall
be provided horizontally across the opening at mid-height, or at maximum
intervals of six (6) inches. The maximum open spacing between bars
for grated inlets shall be six (6) inches in any direction.
(b)
Be sufficiently small to prevent entry of debris
which would clog the storm drainage system.
(c)
Be sized and oriented to provide for safety of
pedestrians, bicyclists, etc.
e.
Storm Drains. This Subsection covers the design of closed piping
for conveyance of storm drainage. Design of open channels and other
conveyances is covered in other Subsections.
(1)
General. Storm drains convey runoff collected by
the inlet system. The storm drain system includes inlets, pipes, channels,
junctions, bends, outlets, and other appurtenances.
(a)
Horizontal
Alignment.
i.
Except for crossings, storm sewers shall not be
located under streets. Storm sewers paralleling curbed streets shall
be located such that the outside edge of the pipe is six (6) inches
minimum behind the back edge of the curb. Pipes shall be aligned in
straight lines. Curved alignments are not allowed.
ii.
Storm sewers located on private property shall
be located within drainage easements and shall be aligned parallel
with property lines unless otherwise approved. Where storm drains
exit the street right-of-way between residential lots, the pipe shall
be extended a minimum of forty (40) feet past the front yard setback
line, or to the estimated location of the rear of the dwellings, whichever
is more. The outside edge of the pipe shall be located a minimum of
five (5) feet from the easement line. Minimum easement widths are
given in Table 12 below.
|
Table 12: Minimum Easement Widths
| |
|---|---|
|
Inside Horizontal Dimension
(inches)
|
Minimum Easement Width
(feet)
|
|
15 to 48
|
15
|
|
54 to 72
|
17.5
|
|
84 and 96
|
20
|
|
Over 96
|
Approval required
|
(b)
Vertical
Alignment.
i.
The recommended minimum slope for storm drain piping
is five-tenths percent (0.5%). Pipe grades may not be less than the
minimum friction slope required to convey the design flow, unless
specifically approved. Maximum recommended grade is ten percent (10%).
A properly designed anchorage may be required for grades above ten
percent (10%) and will be required for grades above fifteen percent
(15%). Storm drains shall have a design velocity range from a minimum
of two (2) fps for the two-year event up to a maximum of fifteen (15)
fps for the 100-year event.
ii.
When changing pipe diameters, the inside tops of
the pipes shall be set at the same elevation. Pipe size shall never
be reduced downstream even though pipe slope and theoretical capacity
may increase. A minimum vertical drop of two-tenths (0.2) feet shall
always be provided across a junction structure, unless otherwise approved.
iii.
Under or within two (2) feet of streets or paved
areas, the top of the pipe shall be located a minimum of twelve (12)
inches below the pavement or curb subgrade, or greater if required
to meet minimum cover and strength requirements for the type of pipe
specified to withstand an AASHTO HS-20 loading. Outside of paved areas,
the top of the pipe shall be located a minimum of twelve (12) inches
below finished earth grade. Box culverts or other relatively wide
and flat conveyance structures may be required to have additional
cover if deemed necessary to support grass or other vegetative cover.
iv.
The vertical clearance between storm drains and
sanitary sewer and water lines shall be twenty-four (24) inches. In
cases where twenty-four (24) inches of vertical clearance cannot be
attained, refer to the City of Battlefield Design Standards for Public
Improvement for complete sanitary sewer separation requirements and
contact the appropriate utility for water line separation requirements.
v.
Vertical drops greater than six (6) feet require
a special design that addresses the need for structure protection
and energy dissipation.
(c)
Pipes.
i.
The minimum allowable inside diameter for any storm
drainpipe on or connecting to storm drain piping in public right-of-way
is fifteen (15) inches. The maximum allowable diameter is nine (9)
feet, unless otherwise approved.
ii.
The minimum allowable slope for pipes less than
thirty-six (36) inches in diameter is five percent (5%), and the maximum
allowable slope is fifteen percent (15%) unless hydraulic conditions
govern.
iii.
Storm sewers may be constructed of any of the
following materials:
|
Material
|
Symbol
|
Standard
|
|---|---|---|
|
Reinforced concrete round pipe
|
RCP
|
ASTM C-79, C1 III
|
|
Reinforced concrete elliptical pipe
|
RCEP
|
ASTM C-507
|
|
Reinforced concrete pipe-arch
|
RCPA
|
ASTM C-478
|
|
Precast concrete flared end sections
|
FES
|
ASTM C-76
|
|
Corrugated, galvanized steel round pipe
|
CMP
|
ASTM A-760/AASHTO M-36
|
|
Corrugated, galvanize steel pipe-arch
|
CMPA
|
AASHTO M-167
|
|
Galvanized steel flared end sections
|
FES
|
ASTM A-760
|
|
Corrugated polyethylene pipe
|
CPP
|
ASTM D-1248
|
|
Cast-in-place reinforced concrete box culverts
|
RCB
|
MODOT Spec.
|
|
Precast concrete box culvert
|
RCB
|
ASTM-789
|
iv.
Cast-in-place concrete pipe, masonry, vitrified
clay, or other pipe not shown above is not allowed unless specifically
approved. Detailed information on structural and hydraulic properties
of the type of pipe referred to above can be found in the Concrete
Pipe Design Manual, the Handbook of Steel Drainage & Highway Construction
Products, and manufacturer's information for corrugated polyethylene
pipe.
v.
Corrugated polyethylene pipe (CPP) is not allowed
within the public right-of-way or public drainage easements, unless
approved in writing by the City of Battlefield.
(d)
Junction
Boxes Or Manholes. A manhole or junction structure must be provided
at each change in direction or grade of the piping, except that bends
may be located at junction structures to provide a perpendicular connection.
Bends must be provided at junction structures if the angle of entry
is less than sixty degrees (60°). Pipes shall be aligned such
that the direction of flow of any incoming pipe is not less than perpendicular
to the direction of flow of the outflow pipe (i.e., flow "against
the grain" shall be avoided).
Access manholes for junction structures shall not be located
within the pavement area for public streets. Junction structures shall
be located such that the outside edge of the access manhole is twelve
(12) inches minimum behind the curb or from the edge of a retaining
wall or other obstruction.
Access manholes shall be provided at a maximum of three hundred
(300) feet spacing along the pipe.
Precast circular manholes, square cast-in-place or precast junction
boxes, or inlets may be used for junction structures.
A standard junction box is shown in Figure SS-18.[24]
i.
Precast Manholes.
(i)
Precast concrete manholes shall conform to the
requirements of ASTM-C478. Cast-in-place circular manholes are not
permitted. The following minimum manhole diameters shall be used:
|
Pipe Diameter
(inches)
|
Minimum Inside Diameter of Manhole
(feet)
|
|---|---|
|
15 to 24
|
4
|
|
27 to 42
|
5
|
|
48
|
6
|
|
24 to 66
|
8
|
|
> 66
|
Special junction structure
|
(ii)
A minimum clearance of two (2) feet measured at
the inside face of the manhole must be maintained between the outside
edge of storm sewer pipes. See Figure SS-7.[25]
[25]
Editor's Note: This figure is included as an attachment to this chapter.
ii.
Junction Boxes.
(i)
Square or rectangular junction boxes may be constructed
of cast-in-place or precast concrete. Minimum horizontal dimensions
for junction boxes are as follows:
|
Pipe Diameter
(inches)
|
Minimum Inside Width of Junction Box
|
|---|---|
|
15 to 30
|
4 feet
|
|
36 to 42
|
5 feet
|
|
48
|
5 feet 6 inches
|
|
54
|
6 feet
|
|
60
|
6 feet 6 inches
|
|
66
|
7 feet
|
|
72
|
7 feet 6 inches
|
|
>72
|
Special approval required
|
(ii)
Junction boxes shall not exceed eight (8) feet
in depth measured from the interior invert of the junction box to
the top of the junction box rim unless structural calculations are
submitted and approved.
(iii)
Precast junction structures shall have a maximum
inside horizontal dimension of eight (8) feet and a maximum depth
of eight (8) feet unless structural calculations are submitted and
approved. Precast junction boxes shall be manufactured by Rose-Con
Pipe, Springfield, Missouri, or be approved by the City.
iii.
Ring And Covers For Inlets, Manholes, And Junction
Boxes. Type A and Type C ring and covers for storm sewers shall be
used. See Figure SS-8 and SS-9[26] for details.
[26]
Editor's Note: These figures are included as an attachment to this chapter.
[24]
Editor's Note: This figure is included as an attachment to this chapter.
(e)
Bends
And Transitions.
i.
As stated in Subsection (F)(4)(e)(1)(d), a manhole or junction structure must be provided at each change in direction or grade of the piping, except that bends may be located at junction structures to provide a perpendicular connection. Bends must be provided at junction structures if the angle of entry is less than sixty degrees (60°).
ii.
In cases where bends and transitions are acceptable,
it may be necessary to provide gradual transitions in size or alignment
to minimize energy losses and potential for blockage. When bends are
necessary, bends at pipe joints should generally not exceed two degrees
(2°) or otherwise cause unacceptable head losses in the system.
Transitions should be gradual and should not decrease the size of
the pipe in the downstream direction. Special structures that control
head losses to an acceptable level may be necessary for other transitions.
(f)
Outlets.
i.
Storm sewer outlets shall be designed to allow expansion
of flow and reduction of velocity, without undue risk of erosion downstream,
and allowing for proper construction and maintenance of cut or embankment
slopes at the outlet. A headwall or flared end section shall be provided
at all pipe outlets. Flared end sections and headwalls shall have
a toe-wall extending a minimum of eighteen (18) inches below grade
at their downstream end to prevent undercutting.
ii.
An erosion resistant lining of concrete or grouted
riprap shall be provided for a distance equal to five (5) times the
diameter of the outlet pipe or the box culvert width, downstream of
the headwall apron or flared end section. The width of the grouted
riprap shall be a minimum of two (2) times the pipe diameter or box
culvert width or five (5) feet, whichever is less. Where velocity
exceeds fifteen (15) feet per second at the pipe outlet an energy
dissipator may be required. Energy dissipators shall be designed as
set forth in the ASCE design manual.
(g)
Clearance
From Other Utilities.
i.
Horizontal Clearance.
|
Utility
|
Minimum Distance From Outside Edge Of Pipe To Centerline
(feet)
|
|---|---|
|
Storm sewer
|
Inside diameter of largest pipe*
|
|
Sanitary sewer
|
5
|
|
Water, gas, electric line, or other utility
|
5
|
|
*
|
Or greater, if needed to allow proper placement and alignment
of flared end sections
|
ii.
Vertical Clearance. A minimum clear distance of
eighteen (18) inches from any other utility line shall be maintained
above or below the storm drainpipe, unless otherwise approved.
(h)
Other Appurtenances. Examples of other specialized
appurtenances include flow splitters and deflectors and flap gates.
Flow splitters separate incoming flow and send it in two or more directions.
Flow deflectors minimize energy losses in manholes, junction chambers,
and flow splitters. Flap gates may be placed on outlets to prevent
backflow in areas subject to high tailwater or flood flow. These are
structures that require individual consideration and specialized design
prior to City acceptance.
(2)
Plan Requirements. Each storm drain line shown
on the plan shall be numbered or lettered (Line 1, Storm 1, Line A,
etc.). Structures in each line shall be numbered or lettered in sequence
beginning at the downstream end of the line. Stationing shall begin
at the downstream end of the line and proceed upstream. Branch lines
shall be numbered consecutively moving in an upstream direction. A
continuous profile shall be drawn for each storm drain line.
(3)
General Safety Requirements. The following safety
criteria apply to all public storm drainage systems:
(a)
Headwalls and wingwalls associated with storm drain
outfalls shall include guardrails, handrails, or fencing in conformance
with highway design safety standards and applicable building codes.
(b)
Handrails shall be required in all areas where
the drop from the headwall or wingwall exceeds thirty (30) inches.
See the Design Standards for Public Improvements for handrail design
standards. Refer to AASHTO standards for safety rails along designated
bikeways.
(c)
Trash racks should be considered at all entrances
to storm drains, based on location and site conditions. Refer to Public
Safety Guidance for Urban Stormwater Facilities (ASCE) for guidance.
When used, inlet racks should have a minimum surface area of four
times the open area of the culvert. Racks at outlets are generally
discouraged.
(4)
Storm Drain Hydraulics.
(a)
General.
i.
The design of a storm drain system requires data
including topography, drainage boundaries, soil types, and locations
of any existing storm drains, inlets, and junction boxes. Identification
of the type and location of utilities to identify potential conflicts
must be completed early in the design process. The drainage area to
each inlet shall be identified and the design flows calculated to
determine the necessary pipe capacity.
ii.
Once the storm drain system is designed, the hydraulic
capacity shall be evaluated for the design storms using energy grade
line (EGL) calculations starting at the downstream terminus of the
system. Hydraulic grade line (HGL) calculations shall be performed
for the design storms. All transitions, bends, entrance and exit conditions,
tailwater conditions, and other losses shall be accounted for in HGL
calculations.
(b)
Design
Storm And Storm Drain Capacity.
i.
Storm sewers shall be designed to convey the peak
flow rate resulting from the required design storm having a rainfall
intensity corresponding to the time of concentration at the point
of interest, or a duration which produces the maximum runoff rate
at the point of interest, depending upon the method used for computing
runoff. It is preferred that storm sewers draining be designed for
runoff rates computed by the Rational Method.
(i)
Major (Emergency) System.
|
A)
|
Total drainage area less than one (1) square mile: 25-year (4%
AEP) storm.
|
|
B)
|
Total drainage area one (1) square mile or more: 100-year (1%
AEP) storm.
|
|
C)
|
In cases where no overland relief area is provided for the difference
between the 25- and 100-year storm, storm sewers shall be designed
to convey the 100-year storm.
|
(ii)
Minor (Convenience) System. Storm sewers shall
be designed to convey only intercepted flow necessary to maintain
allowable street flooding depths. Reductions in peak flow rates to
account for the effects of stormwater detention facilities located
upstream will be allowed only in instances where the detention basin
has been incorporated into an approved hydrologic model of the tributary
watershed.
ii.
All storm drains shall be designed to convey the
twenty-five-year flow with the HGL no higher than the gutter of the
street, and the HGL for the 100-year flow no higher than the top of
curb. Spread inundation criteria shall be met for the two-year and
100-year flows, and all runoffs shall be directed to the downstream
detention and/or drainage system appropriately.
(c)
Hydraulic
and Energy Grade Line Calculations.
ii.
Hydraulic Grade Line. Hydraulic grades are computed
by subtracting the velocity head, 
from the energy head. When the velocity is zero, the hydraulic grade
line coincides with the energy grade line.
from the energy head. When the velocity is zero, the hydraulic grade
line coincides with the energy grade line.iii.
Pipe Capacity.
(i)
Storm sewers shall be designed to convey the peak
flow rate from the design storm while maintaining allowable maximum
and minimum velocities, and without surcharging which would adversely
affect the performance of inlets or other components or the drainage
system, or cause flooding of structures or streets.
(ii)
Pipe capacity and velocity shall be computed using
Manning's Equation:
 | ||
|
where:
| ||
|
Q
|
=
|
rate of flow, cubic feet per second
|
|
n
|
=
|
Manning's roughness coefficient
|
|
A
|
=
|
cross sectional area of flow, square feet
|
|
P
|
=
|
wetted perimeter, feet
|
|
R
|
=
|
hydraulic radius = A/P, feet
|
|
S
|
=
|
slope
|
|
Material
|
n Value
|
|---|---|
|
Reinforced concrete culvert (pipe or box)
|
0.013
|
|
CMP 2-2/3 in x 1/2 in. annular corrugations
|
0.021(1)
|
|
CMP 3 in x 1 in. annular corrugations
|
0.027(1)
|
|
Structural plate CMP 6 in. x 2 in. annular corrugations (5 feet
dia.)
|
0.033
|
|
Polypropylene pipe
|
0.012
|
|
PVC (private development only)
|
0.012
|
|
HDPE (private development only)
|
0.012
|
|
(1)
|
Manning's n for helically corrugated CMP may be less in
certain conditions.
|
iv.
Head Loss Due To Pipe Friction. The friction loss,
hf, due to flow resistance in a storm sewer
is calculated as hf = L x Sf in which L is length of the sewer pipe (ft) and Sf is friction slope (ft/ft) typically taken as the bottom slope of
the pipe as a simplifying assumption for partially full, gravity flow
storm sewers.
v.
Pipe Entrances. Minor head losses for pipe entrance
are computed as follows:
 |
|
where:
|
|
Contraction coefficient, Kc = 0.5 (for
square edge conditions)
|
 |
|
where:
|
|
Expansion coefficient, Ke = 1.0
|
|
Type of Entrance
|
Entrance Coefficient, Ke
|
|---|---|
|
1. Pipe entrance with headwall
| |
|
Grooved edge
|
0.20
|
|
Rounded edge (0.15D radius)
|
0.15
|
|
Rounded edge (0.25D radius)
|
0.10
|
|
Square edge (cut concrete and CMP)
|
0.40
|
|
2. Pipe entrance with headwall and 45° wingwall
| |
|
Grooved edge
|
0.20
|
|
Square edge
|
0.35
|
|
3. Headwall with parallel wingwall spaced 1.25D apart
| |
|
Grooved edge
|
0.30
|
|
Square edge
|
0.40
|
|
4. Projecting entrance
| |
|
Grooved edge
|
0.25
|
|
Square edge
|
0.50
|
|
Sharp edge, thin wall
|
0.90
|
vi.
Pipe Junctions.
(i)
Minor head losses for junction and manhole losses
are computed as follows:
 |
|
where:
|
(ii)
Junction loss coefficient, Kj, for use in the foregoing equation is as defined in Figure SS-22.[27] Other methods of computing junction and manhole losses
are acceptable, provided they are documented in generally accepted
literature.
[27]
Editor's Note: This figure is included as an attachment to this chapter.
vii.
Transitions.
(i)
The energy loss due to a gradual pipe expansion,
hLE, is calculated as follows:
 | ||
|
where:
| ||
|
Ke
|
=
|
expansion loss coefficient from table below
|
|
V1
|
=
|
velocity upstream of the expansion (ft/s)
|
|
V2
|
=
|
velocity downstream of the expansion (ft/s)
|
(ii)
The energy loss due to a gradual pipe contraction,
hLC, is calculated as follows:
 | ||
|
where:
| ||
|
Kc
|
=
|
contraction loss coefficient
|
|
V1
|
=
|
velocity upstream of the expansion (ft/s)
|
|
V2
|
=
|
velocity downstream of the expansion (ft/s)
|
|
In general, Kc = 0.5Ke.
| ||
|
D2/D1
|
Angle of Cone
| ||||||
|---|---|---|---|---|---|---|---|
|
10°
|
20°
|
45°
|
60°
|
90°
|
120°
|
180°
| |
|
1.5
|
0.17
|
0.40
|
1.06
|
1.21
|
1.14
|
1.07
|
1.00
|
|
3
|
0.17
|
0.14
|
0.86
|
1.02
|
1.06
|
1.04
|
1.00
|
viii.
Bend Loss. The energy loss due to a bend, hLB, is calculated as follows:
 |
|
In which:
|
|
V = velocity in bend (ft/sec)
|
|
Δ = angle of curvature in degrees
|
ix.
Exit Loss.
(i)
The energy loss at a storm sewer system outlet,
hLO, is calculated using the following equation:
 | ||
|
where:
| ||
|
Vo
|
=
|
velocity in the outlet pipe (ft/sec)
|
|
Vd
|
=
|
velocity in the downstream channel (ft/sec)
|
(ii)
When a storm sewer discharges into a reservoir,
Vd = O. For discharge to an open channel, Manning's
Equation can be used to estimate Vd based on
channel geometry and roughness.
5.
Culverts And Bridges.
a.
General.
(1)
This Subsection addresses the hydraulic function
of culverts. The hydraulic function involves conveying surface water
through embankments such as roadways and railroads. In addition to
the hydraulic function, a culvert must support loads from construction
equipment, highway, railroad, or other traffic. Therefore, culvert
design involves both hydraulic and structural design considerations,
though this Subsection is focused strictly on the hydraulic aspects
of culvert design.
(2)
Multiple factors have a bearing on the capacity
and overall performance of a culvert. These include size, shape, material,
as well as several other variables. Sizes and shapes of culverts may
vary from small circular pipes to extremely large arch sections used
in place of a bridge.
(3)
The material selected for a culvert is dependent
upon various factors, such as durability, structural strength, roughness,
bedding condition, abrasion and corrosion resistance, and water tightness.
The most commonly used culvert materials are steel (smooth and corrugated)
and concrete.
(4)
The inlet configuration is another factor that
significantly affects the performance of a culvert. The inlet may
consist of a culvert barrel projecting from the roadway fill or mitered
to the embankment slope. Other inlets have headwalls, wingwalls, and
apron slabs or may have standard end sections of concrete or metal.
(5)
The following is a list of culvert shapes and their
applications:
(a)
Circular: most common culvert shape, for general
use.
(b)
Elliptical: often used in lieu of circular pipe
in situations where the available cover depth is limited.
(c)
Arch: suitable for locations where less obstruction
to a waterway is preferred and where foundations are adequate for
structural support.
(d)
Box: suitable for passing large flows and for a
range of site conditions. A box or rectangular culvert lends itself
more readily than other shapes to low allowable headwater situations
since the culvert height may be decreased to satisfy the site constraints
and the width (span) increased to accommodate flow capacity requirements.
b.
Design Information. The hydraulic design of a culvert involves
analyzing the required performance of the culvert to convey flow through
an embankment, such as a road. The designer must select a design flood
frequency, estimate the design discharge for that frequency, and set
an allowable headwater elevation based on the selected design flood
and headwater considerations.
The culvert size and type can only be selected after certain
design criteria have been determined such as the design discharge,
controlling design headwater, slope, tailwater, and allowable outlet
velocity.
(1)
Discharge. The discharge used in culvert design
is usually estimated on the basis of a preselected storm recurrence
interval, and the culvert is designed to operate within acceptable
limits of risk at that flow rate. The design recurrence interval should
be based on the more restrictive criteria set forth in Table 13 below.
|
Table 13: Storm Recurrence Intervals
| ||
|---|---|---|
|
Criterion
|
Criterion Value
|
Design Storm Recurrence Interval
|
|
Drainage area above culvert
|
Less than 1 square mile
|
25-year
|
|
1 square mile or greater
|
100-year
| |
|
Roadway classification
|
Smaller than secondary arterial
|
25-year
|
|
Secondary arterial or greater
|
100-year
| |
|
NOTES:
| ||||
|
1.
|
For all roadways, culvert sizing should accommodate the design
storm and also allow for one (1) foot of freeboard below the sag in
the roadway or below the low chord of a bridge structure, whichever
results in a lower water surface elevation (W.S.E.).
| |||
|
2.
|
For safety purposes, roadway culverts sized for the 25-year
event should also be checked for the 100-year flow. If, during the
100-year event, flow overtops the roadway, then the velocity and depth
must meet the following criterion:
| |||
|
a.
|
V * D is less than or equal to 4, where:
| |||
|
i.
|
V = Velocity of flow in water overtopping roadway (ft/sec)
| |||
|
ii.
|
D = Depth of flow overtopping roadway (ft)
| |||
|
b.
|
If V * D is greater than 4, then the culvert capacity must be
increased until V * D < 4 for the 100-year event.
| |||
(2)
Headwater Depth.
(a)
Culverts
frequently constrict the natural stream flow, which causes a rise
in the upstream water surface. The elevation of the upstream water
surface is termed headwater elevation. The headwater depth is measured
from the invert of the culvert inlet to the water surface of the stream.
In selecting the design headwater elevation, the designer should consider
the following:
i.
Headwater/culvert depth ratio (HW/D) should not
exceed one and one-half (1.5) unless there is justification and sufficient
measures are taken to protect the culvert inlet (for example, a concrete
headwall).
ii.
Anticipated upstream and downstream flood risks,
for a range of return frequency events.
iii.
Hazard to human life and safety (caused by exceeding
the design headwater elevation).
iv.
Damage to the culvert and the roadway.
v.
Traffic interruption.
vi.
Low point in the roadway grade line.
vii.
Roadway elevation above the structure.
viii.
Elevation at which water will flow to the next
cross drainage.
ix.
Relationship of headwater depth to the stability
of the embankment that the culvert passes through.
(b)
The designer should verify that the watershed divides
are higher than the design headwater elevations. In flat terrain,
drainage divides are often undefined or nonexistent, and culverts
should be located and designed for the least disruption of the existing
flow distribution.
(3)
Tailwater Depth. Tailwater is the flow depth in
the downstream channel measured from the invert of the culvert outlet.
A field inspection of the downstream channel should be made to determine
whether there are obstructions that will influence the tailwater depth.
Tailwater depth may be controlled by several factors, including the
stage in a contributing stream, headwater from structure downstream
of the culvert, reservoir water surface elevations, or other downstream
features.
(4)
Outlet Velocity.
(a)
The outlet velocity of a culvert, measured at the
downstream end of the culvert, is usually higher than the maximum
natural stream velocity. This higher velocity can cause streambed
scour and bank erosion for a limited distance downstream from the
culvert outlet.
(b)
Permissible velocities at the outlet will depend
upon streambed type, and the type of energy dissipation (outlet protection)
that is provided. As a general rule, the velocity at the downstream
edge of a project right-of-way or downstream constraint should not
be greater than the preconstruction velocity. Velocities must be non-erosive
to the existing channel; otherwise, downstream improvements may be
required by incorporating some type of outlet protection or energy
dissipation device. Variations in shape and size of a culvert seldom
have a significant effect on the outlet velocity.
c.
Culvert Hydraulics.
(1)
Key Hydraulic Principles. When designing culverts,
the Mannings's Equation, Continuity Equation, and Energy Equation
are the most essential. The three (3) equations are shown below:
|
Mannings Equation:
| ||
 | ||
|
where:
| ||
|
Q
|
=
|
flow rate or discharge (cfs)
|
|
n
|
=
|
Manning roughness coefficient (unitless)
|
|
A
|
=
|
cross sectional area of flow (sq ft)
|
|
R
|
=
|
hydraulic radius (ft)
|
|
S
|
=
|
longitudinal slope (unitless)
|
|
Continuity Equation:
| ||
|
Q = v1A1 = v2A2
| ||
|
where:
| ||
|
Q
|
=
|
flow rate or discharge (cfs)
|
|
v
|
=
|
velocity (ft/sec)
|
|
A
|
=
|
cross sectional area of flow (sq ft)
|
|
Energy Equation:
| ||
 | ||
|
where:
| ||
|
v
|
=
|
velocity (ft/sec)
|
|
g
|
=
|
gravitational acceleration (32.2 ft/sec2)
|
|
p
|
=
|
pressure (lb./ft2)
|
|
y
|
=
|
specific weight of water (62.4 lb./ft3)
|
|
(Note: p/y = pressure head or depth of flow)
| ||
|
z
|
=
|
height above datum (ft)
|
(a)
Energy
And Hydraulic Grade Lines.
The energy grade line, also known as "the line of total head",
is the sum of velocity head v2/2g, the
depth of flow or pressure head p/y, and elevation above an arbitrary
datum represented by the distance z. The energy grade line slopes
downward in the direction of flow by an amount equal to the energy
gradient HL/L, where HL equals the total energy loss over the distance L.
The hydraulic grade line, also known as "the line of piezometric
head," is the sum of the elevation z and the depth of flow or pressure
head p/y.
i.
Closed Conduit Flow. For pressure flow in closed
conduits, p/y is the pressure head, and the hydraulic grade line falls
above the top of the conduit as long as the pressure relative to atmospheric
pressure is positive.
ii.
Open Channel Flow. For open channel flow, the term
p/y is equivalent to the depth of flow and the hydraulic grade line
is the same as the water surface. Where open channel flow is established,
the hydraulic grade line is the same as the water surface.
(b)
Inlet
And Outlet Control. There are two (2) basic types of flow conditions
in culverts: inlet control and outlet control. For each type of control,
a different combination of factors is used to determine the hydraulic
capacity of the culvert.
i.
Inlet Control. A culvert operates under inlet control
when the flow capacity of the culvert is controlled at the inlet by
the following factors:
|
•
|
Depth of headwater
|
|
•
|
Inlet edge configuration
|
|
•
|
Cross sectional area
|
|
•
|
Barrel shape (i.e., circular, elliptical, rectangular, etc.)
|
|
With inlet control, the culvert barrel usually flows only partially
full. Inlets control for culverts occurs under 2 conditions:
| |
|
1.
|
Unsubmerged Inlet - The headwater depth is not sufficient to
submerge the top of the culvert, and the culvert invert slope is supercritical.
This is the less common condition of inlet control.
|
|
2.
|
Submerged Inlet - The headwater submerges the top of the culvert,
and the pipe does not flow fully. This is the more common condition
of inlet control.
|
(c)
Outlet Control. If the headwater is high enough,
the culvert slope sufficiently flat and the culvert sufficiently long,
the control will shift from the inlet to the outlet. In outlet control,
the discharge is a function of the inlet losses, the headwater depth,
the culvert roughness, the culvert length, the barrel diameter, the
culvert slope, the type of outlet and in some cases, the tailwater
elevation. With outlet control, culvert hydraulic performance is determined
by the following factors:
|
•
|
Depth of headwater
|
|
•
|
Inlet edge configuration
|
|
•
|
Cross sectional area
|
|
•
|
Culvert shape
|
|
•
|
Barrel slope
|
|
•
|
Barrel length
|
|
•
|
Barrel roughness
|
|
•
|
Depth of tailwater
|
|
Outlet control for culverts occurs under 2 conditions:
| |
|
1.
|
Partially Full Conduit - The headwater depth is insufficient
to submerge the top of the culvert, and the culvert slope is subcritical,
resulting in the culvert flowing partially full. This is the less
common condition of outlet control.
|
|
2.
|
Full Conduit - The culvert flows full along its length. This
is the more common condition of outlet control.
|
(2)
Energy Losses.
(a)
Inlet Losses. For inlet losses, the governing equations
are the following:
 | ||
|
where:
| ||
|
Q
|
=
|
flow rate or discharge (cfs)
|
|
C
|
=
|
contraction coefficient (dimensionless)
|
|
A
|
=
|
cross sectional area (ft2)
|
|
g
|
=
|
acceleration due to gravity, 32.2 (ft/sec2)
|
|
H
|
=
|
total head (ft)
|
|
He
|
=
|
head loss at entrance (ft)
|
|
Ke
|
=
|
entrance loss coefficient (see table below)
|
|
v
|
=
|
average velocity (ft/sec)
|
|
Entrance Coefficient
| ||
|---|---|---|
|
Type of Entrance
|
Entrance Coefficient, Ke
| |
|
1. Pipe entrance with headwall
| ||
|
Grooved edge
|
0.20
| |
|
Rounded edge (0.15D radius)
|
0.15
| |
|
Rounded edge (0.25D radius)
|
0.10
| |
|
Square edge (cut concrete and CMP)
|
0.40
| |
|
2. Pipe entrance with headwall and 45° wingwall
| ||
|
Grooved edge
|
0.20
| |
|
Square edge
|
0.35
| |
|
3. Headwall with parallel wingwall spaced 1.25D apart
| ||
|
Grooved edge
|
0.30
| |
|
Square edge
|
0.40
| |
|
4. Projecting entrance
| ||
|
Grooved edge
|
0.25
| |
|
Square edge
|
0.50
| |
|
Sharp edge, thin wall
|
0.90
| |
(b)
Friction
Losses.
i.
Friction head loss for pipes flowing partially full
can be determined from the Manning's Equation reformulated to
calculate head loss:
 | ||
|
where:
| ||
|
Hf
|
=
|
frictional head loss in culvert barrel (ft)
|
|
n
|
=
|
Manning roughness coefficient (unitless)
|
|
L
|
=
|
culvert length (ft)
|
|
R
|
=
|
hydraulic radius (=A/p) (ft)
|
|
A
|
=
|
cross sectional area of culvert barrel (ft2)
|
|
p
|
=
|
wetted perimeter of barrel (ft)
|
|
v
|
=
|
average velocity (ft)
|
|
g
|
=
|
acceleration due to gravity, 32.2 (ft/sec2)
|
ii.
Friction head loss for turbulent flow in pipes
flowing full can be determined from the Darcy-Weisbach Equation.
 | ||
|
where:
| ||
|
Hf
|
=
|
frictional head loss (ft)
|
|
f
|
=
|
friction factor (obtained from Moody's diagram)
|
|
L
|
=
|
culvert length (ft)
|
|
D
|
=
|
pipe diameter (ft)
|
|
v
|
=
|
average velocity (ft)
|
|
g
|
=
|
acceleration due to gravity, 32.2 (ft/sec2)
|
(c)
Outlet Losses. For outlet losses, the governing
equations are related to the difference in velocity head between the
pipe flow and the downstream channel at the end of the pipe. The downstream
channel velocity is usually neglected, resulting in the outlet losses
being equal to the velocity head of full flow in the culvert barrel,
given by the following equation:
 | ||
|
Ho
|
=
|
outlet head loss (ft)
|
|
v
|
=
|
average velocity in culvert barrel (ft)
|
|
g
|
=
|
acceleration due to gravity, 32.2 (ft/sec2)
|
d.
Culvert Sizing And Design. Culvert design involves trial and
error to determine the proper culvert size and involves the following
steps:
|
•
|
Select a culvert shape, type, and size with a particular inlet
end treatment.
|
|
•
|
Determine a headwater depth for both inlet and outlet control
given the design discharge, the grade and length of culvert, and the
depth of water at the outlet (tailwater).
|
|
•
|
Compare the largest depth of headwater (as determined from either
inlet or outlet control) to the design criteria. If the design criteria
are not met, continue trying other culverts.
|
|
•
|
Estimate the culvert outlet velocity. Determine if there is
a need for any special features such as energy dissipators, riprap
protection, fish passage, trash/safety rack, etc.
|
|
The hydraulic design of culverts can be achieved using several
different methods, including the following described in this Subsection:
capacity charts, nomographs, and computer applications.
|
(1)
Capacity Charts. Capacity charts can provide a
good understanding of how culvert size requirements vary depending
on multiple variables. Each chart contains a series of curves which
show the discharge capacity per culvert barrel in cfs for each of
several sizes of similar culvert types, given various headwater depths
(measured in feet above the culvert invert at the inlet). Each culvert
size is described by two (2) lines: one (1) solid and one (1) dashed.
The numbers associated with each line are the ratio of the culvert
length, L, in feet, to one hundred (100) times the slope, s, in feet
per foot (ft/ft) (100s). The solid line represents the division between
outlet and inlet control. The dashed lines represent the maximum L/(100s)
ratio for which the curves may be used without modification. Examples
of capacity charts are shown below with the upper chart being for
culvert diameters from eighteen (18) inches to thirty-six (36) inches
and the bottom chart being for culvert diameters from thirty-six (36)
inches to sixty-six (36) incher (refer to FHWA 2005a for capacity
carts):
 |
(a)
Culverts Under Inlet Control. For values of L/(100s)
less than that shown on the solid line, the culvert is operating under
inlet control. The headwater depth is determined from the L/(100s)
value given on the solid line. The solid-line inlet-control curves
are plotted from model test data. The dashed-line outlet-control curves
were computed for culverts of various lengths with relatively flat
slopes. Free outfall at the outlet was assumed; therefore, tailwater
depth is assumed not to influence the culvert performance.
(b)
Culverts
Under Outlet Control.
i.
For culverts flowing under outlet control, the head
loss at the entrance is computed using the loss coefficients previously
given, and the hydraulic roughness of the various materials used in
culvert construction is considered in computing resistance loss for
full or part-full flow.
ii.
Except for large pipe sizes, headwater depths on
the charts extend to three (3) times the culvert height. Pipe arches
and oval pipe show headwater up to 2.5 times their height since they
are used in low fills. The dotted line, stepped across the charts,
shows headwater depths approximately twice the barrel height and indicates
the upper limit of unrestricted use of the charts. Above this line
the headwater elevation should be checked with nomographs or with
computer programs. Also note, the headwater/culvert depth (HW/D) ratio
should not exceed 1.5 unless there is justification and sufficient
measures are taken to protect the culvert inlet.
iii.
The headwater depth given by the charts is actually
the difference in elevation between the culvert invert at the entrance
and the total head; that is, depth plus velocity head for flow in
the approach channel. In most cases, the water surface upstream from
the inlet is so close to this same level that the chart determination
may be used as headwater depth for practical design purposes. Where
the approach velocity is in excess of 3.0 ft/sec, the velocity head
must be subtracted from the curve determination of headwater to obtain
the actual headwater depth.
(c)
Capacity
Chart Procedure. The procedure for sizing the culvert is summarized
below.
i.
List design data: Q = flow or discharge rate (cfs),
L = length of culvert (ft), allowable Hw =
headwater depth (ft), s = slope of culvert (ft/ft), type of culvert
barrel, and entrance.
ii.
Compute L/(100s).
iii.
Find the design discharge, Q in the appropriate
capacity chart (refer to FHWA 2005a for capacity charts).
iv.
Find the L/(100s) value for the smallest pipe that
will pass the design discharge. If this value is above the dotted
line shown in the example capacity charts above, use nomographs or
computer programs to check headwater conditions.
v.
If L/(100s) is less than the value of L/(100s) given
for the solid line, then the value of Hw is
the value obtained from the solid line curve. If L/(100s) is larger
than the value for the dashed outlet control curve, then special measures
must be taken, and the reader is referred to FHWA 2005a.
vi.
Check the Hw value obtained
from the charts with the allowable Hw. If the
indicated Hw is greater than the allowable
Hw, then try the Hw elevation
from the next largest pipe size.
(2)
Nomographs. Examples of nomographs for designing
culverts are presented in the two (2) figures below with the first
figure being an inlet control nomograph and the second figure being
an outlet control nomograph. The use of these nomographs is limited
to cases where tailwater depth is higher than the critical depth in
the culvert.
A disadvantage of the nomographs is that they require trial
and error, whereas the capacity charts are direct. However, a disadvantage
of the capacity charts is they can be used only when the flow passes
through critical depth at the outlet. If the critical depth at the
outlet is less than the tailwater depth, then the nomographs must
be used. Both the capacity charts and nomographs shall give the same
results if either of the two (2) methods are used.
 Inlet Control Nomograph
|
 Outlet Control Nomograph
|
(a)
Nomograph
Procedure.
i.
The nomograph procedure for culvert design requires
the use of both the inlet control and outlet control nomographs (refer
to the respective figures above):
|
•
|
List design data: Q (cfs), L (ft), invert elevations in and
out (ft), allowable Hw (ft), mean and maximum
flood velocities in natural stream (ft/sec), culvert type and entrance
type for first (1st) selection.
| |
|
•
|
Determine a trial size by assuming a maximum average velocity
based on channel considerations to compute the area, A = Q/V.
| |
|
•
|
Find Hw for trial size culvert for inlet
control and outlet control. For inlet control, connect a straight
line through D and Q to scale one (1) of the Hw/D scales and project horizontally to the proper scale, compute Hw, and, if too large or too small, try another size before
computing Hw for outlet control.
| |
|
•
|
Next, compute the Hw for outlet control.
Enter the graph with the length, the entrance coefficient for the
entrance type, and the trial size. Connect the length scale and the
culvert size scale with a straight line, pivot on the turning line,
and draw a straight line from the design discharge on the discharge
scale through the turning point to the head scale (head loss, H).
Compute Hw from the equation:
| |
|
Hw = H + ho -
Ls
| ||
|
where:
| ||
|
Hw
|
=
|
headwater depth (ft)
|
|
H
|
=
|
head loss (ft)
|
|
ho
|
=
|
tailwater depth or elevation at the outlet of a depth equivalent
to the location of the hydraulic grade line (ft)
|
|
L
|
=
|
length of culvert (ft)
|
|
s
|
=
|
slope of culvert (ft/ft)
|
|
For Tw greater than or equal to the top
of the culvert: ho = Tw
| ||
|
For Tw less than the top of the culvert:
 (whichever is greater) | ||
|
ho
|
=
|
critical depth (ft)
|
|
dc
|
=
|
critical depth (ft)
|
|
D
|
=
|
culvert diameter (ft)
|
|
Tw
|
=
|
tailwater depth (ft)
|
|
If Tw is less than dc, the nomographs cannot be used, see Hydraulic Design of Highway
Culverts (FHWA 2005a) for critical depth charts.
| ||
ii.
Compare the computed headwaters and use the higher
Hw to determine if the culvert is under inlet
or outlet control. If outlet control governs and the Hw is unacceptable, select a larger trial size and find another Hw with the outlet control nomographs. Since the smaller
size of culvert had been selected for allowable Hw by the inlet control nomographs, the inlet control for the larger
pipe need not be checked.
(3)
Computer Applications.
(4)
Design Considerations. Because of problems that
arise from topography and other considerations, the actual design
of a culvert installation is more difficult than the simple process
of sizing culverts. The information in the procedure for design is
only guidelines since the problems encountered are too varied and
too numerous to be generalized. However, the actual process presented
should be followed to ensure that a special problem is not overlooked.
(a)
Invert Elevations. After determining the allowable
headwater elevation, the tailwater elevation, and the approximate
culvert length, invert elevations must be assumed. Scour is not likely
in an artificial channel such as a roadside ditch or a major drainage
channel when the culvert has the same slope as the channel. To reduce
the chance of failure due to scour, invert elevations corresponding
to the natural grade should be used as a first trial. For natural
channels, the flow conditions in the channel upstream from the culvert
should be investigated to determine if scour will occur.
(b)
Culvert Diameter. After the invert elevations have
been assumed, the diameter of pipe that will meet the headwater requirements
should be determined. Since small diameter pipes are often plugged
by sediment and debris, it is recommended that pipe smaller than eighteen
(18) inches not be used. Since the pipe roughness influences the culvert
diameter, both concrete and corrugated metal pipes should be considered
in design, if both will satisfy the headwater requirements.
(c)
Limited Headwater. If there is insufficient headwater
elevation to obtain the required discharge, it is necessary to oversize
the culvert barrel, lower the inlet invert, use an irregular cross
section, or use any combination of the preceding to increase the discharge
rate. If the inlet invert is lowered, special consideration must be
given to scour. The use of gabions or concrete drop structures, riprap,
and headwalls with apron and toe walls should be investigated and
compared to obtain a proper design.
(d)
Culvert Outlet. The outlet velocity must be checked to determine if a significant scour will occur downstream during a major storm. If scour is indicated, refer to Subsection (F)(5)(f) of this Subsection ("Protection Downstream of Culverts"). Under-designing the amount of outlet protection is not recommended for economizing during design and construction because downstream channel degradation can be significant, and the culvert outlet can be undermined.
(e)
Minimum Slope. To minimize sediment deposition
in the culvert, the culvert slope must be equal to or greater than
the slope required to maintain a minimum velocity. The slope should
be checked for each design, and if the proper minimum velocity is
not obtained, the pipe diameter may be decreased, the slope steepened,
a smoother pipe used, or a combination of these employed to increase
velocity.
e.
Culvert Inlets. An
often-overlooked fact is that a culvert cannot convey any more water
than can enter the inlet. Frequently, culverts and open channels are
carefully designed with full consideration given to slope, cross section,
and hydraulic roughness, but without regard to the inlet limitations.
Culvert designs using uniform flow equations rarely carry their design
capacity due to limitations imposed by the inlet. The design of a
culvert, including the inlet and the outlet, requires a balance between
cost, hydraulic efficiency, purpose, and topography at the proposed
culvert site. In situations where there is sufficient allowable headwater
depth, a choice of inlets may not be critical, but where there are
constraints such as limited headwater depth, erosion problems, or
where sedimentation is likely, a more efficient inlet may be required
to obtain the necessary discharge for the culvert.
Although the primary purpose of a culvert is to convey flows,
a culvert may also be used to restrict flow. That is, a culvert can
be used to discharge a controlled amount of water while the area upstream
from the culvert is, for example, used for detention storage to reduce
a storm runoff peak. For this case, an inefficient inlet may be the
most desirable choice.
The entrance coefficient, Ke, is a measure
of the hydraulic efficiency at the inlet with lower values indicating
greater efficiency. Entrance coefficients recommended for use are
given in Table 14 below.
|
Table 14: Entrance Coefficients.
| ||
|---|---|---|
|
Type of Entrance
|
Entrance Coefficient, Ke
| |
|
1. Pipe entrance with headwall
| ||
|
Grooved edge
|
0.20
| |
|
Rounded edge (0.15D radius)
|
0.15
| |
|
Rounded edge (0.25D radius)
|
0.10
| |
|
Square edge (cut concrete and CMP)
|
0.40
| |
|
2. Pipe entrance with headwall and 45° wingwall
| ||
|
Grooved edge
|
0.20
| |
|
Square edge
|
0.35
| |
|
3. Headwall with parallel wingwall spaced 1.25D apart
| ||
|
Grooved edge
|
0.30
| |
|
Square edge
|
0.40
| |
|
4. Projecting entrance
| ||
|
Grooved edge
|
0.25
| |
|
Square edge
|
0.50
| |
|
Sharp edge, thin wall
|
0.90
| |
(1)
Projecting Inlets. Projecting inlets shall not
be used. Headwalls, wingwalls, and flared end sections should be used
to maximize efficiency and minimize turbulence, head loss, and erosion.
(2)
Inlets With Headwalls. Headwalls may be used for
a variety of reasons, including increasing the efficiency of the inlet,
providing embankment stability, and providing embankment protection
against erosion. The relative efficiency of the inlet varies with
the pipe material used.
(a)
Corrugated Metal Pipe. A corrugated metal pipe
in a headwall is essentially a square-edged entrance with an entrance
coefficient of approximately 0.4. The entrance losses may be reduced
by rounding the entrance. The entrance coefficient may be reduced
as follows:
(b)
Concrete Pipe. For tongue-and-groove or bell-end
concrete pipes, little increase in hydraulic efficiency is realized
by adding a headwall. The primary reason for using headwalls is for
embankment protection and for ease of maintenance. The entrance coefficients
for concrete pipe are:
(c)
Wingwalls. Wingwalls are used where the side slopes
of the channel adjacent to the entrance are unstable and where the
culvert is skewed to the normal channel flow. Little increase in hydraulic
efficiency is realized with the use of wingwalls, regardless of the
pipe material used and, therefore, the use should be justified for
reasons other than an increase in hydraulic efficiency. For parallel
wingwalls, the minimum distance between wingwalls should be at least
1.25 times the diameter of the culvert pipe.
(d)
Aprons.
i.
If high headwater depths are to be encountered,
or if the approach velocity of the channel will cause scour, a short
channel apron should be provided at the toe of the headwall. This
apron should extend at least one (1) pipe diameter upstream from the
entrance, and the top of the apron should not protrude above the normal
streambed elevation.
ii.
Culverts with wingwalls should be designed with
a concrete apron extending between the walls.
iii.
Aprons must be reinforced to control cracking.
For conditions where scouring may be a problem due to high approach
velocities and special soil conditions such as alluvial soils, a toe
wall is often desirable for apron construction.
(3)
Special Inlets. There is a large variety of inlets
other than the common ones described. Among the other types of special
inlets are special end-sections, which serve as both outlets and inlets,
and which are available for both corrugated metal pipe and concrete
pipe.
(a)
Corrugated Metal Pipe. Special end-sections for
corrugated metal pipe add little to the overall cost of the culvert
and have the following advantages:
(b)
Concrete Pipe.
i.
As is the case with corrugated metal pipe, concrete
special end-sections may aid in increasing the embankment stability
or in retarding erosion at the inlet. They should be used where maintenance
equipment must be used near the inlet or where, for aesthetic reasons,
a projecting entrance is considered too unsightly.
ii.
The hydraulic efficiency of this type of concrete
inlet is dependent on the geometry of the end-section to be used.
Where the full contraction to the culvert diameter takes place at
the first pipe section, the entrance coefficient, Ke, is equal to 0.5, and where the full contraction to the culvert
diameter takes place in the throat of the end-section, the entrance
coefficient, Ke, is equal to 0.25.
(c)
Mitered Inlets.
i.
The use of mitered inlets is predominantly with
corrugated metal pipe and its hydraulic efficiency is dependent on
the construction procedure used. If the embankment is not paved, the
entrance, in practice, usually does not conform to the side slopes,
giving a projecting entrance with Ke =
0.9. If the embankment is paved, a sloping headwall is obtained with
Ke = 0.60 and, by beveling the edges, Ke = 0.50.
ii.
Uplift is an important factor for a mitered inlet.
It is not good practice to use unpaved embankment slopes where a mitered
entrance may be submerged to an elevation one-half (1/2) the diameter
of the culvert above the top of the pipe.
(d)
Long Conduit Inlets. Inlets are important in the
design of culverts for road crossings and other short sections of
conduit; however, they are even more significant in the economical
design of long culverts and pipes. Unused capacity in a long conduit
will result in wasted investment. Long conduits are costly and require
detailed engineering, planning, and design work. The inlets to such
conduits are extremely important to the functioning of the conduit
and must receive special attention. Most long conduits require special
inlet considerations to meet the particular hydraulic characteristics
of the conduit. Generally, on larger conduits, hydraulic model testing
will result in better and less costly inlet construction.
(4)
Improved Inlets.
(a)
Inlet edge configuration is one (1) of the prime
factors influencing the performance of a culvert operating under inlet
control. Inlet edges can cause a severe contraction of the flow, as
in the case of a thin edge, projecting inlet. In a flow contraction,
the effective cross sectional area of the barrel may be reduced to
about one-half (1/2) of the actual barrel cross sectional area. As
the inlet configuration is improved, the flow contraction is reduced,
thus improving the performance of the culvert.
(b)
A tapered inlet is a flared culvert inlet with
an enlarged face section and a hydraulically efficient throat section.
Tapered inlets improve culvert performance by providing a more efficient
control section (the throat). However, tapered inlets are not recommended
for use on culverts flowing under outlet control because the simple
beveled edge is of equal benefit. The two (2) most common improved
inlets are the side-tapered inlet and the slope-tapered inlet. FHWA
(2005a) Hydraulic Design of Highway Culverts provides guidance on
the design of improved inlets.
(5)
Inlet Protection. Inlets on culverts, especially
on culverts to be installed in live streams, should be evaluated relative
to debris control and buoyancy.
(a)
Debris Control.
i.
Accumulation of debris at a culvert inlet can result
in the culvert not performing as designed. The consequences may be
damage caused by inundation of the road and upstream property. The
designer has three (3) general options for addressing the problem
of debris plugging a culvert:
ii.
If the debris is to be retained by an upstream
structure or at the culvert inlet, frequent maintenance may be required.
The design of a debris control structure should include a thorough
study of the debris problem and should consider the following factors:
(i)
Type of debris.
(ii)
Quantity of debris.
(iii)
Expected changes in type and quantity of debris
due to future land utilization.
(iv)
Stream flow velocity in the vicinity of culvert
entrance.
(v)
Maintenance access requirements.
(vi)
Availability of storage.
(vii)
Maintenance plan for debris removal.
iii.
Hydraulic Engineering Circular No. 9, Debris Control
Structures Evaluation and Countermeasures (FHWA 2005b) should be used
when designing debris control structures.
(b)
Buoyancy.
i.
The forces acting on a culvert inlet during flows
are variable and indeterminate. When a culvert is functioning under
inlet control, an air pocket forms just inside the inlet, which creates
a buoyant effect when the inlet is submerged. The buoyancy forces
increase with an increase in headwater depth under inlet control conditions.
These forces, along with vortexes and eddy currents, can cause scour,
undermine culvert inlets, and erode embankment slopes, thereby making
the inlet vulnerable to failure, especially if deep headwater conditions
are present.
ii.
In general, installing a culvert in a natural stream
channel constricts the normal flow. The constriction is accentuated
when the capacity of the culvert is impaired by debris or damage.
iii.
The large unequal pressures resulting from inlet
constriction are, in effect, buoyant forces that can cause entrance
failures, particularly on corrugated metal pipe with mitered, skewed,
or projecting ends. The failure potential will increase with steepness
of the culvert slope, depth of the potential headwater, flatness of
the fill slope over the upstream end of the culvert, and the depth
of the fill over the pipe.
iv.
Anchorage at the culvert entrance helps to protect
against these failures by increasing the deadload on the end of the
culvert, protecting against bending damage, and by protecting the
fill slope from the scouring action of the flow. Providing a standard
concrete headwall or end-wall helps to counteract the hydrostatic
uplift and to prevent failure due to buoyancy.
v.
Because of a combination of high head on the outside
of the inlet and the large region of low pressure on the inside of
the inlet due to separation, a large bending moment is exerted on
the end of the culvert, which may result in failure. This problem
has been noted in the case of culverts under high fills, on steep
slopes, and with projecting inlets. In cases where upstream detention
storage is necessary and headwater depth in excess of twenty (20)
feet is required to restrict discharge, it is recommended to reduce
the culvert size rather than use an inefficient projecting inlet.
f.
Protection Downstream
Of Culverts. In this Subsection, two (2) categories of erosion protection
methods are addressed for the area downstream of culverts: riprap
erosion protection at locations downstream of culvert outlets that
are in-line with major drainage channels and energy dissipation structures.
(1)
In-Line Riprap Protection. Scour resulting from
highly turbulent, rapidly decelerating flow is a common problem at
conduit outlets. The riprap protection suggested below is for outlets
from conduits and culverts with outlet Froude numbers up to 2.5.
(a)
Configuration Of Riprap Protection. The figure
below illustrates typical riprap protection at the outlets of culverts
and major drainageway conduits. The additional thickness of the riprap
just downstream from the outlet is to assure protection from flow
conditions that might precipitate rock movement in this region.
 |
(b)
Required Rock Size. The required rock size for
erosion protection downstream from culvert outlets is selected depending
on whether the culvert is circular or rectangular.
i.
Circular Culvert Outlets. For circular culvert outlets,
refer to the figure below for sizing of rock erosion protection downstream
from circular culverts.
 |
|
Circular culvert outlets figure parameters:
| ||
|
•
|
Q = design discharge (cfs)
| |
|
•
|
Dc = diameter of circular culvert (ft)
| |
|
•
|
Yt = tailwater depth (ft)
| |
|
Circular culvert outlets figure notes:
| ||
|
•
|
Valid for Froude parameter for circular culvert (Q/Dc2.5) = 6 or less.
| |
|
•
|
In cases where Yt is unknown or a hydraulic
jump is suspected downstream of the outlet, use Yt/Dc = 0.40.
| |
|
•
|
The rock size requirements shown on the figure above were determined
assuming that the flow in the circular culvert is not supercritical.
In cases where the flow is supercritical, calculate Da using the equation below and substitute Da for Dc:
| |
 | ||
|
where:
| ||
|
•
|
the maximum value of Da shall not exceed
Dc
| |
|
•
|
Da = parameter to use in place of Dc when flow is supercritical
| |
|
•
|
Dc = diameter of circular culvert (ft)
| |
|
•
|
Yn = normal depth of supercritical flow
in the culvert
| |
ii.
Rectangular Culvert Outlets. For rectangular culvert
outlets, refer to the figure below for sizing of rock erosion protection
downstream from circular culverts.
 |
|
Rectangular culvert outlets figure parameters:
| ||
|
•
|
Q = design discharge (cfs)
| |
|
•
|
W = width of rectangular conduit (ft)
| |
|
•
|
H = height of rectangular conduit (ft)
| |
|
Rectangular culvert outlets figure notes:
| ||
|
•
|
Valid for Froude parameter for rectangular culvert (Q/WH1.5) = 8.0 or less.
| |
|
•
|
In cases where Yt is unknown or a hydraulic
jump is suspected downstream of the outlet, use Yt/H = 0.40.
| |
|
•
|
The rock size requirements shown on the figure above were determined
assuming that the flow in the rectangular culvert is not supercritical.
In cases where the flow is supercritical, calculate Ha using the equation below and substitute Ha for H:
| |
 | ||
|
where:
| ||
|
•
|
the maximum value of Ha shall not exceed
H
| |
|
•
|
Ha = parameter to use in place of H when
flow is supercritical
| |
|
•
|
H = height of rectangular culvert (ft)
| |
|
•
|
Yn = normal depth of supercritical flow
in the culvert
| |
(c)
Extent Of Protection.
i.
The length of the riprap protection downstream from
the outlet depends on the degree of protection desired. If it is necessary
to prevent all erosion, the riprap must be continued until the velocity
has been reduced to an acceptable value.
ii.
The rate at which the velocity of a jet from a
conduit outlet decreases once it has exited the culvert is not well
known. For the procedure recommended here, it is assumed to be related
to the angle of lateral expansion, , of the jet. The velocity is related
to the expansion factor, (1/(2tan)), which can be determined directly
using the two (2) figures below (the first is for circular conduits
and the second is for rectangular conduits), assuming that the expanding
jet has a rectangular shape:
 |
 |
 |
|
Lp = length of protection (ft)
|
|
W = width of the conduit in (ft) (use diameter for circular
conduits)
|
|
Yt = tailwater depth (ft)
|
|
Ɵ = the expansion angle of the culvert flow
|
|
Q = design discharge (cfs)
|
|
V = the allowable non-eroding velocity in the downstream channel
(ft/sec)
|
|
At = required area of flow at allowable
velocity (ft2)
|
iii.
In certain circumstances, the culvert outlet equations
may yield unreasonable results. Therefore, specific requirements for
parameter values are described below:
|
•
|
Circular culverts
| |
|
○
|
Lp should not be less than 3 Dc.
| |
|
○
|
Lp should not be greater than 10 Dc whenever the Froude parameter (Q/Dc2.5) is less than 6.0.
| |
|
○
|
If the Froude parameter is greater than 6.0, increase the maximum
Lp required by 1/4 Dc for each whole number by which the Froude parameter is greater than
6.0.
| |
|
•
|
Rectangular culverts
| |
|
○
|
Lp should not be less than 3H.
| |
|
○
|
Lp should not be greater than 10H whenever
the Froude parameter (Q/WH1.5) is less
than 8.0.
| |
|
○
|
If the Froude parameter is greater than 8.0, increase the maximum
Lp required by 1/4 H for each whole number
by which the Froude parameter is greater than 8.0.
| |
(d)
Multiple Conduit Installations. The procedures outlined in Subsection (F)(5)(f)(1)(a), (b) and (c) can be used to design outlet erosion protection for multi-barrel culvert installations by hypothetically replacing the multiple barrels with a single hydraulically equivalent rectangular conduit. The dimensions of the equivalent conduit may be established as follows:
i.
Distribute the total discharge, Q, among the individual
conduits. Where all the conduits are hydraulically similar and identically
situated, the flow can be assumed to be equally distributed; otherwise,
the flow through each barrel must be computed.
ii.
For all the culverts, compute the Froude parameter
Qi/Dci2.5 (circular conduit) or Qi/WiHi1.5 (rectangular
conduit), where the subscript i indicates the discharge and dimensions
associated with an individual conduit.
iii.
If the installation includes dissimilar conduits,
select the individual conduit with the largest value of the Froude
parameter to determine the dimensions of the equivalent conduit.
iv.
Make the height of the equivalent conduit, Heq, equal to the height, or diameter, of the selected
individual conduit.
v.
The width of the equivalent conduit, Weq, is determined by equating the Froude parameter from
the selected individual conduit with the Froude parameter associated
with the equivalent conduit, (e.g., Q/WiHeq1.5 is Froude parameter
for equivalent rectangular conduit).
(2)
Energy Dissipation Structures.
(a)
Rock protection downstream of conduit and culvert
outlets is appropriate where moderate outlet conditions exist. However,
in cases where high exit velocities or turbulence at culvert outlets
will occur, the outlet structure must be designed to match the receiving
stream conditions. Energy dissipation or stilling basin structures
can provide a high degree of energy dissipation and are generally
effective even with relatively low tailwater control. An energy dissipation
structure should be considered if any of the following situations
exist:
i.
High-energy dissipation efficiency is required,
or where hydraulic conditions approach or exceed the limits for alternate
designs.
ii.
Low tailwater control is anticipated.
iii.
Site conditions dictate use of an energy dissipation
structure, such as public use areas, where plunge pools and standing
water are unacceptable because of safety and appearance, or at locations
where space limitations direct the use of a concrete structure.
(b)
Types of energy dissipation structures addressed
in this Subsection include impact stilling basins, pipe outlets to
baffles chutes, and low tailwater basins.
(c)
Longer conduits with large cross sectional areas
are designed for significant discharges and often with high velocities
requiring special hydraulic design at their outlets. Here, dam outlet
and spillway terminal structure technology is appropriate (USBR 1987).
Type II, III, or IV stilling basins, submerged buckets with plunge
basin energy dissipators and slotted-grating dissipators can be considered
when appropriate to the site conditions. For instance, a plunge basin
may have applicability where discharge is to a wet detention pond
or a lake.
g.
Large Conduits And Bridges. The design criteria described above
are for culverts that will be routinely designed in the City of Battlefield.
For other applications, such as large circular or large rectangular
culverts or bridge hydraulics, the reader is directed to the following
references:
(1)
Large Circular Culverts Or Large Rectangular Culverts.
(a)
Open Channel Hydraulics (Chow 1959). This is a
classic reference that is applicable since large culverts frequently
function hydraulically as open channels.
(b)
Federal Highway Administration Hydraulic Design
of Highway Culverts, Hydraulic Design Series No. 5 (FHWA 2005a). This
is the same standard reference used for the hydraulic design of smaller
culverts.
(2)
Bridges.
(a)
Hydraulics of Bridge Waterways Hydraulic Design
Series No. 1 (FHWA 1978). This is a good basic reference.
(b)
Design Manual for Engineering Analysis of Fluvial
Systems for the Arizona Department of Water Resources (SLA 1985).
This is a prime reference on hydraulics and the three-level sediment
transport analysis, with examples.
(c)
American Association of State Highway and Transportation
Officials, Highway Drainage Guidelines (AASHTO 2007). Chapter 7 of
this document, the Hydraulic Analysis for the Location and Design
of Bridges, provides a good overview of this topic.
6.
Open Channels.
a.
Overview. Natural and engineered open drainage channels are
generally the primary component of the modern major conveyance system.
The use of open systems and their integration into the existing topography
is strongly preferred to the use of closed or lined systems, and early
planning is necessary to accomplish this objective. When present,
natural channels are the preferred system for managing stormwater.
In areas of new development and infrastructure improvements, a channel
is regarded as natural if it has the capacity to adjust either its
bed or banks in response to changes in flow or sediment load. In areas
being redeveloped, streams that have been previously disturbed are
considered natural if they possess a free boundary capable of adjusting
to changes in flow. Often, hydromodification in the watershed necessitates
an engineered naturalized channel where contact with soil and vegetation
occurs but the ability of the stream to meander is limited.
(1)
General.
(a)
Except for roadside ditches and swales, open channels
are nearly always a component of the major (emergency) drainage system.
There are a number of factors which must be considered in determining
whether to specify an open drainageway as opposed to an underground
storm drain: material and installation cost, maintenance costs and
problems, acceptability to the developer or home buyer, public safety,
appearance, etc. Effective planning and design of open drainageways
can significantly reduce the cost of storm drainage facilities, while
enhancing the quality of the development.
(b)
In planning a subdivision, the designer should
begin by determining the location and the width of existing drainageways.
Streets and lots should be laid out in a manner to preserve the existing
drainage system to the greatest degree practical. In addition to reducing
the cost of the drainage system, sediment and erosion control costs
will also be reduced. Constructed channels should be used only when
it is not practical or feasible to utilize existing drainageways.
(2)
CONJUGATE DEPTH (also known as "alternate depth")
CRITICAL DEPTH, dc
FROUDE NUMBER
NORMAL DEPTH, dn
SPECIFIC ENERGY, E
SPECIFIC FORCE, Fm
SUBCRITICAL FLOW
SUPERCRITICAL FLOW
Definitions. As used herein, the following definitions
shall apply:
The corresponding subcritical or supercritical depth having
the same value of specific energy or specific force.
The depth of flow at which the specific energy is a minimum
for a given flow rate and channel cross shape, and a unique relationship
exists between depth and specific energy.
|
Fr =
 |
|
where:
|
|
D = hydraulic depth (feet) = A/T
|
|
A = cross sectional area of design flow (square feet)
|
|
V = average channel velocity (feet/second)
|
|
g = acceleration due to gravity (32.2 ft/s2)
|
|
T = top width of flow (feet)
|
|
For supercritical flow, Fr > 1
|
|
For subcritical flow, Fr < 1
|
|
For critical flow, Fr = 1
|
The depth at which uniform flow occurs when the discharge
rate is constant. Friction and gravity forces are in balance.
The energy per unit weight of fluid,
|
E =
 |
|
where:
|
|
E = specific energy in feet
|
|
V = average channel velocity (feet/second)
|
|
g = acceleration due to gravity (32.2 ft/s2)
|
|
d = depth of flow in feet
|
The sum of forces due to velocity plus hydrostatic pressure
per unit weight of fluid,
|
Fm =
 |
|
where:
|
|
Fm = specific force in cubic feet
|
|
ȳ = depth to center of gravity of the cross section in
ft
|
|
Q = rate of flow in cubic feet per second
|
|
A = cross sectional area of flow in square feet
|
Lower energy, lower velocity flow, which occurs when the
normal depth is greater than the critical depth. Subcritical flow
is controlled by downstream conditions.
High energy, high velocity flow, which occurs when the normal
depth is less than the critical depth. Supercritical flow is controlled
by upstream conditions.
(3)
Open
Systems Requirements. One (1) of the principles of sound urban stormwater
management is the practice of preserving floodplains and natural channels
associated with major waterways. In situations where it is not feasible
to utilize the natural system of channels and floodplains, it is preferable
for engineered systems to be open and vegetated where possible, rather
than enclosed or concrete lined. When planning for open channels to
serve a development, many important factors must be considered, such
as:
(a)
Public safety.
(b)
Permitting.
(c)
Cost, including capital expenses, operations, maintenance,
and replacement.
(d)
Right-of-way, access, and existing utilities.
(e)
Protection of existing natural channels and their
riparian corridors.
(f)
The engineered channel and drainage easement for
the design storm under full watershed development conditions and maximum
potential peak flow.
(g)
Sediment budgets, including conditions with upstream
construction activity and providing for sediment transport competency.
(h)
Watershed or development master plans.
(i)
Existing or anticipated stream instabilities or
meandering, particularly at the interface between natural and engineered
channels.
(j)
Appearance.
(k)
Integration into community, including impact on
property values.
(4)
Submittal Requirements. Open channel plan submittals
must include detailed drawings, background calculations, and supporting
information, including:
(a)
Detailed plan and profile at the appropriate scale
(profile shall include flow line and the top of each bank or channel
wall).
(b)
Water surface profiles (twenty-five- and 100-year).
(c)
All design flow rates and velocities.
(d)
Channel lining details, including seed and plant
selection for vegetated channels.
(e)
Buffer delineation.
(f)
For natural channels, the completed geomorphic
exhibit and channel stability matrix.
(g)
Evidence that relevant permits have been obtained
and associated requirements have been met.
(5)
Maintenance. All major drainageways and open channels
shall be designed to allow regular maintenance. The designer shall
consider access requirements for equipment necessary to maintain or
replace walls, boulders, concrete mats, gabions, turf reinforcement
mats (TRMs), etc. The responsible party must be financially and technically
capable of providing long-term maintenance of facilities, including
those that utilize concrete, grass, or other bioengineered configurations.
(6)
Safety. Public safety shall be the paramount consideration
when designing open channel systems. Representative issues that must
be considered include channel configurations that limit the risk of
a fall into the channel and channel hydraulic designs that minimize
the risk of hazardous conditions, such as high velocities and "reverse
rollers" that can entrap a person downstream from a low head dam.
All vertical walls greater than three (3) feet in height shall have
a safety fence or handrail if the wall is located where the public
may be in close proximity. Warning signs may be necessary in areas
with high risk. Channels that do not have vertical walls should be
designed with side slopes of 3H:1V or flatter to allow for safe exit
from the channel. In cases where this is not feasible, riprap slopes
may have a slope of 2H:1V. All slopes that are to be maintained by
motorized mowers shall be graded to 3H:1V or flatter. Slopes of 4H:1V
or flatter are preferred for safety and aesthetic reasons.
b.
Types Of Flow. Open channel flow is commonly characterized according
to variability with respect to time and space using the following
terms:
|
•
|
Steady flow - conditions at any point in a stream remain constant
with respect to time (Daugherty and Franzini 1977).
|
|
•
|
Unsteady flow - flow conditions (e.g., depth) vary with time.
|
|
•
|
Uniform flow - the magnitude and direction of velocity in a
stream are the same at all points in the stream at a given time (Daugherty
and Franzini 1977). If a channel is uniform and resistance and gravity
forces are in exact balance, the water surface will be parallel to
the bottom of the channel for uniform flow.
|
|
•
|
Varied flow - discharge, depth, or other characteristics of
the flow change along the course of the stream. For a steady flow
condition, flow is termed rapidly varied if these characteristics
change over a short distance. If characteristics change over a longer
stretch of the channel for steady flow conditions, flow is termed
gradually varied.
|
|
For the purposes of open channel design, flow is usually considered
steady and uniform. For a channel with a given roughness, discharge,
and slope, there is only one (1) possible depth for maintaining a
uniform flow. This depth is the normal depth. When roughness, depth,
and slope are known at a channel section, there can only be one (1)
discharge for maintaining a uniform flow through this Subsection.
This discharge is the normal discharge.
| |
(1)
Uniform Flow.
(a)
Open channels having a design flow rate less than
five hundred (500) cfs may be designed assuming uniform flow conditions
in conjunction with computed headwater depths at culverts and other
hydraulic structures or reservoir stages at detention and sediment
basins. Water surface profiles using techniques for gradually varied
flow may be required for design flow rates less than five hundred
(500) cfs where accurate determination flooding depths is necessary
to ensure flood safety.
(b)
Under steady state, uniform flow conditions channel
capacity shall be computed using Manning's Equation:
 |
|
where:
|
|
Q = rate of flow, cubic feet per second
|
|
n = Manning's roughness coefficient
|
|
A = cross sectional area of flow, square feet
|
|
P = wetted perimeter, feet
|
|
R = hydraulic radius = A/P, feet
|
|
S = Sf = friction slope
|
(c)
Computations for all channels designed for uniform
flow conditions shall indicate whether flow is subcritical, critical,
or supercritical. It is preferred that channels be designed for subcritical
flow conditions. Critical flow (0.9 < Fr <1.2) should be avoided
since flow is unstable. Where channels must be designed for supercritical
flow and the Froude number is greater than two point five (2.5), the
conjugate depth for specific force must be determined. Freeboard up
to the conjugate depth may be required if necessary to provide adequate
flood protection.
(2)
Manning's
Roughness Coefficient. When applying Manning's Equation, the
choice of the Manning's roughness coefficient, n, is the most
subjective parameter. The minimum roughness coefficient shall be used
for channel design to check for sufficient channel lining stability
(velocity check) and the maximum roughness coefficient shall be used
to check for hydraulic capacity and to check the minimum velocity
to prevent the occurrence of standing water (flow rate check). Average
roughness coefficient values shall be used for broader applications
such as watershed modeling.
|
Average Roughness Coefficients
| |||
|---|---|---|---|
|
Channel Lining
|
Minimum
|
Average
|
Maximum
|
|
Earthen
|
0.020
|
0.025
|
0.300
|
|
Mowed grass
|
0.025
|
0.030
|
0.035
|
|
Grass - not mowed
|
0.030
|
0.035
|
0.040
|
|
Grass with brush/trees
|
0.040
|
0.050
|
0.060
|
|
Cobble bottom, grass/root side
|
0.030
|
0.040
|
0.050
|
|
Concrete - smooth
|
0.012
|
0.013
|
0.015
|
|
Concrete - rough
|
0.015
|
0.017
|
0.020
|
|
Riprap d50 6 inches
|
0.032
|
0.035
|
0.038
|
|
Riprap d50 9 inches
|
0.035
|
0.038
|
0.040
|
|
Riprap d50 12 inches
|
0.380
|
0.040
|
0.042
|
|
Riprap d50 18 inches
|
0.040
|
0.042
|
0.044
|
|
Riprap d50 24 inches
|
0.042
|
0.044
|
0.047
|
|
Grouted boulders
|
0.025
|
0.032
|
0.400
|
(a)
Froude Number And Flow Regime. Another important
characteristic of open channel flow is the state of the flow, often
referred to as the flow regime. Flow regime is determined by the balance
of the effects of viscosity and gravity relative to the inertia of
the flow. The Froude number, Fr, is a dimensionless number that is the ratio of inertial forces to gravitational forces that defines the flow regime. Flow regimes are characterized as critical, subcritical, or supercritical, based on the Froude Number [equation listed above in Subsection (F)(6)(a)(2)].
i.
Critical Flow.
(i)
Critical flow is defined as flow with Fr = 1.0. Flows with Fr near 1.0
are considered unstable and are likely to tend toward phenomena such
as hydraulic jumps and standing waves, which are both highly turbulent
and lead to a higher risk of erosion or structural failure. Designs
that result in Fr near 1.0 (>0.8 and <1.2)
shall be avoided by adjusting the design of the cross section, roughness,
and slope.
(ii)
Critical velocity, Vc,
can be calculated from the critical hydraulic depth, dc. For a rectangular channel, the critical flow depth is equal to
the critical hydraulic depth (yc = dc), and the critical flow velocity is:
 |
|
where:
|
|
Vc = critical velocity (ft/s)
|
|
g = acceleration of gravity = 32.2 ft/s2
|
|
yc = critical flow depth
|
ii.
Subcritical Flow.
(i)
Subcritical flow is defined as flow with Fr < 1.0. These flows have the following characteristics
relative to critical flows:
|
A)
|
Flow velocity is lower.
|
|
B)
|
Flow depth is greater.
|
|
C)
|
Hydraulic losses are lower.
|
|
D)
|
Erosive power is less.
|
|
E)
|
Behavior is easily described by relatively simple mathematical
equations.
|
|
F)
|
Surface waves can propagate upstream.
|
(ii)
Most stable natural channels have subcritical
flow regimes. Consistent with the philosophy that the most successful
artificial channels utilize characteristics of stable natural channels,
major drainage design shall seek to create channels with subcritical
flow regimes.
iii.
Supercritical Flow.
(i)
Supercritical flow is defined as flow with Fr >1.0. Supercritical flows shall be avoided wherever
possible and have the following characteristics relative to critical
flows:
|
A)
|
Flow velocity is higher.
|
|
B)
|
Flow depth is less.
|
|
C)
|
Hydraulic losses are higher.
|
|
D)
|
Erosive power is greater.
|
|
E)
|
Surface waves propagate downstream only.
|
(ii)
In cases where supercritical flow cannot be avoided,
concrete linings shall be utilized. The channel must be designed to
safely dissipate energy so that the discharge to the downstream reach
is in a non-erosive, subcritical condition.
(3)
Gradually Varied Flow. Open channels having a design
flow rate of five hundred (500) cfs or more and which are not relatively
long with a uniform cross section, shall be designed for gradually
varied flow. Manual computations shall be done using the Direct Step
Method or Standard Step Method. Water surface profiles can be computed
using the Corps of Engineers HEC-RAS Water Surface Profiles program
or the Federal Highway Administration WSPRO program.
(4)
Rapidly Varied Flow.
(a)
Rapidly varied flow conditions shall be avoided
when possible. Where drop structures are required for grass lined
or composite channels, the location of the hydraulic jump and the
length of erosion protection to be provided shall be determined.
(b)
Check dams and other special hydraulic structures
shall be designed as set forth in the ASCE Design Manual.
c.
Channels.
(1)
Natural Channels.
(a)
Perennial Streams and Losing Streams.
i.
The stream channel of perennially flowing streams
or intermittent streams classified as losing streams in the Missouri
Clean Water Laws shall not be modified or channelized except where
unavoidable to construct road crossings or to repair erosion and stabilize
the stream channel.
ii.
Trees and vegetation shall not be removed within
twenty-five (25) feet of the stream bank. Clearing of brush and undergrowth
shall be minimal. It is preferred that existing vegetation remain
within one hundred (100) feet of the stream bank. A typical natural
channel cross section is shown in Figure SS-23.[28]
[28]
Editor's Note: This figure is included as an attachment to this chapter.
iii.
Work within the stream channel may require a US
Army Corp of Engineers (USACE) Department Section 404 permit.
(b)
Tributary Watercourses.
i.
Intermittent streams which have a defined channel
should not be modified or channelized except where unavoidable for
road crossings or to repair erosion and stabilize the stream channel.
No clearing is permitted within twenty-five (25) feet of the stream
bank except to remove underbrush and fallen timber.
ii.
Natural watercourses in which flow is broad and
shallow, and which have no defined channel should not be modified
or channelized. Removal of trees and vegetation within the watercourse
should be avoided as much as practical.
(c)
Determining Flooding Limits For Watercourses.
i.
The area inundated by the peak flow from the 100-year
(one percent (1%) AEP) storm is considered to be the flooding area
for any watercourse. An implicit drainage easement is considered to
exist along the area inundated by the peak flow from the 1% AEP (100-year)
storm.
ii.
For the purpose of preliminary planning and design,
the approximate limits of the floodplain can be determined using approximate
methods. In determining the capacity and depth of flow in natural
watercourses, they shall be analyzed by selecting the most restrictive
channel section for each reach and determining the normal depth by
analyzing the channel as an irregular section using representative
"n" values for each segment of the channel cross section.
(d)
Development Guidelines. Where the width of the
existing drainageway cannot accommodate the needs of the development,
the fringe areas of the drainageway can be filled, and tributary watercourses
may be channelized within the limitations described above. The combination
of filling and channeling shall not increase the estimated high-water
elevation for the 100-year (one percent (1%)) AEP) peak flow rate
by more than one (1) foot over pre-project conditions at the upstream
boundary or any point upstream of the site. Where the effects of increased
frequency of flow or increased velocity may significantly affect the
stability or the stream channel, measures such as grade checks, check
dams or bank stabilization may be required.
(2)
Grass Channels.
(a)
Grass lined channels shall have a minimum slope
of one percent (1%). The bottom slope may be decreased to five-tenths
percent (0.5%) if a concrete trickle channel is provided. In order
to establish growth in the channel bottom, the bottom twelve (12)
inches of the channel depth shall be lined with sod, or suitable erosion
control blanket. A typical grass channel cross section is showing
in Figure SS-24.[29]
[29]
Editor's Note: This figure is included as an attachment to this chapter.
(b)
Manning's roughness coefficient ("n," also
known as "the retardance coefficient") for grass channels shall be
determined based upon the product of the velocity and the hydraulic
radius (V x R) using the chart shown in Figure SS-25.[30] Retardance curve "C" shall be used in determining channel
capacity. Retardance curve "D" shall be used in determining velocity.
[30]
Editor's Note: This figure is included as an attachment to this chapter.
(3)
Low-Flow (Trickle) Channels. Trickle channels shall
be provided in constructed grass channels (not natural channels) where
base flow or perennial flow prevents the establishment or reestablishment
of a sod bottom. A low-flow channel may be necessary under these conditions:
|
•
|
Vegetated channels where:
| |
|
○
|
Baseflow exists.
| |
|
○
|
High peak runoff from developed areas may cause erosion of vegetated
areas.
| |
|
○
|
1-year flow exceeds 5 cfs (for unreinforced grass only).
| |
|
•
|
All types of channel linings in locations where erosion could
potentially occur, such as downstream of point discharges.
| |
|
If conditions warrant a low-flow channel, the low-flow channel
shall be designed to convey the 1-year flow under fully developed
watershed conditions. Variations from this design must be justified
by the hydrologic characteristics of the site.
|
|
Low-flow channel requirements vary by channel type, as listed
below:
| |
|
•
|
In naturalized channels, low-flow channels typically are unlined.
Depending on the projected stresses, riffle areas may require some
reinforcement.
|
|
•
|
In engineered grass-lined channels, riprap, boulders, or a soil-riprap
mix for the low-flow channel lining can provide a stable, vegetated
low-flow channel. Soil and riprap should be mixed prior to placement
for these low-flow channels. Vegetated portions of the channel can
remain dry and easy to mow and maintain.
|
|
•
|
In engineered channels that are not grass-lined, low-flow channels
may consist of riprap, boulders, or concrete, depending on site conditions.
|
|
Types of trickle channels are as follows:
|
(a)
Concrete Trickle Channels. A standard concrete
trickle channel cross section is shown in Figures SS-26 and SS-27.[31] Trickle channel capacity shall be approximately five percent
(5%) of the design flow rate. Concrete trickle channels may be unreinforced
up to a total width of five (5) feet. For total widths of five (5)
feet to ten (10) feet, the trickle channel shall be reinforced with
6 X 6-10-10 welded wire mesh. For widths greater than ten (10) feet,
see requirements for concrete channels. Trickle channel alignment
shall be the same as the overall channel alignment. Radii at changes
in direction shall be the minimum radius required based upon the channel
top width. Capacity of grass channels with trickle channels may be
determined as a composite cross section, or the additional capacity
of the trickle channel can be ignored. Erosion potential at the grass/concrete
interface should be checked. Shear stress or tractive force shall
be determined as follows and shall be limited to the maximum values
set forth below:
 |
|
where:
|
|
τ = unit shear stress (pounds per square foot)
|
|
λ = unit weight of water = 62.4 pounds per cf
|
|
s = channel slope (feet per foot)
|
|
d = distance from the water surface to the channel lining at
the point of interest (feet)
|
|
Critical Sheer Stress
| |
|---|---|
|
Granular Material
|
Critical Sheer Stress (τC)
(pounds per square foot)
|
|
Boulders (100 cm) (39 in)
|
20.295
|
|
Boulders (75 cm) (30 in)
|
15.222
|
|
Boulders (50 cm) (20 in)
|
10.148
|
|
Boulders (25.6 cm) (11 in)
|
5.196
|
|
Riprap (6-8 in)
|
3.132
|
|
Cobbles (6.4 cm) (2.5 in)
|
1.299
|
|
Cobbles and shingles
|
1.100
|
|
Cobbles and shingles, clear water
|
0.910
|
|
Coarse sand (1 mm) (0.4 in)
|
0.015
|
|
Coarse gravel, non-colloidal (GW), clear water
|
0.300
|
|
Coarse gravel, non-colloidal (GW)
|
0.670
|
|
Gravel (2 cm) (0.78 in)
|
0.406
|
|
Fine gravel
|
0.320
|
|
Fine gravel, clear water
|
0.075
|
|
Fine sand (0.125 mm) (0.005 in)
|
0.002
|
|
Fine sand (0.125 mm) (SP)(0.005 in)
|
0.002
|
|
Fine sand (SW), (SP), colloidal
|
0.075
|
|
Fine sand, colloidal, (SW), (SP), clear water
|
0.027
|
|
Graded loam to cobbles, non-colloidal (GM)
|
0.660
|
|
Graded loam to cobbles, non-colloidal (GM), clear water
|
0.380
|
|
Graded silts to cobbles, colloidal (GC)
|
0.800
|
|
Graded silts to cobbles, colloidal (GC), clear water
|
0.430
|
|
Fine-Grained Material
|
Critical Sheer Stress (τC)
(pounds per square foot)
|
|---|---|
|
Resistant cohesive (CL), (CH)
|
1.044
|
|
Stiff clay, very colloidal (CL)
|
0.460
|
|
Stiff clay, very colloidal (CL), clear water
|
0.260
|
|
Moderate cohesive (ML-CL)
|
0.104
|
|
Ordinary firm loam (CL-ML)
|
0.150
|
|
Ordinary firm loam (CL-ML), clear water
|
0.075
|
|
Alluvial silts, colloidal (CL-ML)
|
0.460
|
|
Alluvial silts, colloidal (CL-ML), clear water
|
0.260
|
|
Alluvial silts, non-colloidal (ML)
|
0.150
|
|
Alluvial silts, non-colloidal (ML), clear water
|
0.048
|
|
Sandy loam, non-colloidal (ML)
|
0.075
|
|
Sandy loam, non-colloidal (ML), clear water
|
0.037
|
|
Silt loam, non-colloidal (ML)
|
0.110
|
|
Silt loam, non-colloidal (ML), clear water
|
0.048
|
|
Shales and hardpans
|
0.670
|
|
Other Materials
|
Critical Sheer Stress (τC)
(pounds per square foot)
|
|---|---|
|
Jute net
|
0.460
|
|
Plant cuttings
|
2.090
|
|
Well established dense vegetation to the normal low water
|
2.160
|
|
Geotextile (synthetic)
|
3.010
|
|
Large Woody Debris
|
3.130
|
|
NOTES:
| |
|
For non-cohesive soils, the table values are based on spherical
particles and Shields Equation (see Equation OC-8).
| |
|
For cohesive soils, the values are based on limited testing
as reported in Chow (1988) and U.S. Department of Agriculture Agricultural
Research Service (USDA ARS) (2004).
| |
|
Material type abbreviations:
| |
|
Agriculture Agricultural Research Service (USDA
ARS) (2004)
| |
|
Material type abbreviations:
| |
|
GW - Gravel, well graded
|
GC = Clayey gravel
|
|
SP - Sand, poorly graded
|
CL - Clay
|
|
SW - Sand, well graded
|
CH - Clay, high plasticity
|
|
GM - Silty gravel
|
ML - Silt
|
[31]
Editor's Note: These figures are included as an attachment to this chapter.
(b)
Other Types Of Trickle Channels. Trickle channels
of porous pavers, gravel filled Geoweb, submerged flow wetlands, natural
stone and other materials can be specified, and are encouraged to
improve aesthetics and water quality. However, assurance must be given
that quality control will be maintained during construction and that
adequate maintenance will be provided after construction. Complete
computations and construction specifications must be submitted for
alternative types of trickle channel linings.
(4)
Composite Channels. Many different channel shapes
and lining types are possible. Different shapes and lining types can
be combined in a composite design. In determining the capacity and
depth of flow in composite channels, they shall be analyzed as an
irregular section using representative "n" values for each segment
of the channel cross section. Velocity limitations set forth above
shall be adhered to for each lining type. Allowable shear stress at
the interface between grass or other erodible linings and erosion
resistant linings may not exceed the maximum values. A typical section
of a channel with a concrete inverts and grass slopes if shown in
Figure SS-28.[32]
[32]
Editor's Note: This figure is included as an attachment to this chapter.
(5)
Concrete Channels. Where velocities or slopes cannot
be limited to values required for natural, grass, or composite channels
due to right-of-way or other constraints, concrete channels may be
utilized. Concrete channel shapes will typically be trapezoidal or
rectangular. Other shapes may be used but are less efficient.
Crushed rock bedding and pore pressure relief are required whenever
the lining height exceeds twelve (12) inches. Whenever the concrete
channel bottom is wide enough to accommodate construction or maintenance
equipment [generally eight (8) feet wide or more], it shall be designed
to carry an HS-20 loading and shall be reinforced. Welded wire mesh
or steel reinforcing bars shall be used.
Concrete channels shall be designed for subcritical flow where
possible. Where flow is supercritical, the conjugate depth must be
checked, and additional freeboard may be required. Where slopes must
be decreased to provide stability or maintain subcritical flow, drop
structures should be provided.
(a)
Trapezoidal Concrete Channels. The maximum side
slopes shall be 2:1. Total channel depth is limited to three (3) feet
unless otherwise approved. For depths greater than twelve (12) inches,
the channel slopes shall be reinforced with 6 X 6-10-10 welded wire
mesh. A typical trapezoidal concrete channel section is shown in Figure
SS-29.[33]
[33]
Editor's Note: This figure is included as an attachment to this chapter.
(b)
Rectangular Concrete Channels. Vertical side walls
shall be reinforced to withstand earth pressure and other anticipated
loads. Design for hydrostatic pressure is not required if weep holes
are provided for relief. A toe wall extending a minimum of eighteen
(18) inches below grade shall be provided at the downstream end of
any concrete channel section and should be provided at maximum intervals
of about one hundred (100) feet along the channel. A typical rectangular
concrete channel section is shown if Figure SS-30.[34]
[34]
Editor's Note: This figure is included as an attachment to this chapter.
d.
Engineered Channel
Design Criteria.
(1)
Flow Rate.
(a)
Open channels shall be designed to convey the peak
flow rate resulting from a storm having a rainfall intensity corresponding
to the time of concentration at the point of interest or a duration
which produces the maximum runoff rate at the point of interest, depending
upon the method used for computing runoff. Open channels draining
less than one hundred (100) acres can be designed for runoff rates
computed by the Rational Method. The peak flow rate considered shall
be determined using fully urbanized conditions in the watershed. Effects
of detention basins in reducing peak flow rates in the upstream watershed
will be considered only if the detention basins are included in a
hydrologic model used to estimate the peak flow rate and provided
the detention basins are located in permanent drainage easements.
The design storm frequency shall be as follows:
(b)
Low-flow channels should generally be designed
to convey the one-year flow, although site conditions may justify
a varied design that requires City approval. Any existing perennial
intermittent base flows shall also be considered when designing low-flow
channels.
(2)
Flow Regime.
(a)
To protect channel stability and hydraulic performance,
critical flow conditions shall be avoided. The Froude number, Fr, must be calculated for all unique sections of open
channels for the twenty-five-year flow. Calculating Fr for other frequency flows may be necessary to ensure channel stability.
Fr must first be calculated using the minimum
value of the Manning's roughness coefficient, n.
(b)
In general, the maximum allowable value of Fr is 0.8. However, if values greater than 0.8 are necessary
due to site constraints, the channel shall be designed so that the
flow is supercritical, with a Fr greater than
1.2. In such cases, the calculation should use the maximum value for
Manning's roughness. For supercritical flows, calculation of
the conjugate depth is necessary, and a well-accepted open channel
hydraulics reference should be used. Designs with supercritical flows
require the use of a concrete channel lining. In addition, such designs
must avoid all obstructions, transitions, and curvature. It must be
shown how adjacent properties will be protected from flooding should
a hydraulic jump occur.
(c)
Under certain conditions, values of Fr between 0.8 and 1.2 may be allowed, and the requirement
to calculate conjugate depths may be waived. This exception applies
to channels with a twenty-five-year design flow of twenty (20) cfs
or less when no potential hazards exist.
(3)
Velocity.
(a)
The maximum average channel velocity shall be as
follows for the design flow rate:
|
Channel Type
|
Minimum Velocity
(2-year check)
(ft/s)
|
Maximum Velocity
(25-year check)
(ft/s)
|
|---|---|---|
|
Grass, seed, and mulch
|
2
|
4
|
|
Grass, sod
|
2
|
6
|
|
Grass, TRM
|
2
|
8
|
|
Grass, prevegetated TRM
|
2
|
10
|
|
Manufactured hard lining
|
4
|
12
|
|
Riprap
|
4
|
12
|
|
Concrete
|
4
|
18
|
(b)
Where reduction in velocity due to a reduction
in slope would allow a transition from a concrete to a grass-lined
channel, a grouted riprap lining shall be provided from the point
where the theoretical average channel velocity would be five (5) feet
per second or less, for a distance downstream equal to five (5) times
the theoretical top width of the grass channel. The height of the
riprap lining shall be equal to the height of the concrete lining
upstream.
(4)
Maximum Depth. Unless otherwise approved due to
unavoidable physical or right-of-way constraints, the maximum depth
for the twenty-five-year storm shall be three (3) feet in constructed
channels.
(5)
Slope.
(a)
Longitudinal Slope. Unless otherwise approved due
to unavoidable physical constraints, the minimum centerline grade
for various channels shall be as follows:
(b)
Side Slopes.
i.
For concrete channels, non-vertical side slopes
shall not have a slope steeper than 1H:1V, to allow for safe exit
from the channel. An exception is allowed for short transitions between
vertical and 1H:1V concrete channels.
ii.
A fence with a minimum height of four (4) feet
shall be installed at the top of any slope steeper than 1H:1V for
channels with a depth of three (4) feet or more, where homes, streets,
parking lots, buildings, or other facilities cause people to be in
close proximity.
(6)
Horizontal Alignment. The centerline of constructed
channels shall be aligned parallel with property lines unless otherwise
approved. A radius shall be provided whenever the alignment of a constructed
channel changes by ten degrees (10°) or more. The minimum centerline
radius shall be three (3) times the top width of the design flow.
Horizontal curve data shall be shown on the plans.
(7)
Curvature And Superelevation.
(a)
Curves shall only be used where it is shown they
are necessary due to layout of the development or to create sinuosity
and reduce longitudinal slope. Where curves are used, the centerline
of curvature of the channel shall have a minimum radius of twice the
top width of the design flow (twenty-five-year event), but not less
than one hundred (100) feet.
(b)
Supercritical flow in an engineered open channel
in an urban area may create hazardous conditions. Curvature shall
not be used in a channel under these conditions. If curvature is proposed,
it may be considered with an analysis of conjugate depths and potential
hazards.
(c)
Velocities and depths are higher on the outside
of open channel curves. This rise in water surface on the outside
of a curve is referred to as superelevation. Superelevation must be
calculated for all curves in open channels and accounted for in the
design of the channel and freeboard. For subcritical flows, superelevation
can be estimated by:
 | ||
|
where:
| ||
|
Δy
|
=
|
difference in water surface elevation between the inner and
outer banks of the channel in the bend (resulting from superelevation)
(ft)
|
|
V
|
=
|
mean flow velocity (ft/s)
|
|
T
|
=
|
top width of the channel under design flow conditions (ft)
|
|
G
|
=
|
gravitational constant = 32.2 ft/s2
|
|
rc
|
=
|
radius of curvature (ft)
|
(d)
Velocity shall be calculated utilizing minimum
roughness coefficient values. Because of this increase in velocity,
it is often necessary to provide increased erosion protection along
the outside of bends. Riprap shall be used when the velocity of the
upstream reach for the twenty-five-year storm is greater than eight
(8) ft/s.
(e)
Increased erosion protection based on higher bend
velocities shall apply to the outside half of the channel bottom and
on the channel side slope for the entire length on the outside of
the bend, plus a distance of two times the top width downstream of
the bend. In cases where an outside bend in a grass-lined channel
needs protection, riprap shall be covered, if possible, with soil
and vegetation to provide a grassed-lined channel appearance. Buried
riprap may lose vegetated cover in a major flood and require reburial
and revegetation.
(8)
Freeboard.
(a)
For channels designed for subcritical flow conditions,
a minimum of one (1) foot of freeboard shall be provided between the
design high water elevation and the top of the channel. Freeboard
shall be increased on the outside of curves according to the following
formula:
 |
|
where:
|
|
h = superelevation (feet)
|
|
V = average channel velocity (feet/second)
|
|
T = top width of flow (feet)
|
|
g = acceleration due to gravity (32.2 ft/s2)
|
|
rc = centerline radius of channel (feet)
|
(b)
For channels designed for supercritical flow, additional
freeboard may be required depending upon the risk of damage which
could occur if flow were to become subcritical due to debris or other
obstructions.
(c)
For concrete channels, the required freeboard is
six (6) inches above the twenty-five-year water surface.
(d)
For channels where the twenty-five-year flow depth
is twelve (12) inches or less, the channel shall have a freeboard
of six (6) inches above the twenty-five-year water surface. For all
channel types, the 100-year water surface shall remain within the
drainage easement.
(e)
In cases where curves exist, freeboard must be
above the water surface calculated by adding the superelevation to
the normal water surface elevation. Where design conditions are supercritical
in nature, the freeboard should take into consideration the conjugation
depths from hydraulic jumps.
(9)
Roadside Ditches. Roadside ditches shall be designed
for a maximum depth of two (2) feet measured from the roadway shoulder
and maximum 3:1 side slope. Roadside ditches shall be grass lined
and shall conform to the same velocity requirements as grass lined
channels. The bottom six (6) inches of the ditch depth shall be lined
with sod or erosion control blanket, or the developer must assume
maintenance responsibility for the ditch until growth is firmly established.
A security agreement or performance bond will be required during the
maintenance period. Where the full flow velocity in the ditch exceeds
five (5) feet per second, a concrete ditch liner shall be provided.
Typical sections of roadside ditches can be found in Figure SS-32.[35]
[35]
Editor's Note: This figure is included as an attachment to this chapter.
(10)
Linings.
(a)
Riprap Lining.
i.
The use of riprap for channel linings is discouraged
primarily due to poor construction practice. Because of the amount
of labor required to properly place and chink stones into a stable
mass, loose riprap is seldom stable. Further, gradations of stone
tend to be highly variable and poorly controlled. Loose riprap is
susceptible to silting in, encouraging growth of weeds and vegetation,
and creating a maintenance and appearance problem. These problems
can be partially overcome by grouting the riprap; however, construction
practice for grouted riprap is equally poor resulting in a highly
variable penetration by the grout.
ii.
Riprap linings are best specified for only short
distances in zones where erosion potential is high. Where riprap is
specified, it should be grouted to minimize maintenance problems,
unless the installation is temporary. The maximum stone size should
be twelve (12) inches. The riprap shall be laid over a non-woven filter
fabric in order to prevent undercutting of the subgrade. A typical
riprap lining is shown in Figure SS-31.[36]
[36]
Editor's Note: This figure is included as an attachment to this chapter.
(b)
Other Types Of Erosion Resistant Channel Linings.
Designers are encouraged to use other types of linings in order to
reduce costs and improve the appearance of drainage channels. Invert
lining materials include concrete, reno mattresses, gravel filled
Geo-web, Geo-web filled with lean concrete, etc. Sidewall lining materials
include gabions, and precast concrete units, such as Keystone blocks,
Loffelstein units, Windsor stone, and many other types of precast
units. In specifying any type of these linings, the manufacturer's
installation instructions shall be strictly followed.
(11)
Easements. All constructed channels shall be located
within drainage easements. Natural channels draining five (5) or more
acres shall be located in drainage easements. The minimum easement
width shall be the top width of the 100-year peak flow rate. Adequate
means of access shall be provided for maintenance equipment. Additional
easement width shall be provided if required to provide maintenance
access. No fences or obstructions of any type are permitted within
drainage easements containing open channels.
(12)
Outfalls.
(a)
Outfalls into channels must be designed with consideration
given to the nature and condition of the receiving channel. Such outfalls
shall be perpendicular to flow or directed downstream. Any protrusions
of pipes or other structures into the channel must be trimmed flush
with the main channel wall or bank.
(b)
Discharges into natural, vegetated, or reinforced
vegetated channels shall be at the flow line, in a manner consistent
with the channel outfalls for natural channels. Vegetated or reinforced
vegetated channels are generally not capable of withstanding point
discharges with high velocities; therefore, the incoming conveyance
should be designed to minimize velocity. Energy dissipation, such
as a headwall or riprap protection, shall be designed around the outfall
to minimize bank, channel, or wall erosion. Energy dissipation in
the main channel may be necessary to withstand the flows that occur
there.
(c)
Discharges into channels lined with concrete or
riprap generally require no special protection against erosion. Discharges
into hard-lined channels should be a minimum of one (1) foot above
the flow line.
(13)
Utility Clearance. A minimum clear distance of
twelve (12) inches vertically from any other utility line shall be
maintained below the channel lining, unless otherwise approved. Utilities
will not be permitted to cross through the channel flow area.
(14)
Plan Requirements. Each channel shown on the plan
shall be numbered or lettered (Line 1, Storm 1, Line A, etc.). Channel
segments shall be included in profiles of the storm sewer lines of
which they are a component. Stationing shall begin at the downstream
end of the channel and proceed upstream. Stations shall be called
out on the plan and profile at all changes in direction or points
of curvature and tangency.
e.
Drop Structures. Where the channel slope must be decreased to
provide stability, maintain subcritical flow, or reduce velocity to
acceptable levels, drop structures may be provided. Grass lined channels
shall be provided with erosion-resistant linings downstream to the
point at which the average channel velocity has returned to the allowable
rate for the type of channel lining provided. Drop structures for
vertical wall channels shall be designed in accordance with the ASCE
Design Manual or the U.S. Bureau of Reclamation Design of Small Canal
Structures. Drop structures for trapezoidal channels shall be designed
in accordance with the City of Tulsa Design Criteria or King's
Handbook of Hydraulics.
7.
Detention For Flood Control.
a.
General. This Subsection covers the design of detention facilities
whose primary purpose is to provide flood control by controlling rates
of runoff. Detention facilities may also be utilized to improve the
quality of urban stormwater runoff. Both flood control and water quality
benefits can be provided in one (1) basin, if properly designed.
b.
Policy. Prior to the development of the land, surface conditions
provide a higher percentage of permeability and a longer time of concentration.
With the construction of buildings, parking lots, etc., permeability
and the time of concentration are significantly decreased, resulting
in an increase in the rate, volume, and frequency of runoff.
These changes result in increased flooding risk to downstream
structures since flooding depths will rise as the rate of runoff increases.
The increased volume and frequency of runoff can cause erosion damage.
In order to minimize these effects, stormwater detention requirements
have been established. All new non-agricultural construction is required
to provide stormwater detention facilities. Detention requirements
may be waived upon written approval of the City of Battlefield in
any of the following cases:
|
1.
|
Construction of such a facility would, due to timing of outflows,
have an adverse effect on downstream properties by increasing peak
rates of runoff, as demonstrated by engineering computations.
|
|
2.
|
The developer enters into a written agreement with the County
and affected property owners to provide storm drainage improvements
downstream of the development in lieu of constructing on-site detention
facilities as set forth below.
|
|
3.
|
Due to the small size of the development, it can be demonstrated
that the detention facility would result in no beneficial effect to
downstream properties. Detention basins having a required volume of
five thousand (5,000) cubic feet or less are considered as providing
only marginal benefits.
|
|
In Cases 1 and 3 above, the City may, in the future, impose
a fee in lieu of detention to be utilized for maintenance or improvement
of storm drainage facilities in the same watershed in which the proposed
development is located.
| |
|
Detention requirements cannot be waived if there are residential
or other structures downstream of the site which have a high flooding
risk.
|
(1)
Construction Of Improvements In Lieu Of Detention.
(a)
In cases where channelization or other improvements
can be shown to be more effective than detention in reducing the flooding
hazard to downstream properties and where no adverse effects to downstream
properties will result from construction of such improvements, the
City may enter into an agreement with the applicant to accept compensation
and/or construction of off-site improvements in lieu of constructing
on-site detention facilities.
(b)
The developer's contribution will be determined
based upon the net financial gain which the developer would realize
if the detention facility were not built. This amount will generally
be equal to the construction cost of the detention facility plus revenue
from sale of additional lots or increased value of lots, less the
cost of developing the lots, including utilities and streets, financing
costs, sales costs, and reasonable profit.
(c)
Where the developer's contribution is not
sufficient to construct the necessary improvements to completely remedy
flooding problems to structures downstream, the City must demonstrate
that the necessary funding has been secured prior to accepting payment
or improvements in lieu of detention. Where the developer's contribution
is more than the actual cost of the necessary improvements, the City
shall retain the balance and such funds shall be utilized for planning
or construction drainage improvements in the same watershed.
c.
DRY DETENTION BASIN
FULLY URBANIZED CONDITIONS
HIGH FLOODING RISK
OFF-LINE DETENTION FACILITY
ON-LINE DETENTION BASIN
POST-PROJECT CONDITIONS
PRE-PROJECT CONDITIONS
RETENTION BASIN
WET DETENTION BASIN
Definitions. As used herein, the following definitions shall
apply:
A detention basin which holds water only during and shortly
after runoff events.
The topography, surface cover, and other hydrologic conditions
in the watershed as they will be after all areas in the watershed
have been developed in accordance with current zoning designations,
as provided in the City of Battlefield Comprehensive Plan, or as can
otherwise be reasonably anticipated.
Residences or other structures will be defined as having
a high flooding risk when the lowest point on the structure at which
surface runoff may gain entry is located at, or below, the estimated
flooding level which would result from a storm with an annual exceedance
probability (AEP) of ten percent (10%) or greater under conditions
existing in the basin prior to development of the applicant's
property (i.e., affected by the "ten-year" storm for pre-project conditions).
A basin or basins located outside of the primary watercourse,
which usually allows off-site flows to pass through the site without
passing through the detention basin. Where needed for peak flow reduction
at the point of interest, a portion of the flow in the main watercourse
may be intercepted and passed through the detention basin through
the use of side-flow weirs or similar diversions.
A basin which is located on the mainstream of a watercourse
and which intercepts on-site as well as off-site flows.
The topography, surface cover, and other hydrologic conditions
in the watershed as they will be after construction of the proposed
project.
The topography, surface cover, and other hydrologic conditions
in the watershed being considered, as they exist prior to the proposed
project.
This term is often utilized for wet basins and basins which
retain runoff for an extended period of time. The term "detention
basin" will be used to refer to all such facilities in the City of
Battlefield.
A basin which contains a permanent impoundment of water.
Flood storage volume is provided above the permanent water surface.
d.
Types Of Detention.
(1)
Detention basin facilities fall into two (2) categories
regarding ownership, design aspects, and maintenance. Facilities planned
on an individual-site basis are referred to as on-site or private
facilities. Facilities that are planned to serve multiple lots, a
subdivision, or larger area are referred to as public or regional
facilities. Requirements for detention basins may vary depending on
the development situation, including:
(a)
Single Lot Commercial. Generally, these are developments
on lots that are not part of a subdivision. Basins shall be designed
for full development of the lot based on zoning unless land use restrictions
dictate less land is available for development. Construction of detention
may be phased when only part of the lot is proposed to develop. In
these cases, the location and size of detention facilities for fully
developed conditions shall be located and documented.
(b)
Residential Or Commercial Subdivision. These are
developments that involve the subdivision of property. One (1) or
more basins may be required depending on natural drainage patterns.
(c)
Multiple Properties. Multiple properties or developments
may be served by a regional basin that is not within the boundary
of the development.
(2)
Generally, the type of detention is determined
by the required design objectives and the appearance and function
desired by the developer. Detention basins may fall into one (1) of
the following design types:
(a)
Dry: designed for several different frequency rainfalls
for flood control only and drains over a relatively short period of
time (<12 hours). The outlet is typically made up of orifices and/or
weirs.
(b)
Extended: designed for pollutant removal and possibly
flood control and drains over an extended period of time (24 to 48
hours). The outlet is typically made up of a filtered control as well
as orifices and/or weirs.
(c)
Wet: contains a permanent pool of water and is
designed for pollutant removal, flood control, and often aesthetics.
May be designed to drain down to the permanent pool level over a short
or long period of time.
(3)
Storage may also be present in features such as
sinkholes and the upstream side of railroad and highway embankments.
When planning a development along a major waterway, upstream existing
storage should be accounted for when calculating existing flow rates
but generally should not be accounted for when calculating ultimate
future peak flow rates. Exceptions include storage that is dedicated
for perpetuity and has adequate assurances for long-term maintenance.
(4)
In developments where an off-site area drains across
the property, the developer must consider whether to construct the
basin in-line and direct off-site runoff through the basin or construct
it off-line and convey the off-site runoff so that it bypasses the
basin. In-line and off-line storage are defined as:
(a)
In-Line Storage. A facility located in-line with
the drainageway that captures and routes the entire flood volume.
A disadvantage with in-line storage is that it must be large enough
to store and convey the total flood volume of the entire tributary
catchment, including off-site runoff, if it exists. A U.S. Army Corps
of Engineers (USACE) Section 404 permit for dredge and fill activities
within the waters of the United States and a Section 401 Water Quality
Certification from the Missouri Department of Natural Resources (MDNR)
are typically required for in-line storage. The developer shall contact
the USACE to determine permit requirements if an in-line basin is
proposed.
(b)
Off-Line Storage. A facility located off-line from
the drainageway that receives runoff from a smaller drainage area
or from a particular site. These facilities are often smaller but
may require permitting similar to in-line storage facilities. For
all types of basins, the designer should consider safety, aesthetics,
and multi-purpose uses during both wet and dry conditions. The use
of other specialists such as landscape architects, biologists, and
planners are encouraged to achieve these objectives.
e.
Hydrologic And Hydraulic Design. Detention facilities should
be designed and constructed in a manner to enhance the aesthetic and
environmental quality of developments in the City as much as possible,
adding to rather than detracting from property values. City of Battlefield
encourages designs which utilize and enhance natural settings, provide
good quality open space, and minimize disturbance and destruction
of wooded areas, natural channels, and wetlands.
Where detention volume can be provided by utilizing natural
valleys, existing wooded areas should be allowed to remain. Detention
ponds do not have to be graded to geometric shapes or cleared of forested
areas in order to comply with City requirements.
The use of landscaping and alternative materials to improve
the appearance of spillways, outlet structures, erosion control, and
energy dissipation structures is encouraged.
Detention basins may be designed to be "wet" or "dry." Parking
lots may be utilized for detention storage, provided the maximum depth
does not exceed twelve (12) inches during an event with a one percent
(1%) exceedance probability. Underground detention storage may also
be utilized. The use of rooftop detention is discouraged. Detention
basins may be designed to be "on-line" or "off-line."
Large regional detention basins are more effective in providing
flood control, as well as water quality benefits, than smaller facilities
provided on each site. City of Battlefield currently has no program
for regional detention. Where feasible, developers are encouraged
to work together to provide common detention areas.
Detention basins shall be located within a single lot or property.
(1)
Easements.
(a)
All detention basins serving more than one (1)
lot or property shall be located within a drainage easement.
(b)
At a minimum, the easement shall include the area
of the dam, the area downstream of the dam to a point twenty (20)
feet downstream of the end of the outlet structure, including the
area provided for erosion control or energy dissipation; and the area
covered by the reservoir including freeboard, plus an additional twenty
(20) feet around the perimeter.
(c)
Detention basins for a development may be located
on adjoining property downstream from the development provided that
a drainage easement is obtained and adequate means of maintenance
access (including ingress/egress easements where necessary) is provided.
The easement shall be granted to the developer or to the property
owners' association. Where the detention basin does not immediately
adjoin the development, a drainage easement covering the area inundated
by the peak flow from the one percent (1%) AEP (100-year) storm shall
be provided to connect the development site with the detention basin.
(2)
Design
Methods.
(a)
Analytical Methods.
i.
Detention storage volume shall be determined by
hydrograph methodologies and reservoir routing techniques. Preferred
methods for use in detention basin design are those included in the
Corps of Engineers HEC-1 Flood Hydrograph Package and the Soil Conservation
Service's TR-55 and TR-20.
ii.
The designer may choose to use other methods than
those listed above, provided that the method is documented in generally
accepted engineering literature and is used within the limitations
stated for the method.
(b)
Computations For Small Sites.
i.
Where the site area is less than five (5) acres
of one- and two-family dwellings, or where the site area for other
zoning designations is less than two (2) acres, detention volume computations
may be performed by the methods of the Soil Conservation Service TR-55.
ii.
Runoff volumes shall be computed for pre- and post-project
conditions, and the required volume determined by subtracting the
pre-project runoff volume from the post-project runoff volume. The
outlet structure shall be designed to limit the runoff rate for the
design storms to pre-project values at the stage where the required
volume for each storm frequency is contained in the basin.
(c)
Design Storms.
i.
Detention basins shall be designed on the basis
of multiple storm recurrence frequencies to ensure that they provide
flood protection for both frequent storms and large infrequent storms.
A minimum of three (3) recurrence frequencies, the fifty percent (50%),
ten percent (10%) and one percent (1%) AEP storms (the "two-, ten-
and 100-year" storms) must be considered.
ii.
The duration of the design storm used to compute
the difference in runoff volume between pre-project and post-project
conditions shall be that which produces the maximum rate of runoff
at the point under consideration for post-project conditions. The
minimum design storm duration utilized shall be one (1) hour.
(d)
Runoff Models.
i.
The runoff model must include the entire drainage
basin upstream of the proposed detention ponds. The model shall be
prepared in sufficient detail to ensure that peak runoff rates are
reasonably accurate. Runoff models shall be developed for the following
cases:
ii.
Cases 1 and 2 are utilized to determine the required
detention volume and the type of outlet structure to be provided and
shall be analyzed for the three (3) storm recurrence frequencies required
above. Detention facilities shall be designed such that peak outflow
rates from the facility for Case 2 are no greater than the rates determined
in Case 1 for each of the three (3) storm recurrence frequencies required.
The storage volume provided shall not be less than the difference
in total runoff volume between Case 1 and Case 2. Case 3 is used to
determine the size of the overflow spillway. Case 3 needs only be
analyzed for the one percent (1%) AEP 100-year storm. If downstream
safety considerations warrant, it may be necessary to size a spillway
for greater than a 100-year event.
(e)
Spillways And Outlet Structure Hydraulics.
i.
Outlet structures consist of culverts, weirs, orifices,
and other hydraulic elements for which reliable data is available.
Weir coefficients shall be as given in King's Handbook of Hydraulics.
Coefficients for broad-crested weirs interpolated from the values
given in King's Handbook are given in Table 15 below.
|
Table 15: Discharge Coefficients for Broad-Crested Weirs
| |||
|---|---|---|---|
|
Depth
(ft.)
|
Coefficient for 6" thick wall
|
Coefficient for 8" thick wall
|
Coefficient for 12" thick wall
|
|
0.20
|
2.80
|
2.77
|
2.69
|
|
0.25
|
2.83
|
2.79
|
2.70
|
|
0.30
|
2.86
|
2.80
|
2.71
|
|
0.40
|
2.92
|
2.84
|
2.72
|
|
0.50
|
3.00
|
2.90
|
2.74
|
|
0.60
|
3.08
|
2.95
|
2.75
|
|
0.70
|
3.19
|
3.03
|
2.80
|
|
0.75
|
3.25
|
3.08
|
2.83
|
|
0.80
|
3.30
|
3.12
|
2.85
|
|
0.90
|
3.31
|
3.16
|
2.92
|
|
1.00
|
3.32
|
3.20
|
2.98
|
|
1.25
|
3.32
|
3.25
|
3.11
|
|
1.50
|
3.32
|
3.29
|
3.24
|
|
1.75
|
3.32
|
3.31
|
3.27
|
|
2.00
|
3.32
|
3.32
|
3.30
|
|
2.50
|
3.32
|
3.32
|
3.31
|
|
>2.50
|
3.32
|
3.32
|
3.32
|
ii.
Capacity of broad-crested slot and V-notch weirs
shall be determined by the following formula, developed by Joe Wilson,
Kerry Scott, and Larry Wolf at the University of Missouri-Rolla:
|
Q = 0.86H + (3.65w + 5.82z)H1.5
| ||
|
where:
| ||
|
Q
|
=
|
flow rate in cubic feet per second
|
|
H
|
=
|
upstream head (ponded depth above slot invert plus any velocity
head) in feet
|
|
H = 6 feet maximum
| ||
|
w
|
=
|
slot invert width perpendicular to flow, in feet
|
|
0.333 < w < 2.0 feet
| ||
|
z
|
=
|
slope of slot sides expressed in terms of z horizontal to 1
vertical
|
|
0 < z < 0.6
| ||
iii.
Weir coefficients for trapezoidal weirs shall
be determined based upon the ratio of headwater depth to crest width
as shown in Figure SS-33.[37]
[37]
Editor's Note: This figure is included as an attachment to this chapter.
iv.
Culvert capacities shall be determined using the
methods in Federal Highway Administration HDS-5.
v.
Weir coefficients for trapezoidal weirs where the
depth of flow over the weir is small in comparison to the width of
the weir crest shall be determined in accordance with Figure III-11
of Federal Highway Administration HDS-5.
vi.
Discharge coefficient for all orifice shapes shall
be six tenths (0.6) unless supporting data is submitted for other
values.
vii.
Where outlet structure capacities are determined
automatically by the software used in performing the detention basin
analysis, values included in the software package may be used provided
they are generally accepted and properly documented.
f.
Final Design Considerations.
(1)
Potential For Multiple Uses. When designing a detention
facility, multi-purpose uses, such as active or passive recreation
and wildlife habitat, are encouraged in addition to providing the
required storage volume. Facilities used for recreation should be
designed to inundate no more frequently than every two (2) years.
In certain situations, it may be beneficial to utilize a portion of
a parking lot, along the fringe of a detention basin for additional
flood volume storage. However, the depth of flooding in the paved
areas shall not exceed twelve (12) inches during an event with a one
percent (1%) annual exceedance probability and the paved surfaces
shall be outside of the area ponded by the water quality capture volume.
(2)
Detention Basin Location. Detention basins should
be located at the natural low point of the site and must discharge
to the natural drainage location to minimize downstream impacts.
(3)
Detention Basin Grading. Detention basin grading
shall conform to the natural topography of the site to the maximum
extent practical. Developments should be laid out around the existing
waterways and the proposed detention basin. Layouts conforming to
existing topography often reduce construction costs, land disturbance,
and maintenance costs, and increase aesthetic quality. Existing slopes
should be used to the maximum extent practical. Significant modifications
to existing topography may require geologic impact studies and geotechnical
analysis, particularly where shallow bedrock is believed to be present.
(4)
Geometry Of Storage Facilities. The geometry of
a detention facility depends on specific site conditions such as adjoining
land uses, topography, geology, existing natural features, volume
requirements, etc. The following criteria apply to the geometry of
detention facilities:
(a)
In some cases, to minimize erosion, a low-flow
channel may be provided where the two-year design flow exceeds five
(5) cfs. These are less desirable in water quality basins or where
grass contact or infiltration is desired.
(b)
Lining and surfaces shall be based on design velocities and flow characteristics in accordance with Subsection (F)(6), Open Channels.
i.
Riprap lining should be used only when design constraints
prevent the channel design velocity from falling within the allowable
range for vegetated channels.
ii.
Dry and extended detention basins shall have a
vegetated bottom and side slopes unless design velocity or slope is
not within the allowable range for vegetation.
(c)
Where bedrock is encountered when excavating the
detention basin, it is not required to excavate and remove the bedrock
so long as the design of the basin can be altered to meet the City's
standards.
(d)
The water quality portion of a facility should
be shaped with a gradual expansion from the inlet and a gradual contraction
toward the outlet, thereby minimizing short-circuiting.
(e)
Storage facilities shall not be any closer than
five (5) feet from a building.
(5)
Embankments And Cut Slopes. The design for an embankment
of a stormwater detention or retention storage facility should be
based upon a site-specific engineering evaluation. The embankment
should be designed to prevent catastrophic failure during the 100-year
and larger storms. The following criteria apply in many situations:
(a)
Maximum And Minimum Slopes. The maximum slopes
of excavated or embankments slopes shall be 3:1. 4:1 slopes are preferred.
Natural slopes exceeding 3:1 may be utilized provided that they remain
undisturbed. The minimum allowable slope on the bottom of the basin
shall be one percent (1%) unless a trickle channel is provided. The
embankment's side slopes should be well vegetated, and riprap
protection (or the equivalent) may be necessary to protect it from
wave action and bank erosion.
(b)
Freeboard. For basins with a surface area of two
(2) acres of less, a minimum freeboard of twelve (12) inches shall
be provided above the design stage for the one percent (1%) AEP (100-year)
storm. For surface areas greater than two (2) acres but less than
ten (10) acres, two (2) feet of freeboard shall be provided. Greater
depths of freeboard may be required for impoundments having a surface
area greater than ten (10) acres.
(c)
Settlement. All earth fills should be free from
unsuitable materials and all organic materials such as grass, turf,
brush, roots, and other material subject to decomposition. The fill
material in all earth dams and embankments should be compacted to
at least ninety-five percent (95%) of the maximum density obtained
from compaction tests performed by the Modified Proctor method in
ASTM D698. Additional height should be considered to account for settlement,
particularly for larger facilities.
(d)
Emergency Spillway. An emergency spillway shall
be designed to convey flows that exceed the primary outlet capacity.
The spillway shall be sized to safely pass the flow from the 100-year,
twenty-four-hour rainfall event with no overtopping of the embankment.
The flow capacity of other components of the outlet works may be considered
when designing the emergency spillway. An emergency spillway may be
waived for embankments of two (2) feet in height or less and no safety
risks exist immediately downstream.
(6)
Spillways And Outlet Structures.
(a)
Any type of outlet structure and overflow spillway
can be utilized provided the required hydraulic characteristics of
the structure can be maintained and provided that no undue maintenance
burdens are placed upon the owner of the detention basin. Outlet structures
and spillways shall be provided with an adequate stilling area downstream
to reduce velocities to acceptable levels. Outlet structures shall
be set back to a minimum distance from the downstream property line
to allow for the pre-project velocity and spread of flow to be maintained
at the downstream property line.
(b)
Where concrete or other types of retaining walls
exceed three (3) feet and six (6) inches in height, a four (4) feet
high chain-link or solid fence must be provided.
(c)
Spillways and outlet structures shall be provided
with toe-walls extending a minimum depth of eighteen (18) inches below
finish grade at the upstream and downstream ends in order prevent
undercutting.
(d)
Spillway sidewalls shall extend in height to the
top of the dam.
(7)
Concrete Retaining Walls.
(a)
The use of vertical retaining walls for detention
basin impoundments is discouraged, due to cost and appearance considerations.
However, concrete retaining walls are frequently utilized to minimize
the area required for detention basins.
(b)
Where concrete retaining walls exceed three (3)
feet and six (6) inches in height, a four (4) feet high chain-link
or solid fence must be provided. The maximum depth of detention basins
using vertical walls shall be four (4) feet.
(c)
Concrete retaining walls shall be designed to withstand
earth and hydrostatic pressures. Walls longer than fifty (50) feet
shall be provided with expansion and contraction joints at appropriate
intervals.
(8)
Other Types Of Retaining Walls. Where retaining
walls must be utilized to conserve space, the use of other types of
materials is encouraged in order to reduce costs and improve the appearance
of detention basins. Alternative retaining wall materials include
gabions and precast concrete units, such as Keystone blocks, Loffelstein
units, Windsor stone, and many other types of precast units. In specifying
any type of these linings, the manufacturer's installation instructions
shall be strictly followed.
(9)
Earth Dams.
(a)
Dams shall be constructed to the maximum slopes
specified above. Dams shall be constructed of properly compacted earth
fill and shall be keyed into existing ground to reduce the risk of
leakage or failure.
(b)
Dams less than ten (10) feet in height shall be
keyed in a minimum of two (2) feet below existing grade. Deeper keys
may be required for taller dams.
(c)
The minimum embankment width at the top of the
dam shall be three (3) feet. Greater widths may be required for dams
exceeding ten (10) feet in height.
(d)
Dams greater than thirty-five (35) feet in height
are subject to regulation by the State dam safety program and shall
meet requirements of the dam safety program.
(10)
Wet Ponds.
(a)
Where wet ponds are specified, the pond lining
must be designed to retain water. Geologic conditions in Greene County
frequently make it difficult for impoundments to hold water. Site
soil conditions shall be evaluated by a soils engineer and an appropriate
lining provided.
(b)
Wet ponds shall have a minimum permanent pool depth
of four (4) feet to minimize algae growth. Designers and developers
are encouraged to consult with the Missouri Department of Conservation
regarding pond management techniques, stocking fish, etc.
(11)
Linings. Detention facilities may benefit from
an impermeable clay or synthetic liner for a number of reasons. Stormwater
detention and retention facilities have the potential to raise the
groundwater level in the vicinity of the basin. If the basin is close
to structures or other facilities that could be damaged by raising
the groundwater level, consideration should be given to lining the
pond. An impermeable liner may also be warranted in a retention basin
where the designer seeks to limit seepage from a permanent pond. Alternatively,
there are situations where the designer may seek to encourage seepage
of stormwater into the ground. In this situation, a layer of permeable
material may be warranted.
(12)
Inlets. Inlets shall incorporate energy dissipation
and/or linings to limit erosion. In addition, forebays or sediment
traps should be considered at significant inflow points to storage
facilities to settle a significant portion of the sediment being delivered
by stormwater to the facility. Forebays will need regular maintenance
to reduce the sediment being transported and deposited on the storage
basin's bottom.
(13)
Outlet Works. Outlet works should be sized and
structurally designed to release at the specified flow rates without
structural or hydraulic failure. A concentrated discharge to a natural
channel shall have a property line setback of a minimum of five (5)
times the effective diameter of the conveyance structure.
(14)
Trash Racks. Trash racks should be sufficiently
sized to not interfere with the hydraulic capacity of the outlet and
must be designed in a manner that is protective of public health,
safety, and welfare.
(15)
Vegetation. The type of vegetation specified for
a newly constructed storage facility is a function of the frequency
and duration of inundation of the area, soil types, whether native
or non-native vegetation is desired, and other potential uses (park,
open space, etc.) of the area. A planting plan should be developed
for new facilities to meet their intended use and setting in the urban
landscape. Generally, trees and shrubs are not recommended on dams
or fill embankments.
(16)
Access. Access to the bottom, inflow, forebay,
and outlet works areas shall be provided for maintenance vehicles.
(17)
Geotechnical Considerations. The designer must
account for the geotechnical conditions of the site. These considerations
may include issues related to embankment stability, geologic hazards,
seepage, and other site-specific issues. It may be necessary to confer
with a qualified geotechnical engineer during both design and construction,
especially for larger detention and retention storage facilities.
(18)
Environmental Permitting And Other Considerations.
(a)
The designer must account for environmental considerations
surrounding the facility and the site during its selection, design,
and construction. These can include regulatory issues such as:
(b)
There are also non-regulatory environmental issues
that should be considered. Detention facilities can become breeding
grounds for mosquitoes unless they are properly designed, constructed,
and maintained. Area residents may object to facilities that impact
riparian habitat or wetlands. Considerations of this kind must be
carefully considered, and early discussions with relevant Federal,
State, and local regulators are recommended.
g.
Ownership And Maintenance.
(1)
The City of Battlefield provides no maintenance
of detention facilities located on private property. Maintenance must
be provided by the owner of the property upon which the detention
basin is located. Where detention basins are located in common areas
or adjoining off-site areas, the property upon which the basin is
located shall remain in the ownership of the property owners'
association. Where a property owners' association is formed,
restrictive covenants which provide for collection of fees for maintenance
of the detention facilities shall be filed in the office of the Greene
County Recorder of Deeds. Restrictive covenants must be approved by
the City legal counselor prior to filing of the final plat.
(2)
Maintenance considerations during design include
the following:
(a)
Bank slopes, bank protection, and vegetation types
are important design considerations for site aesthetics and maintainability.
(b)
Permanent ponds should have provisions for complete
drainage for sediment removal or other maintenance. The frequency
of sediment removal will vary among facilities, depending on the original
volume set aside for sediment, the rate of accumulation, rate of growth
of vegetation, drainage area erosion control measures, and the desired
aesthetic appearance of the pond.
(c)
Adequate dissolved oxygen supply in ponds (to minimize
odors and other nuisances) can be maintained by artificial aeration.
Use of fertilizer and pesticides adjacent to the permanent pool pond
should be carefully controlled.
(d)
French drains or the equivalent are almost impossible
to maintain and should be used with discretion where sediment loads
are apt to be high.
(e)
Underground tanks or conduits designed for detention
should be sized and designed to permit pumping. Multiple entrance
points should be provided to remove accumulated sediment and trash.
(f)
Detention facilities should be designed with sufficient
depth to allow accumulation of sediment for several years prior to
its removal.
(g)
Permanent pools should be of sufficient depth to
discourage excessive aquatic vegetation on the bottom of the basin,
unless specifically provided for water quality purposes.
(h)
Trash racks and/or fences are often used to minimize
hazards. These may become eyesores, trap debris, impede flows, hinder
maintenance, and, ironically, fail to prevent access to the outlet.
On the other hand, desirable conditions can be achieved through careful
design and positioning of the structure, as well as through landscaping
that will discourage access (e.g., positioning the outlet away from
the embankment, etc.). Creative designs, integrated with innovative
landscaping, can be safe and can also enhance the appearance of the
outlet and pond.
(i)
To reduce maintenance and avoid operational problems,
outlet structures should be designed with no moving parts (i.e., use
only pipes, orifices, and weirs). Manually and/or electrically operated
gates should be avoided. To reduce maintenance, outlets should be
designed with openings as large as possible, be compatible with the
depth-outflow relationships desired, and be designed with water quality,
safety, and aesthetic objectives in mind. Outlets should be robustly
designed to lessen the chances of damage from debris or vandalism.
The use of thin steel plates as sharp-crested weirs should be avoided
because of potential accidents, especially with children. Trash racks
must protect all outlets, especially ones made of a thin plate.
h.
Submittals. The following information must be submitted with
detention basin designs:
(1)
Information regarding analytical methods and software
to be used, including:
(2)
Map(s) showing subbasin delineation, topography,
presumed flow routes, and pertinent points of interest for pre-project,
post-project, and fully urbanized conditions.
(3)
Map showing hydrologic soil types.
(4)
Routing diagram for each runoff model condition.
(5)
A summary of subbasin characteristics used for
program input.
(6)
Stage-area or stage-storage characteristics for
the basin in tabular or graphic form.
(7)
Stage-discharge characteristics for the outlet
structure and overflow spillway in tabular or graphic form; hydraulic
data for weirs, orifices, and other components of the control structure.
(8)
A printout of the input data file.
(9)
A printout of program output, including plots of
hydrographs. (These are intended to be the printer plots generated
by the software.)
8.
Water Quality.
a.
General.
(1)
This Subsection covers the design of Best Management
Practices (BMPs) to minimize the adverse effects of urban stormwater
runoff on the quality of receiving waters.
(2)
The requirements of this Subsection will apply
to all new developments that drain into sinkholes. As the role which
urban runoff from the Springfield metropolitan area plays in the quality
of the James River and Table Rock Lake becomes better understood,
it is anticipated that water quality requirements will be extended
to watersheds of the James River and its tributaries. It is recognized
that specific water quality standards, other than those contained
in the Missouri Clean Water Laws, have not been developed or adopted
for these receiving waters. The objective of this policy is not to
meet specific reductions of targeted pollutants, but rather to provide
a generally effective level of pollutant removal by using reasonable,
cost-effective measures. The goal is to minimize, to the maximum extent
practical, adverse impacts on the quality of the receiving water.
b.
Water Quality Requirement. The water quality requirement is
to reduce the discharge of pollutants by following the site planning
and design principles and criteria described herein and managing the
water quality control volume (WQCV) using approved stormwater control
measures (SCMs) that reduce the discharge of pollutants through treatment
or runoff reduction and are properly designed, constructed, and maintained.
The water quality requirement applies to new development and redevelopment
projects within the City limits of Battlefield that disturb one (1)
acre or greater, including projects less than one (1) acre that are
part of a larger common plan of development or sale that will disturb
one (1) or more acres over the life of the project.
(1)
Water Quality Capture Volume. Water quality BMPs
shall be designed to capture the runoff from the 90th percentile rainfall
for Greene County as well as to capture the first flush of pollutants
from directly connected impervious areas within the proposed development.
The required water quality capture volume (WQCV) to be used in design
of extended wet and dry detention basins and other BMPs whose design
is based upon capture and treatment of stormwater, shall be the greater
of the following:
|
•
|
The first one-half (1/2) inch of runoff from the directly connected
impervious area (DCIA) in the development; or
|
|
•
|
The runoff resulting from total rainfall depth of one (1) inch
in twenty-four (24) hours over the entire development.
|
(a)
Short Cut Method. The Short Cut Method (Claytor
and Schueler, 1996) computes Rv based on percent
impervious cover. It is recommended when the site consists of predominately
one type of land surface. The Short Cut Method uses the following
equation to calculate the WQCV:
|
WQCV = (P)(Rv)(A)
| ||
|
where:
| ||
|
WQCV
|
=
|
water quality capture volume (ft3)
|
|
P
|
=
|
rainfall depth (ft) = 1 inch for new development or 0.5 inch
for redevelopment
|
|
Rv
|
=
|
volumetric runoff coefficient = 0.5 + 0.009I
|
|
I
|
=
|
percent impervious cover (in percent, e.g., 80% = 80) (for redevelopment,
use 100%)
|
|
A
|
=
|
total site area for new development or impervious area for redevelopment
(acres)
|
(b)
Small Storm Hydrology Method. The Small Storm Hydrology
Method (Claytor and Schueler, 1996), computes Rv based on the specific characteristics of the pervious and impervious
surfaces of the drainage area. The Rv to be
used for each cover type is provided in Table 16 below. The WQCV can
be calculated using the following equation:
|
WQCV = (P)(weighted Rv)(A)
|
|
where:
|
|
WQCV = water quality capture volume (ft3)
|
|
P = rainfall depth (ft) = 1 inch
|
|
Weight Rv = [(Rv1 * A1) + (Rv2 * A2)+. . . (Rvi * Ai)]/A
|
|
Rvi = volumetric runoff coefficient for
cover type i
|
|
Ai = area of cover type i (acres)
|
|
A = total site area (acres)
|
|
Table 16: Volumetric Runoff by type of cover
| |||||||
|---|---|---|---|---|---|---|---|
|
Flat roofs and large unpaved parking lots
|
Pitched roofs and large impervious areas (large parking lots)
|
Small impervious areas and narrow streets
|
Urban pervious areas
|
Forest cover
| |||
|
Hydrologic Soil Group B
|
Hydrologic Soil Groups C and D
|
Hydrologic Soil Group B
|
Hydrologic Soil Group C
|
Hydrologic Soil Group D
| |||
|
0.84
|
0.97
|
0.7
|
0.11
|
0.21
|
0.03
|
0.4
|
0.5
|
(2)
Designing For Runoff Reduction And Targeted Pollutants.
(a)
Development significantly increases the volume
of runoff compared to predevelopment conditions, contributing to increased
pollutant loads and hydrologic stream impacts, including erosion and
aquatic habitat degradation. To address these impacts, consideration
should be given to runoff reduction during site design and SCM selection
and design. This can be accomplished through site planning and design
techniques such as tree preservation and planting, natural area conservation,
and minimizing grading and impervious surfaces, all of which contribute
to runoff reduction. SCM selection and design can incorporate moderate
to high performing runoff reduction SCMs and/or use a treatment train
approach of more conventional SCMs such as vegetated filter strips,
grass channels, and extended detention in series. The runoff reduction
and pollutant removal performance of SCMs in series is greater than
their use as stand-alone practices. Table 17 below gives typical runoff
reduction percentages for SCMs. Volume reduction also has economic
benefits, including potential reductions in storage requirements for
minor and major events, reduced extent and sizing of conveyance infrastructure,
and cost reductions associated with addressing channel stability issues.
|
Table 17: Typical Runoff percentages for SCMs
| |
|---|---|
|
SCM
|
Runoff Reduction
|
|
Vegetated filter strip
| |
|
Natural area
|
50% to 75%
|
|
Lawn/landscaping
|
25% to 50%
|
|
Grass channel (meeting minimum residence time)
|
10% to 20%
|
|
Pervious pavement
|
45% to 75%
|
|
Bioretention
|
40% to 80%
|
|
Extended dry detention basin
|
0% to 15%
|
|
Extended wet detention basin
|
0%
|
|
Constructed wetland pond
|
0%
|
|
Green roof
|
45% to 60%
|
|
Proprietary SCMs
|
Based on site specific design
|
|
Rainwater harvesting
|
40%; may be higher based on site specific design
|
|
Natural area conservation
|
% based on calculated WQCV credit [see Subsection (F)(8)(b)]
|
|
Natural area restoration
|
% based on calculated WQCV credit [see Subsection (F)(8)(b)]
|
|
Tree preservation
|
% based on calculated WQCV credit [see Subsection (F)(8)(b)]
|
|
Tree planting
|
% based on calculated WQCV credit [see Subsection (F)(8)(b)]
|
(b)
SCMs vary in their pollutant removal efficiencies
for various pollutants. Common urban pollutants include nutrients,
sediment, and bacteria. Most of the SCMs in this Subsection are known
to provide moderate to very good removal of sediment and nutrients.
Typical effectiveness of SCMs for bacteria removal is generally not
as good. SCM selection and design for commercial and industrial facilities
should take into consideration pollutants specific to the facility
such as heavy metals. Table 18 below gives the typical effectiveness
of SCMs for targeted pollutants.
|
Table 18: Effectiveness of SCMs
| ||||
|---|---|---|---|---|
|
SCM
|
Sediment/Solids
|
Nutrients
|
Total Metals
|
Bacteria
|
|
Vegetated filter strip
|
Good
|
Moderate
|
Good
|
Poor
|
|
Grass channel
|
Good
|
Moderate
|
Good
|
Poor
|
|
Pervious pavement
|
Very good
|
Good
|
Good
|
Unknown
|
|
Bioretention
|
Very good
|
Moderate
|
Good
|
Moderate
|
|
Extended detention basin
|
Good
|
Moderate
|
Moderate
|
Poor
|
|
Retention pond
|
Very good
|
Moderate
|
Moderate
|
Moderate
|
|
Constructed wetland pond
|
Very good
|
Moderate
|
Good
|
Poor
|
|
Green roof
|
Unknown
|
Unknown
|
Unknown
|
Unknown
|
|
Proprietary SCMs
|
Variable
|
Variable
|
Variable
|
Variable
|
(3)
Water Quality SCM Design In Floodplains. When developing
in or near a floodplain, the bottom of the water quality SCM shall
be above the one-year flood elevation.
(4)
Water
Quality Requirements for Sinkholes.
(a)
The following requirements will apply to any new
development within sinkhole drainage areas:
i.
Stormwater runoff from any new development for which
the total impervious area exceeds ten percent (10%) of the total land
area of the development, must be directed through an extended wet
or dry detention basin, or other properly designed BMP, prior to discharge
from the site.
ii.
Runoff from fueling areas and other areas having
a high concentration of pollutants will be required to be directed
to a sand filter or other properly designed BMP which provides filtration
as well as settling.
iii.
The required volume for capture and treatment
shall be designed as the water quality capture volume (WQCV).
iv.
Detention storage must be provided to limit the
peak flow rate from the fifty percent (50%) AEP (two-year) storm to
pre-project values.
c.
Water Quality Design Principles.
(1)
Consider Stormwater Early. Stormwater site planning
and design should be considered early in the concept phase of development.
Site planning is a step that has typically received little attention
from a stormwater design perspective. When considered early, strategies
to meet stormwater requirements through low-cost practices that minimize
runoff are most easily achieved, and SCM design issues are minimized.
(2)
Minimize The Amount Of Runoff. The total quantity
of pollutants transported to receiving waters can be minimized most
effectively by minimizing the amount of runoff. Both the quantity
of runoff and the amount of pollutant wash-off can be minimized by
reducing the amount of directly connected impervious area (DCIA).
Impervious areas are considered connected when runoff travels directly
from roofs, drives, pavement, and other impervious areas to street
gutters, closed storm drains or concrete, or other impervious lined
channels. Impervious areas are considered disconnected when runoff
passes as sheet flow over grass areas, or through properly designed
BMP's, prior to discharge from the site.
(3)
Maximize Contact With Grass And Soil. The opportunity
for pollutants to settle out is maximized by providing maximum contact
with grass and soil. Directing runoff over vegetative filter strips
and grass swales enhances settling of pollutants as the velocity of
flow is reduced. Infiltration of runoff into the soil is also increased.
(4)
Maximize Holding And Settling Time. According to
ASCE, the most effective runoff quality controls reduce the runoff
peak and volume. The next most effective controls reduce peak runoff
rates only. For small storms, the runoff rate should not exceed the
pre- project peak flow rate from the fifty percent (50%) AEP (two-year)
storm. Most obnoxious pollutants (exceptions include water soluble
nutrients and metals) can be settled out. By reducing the rate of
outflow and increasing the time of detention storage, settling of
pollutants and infiltration of runoff is maximized.
(5)
Design For Small, Frequent Storms. Drainage systems
for flood control are designed for large, infrequent storm events.
In contrast, stormwater quality controls must be designed for small,
frequent storm events. In Greene County ninety percent (90%) of all
twenty-four (24) hour rainfalls are one (1) inch or less. Most pollutants
are washed off in the "first flush," generally considered the first
one-half (1/2) inch of runoff.
(6)
Utilize BMPs In Series Where Possible. Performance
monitoring of BMPs in Florida, Maryland, and Delaware has shown that
the combined effect of providing several BMPs in a series can be much
more effective in reducing the level of pollutants than providing
a single BMP at the point of discharge. To the greatest extent practical,
runoff should be directed first to vegetative filter strips, then
to grass swales or channels, and then to extended detention basins,
sand filters, etc.
(7)
Incorporate Both Flood Control And Water Quality
Objectives In Designs, Where Practical. Incorporating both flood control
and water quality criteria into a single stormwater management facility
is not only possible but is encouraged. Whenever practical, combining
several objectives, such as water quality enhancement and flood control,
maximizes the cost-effectiveness of stormwater management facilities.
(8)
Use Open Channels For Conveyance. Natural channels
should be preserved when feasible and stabilized if needed. Open,
vegetated channels for site conveyance are preferred rather than enclosed
or concrete lined channels and can be used to reduce or meet water
quality requirements when properly designed.
(9)
Protect Karst Features. Sinkholes, springs, caves,
and other karst features require special protection to minimize groundwater
contamination and instability. Site design and SCM selection should
focus on small-scale, distributed practices and sheet flow to avoid
concentrating large volumes of runoff which can result in collapses
in karst areas.
(10)
Design For Industrial/High Risk Runoff And Pollutant
Types. Site specific SCMs should be incorporated into sites with activities
or materials that have the potential to discharge significant pollutant
loads. Such sites are generally regulated under NPDES industrial stormwater
permits and the location and type of potential pollutant sources should
be considered during site design and selection of SCMs to aid in NPDES
permit compliance. Site and building design should consider specific
needs such as materials storage or operations that may require source
controls and/or containment or treatment SCMs. Non-NPDES regulated
sites may also have specific pollutant types or hot spots such as
fueling stations that be considered when selecting and designing SCMs.
Infiltration SCMs such as pervious pavement or bioretention may not
be appropriate for sites with higher concentrations of hydrocarbons,
metals, or other toxics unless an impermeable liner is provided to
design the SCM for filtration only.
d.
SCM Selection And Design Considerations. The following are general
considerations when selecting and designing SCMs.
(1)
Physical Site Characteristics. Physical characteristics
of a site should drive the site design and SCM selection, including
topography, vegetation, soils, contributing drainage area, groundwater,
baseflows, and karst features. A fundamental concept of low-impact
design (LID) is preservation and protection of site features, including
wetlands, drainageways, soils that are conducive to infiltration,
tree canopy, etc., that provide water quality and other benefits.
LID stormwater treatment systems are also designed to take advantage
of these natural resources. For example, if a portion of a site is
known to have soils with high permeability, this area may be well-suited
for rain gardens or pervious pavement.
(2)
Space Constraints. Space constraints are frequently
cited as feasibility issues for SCMs, especially for high-density
development and redevelopment sites. In some cases, constraints due
to space limitations arise because adequate space for SCMs is not
considered early enough in the planning process. This is most common
when a site plan for roads, structures, etc., is developed and SCMs
are squeezed into the remaining spaces. The most effective and integrated
SCM designs begin by determining areas of a site that are best suited
for SCMs (e.g., natural low areas, areas with well-drained soils)
and then designing the layout of roads, buildings, and other site
features around the existing drainage and water quality resources
of the site. Allocating a small amount of land to water quality infrastructure
during early planning stages will result in better integration of
water quality facilities with other site features. Often, green spaces
can be dual purpose for meeting zoning open space/landscaping requirements
and stormwater management.
(3)
Targeted Pollutants And SCM Processes. SCMs have
the ability to remove pollutants from runoff through a variety of
physical, chemical, and biological processes. The processes associated
with a SCM dictate which pollutants the SCM will be effective at controlling.
Pollutant load reduction is also affected by hydrologic processes.
In addition to pollutant removal capabilities, many SCMs offer channel
stability benefits in the form of reduced runoff volume and/or reduced
peak flow rates for frequently occurring events. Brief descriptions
of several key processes are listed for each SCM in Table 19 below.
|
Table 19: Key processes by SCM
| ||||||||
|---|---|---|---|---|---|---|---|---|
|
SCM
|
Hydrologic Processes
|
Treatment Processes
| ||||||
|
Peak
|
Volume
|
Physical
|
Chemical
|
Biological
| ||||
|
Flow Attenuation
|
Infiltration
|
Evapo-transpiration
|
Sedimentation
|
Filtration
|
Straining
|
Adsorption/Absorption
|
Biological Uptake
| |
|
Grass channel
|
I
|
S
|
I
|
S
|
S
|
P
|
S
|
S
|
|
Vegetated filter strip
|
I
|
S
|
I
|
S
|
S
|
P
|
S
|
S
|
|
Green roof
|
P
|
S
|
P
|
N/A
|
P
|
N/A
|
I
|
P
|
|
Pervious pavement
|
P
|
P
|
N/A
|
S
|
P
|
N/A
|
N/A
|
N/A
|
|
Bioretention
|
P
|
P1
|
S
|
P
|
P
|
S
|
S2
|
P
|
|
Extended detention basin
|
P
|
I
|
I
|
P
|
N/A
|
S
|
S
|
I
|
|
Retention pond
|
P
|
I
|
P
|
P
|
S
|
S
|
P
|
P
|
|
NOTES:
| ||||||||
|
P = Primary; S = Secondary; I = Incidental; N/A = Not Applicable
| ||||||||
|
1
|
Depending on presence and design of an underdrain
| |||||||
|
2
|
Depending on soil media
| |||||||
(4)
Pretreatment. Forebays or other pretreatment is
recommended and/or required for SCMs, including extended detention
and rain gardens. The purpose of forebays is to settle out coarse
sediment prior to reaching the main body of the facility. It is extremely
important that sediment loading be controlled for SCMs that rely on
infiltration, including pervious pavement systems and rain gardens.
Pretreatment can ensure long-term functionality and reduce maintenance
of SCMs.
(5)
Volume Reduction.
(a)
Site design and SCM selection and design should
consider runoff volume reduction. Infiltration-based SCMs can be designed
with or without underdrains, depending on soil permeability and other
site conditions. The most substantial volume reductions are generally
associated with SCMs that have permeable sub-soils and allow infiltration
to deeper soil strata and eventually groundwater. For SCMs that have
underdrains, there is still potential for volume reduction although
to a lesser degree. As runoff infiltrates through SCM soils to the
underdrain, moisture is retained by soils; the moisture eventually
evaporates or is taken up by vegetation, resulting in volume reduction.
Runoff that drains from these soils via gravity to the underdrain
system behaves like interflow from a hydrologic perspective with a
delayed response that reduces peak rates. Although the runoff collected
in the underdrain system is ultimately discharged to the surface,
on the time scale of a storm event there are volume reduction benefits.
(b)
Although effects of evapotranspiration are inconsequential
on the time scale of a storm event, on an annual basis, volume reduction
due to evapotranspiration in vegetated SCMs such as bioretention can
be an important component of the hydrologic budget. Between events,
evapotranspiration lowers soil moisture content, providing additional
storage capacity for subsequent events. The volume reduction provided
by a particular SCM type will be influenced by site-specific conditions
and SCM design features.
(6)
Treatment Train. The term "treatment train" refers
to multiple SCMs in series (e.g., a disconnected roof downspout draining
to a grass channel draining to an extended detention basin). Engineering
research over the past decade has demonstrated that treatment trains
are one (1) of the most effective methods for management of stormwater
quality (WERF 2005). Advantages of treatment trains include:
(a)
Multiple Processes For Pollutant Removal. There
is no "silver bullet" for a SCM that will address all pollutants of
concern as a stand-alone practice. Treatment trains that link together
complementary processes expand the range of pollutants that can be
treated and increase the overall efficiency of the system for pollutant
removal.
(b)
Redundancy. Given the natural variability of the
volume, rate and quality of stormwater runoff and the variability
in SCM performance, using multiple practices in a treatment train
can provide more consistent treatment of runoff than a single practice
and provide redundancy in the event that one component of a treatment
train is not functioning as intended.
(c)
Maintenance. SCMs that remove trash, debris, coarse
sediments, and other gross solids are a common first stage of a treatment
train. From a maintenance perspective, this is advantageous since
this first stage creates a well-defined, relatively small area that
can be cleaned out routinely. Down-gradient components of the treatment
train can be maintained less frequently and will benefit from reduced
potential for clogging and accumulation of trash and debris.
(7)
On-Site And Subdivision SCMs. SCMs can be on-site,
meaning they are located on the lot they are serving, or they can
be in subdivision common areas or easements that serve multiple lots.
SCMs that serve multiple lots can be an efficient means of meeting
water quality requirements in a common facility that is often maintained
by a property owners' association. However, a single subdivision
SCM may not provide significant runoff volume reduction and does not
provide the benefits of a treatment train approach. To achieve these
benefits, an extended detention basin might be combined with downspout
disconnection. Residential subdivisions usually already incorporate
disconnection of roof runoff by directing downspouts to lawns. Disconnection
of downspouts is an option for commercial buildings as well. Other
options include vegetated filter strips for sheet flow from parking
lots, grass channels to convey runoff to the extended detention basin,
and other SCMs such as pervious pavement and rain gardens on the individual
lots. This treatment train approach can reduce the WQCV and detention
volume needed in the extended detention basin while providing volume
reduction and a range of water quality treatment processes that will
minimize hydromodification and provide better water quality than a
stand-alone extended detention basin.
(8)
Integration With Flood Control. In addition to
water quality, most projects will require detention for flood control,
whether on-site or in a facility that serves multiple lots. It can
be efficient to combine water quality and flood control facilities.
Examples include extended detention basins and pervious pavement designed
to provide the WQCV and flood control storage. SCMs can also reduce
required detention volume through lower curve numbers and decreased
time of concentration.
(9)
On-Line SCMs And Off-Site Drainage. On-line refers
to locating a SCM such that runoff from upstream of the development
flows through it. Generally, on-line SCMs to capture the WQCV are
strongly discouraged, especially in a natural channel. It is preferable
for natural channels to be preserved and SCMs to be located off-line.
On-line SCMs may require Federal and state permits under Section 404
of the Clean Water Act if located in a jurisdictional waterway. There
may be situations where SCMs may be located in an area that receives
some off-site drainage. This may be acceptable if the off-site drainage
is minimal and will not affect the integrity and functionality of
the SCM. In these cases, the SCM does not need to be sized for the
WQCV for the off-site drainage but special design considerations may
be needed to ensure the SCM can handle the off-site drainage while
still providing the intended water quality treatment or volume reduction
for the on-site drainage.
(10)
Land Use, Compatibility With Surroundings, And
Safety.
(a)
SCMs can add interest and diversity to a site,
serving multiple purposes in addition to providing water quality functions.
Gardens, plazas, rooftops, and even parking lots can become amenities
and provide visual interest while performing water quality functions
and reinforcing urban design goals for the neighborhood and community.
The integration of SCMs and associated landforms, walls, landscapes,
and materials can reflect the standards and patterns of a neighborhood
and help to create lively, safe, and pedestrian-oriented districts.
The quality and appearance of SCMs should reflect the surrounding
land use type, the immediate context, and the proximity of the site
to important civic spaces. Aesthetics will be a more critical factor
in highly visible urban commercial and office areas than at a heavy
industrial site. The standard of design and construction should maintain
and enhance property values without compromising function (WWE et
al. 2004).
(b)
Public Access To SCMs Should Be Considered From
A Safety Perspective. The highest priority of engineers and public
officials is to protect public health, safety, and welfare. SCMs must
be designed and maintained in a manner that does not pose health or
safety hazards to the public. As an example, steeply sloped and/or
walled ponds should be avoided. Where this is not possible, emergency
egress, lighting, and other safety considerations should be incorporated.
Facilities should be designed to minimize mosquito breeding, which
can be a nuisance and a public health concern (e.g., West Nile virus).
The potential for nuisances, odors, and prolonged soggy conditions
should be evaluated for SCMs, especially in areas with high pedestrian
traffic or visibility.
(11)
Maintenance. Maintenance is an important consideration
in SCM selection and should be considered early in the planning and
design phase. Even when SCMs are thoughtfully designed and properly
installed, they can become eyesores, breed mosquitoes, and cease to
function if not properly maintained. SCMs can be more effectively
maintained when they are designed to allow easy access for inspection
and maintenance and take into consideration factors such as property
ownership, type of maintenance, visibility, and vehicle and equipment
access. An important consideration for a rain garden with plantings
is whether the property owner can commit to maintaining it as a landscape
feature that requires weeding, watering, and replacement of mulch
just like other site landscaping. Selection of pervious pavement should
consider the need for periodic vacuum sweeping.
e.
Plant Selection.
(1)
Landscaped SCMs are a good choice where landscaping
is already required by the zoning regulations, such as interior and
perimeter parking lot landscaping and buffer yard landscaping. Such
areas can be designed as rain gardens, vegetated filter strips, grass
channels, or in some cases, small extended detention basins. Vegetated
filter strips, grass channels, and extended detention basins that
are turf grass with trees and shrubs are generally easiest to maintain
for most property owners because they will already be mowing other
areas. Fully landscaped SCMs such as rain gardens with plantings and
mulch require a higher level of commitment to maintain, including
weeding and remulching. Often, non-SCM landscape beds around buildings
get maintained very well but landscaped SCMs such as rain gardens
get neglected. Fully landscaped SCMs should be designed with a plant
palette and mulch that blends in with other landscape beds so that
they get maintained equally well. Trees and shrubs are good options
for ease of maintenance. When incorporating grasses and perennials,
a simple plant palette of a few easily recognizable species will be
easier to maintain. Native plants are best adapted to our region's
climate and generally require minimal watering once established and
no chemical fertilizers or pesticides. Many native plants are particularly
well-suited for SCMs because they can withstand wet conditions followed
by dry periods. Native plants also provide important habitat and food
sources for insects, birds, and animals that play important roles
in our ecosystem. For these reasons, Missouri native plants should
be selected when choosing plants for SCMs. The native species is preferable,
but cultivars of native plants are acceptable and are sometimes preferred
due to characteristics such as being more compact or more readily
available. To provide additional flexibility, non-native plants may
be used that are climate tolerant to the local hardiness zone. Any
non-native species selected shall be non- invasive. Native plant information
is available from the Missouri Grow Native! program (www.grownative.org).
(2)
Trees are highly recommended for SCMs, including
rain gardens and the bottom of extended detention basins (with proper
species selection and maintenance procedures to address clogging from
leaves). Trees provide stormwater benefits through interception and
evapotranspiration of rainfall, improved soil infiltration, and uptake
of pollutants. Trees provide many other environmental, social, and
economic benefits as well, including improved air quality and increased
property values.
f.
Operation And Maintenance Plan And Agreement. Water quality
SCMs are designed to reduce and/or treat runoff to reduce stormwater
pollutant loads and therefore may require higher levels of maintenance
to serve their designed functions. An operation and maintenance plan
and agreement shall be submitted for approval by the City for all
SCMs required to meet water quality requirements, flood control detention
requirements, or zoning conditions in City code. Deficiencies identified
through self-inspections or inspections by the City shall be addressed
in a timely manner.
g.
Stormwater Control Measures.
(1)
Vegetative Filter Strips.
(a)
Vegetative filter strips consist either of areas
of undisturbed vegetation in good condition, including trees, grass,
sod, or other vegetative cover which meets the objectives for this
BMP, or areas where new vegetation has been established. Vegetative
filter strips shall be provided in areas of sheet flow only. The hydraulic
loading for filter strips shall not exceed 0.05 cfs per lineal foot
of filter strip length for the fifty percent (50%) AEP (two-year)
storm [equal to the runoff per unit width from a four hundred (400)
feet length of impervious area].
(b)
The minimum width of the filter strip shall not
be less than twenty percent (20%) of the length of the sheet flow
from the upstream impervious surface, and in no case shall be less
than six (6) feet. The slope along the width of the filter strip shall
not exceed 4:1 (25%).
(c)
Typical details for vegetative filter strips are
shown in Figure SS-51.[38]
[38]
Editor's Note: This figure is included as an attachment to this chapter.
(2)
Grass
Swales.
(a)
Grass swales may be provided to convey runoff from
vegetative filter strips and impervious areas to BMPs designed for
capture and temporary storage of runoff. Design criteria for grass
swales shall be as follows:
(b)
Roughness coefficients for use in the design of grass swales shall be determined as set forth in Subsection (F)(6)(b)(2). Grass swales shall be lined with sod or seeded and covered with suitable erosion control blanket and mulch.
(c)
Typical details for grass swales are shown in Figure
SS-52.[39]
[39]
Editor's Note: This figure is included as an attachment to this chapter.
(3)
Directly
Connected Impervious Area (DCIA).
(a)
Impervious areas are considered connected when
runoff travels directly from roofs, drives, pavement, and other impervious
areas to street gutters, closed storm drains or concrete, or other
impervious lined channels.
(b)
In order for an impervious area to be considered
disconnected, runoff from the area must pass through a vegetative
filter strip or other BMP meeting the requirements set forth in this
Subsection. For determining the amount of impervious area, the following
assumptions shall apply in the absence of more detailed data:
(c)
If gutter downspouts are directed to drain toward
lawn areas, seventy-five percent (75%) of the roof area shall be considered
disconnected.
(d)
Connected and disconnected impervious areas are
illustrated in Figure SS-50.[40]
[40]
Editor's Note: This figure is included as an attachment to this chapter.
(4)
Permeable
Interlocking Concrete Pavers (PICP). Permeable interlocking concrete
pavers are comprised of a layer of concrete pavers separated by joints
filled with small stones. Water enters joints between solid concrete
pavers and flows through an "open-graded" base, i.e., crushed stone
layers with no small or fine particles. The void spaces among the
crushed stones store water and infiltrate it back into the soil subgrade
or into an underdrain. Some general design considerations are listed
below:
(a)
The design engineer shall reference the following
resources published by the Interlocking Concrete Pavement Institute:
(b)
The paving units supplied to construct the PICP
shall meet the requirements in ASTM C936 and be designed for use as
PICP.
(c)
Consideration should be given to the type of traffic
loads placed upon the PICP. An engineer experienced with pavement
design shall provide input on this aspect early in the design phase.
i.
The minimum pavement section subject to vehicular
traffic shall be (from top to bottom) three and one eighths (3 1/8)
inch-thick paving units, two-inch-thick bedding stone (typically ASTM
No. 8 or 9 stone), four-inch-thick layer of base stone (ASTM No. 57
or similar size), and a layer of subbase stone (ASTM No. 2 or similar
size).
ii.
The thickness of the subbase will vary depending
on storage and anticipated traffic loads as described in ICPI guidance
literature. However, a minimum six-inch-thick subbase will be required
for all applications without an underdrain and nine-inch thick when
using an underdrain. Alternate paving units and stone thicknesses
may be proposed for residential uses or very light traffic loads.
The paver joints shall be filled with aggregate meeting manufacturer's
specs, typically ASTM No. 8.
(5)
Bioretention (Rain Garden). Bioretention and rain
garden are often used interchangeably to refer to an engineered, depressed
landscape area designed to filter, uptake, and infiltrate stormwater
runoff through the natural processes of plants, microbes, and soil
(APWA/MARC, 2012). The term bioretention refers to the ability of
the biomass to retain stormwater and remove pollutants. Bioswale is
another related term that often refers to a linear bioretention feature.
Depending on in-situ soil and other design considerations, bioretention
can be designed without an underdrain to allow full infiltration,
or with an underdrain. During a storm, runoff ponds in the depressed,
vegetated surface of the bioretention where a combination of processes
occurs that includes evapotranspiration and pollutant uptake by plants
and, depending on design, infiltration into the underlying in-situ
soil and/or filtration through a porous bioretention soil mix before
discharging through an underdrain. Bioretention is best suited for
meeting the water quality volume requirement but may be designed to
contribute towards meeting the flood control detention requirement
as well if properly designed.
(6)
Extended
Dry Detention Basins.
(a)
Extended dry detention basins may be provided to
capture and provide temporary storage for the required water quality
capture volume. Extended dry detention basins shall be placed outside
of the primary watercourses which allow off-site flows to pass through
the development (i.e., "off-line") where possible. Design criteria
for extended dry detention basins shall be as follows:
i.
Volume. Minimum volume shall be one hundred twenty-five
percent (125%) of the required water quality capture volume (WQCV).
Detention basins for water quality may be combined with detention
basins for flood control. Effects of the WQCV may be considered in
the design for flood control.
ii.
Drain Time. The WQCV shall be released over a minimum
period of twenty-four (24) hours and a maximum period of forty-eight
(48) hours.
iii.
Outlet Structure. Outlet structures shall consist
of a perforated riser pipe, outlet pipe and gravel filter material
as shown in Figures SS-52 and SS-53.[41] The minimum allowable riser pipe diameter is eight (8)
inches. The riser pipe shall be connected to an outlet pipe of equal
of greater diameter. The outlet pipe shall have adequate capacity
to carry the maximum rate of flow from the riser pipe. Material for
the riser pipe shall be Schedule 40 PVC, ductile iron, or corrugated,
galvanized metal. A removable cap shall be provided at the top of
the riser pipe.
[41]
Editor's Note: These figures are included as an attachment to this chapter.
(b)
The cap shall have a one-inch diameter hole for
air relief. The outlet pipe shall be bedded in firmly compacted clay,
free of stones. For dams exceeding ten (10) feet in height, an anti-seep
collar shall be provided around the pipe. The number of rows of perforations,
number of perforations per row and diameter of perforations for the
riser pipe shall be specified on the plans. Perforation pattern shall
be determined based upon orifice calculations to provide for release
of the WQCV over the specified time. Perforations shall meet the following
requirements:
(c)
Where the basin is to be utilized as a water quality
BMP only, twelve (12) inches minimum freeboard shall be provided above
the WCQV.
(d)
A typical plan and section for extended dry detention
basins is shown in Figure SS-55.[42]
[42]
Editor's Note: This figure is included as an attachment to this chapter.
(7)
Extended
Wet Detention Basins.
(a)
Extended wet detention basins may be provided to
capture and provide temporary storage for the required water quality
capture volume. Extended wet detention basins shall be placed outside
of the primary watercourses which allow off-site flows to pass through
the development (i.e., "off-line") where possible. Design criteria
for extended wet detention basins shall be the same as for extended
dry detention basins, with the following exceptions:
i.
The volume of the permanent pool should not be less
than 1.0 to 1.5 times the WQCV.
ii.
A bench area (littoral zone) with a width of ten
(10) feet shall be provided as shown in Figure SS-56.[43] It is preferred that emergent aquatic vegetation be provided
in this zone.
[43]
Editor's Note: This figure is included as an attachment to this chapter.
iii.
It is recommended that a minimum of twenty-five
percent (25%) of the WQCV be provided in the upper eighteen (18) inches
of depth. A maximum of fifty percent (50%) of the permanent pool volume
shall be provided in the upper eighteen (18) inches of depth.
iv.
The depth of the principal portion of the permanent
pool shall be a minimum of four (4) feet.
v.
It is preferred that a forebay meeting the same
requirements as specified for dry detention basins, be provided.
vi.
Where perforated riser pipes are not encased in
gravel, only corrugated metal or ductile iron pipes may be used.
(b)
Where the basin is to be utilized as a water quality
BMP only, twelve (12) inches minimum freeboard shall be provided above
the WCQV.
(c)
A typical plan and section for extended wet detention
basins is shown in Figure SS-56.[44]
[44]
Editor's Note: This figure is included as an attachment to this chapter.
(8)
Trickle
(Low-Flow) Channels.
(a)
Trickle channels shall be provided to provide grade
control and to minimize chronic wet areas. Trickle channels shall
be constructed of six-inch stone or other porous medium.
(b)
A typical trickle channel cross section is shown
in Figure SS-54.[45]
[45]
Editor's Note: This figure is included as an attachment to this chapter.
(9)
Sand Filters.
(a)
Runoff from fueling plazas, vehicle maintenance
areas, solid waste storage or transfer areas, and other areas having
potentially high concentrations of contaminants shall be passed through
a sand filter prior to discharge to receiving water. Total impervious
area draining to a sand filter will generally be one (1) acre or less.
Sand filters shall be provided with a sedimentation chamber and a
filtration chamber.
(b)
A typical sand filter is shown in Figure SS-57.[46]
[46]
Editor's Note: This figure is included as an attachment to this chapter.
(10)
Other Structural SCMs. Constructed wetlands, porous
pavements and other structural BMPs for which detailed design criteria
can be documented in generally accepted literature can be provided
in addition to, or in lieu of, the BMPs described above, provided
the objectives of this Subsection can be met. The use of infiltration
basins and trenches is discouraged due to possible adverse impacts
on groundwater.
h.
Stormwater Control Measures - Basin Design Criteria.
(1)
Forebay. It is preferred that a forebay be provided
to dissipate energy from incoming flows and to trap settleable sediment
entering the basin. The forebay should be separated from the remainder
of the basin by an earth dike. The top of the dike shall be set six
(6) inches above the stage of the WQCV. Outflow from the forebay to
the basin shall be through a gravel filter. The top of the gravel
filter shall be set equal to the stage of the WQCV. The volume of
the forebay shall be a minimum of ten percent (10%) and a maximum
of twenty percent (20%) of the WQCV. The volume of the forebay is
considered to be part of the required WQCV, not additional volume.
(2)
Length To Width Ratio For Detention Basins. The
optimal length to width ratio for a water quality detention basin
is four (4). The length to width ratio should be no less than two
(2). The minimum allowable length to width ratio is one (1).
(3)
Overflow Spillways. Where the basin is to be utilized
as a water quality BMP only, a spillway or outlet structure capable
of passing the peak flow from a one percent (1%) AEP (100-year) storm
for the drainage area upstream of the basin, shall be provided. The
lowest point on the spillway or outlet structure shall be set at the
top of the WCQV.
i.
Operation And Maintenance. The City of Battlefield provides
no maintenance of water quality BMPs located on private property.
Maintenance must be provided by the owner of the property upon which
the BMP is located. Extended detention basins and wetlands or other
"capture and storage" BMPs shall be located within a single lot or
property, within a designated drainage easement. Where BMPs are located
in common areas or adjoining off-site areas, the property upon which
the BMP is located shall remain in the ownership of the developer
or property owners' association. Where a property owners'
association is formed, restrictive covenants which provide for collection
of fees for maintenance of the BMPs shall be filed in the office of
the Greene County Recorder of Deeds. Restrictive covenants must be
approved by the City legal counselor prior to filing of the final
plat.
9.
Sinkholes And Karst Features.
a.
General.
(1)
The City of Battlefield is located on the Springfield
Plateau of the Ozarks physiographic region. The area is underlain
by Mississippian Age limestone, which is highly susceptible to solutional
weathering. This geology is commonly referred to as "karst" and is
characterized by numerous sinkholes, losing streams, springs, caves,
fracture trends, and other related features. As a result, a complex
and often fragile interaction exists between surface and groundwater,
requiring special consideration and protection. Development in areas
with karst geology can present certain hazards, such as unstable soil
foundation for structures, flood hazards, groundwater contamination,
and public safety hazards related to collapses. Requirements, design
standards, and methods to address these hazards and protect karst
features are contained in this Subsection.
(2)
The general policy in addressing karst hazards
and features shall be based on the following stepped approach:
(a)
Avoidance. Construction in or around karst features
shall be avoided. Exceptions will be made only in situations where
it can be conclusively demonstrated that there are no practical alternatives
to such construction.
(b)
Minimization. In cases where there is no practical
alternative to avoid karst features, measures which will have minimal
impact on the karst feature or receiving water may be proposed. Plans
for minimal alteration can be approved provided it is conclusively
demonstrated that the proposed plan has the least impact to others
or the environment.
(c)
Mitigation. Potential impacts of construction on
karst features and receiving waters must be studied and assessed,
and recommendations made for mitigation of potential impacts upon
flooding, structural stability, and groundwater quality before the
development plan can be approved. The degree and sophistication of
study required will increase in proportion to the potential impacts.
(3)
Because karst features can occur in carrying forms
and severity, each feature must be addressed on an individual basis.
However, for the purpose of establishing standards, sinkholes will
be referred to in this Subsection as being in one (1) of two (2) broad
categories: solution sinkholes or collapse sinkholes.
(a)
Solution sinkholes have a defined drainage area
and will generally be shown on topographic maps as a depression. Development
concerns related to solution sinkholes that must be addressed include
flood hazards and soil stability within the geologic rim. When runoff
from a development is draining to a solution sinkhole, impacts to
groundwater quality must be addressed through water quality protection
measures.
(b)
Collapse sinkholes are areas of karst-related subsidence
with no defined drainage area when occurring outside of a solution
sinkhole. Collapse sinkholes can occur within a solution sinkhole
and are commonly referred to as an "eye." Stabilization of collapse
sinkholes requires a permit from the Building Department. A report
by a qualified professional may be waived if the feature is a minor
feature outside of the geologic rim of a solution sinkhole and no
development is proposed in the area. For public health and safety
reasons, small collapses outside of a solution sinkhole to be filled
and stabilized in accordance with the City standard or recommendation
of a qualified professional that is approved by the City.
b.
ALTERED SINKHOLE
COLLAPSED SINKHOLE
HEAVY EQUIPMENT
LIGHT EQUIPMENT
QUALIFIED GEOLOGIST
QUALIFIED PROFESSIONAL ENGINEER
SINKHOLE
SINKHOLE CLUSTER AREA
SINKHOLE EYE
SINKHOLE FLOODING AREA
SINKHOLE RIM
SINKHOLE WATERSHED
TERMINAL SINKHOLE
VIRGIN SINKHOLE
Definitions. As used herein, the following definitions shall
apply:
A sinkhole which has been filled, excavated, or otherwise
disturbed.
A subsidence or cave-in of the ground surface caused when
soil overburden can no longer be supported by underlying strata due
to the presence of subsurface solution cavities.
Motorized equipment having a gross weight of more than six
(6) tons.
Motorized equipment weighing six (6) tons or less.
A person registered to practice geology according to the
laws of the State of Missouri, and who by reason of technical education
and experience has a background in the fundamentals of storm drainage
and karst geology.
A person registered to practice engineering according to
the laws of the State of Missouri, and who by reason of technical
education and experience has a background in the fundamentals of storm
drainage and karst geology.
Any depression in the surface of the ground, with or without
collapse of adjacent rock, that provides a means through which surface
water can come into contact with subsurface water. Sinkhole depressions
may be gradual or abrupt; they may or may not have a well-defined
eye. While most sinkholes can be defined as the area within a "closed
contour," some sinkholes, such as those located on the sides of hills
and in stream valleys, may not. All sinkholes provide discreet points
of recharge to groundwater.
An area containing two (2) or more sinkholes located in close
proximity, generally interconnected by groundwater conduits.
Generally, a visible opening, cavity, or cave in the bottom
of a sinkhole, sometimes referred to as a "swallow hole."
The area inundated by runoff from a storm with an annual
exceedance probability of one percent (1%) and a duration of twenty-four
(24) hours [eight (8) inches in Greene County].
The perimeter of the sinkhole depression. The sinkhole rim
will generally vary in elevation.
The ground surface area that provides drainage to the sinkhole.
This area extends beyond the sinkhole depression and generally crosses
property boundaries.
The lowest sinkhole in a sinkhole cluster to which any surface
water overflowing from other sinkholes in the cluster will flow.
A sinkhole which has never been altered or disturbed.
c.
Sinkhole Permit And
Report Requirements. A grading permit must be obtained prior to any
alteration of sinkholes or if any construction including the operation
of any motorized equipment is within one hundred (100) feet of a cave,
spring, or losing stream, or within twenty-five (25) feet of a sinkhole
rim, as defined by the most restrictive of the following: geologic
rim as determined by a qualified professional engineer or geologist,
topographic rim as determined by a qualified professional engineer
or geologist, sinkhole rims shown on available sinkhole maps, or other
best available data.
(1)
Permit Requirements. Application for a sinkhole
permit requires the following:
(a)
A plan must be submitted containing measures to
minimize impacts on the sinkhole. The plan shall contain a sinkhole
evaluation, geologic evaluation, and flood evaluation, where applicable.
(b)
An analysis of the drainage from a development
to a sinkhole must be provided.
(c)
In general, development within the rim of a sinkhole
is prohibited; however, in special circumstances when no other practical
alternative exists and documentation is provided in accordance with
this Subsection, the City engineer and Building Inspector may approve
development within the rim of a sinkhole, provided the developer can
demonstrate there will be no significant impacts upon flooding, stability
of structures, water quality, or other natural resources on the site
or adjoining properties.
(d)
For any land with a required sinkhole-related non-buildable
area or restricted fill area, the developer shall place the following
notes on the final subdivision plat and/or development plan:
i.
The sinkhole-related non-buildable areas or restricted
fill areas shown on this plan have been determined based on the study
and recommendation of a professional engineer or geologist. However,
approval of this plan is not to be interpreted as any guarantee that
future sinkhole activity will not occur due to either natural or human
activities.
ii.
Any sinkhole-related non-buildable area identified
here has been determined to be unsuitable for any construction activity,
and no buildings, parking areas, land disturbance or other structures
shall be permitted within this area.
iii.
Any sinkhole or restricted fill area identified
here has been determined to be unsuitable for soil bearing foundation,
and the entire structure of any building (including the floor system)
constructed therein must be founded on solid rock, or as determined
by the director of building development services.
iv.
The lowest enclosed space of any structure within
or adjacent to a sinkhole flooding area shall be a minimum of five
(5) feet above the flooding elevation where there is no overflow from
the sinkhole from the critical flood event, or one (1) foot above
the flooding elevation determined by the overflow elevation calculated
for the critical flood event, whenever the difference between the
topographic rim and flooding elevation is less than five (5) feet.
v.
Water quality protection measures must be provided.
(2)
Sinkhole Evaluation. A written evaluation including
the following information shall be made for all development sites
upon which sinkholes are fully or partially located. The sinkhole
evaluation report must include the following items:
(a)
Site Plan And Area Map.
i.
The site plan must show the following item with
respect to location of proposed construction, proposed or existing
property lines, and existing structures:
(i)
Sinkholes.
|
A)
|
Location and limits of the area of the sinkhole depression as
determined by field surveys or other reliable and accurate methods
(location of sinkholes based solely upon USGS 7-1/2 Minute Series
Quadrangle Maps will not be considered sufficient unless field verified).
|
|
B)
|
Location and elevation of the sinkhole eye or low point.
|
|
C)
|
Topographic contours at maximum intervals of one (1) foot (larger
contour intervals may be used if deemed sufficiently accurate), and
spot elevations sufficient to determine the low point on the sinkhole
rim and the profile of the potential overflow area.
|
|
D)
|
Minimum elevation at which floodwaters can gain entry to any
existing structures located within or on the sinkhole rim.
|
|
E)
|
Elevation of any roadway located within or adjacent to the sinkhole.
|
(ii)
Other Geologic Features. Location of caves, springs,
faults, fracture trends, and geologic mapping units based upon the
information from the Greene County Resource Management Department
or other reliable sources.
(iv)
Existing Watercourses. Storm sewers, culverts,
or other existing watercourses which drain into the sinkhole.
(v)
Proposed Discharge Points. The location type and
size of all points at which concentrated discharges of stormwater
into the sinkhole are proposed. The drainage area to each point of
concentrated discharge shall be delineated on the plan and the size
of drainage area noted.
(vi)
Supply Sources. Existing and proposed wells or
other water supply sources.
ii.
An area map showing the sinkhole watershed area
must be provided. Where the site is located in a sinkhole cluster
area, the map area shall be extended to include in the watershed area
any sinkholes located downstream of the site which may receive overflow
drainage from the site.
iii.
The approximate location of public or private
water supply sources such as springs or wells within five hundred
(500) feet of the site, and boundaries of any known recharge areas
to wells, springs, or caves as determined from information available
from the Greene County Resource Management Department, Watershed Committee
of the Ozarks, Missouri Department of Natural Resources, Missouri
Department of Conservation, or other reliable sources shall be shown.
(b)
Flooding Evaluation. Maximum estimated flooding
elevations shall be determined for each sinkhole for both pre-project
and post-project conditions, assuming no subsurface outflow from the
sinkhole.
i.
Runoff Volume. The volume of runoff considered shall
be that which results from a rainstorm with an annual exceedance probability
(AEP) of one percent (1%) (100-year storm) and a duration of twenty-four
(24) hours. The runoff volume shall be determined by the SCS Curve
Number Loss Method.
ii.
Sinkhole Flooding Area.
(i)
For sinkholes with a tributary drainage area small
enough that it is unlikely the entire sinkhole would flood, the sinkhole
flooding area can be conservatively estimated as the area below the
low point on the sinkhole rim without further analysis.
(ii)
Where the estimated volume of runoff exceeds the
volume of the sinkhole depression, the depth of overflow shall be
estimated (using reservoir routing methods), and the sinkhole flooding
area can be estimated as the area below the maximum flooding elevation.
Where the volume of the sinkhole is sufficiently large that storage
in the sinkhole depression will materially affect estimated outflow
rates, reservoir routing can be performed, if desired, to determine
the maximum flood stage in the sinkhole.
(iii)
In sinkhole cluster areas, the overflow volume
shall be included in determining the maximum estimated flooding elevations
in the next downstream sinkhole. This analysis shall continue downstream
until the lowest sinkhole of the sinkhole cluster is reached or until
overflow reaches a surface watercourse.
iii.
Flooding Considerations.
(i)
No further flooding analysis will be required,
provided that the post-project flooding area of any sinkhole which
receives drainage from the site is located entirely on the development
site.
(ii)
If the post-development sinkhole flooding area
is located fully or partially on another property, the following conditions
apply:
|
A)
|
The post-development sinkhole flooding area shall be contained
within a drainage easement restricting structures; and
| ||||
|
B)
|
Any flow leaving the proposed development shall be contained
within a drainage easement until it reaches the receiving sinkhole.
This easement shall contain the runoff from the critical storm event
with an annual exceedance probability of one percent (1%). The critical
storm event is defined as the storm event with an annual exceedance
probability of one percent (1%) that produces the highest peak flow,
regardless of duration.
| ||||
|
C)
|
Where it is not possible for a drainage easement to contain
the sinkhole flooding area, it must be shown that:
| ||||
|
1)
|
The proposed development will not cause a rise in the flood
elevation within a reasonable tolerance [one-tenth (0.1) ft]; or
| ||||
|
2)
|
The impacts of both the proposed development and any future
developments in the watershed will not impact any existing structures
or improvements and will not increase the flooding elevation by more
than one (1) foot. The increase in the flooding elevation shall be
distributed proportionately based on watershed size, e.g., if the
development is twenty percent (20%) of the watershed then they can
increase the flooding elevation by twenty percent (20%) of one (1)
foot or two tenth (0.2) feet. This can be determined by calculating
the runoff rates and volumes from the entire watershed, assuming fully
developed conditions based on current zoning and potential future
land use and calculating the resulting water surface elevation (WSE).
| ||||
|
3)
|
The following alternatives, listed in order by preference, may be used individually or in combination, if needed, to comply with Subsection (F)(1)(c)(2)(b)(iii)(ii)(A) or (B):
| ||||
|
1.
|
Stormwater control measures (SCMs) that reduce runoff volume
such as bioretention, pervious pavements, etc. Small-scale, distributed
practices are preferred over centralized, large-scale practices in
karst areas.
| ||||
|
2.
|
Detention Storage. Since traditional detention storage has little
to no impact on the volume of runoff from a site, it is seldom the
solution for impacting the WSE of an adjacent sinkhole. However, in
the case where detention is warranted, the following conditions must
be met:
| ||||
|
a.
|
It must be shown that the peak basin outflow is less than the
existing peak rate of runoff from the site and less than the discharge
rate of the sinkhole. (See below.)
| ||||
|
b.
|
Compensatory Excavation Within The Sinkhole Flood Area. Karst
features can have a significant, and often unknown, impact on subsurface
hydrology and groundwater quality. Therefore, compensatory excavation
within the sinkhole flooding area will generally not be permitted.
In rare cases, where there are exceptional conditions, alternative
measures, such as compensatory excavation, may be permitted with the
approval of the City Engineer and Building Inspector, provided the
following conditions are satisfied:
| ||||
|
i.
|
Such alternative creates no adverse impact on groundwater, sinkhole
stability, flood conditions, or other properties. If, at the City's
discretion, excavation to the sinkhole has the potential to cause
an adverse impact, the City may deny the request to excavate within
the sinkhole.
| ||||
|
ii.
|
A comprehensive erosion and sediment control plan is developed
to keep sediment confined to the excavation site. This plan would
likely include additional control measures and inspection beyond the
scope of a traditional plan.
| ||||
(iii)
The
lowest enclosed space for all new structures within or adjacent to
a sinkhole flooding area shall be:
|
A)
|
A minimum of five (5) feet above the flooding elevation where
there is no overflow from the sinkhole from the critical flood event;
or
|
|
B)
|
One (1) foot above the flooding elevation determined by the
overflow elevation calculated for the critical flood event, whenever
the difference between the topographic rim and flooding elevation
is less than five (5) feet.
|
(iv)
When existing improvements are below the 100-year
flooding elevation, an evaluation of the impacts during higher frequency
or shorter duration rainfall events may be required. It shall be shown
that runoff rates and volumes from a proposed development will not
increase the flooding frequency for any such structure or improvement.
iv.
Detailed Flooding Analysis. In cases where the
conditions set forth in the section immediately above cannot be met,
detention basins must be constructed outside of the sinkhole flooding
area. The detention facility must have sufficient volume to store
the increase in total runoff volume due to the development. Outflow
rates cannot exceed pre-project values.
v.
Determination Of Discharge Capacity Of Sinkhole.
In the event that the discharge rate of a sinkhole needs to be estimated
in order to size off-site detention, the following guidance is provided:
(i)
The stage-discharge relationship for the sinkhole
shall be estimated by monitoring the sinkhole during at least two
storm events exceeding one (1) inch of runoff in a six-hour period.
(ii)
The sinkhole shall be monitored immediately after
the storm event to document the stage at various times to better estimate
the stage-discharge relationship.
(iii)
In sinkhole complexes, receiving or terminal
sinkholes must also be analyzed if they receive overflow from upstream
sinkholes.
(iv)
Rainfall depths and intensities shall be determined
based on a recording rain gauge or readings from the nearest City
of Springfield rain gauge at fifteen-minute intervals.
(v)
The discharge rate shall be estimated by adjusting
the stage-discharge relationship of the reservoir routing model until
the reservoir stages in the model correlate with the observed stages
in the sinkhole (within one tenths (0.1) feet).
(vi)
The maximum observed stage in the sinkhole shall
be surveyed and photographs provided where debris lines are used as
evidence of the maximum stage.
(vii)
The volume of runoff storage in the sinkhole(s)
can be counted toward stormwater detention requirements, provided
that erosion and sediment control and water quality requirements,
in accordance with City Code and this manual, are satisfied.
vi.
Diversion To Surface Watercourse.
(i)
As an alternative, where feasible, increased post-project
runoff may be diverted to a surface watercourse, provided that any
increase in peak runoff rate in the receiving watercourse does not
create or worsen existing flooding problems downstream, and the diverted
stormwater remains in the same surface watershed.
(ii)
Storm sewers, open channels, and other appurtenances
provided for diversions shall be designed in accordance with applicable
sections of these Design Standards.
(iii)
The effect of diverted water on downstream watercourses and developments, and requirements for additional detention facilities prior to release of runoff to the surface watercourses shall be determined as set forth in Subsection (F)(7). Effects of the diversion shall be shown by reservoir routing analysis. Routing of excess runoff shall be considered satisfactory when it can be demonstrated that the post-project flooding elevation in the sinkhole is at least one (1) foot below the minimum elevation at which floodwaters can gain entry to any existing structures and does not exceed the preproject flooding elevation by more than one (1) foot in any case.
(3)
Water Quality Protections.
(a)
Sinkhole conduits provide direct recharge routes
to groundwater. As a result, these conduits provide a route for polluted
runoff to enter drinking water supplies that are otherwise protected
and often being consumed with no treatment. Protection of water quality
entering sinkholes protects the quality of area wells, caves, springs,
and streams.
(b)
With regard to groundwater quality, three (3) factors
must be considered: receiving groundwater use, relative groundwater
contamination hazard associated with the proposed development, and
water quality management measures to reduce pollutant levels.
i.
Receiving Groundwater Use. The Sinkhole Evaluation
Report shall identify whether the site lies within a critical area
based upon information available from the Greene County Resource Management
Department or other reliable sources. Where disagreements may arise
over whether a site is located within a particular recharge area,
dye tracing may be required for confirmation of the destination of
water discharged through the sinkhole.
(i)
Critical Areas. The following areas are classified
as critically sensitive to contamination from urban runoff:
|
A)
|
Areas with one hundred (100) feet of private water supply wells.
|
|
B)
|
Areas with three hundred (300) feet of public water supply wells.
|
|
C)
|
Areas within five hundred (500) feet of springs used for public
or private water supply.
|
|
D)
|
Areas within one thousand (1,000) feet of caves providing habitat
to rare or endangered species such as the Ozark cavefish.
|
|
The distances listed above may be extended in any instance where
the recharge area for a well, spring, or cave has been determined
by studies by a qualified engineer or geologist.
|
(ii)
Sensitive Areas. All other sinkhole areas will
be classified as sensitive for groundwater contamination.
ii.
Groundwater Contamination Hazard. The relative
potential for groundwater contamination will be classified as moderate,
high, or very high depending upon the type of land use, development
density, and the amount of directly connected impervious area.
(i)
Moderate Hazard.
|
A)
|
Residential developments on sewer, provided directly connected
impervious areas discharging to the sinkhole is less than one (1)
acre.
|
|
B)
|
Parks and recreation areas.
|
|
C)
|
Low-density commercial and office developments provided directly
connected impervious areas discharging to the sinkhole is less than
one (1) acre.
|
|
D)
|
Discharge from land disturbance areas less than one (1) acre.
|
(ii)
High Hazard.
|
A)
|
Concentrated discharge from streets, parking lots, roofs and
other directly connected impervious areas having an area greater than
one (1) acre and less than five (5) acres.
|
|
B)
|
Multi-family residential developments and higher intensity office
developments provided the directly connected impervious areas discharging
to the sinkhole is less than five (5) acres.
|
|
C)
|
Discharge from land disturbance areas greater than one (1) acre
and less than five (5) acres.
|
(iii)
Very High Hazard.
|
A)
|
Collector streets in industrial and manufacturing zones, all
arterial streets, and highways.
|
|
B)
|
Railroads.
|
|
C)
|
Concentrated discharge from streets, parking lots, roofs and
other directly connected impervious areas having an area greater than
five (5) acres.
|
|
D)
|
Commercial, industrial, and manufacturing areas in Zoning Districts
"C-2," and M-1."
|
|
E)
|
Individual wastewater treatment systems.
|
|
F)
|
Commercial feedlots or poultry operations.
|
|
G)
|
Discharge from graded areas greater than five (5) acres.
|
iii.
Water Quality Management Measures. For sinkholes
where the surrounding drainage area is small enough that the area
draining to the sinkhole flows predominantly as "sheet flow," potential
impacts on water quality can be addressed in many cases by erecting
and maintaining reliable silt control barriers around the sinkhole
during construction and providing a vegetative buffer area around
the sinkhole to filter out potential contaminants.
Where inflow is concentrated, the degree of effort required
to capture and filter out contaminants increases significantly. Concentrated
inflow occurs naturally when the sinkhole watershed area reaches a
sufficient size for watercourses leading into the sinkhole to form.
Concentrated surface flows result as urbanization occurs due to construction
of roads, storm sewers, and drainage channels. Subsurface flows can
become concentrated through utility trenches. Required water quality
management measures are as set forth below:
(i)
Moderate Hazard.
|
A)
|
Sediment And Erosion Control.
| |
|
1)
|
Existing ground cover shall not be removed within twenty-five
(25) feet of the sinkhole flooding area, and a silt barrier shall
be erected and maintained around the outer perimeter of the buffer
area. Vegetative cover must be of sufficient quality and density to
provide desired filtration.
| |
|
2)
|
A ditch check(s) will be required at each point where concentrated
flow is discharged into the sinkhole.
| |
|
B)
|
Permanent Management Measures.
| |
|
1)
|
Where flow into the sinkhole occurs as sheet flow, water quality
requirements can be satisfied by maintaining a permanent vegetative
buffer area with a minimum width of twenty-five (25) feet around the
sinkhole flooding area.
| |
|
2)
|
Concentrated flows may be discharged into the sinkhole through
grassed swales and channels designed for non-erosive velocities. Temporary
erosion control measures such as sodding, or erosion control blankets
shall be provided.
| |
(ii)
High Hazard.
|
A)
|
Sediment And Erosion Control. A sediment basin will be required
at each point where concentrated flows are discharged into the sinkhole.
|
|
B)
|
Permanent Management Measures. Extended wet or dry detention
basins shall be provided at all points of concentrated discharge.
Other Best Management Practices may be specified, provided that their
performance is equal to that of extended detention basins.
|
(iii)
Very
High Hazard.
|
A)
|
Sediment And Erosion Control. A sediment basin will be required
at each point where concentrated flows are discharged into the sinkhole.
Specific limits may be placed on the area which can be graded at any
one (1) time and on the length of time allowed from initial disturbance
to stabilization.
|
|
B)
|
Permanent Management Measures. Runoff from all areas must pass
through extended wet or dry detention basins. Other Best Management
Measures may be specified, provided that their performance is equal
to that of extended detention basins.
|
(4)
Development Requirements.
(a)
Stormwater Detention In Sinkholes. Where flooding
considerations and water quality considerations can be met, the volume
of runoff storage in sinkholes can be counted toward stormwater detention
requirements. Excavation within the sinkhole flooding area to provide
additional detention storage is not allowed.
(b)
Modification Of Sinkholes To Increase Outflow Rates.
Increasing outflow rates in sinkholes by excavating the sinkhole eye
or installing disposal wells for diverting surface runoff to the groundwater
system is prohibited, unless clear and imminent danger to public health
and safety can be demonstrated.
(c)
Setback And Use Restrictions.
i.
New construction of any of the following shall not
be permitted within twenty-five (25) feet of the sinkhole rim, unless
special measures are approved to address structural and water quality
concerns:
ii.
New construction of any of the following may be
permitted within the sinkhole rim, provided that they are set back
a minimum of twenty-five (25) feet of the sinkhole flooding area:
(i)
Residential structures, provided the lowest floor
elevation is set a minimum of five (5) feet above the sinkhole flooding
elevation, or one (1) foot above the lowest elevation on the sinkhole
rim, whichever is less, and provided that a statement of a qualified
engineer is submitted indicating that foundation conditions are suitable
for residential structures.
(ii)
Swimming pools.
(iii)
Underground utilities other than sanitary sewer,
if provisions are made to prevent migration of groundwater along the
trench.
iii.
Use of pesticides and fertilizers within twenty-five
(25) feet of the sinkhole rim is prohibited, unless such usage is
in accordance with a management plan approved by the City of Battlefield.
iv.
Use of heavy construction equipment is prohibited.
v.
Recreational facilities such as hiking, jogging,
and bicycling trails, playgrounds, exercise courses, and grass playing
fields are permitted within the sinkhole flooding area, provided they
are not located within the eye of the sinkhole.
vi.
Clearing and pruning of trees and undergrowth,
and limited grubbing of roots is permitted.
vii.
Landscaping and minor gardening is permitted outside
of the sinkhole eye, provided erosion and sediment discharge is limited
through use of minimum tillage and mulches.
viii.
Construction of light incidental landscaping
and recreational structures such as playground equipment, etc., is
permitted except in the sinkhole eye.
ix.
Facilities which involve storage or handling of
hazardous or toxic materials shall not be permitted in sinkhole watershed
areas.
x.
No public street shall be placed below an elevation
of at least one (1) foot above the sinkhole flood elevation resulting
from the 100-year, twenty-four-hour rainfall with no outlet.
(d)
Collapsed Sinkholes.
i.
Collapsed sinkholes may be stabilized and filled
using approved techniques provided a sinkhole evaluation has been
completed by a qualified engineer or geologist, and a grading permit
is issued prior to construction. An example of such stabilization
can be found in Figure SS-4.[47]
[47]
Editor's Note: This figure is included as an attachment to this chapter.
ii.
The probable cause of the collapse and potential
adverse impacts of filling the collapse shall be investigated and
information submitted with the grading permit application.
d.
Other Karst Features. In addition to sinkholes, other karst
features shall be protected, including caves, springs, losing streams,
and exceptional geologic features.
(1)
Caves.
(a)
Any cave feature that may be accepting or discharging
water shall be treated as a sinkhole eye with all applicable restrictions
and setbacks. No proposed construction shall be located within one
hundred (100) feet of a known cave alignment unless a report prepared
by a qualified professional engineer or geologist is submitted and
approved by the City of Battlefield, verifying that the cave will
not be materially altered by the development, and sound foundations
or the support for the development will not be subject to collapse
or undue settling.
(b)
The entrances of caves shall be protected against
unauthorized entry, while allowing for the unimpeded flow of groundwater
and without disruption to habitat for cave-dwelling animal species.
Plans for cave entrance protection must be approved by the City of
Battlefield prior to construction.
(2)
Springs. No new construction will be permitted
within one hundred (100) feet of a spring unless a report, prepared
by a qualified engineer or geologist verifying that the quantity and
quality of the spring flow will not be materially altered by the proposed
construction, is submitted, and approved by the City of Battlefield.
(3)
Other Features. Developments containing any other
significant karst features shall be designed to protect the features
to the maximum extent practicable, shall take measures to protect
all improvements from potential impacts, and shall take measures to
protect the health, safety, and welfare of the public.
10.
Easements And Maintenance.
a.
General.
(1)
Drainage easements shall be provided for all conveyances
of runoff to the public drainage system outside of public right-of-way.
The public drainage system begins at the point where drainage from
one (1) property or public right-of-way drains onto another property
or public right-of-way. The required easement widths and maintenance
responsibilities for the drainage system are covered in this Subsection.
(2)
Proper maintenance of stormwater control facilities
is essential for effective flood control, water quality management,
and the health, safety, and welfare of the public. Maintenance includes
both routinely scheduled activities and non-routine repairs that may
be required after heavy storm events or other unforeseen problems.
Designing facilities with maintenance in mind is critical for long-term
functionality. Successful long-term maintenance is dependent on many
factors, including appropriate design, good access, a maintenance
plan that is adequately developed and funded, and maintenance practices
that are in accordance with good public works standards.
(3)
Easements for the storage and conveyance of stormwater
and maintenance of the stormwater system may be established by any
of the following methods:
(a)
Identification on a recorded plat drawing.
(b)
Recording the easement in written form (paper easement).
(c)
Prescriptive easement. (Easements that a public
entity inherently owns along waterways that are part of the public
drainage system or have been historically improved and maintained
by the public entity.)
(4)
This Subsection provides a performance-based maintenance
standard to maintain function and safety throughout the stormwater
system. The guidelines provided herein to achieve this standard are
not all-inclusive and should be applied with common sense and good
engineering judgment.
b.
Inspections. Regular inspections of stormwater control measures
and drainage facilities are key to maintaining a properly functioning
and safe drainage system. At a minimum, inspections should be made
by property owners on an annual basis. In addition, inspections should
occur on a regular basis, particularly after rainfall, to determine
if any changes have occurred that require action to maintain the functionality
and safety of the drainage system.
c.
Easement Requirements. Drainage easements shall be provided
for all public drainages flowing across any proposed development.
Generally, private, on-site drainage does not require a drainage easement.
In some cases, additional drainage improvements and easements may
be required upstream or downstream of a new development to address
potential impacts of the development.
(1)
Minimum Boundaries. Easements must be provided
to contain the 100-year flow based on proposed elevation contours
of the site and fully developed conditions of the contributing watershed.
The minimum width of a required drainage easement is determined based
on the type of drainage facility, as summarized in Table 20 below,
assuming the improvement is centered within the easement. Additional
width may be required for maintenance access.
|
Table 20: Minimum Easement Widths
| |
|---|---|
|
Inside Horizontal Dimension
(inches)
|
Minimum Easement Width
(feet)
|
|
15 to 48
|
15
|
|
54 to 72
|
17.5
|
|
84 and 96
|
20
|
|
Over 96
|
Approval required
|
(a)
Enclosed System. Easements for an enclosed drainage
system and constructed open channels must be adequate to allow for
future maintenance of the structure, including its possible removal
and replacement. Flowline depths greater than four (4) feet may warrant
widths exceeding these minimums. When the flowline depth of an enclosed
drainage system or constructed open channel exceeds four (4) feet,
the drainage easement should extend from the edge of the structure
for a distance equal to the depth of the flowline plus one (1) foot.
If the enclosed system is designed for the twenty-five-year flow and
the 100-year flow results in an overflow on the ground surface, the
required easement width will shall be governed by the width of the
ground surface overflow if it is wider than the minimums listed in
the table above.
(b)
Constructed Open Channels. Easements must be adequate
to allow for future maintenance of the channel, including possible
removal and replacement. In the case of vegetated channels, the easement
shall cover the entire channel. In the case of structural channels,
the easement shall extend five (5) feet beyond the outside edge of
the top of the structure. When the flowline depth exceeds four (4)
feet, the drainage easement should extend from the edge of the structure
for a distance equal to the depth of the flowline plus one (1) foot.
In any event the width of the easement shall not be less than that
required to contain the 100-year flow.
(c)
Natural Channels. Easements must be adequate to
encompass the 100-year flood boundary under fully developed watershed
conditions and the most restrictive flow conditions.
(2)
Land
Use Restrictions.
(a)
Drainage easements are areas that, based on engineering
analysis, have been determined to be necessary for the conveyance
of the 100-year flow, are anticipated to be inundated by the 100-year
flood, or are necessary for the maintenance of the drainage system.
These areas must be kept free and clear of obstructions that could
impede the flow of water, development that could be damaged by inundation,
or development that could create a safety risk or nuisance for the
public. No grading or placement of fill, structures, fences, or parking
lots shall be permitted within a drainage or detention easement without
approval by the Building Inspector. Such approval may require an engineering
analysis to clearly demonstrate any of the following:
i.
There will be no flooding impact on adjacent properties.
ii.
The 100-year flood will remain within a drainage
easement.
iii.
No safety hazard or nuisance to the public will
be caused.
iv.
The drainage system can be properly maintained.
v.
For structures, the proposed structure must be properly
flood-proofed as required by Building Development Services. When encroachment
into the easement involves an enclosed structure, the area of encroachment
shall be vacated as a drainage easement.
vi.
For parking lots, there shall be no water depths
in the area exceeding twelve (12) inches during the 100-year flood.
(b)
For fences, an exception will be made when it can
be shown that reasonable action has been taken to allow for the conveyance
of the 100-year flow, and the conditions listed above have been met.
Chain-link fences are generally considered to be acceptable in drainage
easements with the exception of areas where concentrated flows exist,
and vegetation or other debris may collect on the fence.
(c)
The City, as necessary to maintain the drainage
system and the flow of water, retains the right to remove any structures,
fences, fill, or parking lot or other facility used for the movement
of vehicular or pedestrian traffic placed within a drainage easement
without approval of the Building Department.
(d)
The construction of buildings and other permanent
structures over the public stormwater system should be avoided to
the maximum extent practicable. Where no feasible alternative exists,
a structure may be built over the public stormwater system upon the
approval of the City Administrator and execution and recording of
a build over agreement on a form provided by the City which at a minimum
shall specify the following:
i.
City shall have the right to repair, maintain and
replace the stormwater infrastructure as may be necessary, including
the right to enter property, excavate and remove portions of the building
or structure as may be required to gain access to the stormwater infrastructure
in connection with such work.
ii.
Any damage to a building or structure resulting
from repair, maintenance, or replacement of the stormwater infrastructure
shall be the sole responsibility of the property owner.
d.
Maintenance Responsibility. Maintenance of drainage facilities
is generally the responsibility of the entity owning the facility.
Maintenance responsibilities may be further clarified in other legally
binding documents such as recorded final plats, recorded paper easements
and subdivision covenants. Additionally, information regarding how
the facility is to be maintained may be found in the original construction
documents and approved operation and maintenance plan and agreement.
(1)
Subdivisions.
(a)
Generally, all drainage facilities in new subdivisions
that are outside the public right-of-way shall be maintained by a
property owners' association or the property owner. Larger facilities
within a subdivision, such as detention basins, channels, and large
boxes and pipes, shall be located within a common area that is owned
and maintained by the association. The following statement shall be
placed on all final plats:
All common areas shall be considered drainage easements. All
common areas are to be maintained by the property owners' association.
All drainage easements are to be maintained by the property owner.
(b)
Smaller facilities within a subdivision, such as
small pipes and swales, are typically within a drainage easement maintained
by the property owner. Generally, for facilities maintained by individual
homeowners, the property owner must maintain the surface (trash pickup,
mowing, minor erosion repair), and the City will correct major deficiencies
such as structural failure of a box, pipe or wall, or a major erosion
problem.
(c)
If the party with primary responsibility fails
to properly maintain any drainage facility and the City has notified
the party of the deficiency, the City shall have the right to enter
the property in order to maintain the facility and charge the primary
responsible party for any costs associated with the work.
(2)
Existing Facilities With No Easement.
(a)
Existing drainage facilities that are not within
a drainage easement shall be maintained by the property owner. On
major waterways where it is determined the City has a prescriptive
easement, the City may conduct maintenance in the form of brush or
tree removal, removal of large amounts of debris or sediment, stream
stabilization, or structural repairs. Maintenance may be conducted
to maintain flow capacity, reduce pollution and sediment into the
waterway, and maintain the safety, health, and welfare of the public.
(b)
If a drainage easement does not exist, the responsibility
to maintain the facility falls to the property owner. The City may
accept an easement from the property owner or assume maintenance responsibility
through a prescriptive easement. In any case, minor maintenance of
the surface, including mowing and trash pickup, is the responsibility
of the property owner.
(3)
Major
Drainage Facilities. Major drainage facilities include large channels,
detention basins, hydraulic structures, and culverts.
(a)
Major Channels And Floodplains. Major drainage
channels may be natural or constructed. Natural channels and their
floodplains may consist of grass, trees, roots and other vegetation,
cobble, boulders, bedrock, soil, or other natural materials. Constructed
channels may consist of grass, concrete, riprap, blocks, or other
materials. Maintenance requirements for each channel type are discussed
below.
i.
Natural Channels. Maintenance of natural channels
and their floodplains should be conducted with great care. Natural
channels can be dynamic in nature, and it can be difficult to predict
how they will respond to changes made to them. In areas where the
entire floodplain has been preserved as open space, natural channels
can generally be left to move and change. Maintenance intervention
may be necessary in cases where debris, sediment or channel movement
is threatening the integrity of a structure, causing a potential flood
hazard, or causing excessive erosion or stream degradation. In areas
where development has encroached into floodplains or is near a natural
channel, the channel and floodplain should be kept clear of debris,
structures, fill, fences, and other potential blockages. Excessive
vegetation growth should be controlled to maintain channel capacity
and prevent damage to adjacent properties.
ii.
Constructed Channels. Maintenance of constructed
channels must include maintaining the original design capacity and
structural integrity of the channel. The channel capacity should never
be decreased by maintenance activities unless a thorough engineering
study has concluded the action is acceptable. Maintenance of concrete
channels can include sediment removal, structural and subgrade repairs,
and vegetation control.
(b)
Enclosed Systems And Culverts. Box culverts and
pipes shall be kept clear of debris and sediment. Any removed debris
or sediment shall be hauled from the site rather than placed in the
drainage system. Flushing shall be completed only when limited access
makes it absolutely necessary. Any structural deficiencies such as
cracked or damaged concrete shall be reported to the Building Department
and corrected with the assistance of a qualified engineer.
(c)
Detention Basins. Detention storage includes dry
detention, extended detention, and wet detention ponds. The following
maintenance measures shall be implemented on all detention basins:
i.
Storage volume in basins must be preserved through
regular maintenance and removal of sediment. Sediment should be removed,
and the basin returned to design grades when either a sediment depth
of six (6) inches exists or more than ten percent (10%) of the design
volume has been lost. Sediment removal in wet ponds requires draining
of the pond.
ii.
The storage area and outlet structure shall be
inspected to ensure that they are functional, free from debris and
have no structural deficiencies in need of repair.
iii.
Erosion of riprap, vegetation, or soil, particularly
near discharge pipes into the basin, shall be repaired and restored
to the original design.
iv.
Vegetation and aesthetic features, including fences,
shrubs, trees, native grasses, and water quality vegetation shall
be maintained to function and provide safety to the public.
v.
Basins should be inspected on an annual basis. Additional
periodic inspections should be made, particularly after rainfall events,
to ensure the basin meets the requirements of this Subsection and
is functional.
vi.
Seed and mulch, sod, or other necessary erosion
and sediment control Best Management Practices (BMPs) shall be placed
immediately after any excavation or grading is complete to minimize
erosion and discharge of sediment to the drainage system.
vii.
Routine maintenance to return a facility to its
intended designed condition may be conducted without specific permission
by the City. Modified designs shall be submitted to the City Engineer
and Building Inspector.
(d)
Hydraulic Structures. Maintenance of hydraulic
structures, including riprap, grade control structures, or any other
structures in the drainage system, may include the following:
(4)
Water Quality SCMs. Water quality SCMs are designed
to reduce and/or treat runoff to reduce stormwater pollutant loads
and therefore may require higher levels of maintenance to serve their
designed functions. An operation and maintenance plan and agreement
shall be submitted for approval by the City for all SCMs required
to meet the water quality requirements in Subsection(F)(8). The operation
and maintenance plan and agreement shall meet requirements set forth
by the City Engineer Building Inspector and shall be recorded with
the Greene County Recorder of Deeds. To ensure the long-term operation
and maintenance of SCMs, the property owner shall conduct annual self-inspections
of the SCMs and reporting of these inspections in accordance with
schedules, inspection forms, and reporting procedures set forth by
the City engineer. Deficiencies identified through self-inspections
or inspections by the City shall be addressed in a timely manner.
(5)
Mowing And Vegetation Management. Property within
the City is required to be mowed and maintained to meet the City Code.
11.
Erosion and Sediment
Control.
a.
General. The goal of the regulation is to effectively minimize
erosion and discharge of sediment from construction sites by application
of relatively simple and cost-effective Best Management Practices
(BMPs).
b.
General Guidelines. General guidelines for erosion and sediment
control are listed below. Sediment and erosion control plans must
demonstrate consistency with these guidelines:
(1)
Minimize the area disturbed by construction at
any given time.
(2)
Stabilize disturbed areas as soon as possible by
reestablishing sod, other forms of landscaping, and completing proposed
structures, pavements, and permanent storm drainage systems.
(3)
Provide for containment of sediment until areas
are stabilized.
(4)
Provide permanent erosion control by constructing
and maintaining the permanent storm drainage system and maintaining
vegetative cover, pavements, and other surface coverings in good condition.
(5)
Avoid environmentally sensitive areas. Streams,
springs, sinkholes, lakes, or wetlands are easily affected by sediment
from construction sites. Careful planning and additional controls
are needed when construction sites are located in, or in close proximity,
to these areas.
(6)
Recognize sheet flow vs. concentrated flow. In
areas where runoff occurs primarily as sheet flow, containment of
sediment is relatively simple. In these areas, straw or hay bales,
silt fences, and vegetative filter areas can be highly effective.
Where flow is concentrated, containment of sediment becomes more difficult
as the rate and volume of flow increases. In these areas, more elaborate
controls such as sedimentation basins must be provided.
(7)
Recognize temporary vs. permanent controls. The
greatest potential for soil erosion occurs during construction.
(a)
Temporary controls are those which are provided
for the purpose of controlling erosion and containing sediment until
construction is complete. Temporary controls include straw or hay
bale dikes, silt fences, erosion control blankets, etc., which are
not needed after the area is stabilized.
(b)
Permanent controls consist of vegetative cover,
riprap, concrete trickle channels, detention basins, etc., which will
remain in place through the life of the development.
(c)
It is possible for the same feature to serve both
a temporary and permanent purpose. The difference between temporary
and permanent erosion control should be clearly recognized in preparing
an erosion and sediment control plan.
c.
Grading Permits.
(1)
Grading Permit Requirements.
(a)
A grading permit must be obtained before any land
is graded for non-agricultural purposes. Grading is defined as any
excavation or filling or a combination thereof. Grading of agricultural
land is considered non-agricultural whenever soil is excavated for
sale off the site or soil from other properties is brought onto the
site.
(b)
The City of Battlefield may waive the requirement
for a grading permit in the following cases:
i.
Sites where one (1) acre or less is graded, provided
the graded area is located a distance of twenty-five (25) feet or
more from a spring, sinkhole, cave, wetland, watercourse, or floodplain,
and where the proposed construction does not include the construction
of stormwater detention basins or other drainage facilities.
(i)
Lots in new subdivisions will be considered part
of the entire subdivision site area.
ii.
The following activities, provided they are not
located within twenty-five (25) feet of a spring, sinkhole, cave,
wetland, or watercourse:
(i)
Grading for single-family residences.
|
A)
|
Lot grading done as a part of an overall subdivision plan to
make lots buildable or prepare lots for sale is not exempt.
|
(ii)
Grading and repair of existing roads or driveways.
(iii)
Cleaning
and routine maintenance of roadside ditches or utilities.
(iv)
Utility construction where the width of the disturbed
area for trench excavation and backfill is twenty (20) feet or less.
iii.
Emergency construction required to repair or replace
roads, utilities, or other items affecting the general safety and
well-being of the public.
(c)
For emergency construction sites which would otherwise
be required to obtain a permit and for which remedial construction
will take more than fourteen (14) calendar days, application for the
permit must be made within three (3) calendar days from the start
of construction.
(2)
Permit Procedure. The following items must be submitted
prior to issuance of a grading permit:
(a)
Completed grading permit application signed by
the property owner or his legally authorized agent.
(b)
Grading permit fee.
(c)
An approved sediment and erosion control plan (SECP).
(d)
Performance bond or other required security.
(e)
For sites where five (5) acres or more of land
are disturbed, a copy of the Missouri State operating permit.
(f)
Other State or Federal permits, if required.
(3)
Submittal and Approval Procedure.
(a)
Subdivisions. A sediment and erosion control plan
(SECP) shall be submitted for review along with the plans for the
subdivision improvements. Grading permits for subdivisions can be
issued after approval of the plans for the subdivision improvements
by the City of Battlefield, and the items listed above are received.
(b)
Buildings. Two (2) copies of the sediment and erosion
control plan (SECP) shall be submitted to the Building Regulations
Department along with the building plans. Grading permits can be issued
after approval of the SECP by the City of Battlefield, and storm drainage
plans and the items listed above are received.
(c)
Other Sites. Other sites include borrow and spoil
areas, gravel mining areas, and any other sites where a subdivision
plat or a building permit is not required. Two (2) copies of the sediment
and erosion control plan (SECP) shall be submitted to the City of
Battlefield for review. A grading permit can be issued after approval
of the SECP by the City of Battlefield and the items listed above
are received.
(4)
Sediment And Erosion Control Plan (SECP).
(a)
Professional Qualifications. Sediment and Erosion
Control plans must be prepared by and bear the seal of an engineer,
land surveyor, architect, landscape architect, or geologist registered
to practice in the State of Missouri or by a certified professional
in erosion and sediment control (CPESC) who has attained certification
by the Soil & Water Conservation Society. When the total area
of the site exceeds five (5) acres, or the drainage area of any watershed
for which an element of the plan must be designed exceeds five (5)
acres, the plan must be prepared under the supervision of an engineer
registered in Missouri.
(b)
Plan Requirements. The sediment and erosion control
plan must be drawn to scale and must include the following items:
i.
Location map at a scale of 1" = 2,000'.
ii.
Legal description of property.
iii.
North arrow and scale.
iv.
One-Call utility notification symbol.
v.
Title block.
vi.
Signature block for City of Battlefield approval.
vii.
Design professional's seal. Existing topographic
contours at five (5) feet maximum intervals.
viii.
Proposed grades.
ix.
Existing and proposed utilities.
x.
Existing ground covering (open areas, tree masses,
etc.).
xi.
Existing buildings, drives and pavements.
xii.
Proposed buildings or other structures, drives,
and pavements.
xiii.
Limits of area to be disturbed (shading preferred).
xiv.
Location of erosion and sediment controls.
xv.
Details of non-standard erosion and sediment controls.
xvi.
Seeding and mulching requirements.
xvii.
Total site area, total disturbed area.
xviii.
Location of stockpile areas, staging areas,
etc.
xix.
Location of temporary construction entrance.
(5)
Bond Requirements.
(a)
Subdivisions. A security agreement or other form
of security acceptable to the County in the amount of the value of
the required sediment and erosion controls, including the storm drainage
system, must be received prior to issuance of the grading permit.
(b)
Buildings. A security agreement or other form of
security acceptable to the County in the amount of the value of the
required sediment and erosion controls, including the storm drainage
system, must be received prior to issuance of the grading permit.
(c)
Other Sites. Only cash bonds will be accepted for
sites where a subdivision plat or building permit is not required.
A cash bond is obtained by submitting the required bond amount to
the City of Battlefield office in the form of cash, cashier's
check, or money order, and obtaining a receipt.
(d)
Amount Of Security. The amount of security will
be one thousand dollars ($1,000.00) per graded acre for seeding and
mulching, plus the estimated construction cost for permanent sediment
and erosion control measures specified in the SECP. This includes
all elements of the storm drainage system.
(e)
Release of Bond.
i.
Bond will be released one (1) year after seeding
and mulching is complete, provided vegetation is firmly established.
If vegetation is not firmly established at this time, the bond will
be forfeited, and the work will be completed under the direction of
the City.
ii.
Bonds may be released sooner if vegetation is firmly
established. Vegetation will be considered firmly established when
it has survived from the permanent seeding season in which it is placed
to the next permanent seeding season and growth has been established
on all eroded areas which have been noted for repair.
d.
Other Permits.
(1)
NPDES Stormwater Permit. When the area of land
disturbance is five (5) acres or more, an application for a stormwater
discharge permit must be submitted to the Missouri Department of Natural
Resources. Permit requirements are set forth in 10 CSR 20-6.200 of
the Missouri Clean Water Laws. For sites requiring a State permit,
the following procedure applies:
(a)
The applicant submits MDNR forms E and G, the MDNR
fee (with check made payable to "Director of Revenue").
(b)
MDNR reviews the application.
(c)
The sediment and erosion control plan are submitted
to the City of Battlefield with a copy of the permit.
(d)
A City permit can be issued upon receipt of a copy
of the State permit. Construction can commence only after issuance
of the City grading permit.
(2)
"404" Permit. Grading activities in streams or
wetlands may require a US Army Corps of Engineers (USACE) permit under
Section 404 of the Clean Water Act. It is the obligation of the property
owner or operator to contact the Corps of Engineers to determine whether
a permit is required whenever working in these areas. A copy of the
Corps of Engineers written determination, where applicable, shall
be provided prior to issuance of the grading permit.
e.
Design Standards c\And Criteria.
(1)
Grading.
(a)
Maximum Grades. Cut or fill slopes shall not exceed
three (3) horizontal to one (1) vertical (3:1). 4:1 slopes are preferred
where possible.
(b)
Maximum Height. Cut or fill slopes shall not exceed
fifteen (15) feet in vertical height unless a horizontal bench area
at least five (5) feet in width is provided for each fifteen (15)
feet in vertical height.
(c)
Minimum Slope. Slope in grassed areas shall not
be less than one percent (1%).
(d)
Construction Specifications. Construction of private
and public streets must comply with specifications set forth. For
all other areas, construction specifications stating requirements
for stripping, materials, subgrade compaction, placement of fills,
moisture and density control, preparation, and maintenance of subgrade
must be included or referenced on the plans or accompanying specifications.
(e)
Spoil Areas. Broken concrete, asphalt, and other
spoiled materials may not be buried in fills within proposed building
or pavement areas. Outside of proposed building and pavement areas,
broken concrete, asphalt, or stone may be buried in fills, provided
it is covered by a minimum of two (2) feet of earth. Burying of other
materials in fills is prohibited.
(f)
Stockpile Areas. Location of proposed stockpile
areas shall be outlined in the plans and specifications for proper
drainage included.
(g)
Borrow Areas. The proposed limits of temporary
borrow areas shall be outlined in the plans and a proposed operating
plan described in the SECP. At the time borrow operations are completed,
the area shall be graded in accordance with the criteria set forth
above and vegetation reestablished.
(2)
Sediment Control.
(a)
Existing Vegetative Filter Area.
i.
Existing vegetative filter areas may be used where:
(i)
Unconcentrated sheet flow occurs.
(ii)
An area of existing vegetation a minimum of twenty-five
(25) feet in width can be maintained between the area to be graded
and a property line, watercourse, sinkhole, spring, wetland, or waterbody.
(iii)
Existing ground slope is no greater than five
to one (5:1) or twenty percent (20%).
(iv)
The existing vegetative growth is of sufficient
density and in sufficiently good condition to provide for filtration
of sediment.
ii.
The minimum width of the vegetative filter area
shall be twenty percent (20%) of the width of the tributary area.
Vegetative filter areas can be used as both a temporary and permanent
practice.
(b)
Straw Bale Dike or Silt Fence.
i.
Containment areas constructed of hay or straw bales
or silt fence may be provided in areas where:
(i)
Unconcentrated sheet flow occurs.
(ii)
An area of existing vegetation a minimum of twenty-five
(25) feet in width cannot be maintained between the area to be graded
and a property line, watercourse, sinkhole, spring, wetland, or classified
lake.
(iii)
The maximum width of cleared area upslope of
the bale dike or silt fence is as set forth below:
|
Slope of Cleared Area
|
Maximum width upslope of dike/silt fence
(feet)
|
|---|---|
|
2% to 5%
|
100
|
|
5% to 20%
|
50
|
|
> 20%
|
25
|
ii.
Either cereal grain straw or hay may be used for
bale dikes. Silt fence may be used in lieu of hay or straw bales.
Straw bale dikes must be installed level, that is, "along the contour,"
in order to avoid creating points of concentrated overflow. Straw/hay
bale dikes and silt fences must be periodically inspected and replaced
as necessary if deteriorated. Hay bale dikes and silt fences are temporary
practices. Straw bale dikes shall be constructed as shown in Figure
SS-34.[48] Silt fence shall be constructed as shown in Figure SS-35.[49]
[48]
Editor's Note: This figure is included as an attachment to this chapter.
[49]
Editor's Note: This figure is included as an attachment to this chapter.
(c)
Temporary Containment Berm.
i.
Temporary containment berms may be used in lieu
of straw bale dikes or silt fence, under the same conditions set forth
above. An overflow area six (6) inches below the top of the berm and
five (5) feet in length or an approved alternative must be provided
for each two hundred (200) feet of berm length. The overflow area
shall be lined with six (6) mil or thicker polyethylene plastic, six
(6) ounces or heavier non-woven filter fabric, or other approved lining.
Plastic and fabric liners shall be held in place by covering the perimeter
with earth or weighing down with large rock or sandbags.
ii.
Containment berms and swales must be installed
level, "along the contour." Accumulated sediment must be removed when
it reaches one-third (1/3) of the berm height. Temporary containment
berms and accumulated sediment must be completely removed after the
tributary area is stabilized. Temporary containment berms shall be
constructed as shown in Figure SS-36.[50]
[50]
Editor's Note: This figure is included as an attachment to this chapter.
(d)
Inlet Protection. This practice consists of protecting
the inlet perimeter or opening with straw bales, silt fence or sandbags.
The purpose of this practice is to keep sediment from collecting in
storm drains. This practice is also useful when site conditions prevent
locating a sediment basin downstream of the storm sewer outfall. Inlet
protection described in this paragraph cannot be used where blockage
of the inlet opening would result in flooding of residential dwellings,
buildings, streets or roads, or off-site property.
i.
Curb Inlets. Curb inlets can be protected from sediment
entry by placing sandbags over the inlet opening. Sandbags must be
replaced when deteriorated and removed when the area has been stabilized.
Accumulated sediment must be removed from the street after each rainfall.
Curb inlet protection is shown in Figure SS-37.[51]
[51]
Editor's Note: This figure is included as an attachment to this chapter.
ii.
Area Inlets. In paved areas, area inlets can be
protected by placing gravel filled sandbags up to two (3) courses
high around the perimeter of the inlet. Outside of paved areas or
before pavement is placed, area inlets can be protected by installing
a silt fence of straw bale dike around the inlet perimeter. Type DI-1
inlets can be protected by placing sandbags over the openings. Accumulated
sediment must be removed prior to final approval. Area inlet protection
is shown in Figure SS-38.[52]
[52]
Editor's Note: This figure is included as an attachment to this chapter.
(e)
Diversion. Where flow must be diverted into sediment
basins or other sediment retaining facilities, diversion berms or
swales or other approved means of diverting runoff may be specified.
Where sediment enters a street which is up-grade from an existing
street, means must be provided to divert runoff to a sediment basin
before discharge from the site. The method of diversion will vary
depending upon the phase of construction. After initial grading, an
earth berm can be used. This is no longer possible after the street
subgrade is completed, and curbs are installed. After the street pavement
is completed, sandbags can be used to divert the runoff into inlets
for discharge into the sediment basin. Diversion of street runoff
is show in Figure SS-39 and Figure SS-40.[53]
[53]
Editor's Note: These figures are included as an attachment to this chapter.
(f)
Gravel Filter Dam.
i.
Where concentrated flow occurs and less than two
(2) acres of tributary drainage area are graded (i.e., a sediment
basin is not required) or where construction of a sediment basin is
not feasible, a gravel filter dam shall be provided prior to discharge
of runoff from the property.
ii.
Gravel filter dams consist of a layer of filter
fabric and crushed rock covering the upstream side of a riprap dike.
Riprap shall be six (6) and twelve (12) inches in size. Filter fabric
may be woven or non-woven, Mirafi 500X, Mirafi 150NL, or equal. The
purpose of the filter fabric is to remove sediment particles as water
flows through it. The layer of crushed rock provides additional filtration
protects the filter fabric and holds it in place.
iii.
Where gravel filter dams are used as sediment
basin outlets, one (1) square foot of filter fabric area shall be
provided for each one thousand (1,000) cubic feet of storage. The
minimum area provided shall be four (4) square feet.
iv.
Where gravel filter dams are used as ditch checks
in channels, the gravel filter area shall extend throughout the width
of the dam. Riprap stilling basins shall be provided downstream of
the filter dam where discharge is to a grass channel.
v.
Gravel filter dam details are shown in Figure SS-41
and Figure SS-42.[54]
[54]
Editor's Note: These figures are included as an attachment to this chapter.
(g)
Sediment Basin.
i.
Sediment basins shall be provided for all areas
where concentrated flow occurs from an area of five (5) or more acres
and vegetative cover has been stripped from more than two (2) acres.
Sediment basins shall be designed to detain the first one-half (1/2)
inch of runoff from the graded area for a period of at least twenty-four
(24) hours [approximately two thousand (2,000) cubic feet per acre
graded].
ii.
Sediment basins shall have an outflow control structure
capable of providing the required detention time. Outflow control
structures shall consist of a gravel filter dam or a perforated riser
pipe. Sediment basins shall also be provided with an overflow structure
capable of passing the peak flow rate for storms up to and including
the ten percent (10%) AEP (ten-year) storm. The required sediment
control volume shall be provided below the elevation of the overflow
structure. One (1) foot of freeboard shall be maintained over the
ten-year high water elevation.
iii.
Perforated riser pipes shall have a minimum diameter
of eight (8) inches and shall be constructed of schedule SDR35 or
stronger PVC pipe, galvanized corrugated metal pipe, or other approved
pipe material. Riser pipes must be provided with a cap. Plans shall
specify the height of the riser pipe above the basin floor, the number
and spacing of rows of perforations, and the number and diameter of
perforations per row. One and one-half (1 1/2) inch crushed rock
shall be placed around the riser pipes to act as a filter.
iv.
Outlet pipes shall have a minimum diameter of eight
(8) inches and may be constructed of corrugated polyethylene pipe,
corrugated metal pipe, SDR 35 or stronger PVC or reinforced concrete
pipe. Overflow spillways must be constructed of riprap, concrete,
or other approved, non-erodible material.
v.
Detention ponds can be used for temporary sediment
basins, provided it can be demonstrated that flood control requirements
can be met as well as sediment control requirements. Accumulated sediment
must be removed, and vegetation established prior to final release
of security.
vi.
Typical sediment basin details are shown in Figure
SS-43, Figure SS-44, and Figure SS-45.[55]
[55]
Editor's Note: These figures are included as an attachment to this chapter.
(3)
Erosion Protection.
(a)
Seeding And Mulching. All disturbed areas must
be revegetated before temporary sediment controls can be removed.
Requirements for re-vegetated areas are as follows:
i.
Topsoil. Spreading of topsoil is required for permanent
seeding areas only. Topsoil stripped from the site shall be stockpiled
for reuse. A minimum of four (4) inches loose depth (before rolling
or compacting) of topsoil must be spread on the area to be seeded.
ii.
Lime. After topsoil is spread, lime shall be spread
at the rate of eight hundred (800) to nine hundred (900) pounds effective
neutralizing material (ENM) per acre.
iii.
Fertilizer. Fertilizer shall be 13-13-13, [thirteen
(13) pounds each of nitrogen, phosphorus, and potassium per one hundred
(100) pounds] and shall be applied at a rate of four hundred (400)
to five hundred (500) pounds per acre.
iv.
Seed. Seed mix shall consist of sixty percent (60%)
to eighty percent (80%) Kentucky 31 tall fescue and twenty percent
(20%) to forty percent (40%) annual ryegrass. Purity shall be at least
ninety-seven percent (97%), germination shall be at least eighty-five
percent (85%). Seed mixture shall be applied at a rate of four hundred
(400) to five hundred (500) pounds per acre.
v.
Mulch.
(i)
Type 1 Mulch. Where slopes are less than 4:1, cereal
grain mulch is required at the rate of one hundred (100) pounds per
one thousand (1,000) square feet [four thousand five hundred (4,500)
pounds per acre]. Cereal grain mulch shall meet the requirements of
Section 802 of the Missouri State Specifications for Highway Construction
(State specifications) for Type 1 mulch. Mulch may be applied by hand;
however, it must be evenly spread. It is preferred that mulch be applied
with a mechanical blower. Type 1 mulch must be thoroughly wetted after
application.
(ii)
Type 3 Mulch. Where slopes are 4:1 or greater,
Type 3 mulch ("hydro-mulch") meets the requirements of Section 802
of the State specifications. Type 3 mulch shall be applied at a minimum
rate of two thousand (2,000) pounds per acre.
vi.
Permanent Seeding Season. Permanent seeding seasons
run from March 1 to June 1 and from August 15 to November 1. Where
possible, operations shall be scheduled to allow final seeding during
these periods. When seeding cannot be completed during these times,
areas shall be seeded and mulched upon completion of grading with
the amounts of lime, fertilizer, seed, and mulch specified above,
regardless of the season. Any areas where growth has not been established
shall be reseeded during the next seeding season.
vii.
Temporary Seeding. Temporary seeding shall be
applied to lot areas, building areas and other areas planned to receive
other permanent coverings. Spreading of topsoil is not required in
temporary seeding areas. Lime, fertilizer, seed, and mulch shall be
applied at the rates specified above.
viii.
Maintenance. Areas seeded between March 1 to
June 1 or between August 15 to November 1 must be maintained until
growth is firmly established.
ix.
Other Specifications. Other seeding and mulching
specifications may be used with the written approval of the City of
Battlefield.
(b)
Cut And Fill Slopes.
i.
Cut and fill slopes shall be protected from erosion
by construction of straw bale dikes, silt fences, diversion berms,
or swales along the top of the slope. Where drainage must be carried
down the slopes, pipe drains, concrete flumes, riprap chutes, or other
impervious areas must be provided. Suitable erosion control measures
such as riprap stilling basins, must be provided at the bottom of
the slope. Diversions shall be maintained until permanent growth is
firmly established on the slopes.
ii.
Typical diversion details are shown in Figure SS-46.[56] Riprap chute details are shown in Figure SS-47.[57]
[56]
Editor's Note: This figure is included as an attachment to this chapter.
[57]
Editor's Note: This figure is included as an attachment to this chapter.
(c)
Channels And Swales. Permanent channels and swales
shall be provided with a stabilized invert.
(d)
Storm Sewer And Culvert Outlets. Erosion protection
shall be provided at storm sewer and culvert outlets.
(e)
Ditch Checks.
i.
Straw bale ditch checks have proven to be generally
ineffective due to improper installation and inability of bales to
withstand the force of concentrated flow of water. Ditches, channels,
and swales should be stabilized as soon as possible after grading
by lining with erosion control blanket, sod, or installing permanent
linings.
ii.
Where ditches, channels, or swales cannot be stabilized
within thirty (30) days after grading, rock check dams or sandbag
check dams must be provided. Rock check dams may be used in ditches
with a design water depth of up to two (2) feet for the two-year storm.
Sandbag check dams may be used in ditches with a design water depth
of up to one (1) foot for the two-year storm.
iii.
[58]
Editor's Note: This figure is included as an attachment to this chapter.
[59]
Editor's Note: This figure is included as an attachment to this chapter.
(4)
Temporary Construction Entrance.
(a)
A minimum of one (1) temporary construction entrance
is required at each site. Additional temporary entrance may be provided
if approved. The location of each construction entrance shall be shown
on the SECP. Only construction entrances designated on the sediment
and erosion control plan may be used. Barricades shall be maintained
if necessary to prevent access at other points until construction
is complete.
(b)
Construction entrances shall be constructed of
one and one-half inches (1 1/2) clean crushed limestone and shall
be a minimum of twenty-five (25) feet wide and fifty (50) feet long.
Minimum thickness of crushed limestone surface shall be six (6) inches.
Additional two (2) inch lifts of crushed limestone shall be added
at the discretion of the City if the surface of the initial drive
deteriorates or becomes too muddy to be effective. In locations where
an existing drive or street extends at least fifty (50) feet into
the site, the existing drive may be designated as the construction
entrance, and construction of a new gravel entrance is not required,
unless job conditions warrant.
(c)
A permit must be obtained from the Greene County
Highway Department for temporary construction entrances on County
roads. A permit must be obtained from the Missouri Department of Transportation
(MODOT) whenever the entrance is located on State right-of-way.
(5)
Cleaning Streets. Streets, both interior and adjacent
to the site, shall be cleaned of sediment after each rainfall of one-half
(1/2) inch or more and at the end of construction and prior to release
of escrow.
(6)
Dust Control. The contractor will be required to
use water trucks to wet haul roads and construction areas to minimize
dust leaving the site when conditions warrant.
(7)
Sequencing And Scheduling. Costs of sediment and
erosion control can be minimized if proper consideration is given
to sequencing and scheduling construction. Any special sequencing
and scheduling considerations must be noted on the SECP.
G.
(Reserved)
H.
Streets, Alleys, Cul-De-Sacs, And Intersections.
1.
Streets.
a.
Street Construction. City streets shall be constructed of Portland
cement concrete with integral curb (or concrete curb and gutter) or
bituminous plant mix roadway with a concrete curb and gutter. Alley
pavement shall be of either asphalt or concrete design, with an inverted
crown and the curb omitted. Asphaltic streets will require bituminous
or "full depth" asphalt base.
b.
Roadway Sections. Typical roadway sections showing various widths
of roadway and right-of-way and required thickness are as shown on
Figure ST-1[60] included in these design standards. Expressways and arterial
streets should be designed according to MoDOT Standards.
[60]
Editor's Note: This figure is included as an attachment to this chapter.
c.
Street Design. In the preparation of street design, the following
criteria must be observed. These controls are intended to be the absolute
minimum (or maximum) permitted. Any design not meeting this requirement
must have prior approval. Road classification greater than those listed
should be designed according to MoDOT standards.
(2)
Vertical Curves. The length of vertical curves
shall be no less than that determined by the formula:
|
L = KA
|
|
where:
|
|
L = Length of vertical curve
|
|
A = Algebraic difference in grades
|
|
K = Determined by following table:
|
|
Table of "K" Values
| ||
|---|---|---|
|
Type
|
Crest
|
Sag
|
|
Arterial
|
61
|
79
|
|
Collector
|
44
|
64
|
|
Local non-residential
|
19
|
37
|
|
Local residential
|
12
|
26
|
(3)
Centerline Radii and Superelevation.
|
Type
|
Minimum centerline radii
(R)
|
Maximum super elevation
(E)
|
|---|---|---|
|
Arterial
|
R = 600 feet
|
E=0.04
|
|
Collector
|
R = 400 feet
|
E=0.03
|
|
Local non-residential
|
R = 300 feet
|
E=0.02
|
|
Local residential
|
R = 175 feet
|
E=0.02
|
|
*
|
Minimum length of super elevation runout = 100 feet
|
(4)
Minimum Curb Radii at Intersections:
|
Type
|
Intersecting Residential Local
(feet)
|
Street Non-Residential Local and Collector
(feet)
|
|---|---|---|
|
Arterial
|
30
|
50
|
|
Collector
|
20
|
30
|
|
Local residential
|
15
|
20
|
|
Local non-residential
|
20
|
30
|
(5)
Minimum Safe Stopping Sight Distance:
|
Type
|
Distance
(feet)
|
|---|---|
|
Arterial
|
325
|
|
Collector
|
250
|
|
Local non-residential
|
200
|
|
Local residential
|
150
|
(6)
Minimum Safe Stopping Distance at Intersections:
|
Type
|
Distance
(feet)
|
|---|---|
|
Arterial
|
500
|
|
Collector
|
450
|
|
Local non-residential
|
300
|
|
Local residential
|
250
|
(7)
Intersections.
(a)
All curb returns shall be designed with a wheelchair
ramp, meeting the requirements of Figure ST-10 or Figure ST-11[61] included in these design standards. No drainage structures
shall be allowed in the wheelchair path. Intersections shall be approached
on all sides by leveling areas. Where the approach grade for either
or both streets exceed three percent (3%), the leveling area shall
be a minimum length of one hundred (100) feet measured from the intersection
of the edge of gutter flag or edge of road, within which no grade
shall exceed a maximum of three percent (3%) with a maximum crossfall
of six (6) inches at the throat of the radius returns of the intersecting
street. Right angle intersections shall be used whenever practicable.
When local streets intersect collector or arterial streets, the angle
of intersection of the street centerlines shall not be less than seventy-five
degree (75°). A diagonal sight distance easement must be provided
on the property lines substantially parallel to the chord of the curb
radius.
[61]
Editor's Note: These figures are included as an attachment to this chapter.
(b)
Elevations at street intersections shall be computed
by extending curb grades to the P.I. of the intersection of curbs.
A minimum of three-tenths (0.3) feet fall around a curb return is
required. Elevations around the curb return and centerline stationing
at all radius points shall be shown on the plan.
(8)
Plan. The following information shall be shown
on the plan portion of each plan sheet:
(a)
Width of right-of-way.
(b)
Width of pavement (back-to-back of curbs).
(c)
Curb and right-of-way radii with elevation and
stationing.
(d)
Location and size of existing utilities, meters,
valves, poles, street markers, signs, traffic signals, trees, shrubs,
drainage ditches, structures, storm sewers, easements, sanitary sewers,
and manholes. The proposed location of any of the above must also
be shown. Central angle, centerline radius, arc length, and tangent
distance of horizontal curves. Stationing of beginning and end of
paving, PC and PT stationing of curves and tie to lot corners. All
lot dimensions.
(9)
Profile. The following information shall be shown
on the profile portion of each plan sheet:
(a)
Existing ground lines at the centerline with elevations
shown at fifty (50) foot intervals.
(b)
Proposed grade at the centerline.
(c)
Proposed top of curb elevation and stationing at
areas where typical cross sections are not applicable.
(d)
Centerline elevations and stationing at beginning
and end of paving, beginning, end, and P.I. of vertical curves, and
mid-ordinate of vertical curves.
(e)
Elevation and station of low point of sags.
(f)
Top of curb shall be noted.
(11)
Cul-De-Sacs. Information needed on cul-de-sacs
is shown on Figure ST-5,[62] included in these design standards. Details for temporary
dead end and permanent dead ends are shown Figure ST-19 and Figure
ST-20.[63]
[62]
Editor's Note: This figure is included as an attachment to this chapter.
[63]
Editor's Note: These figures are included as an attachment to this chapter.
(12)
Expansion Joints. Expansion joints in concrete
paving shall be placed as shown on standard drawings at intersections
unless otherwise shown on plans and at all structures crossing the
roadway such as bridges, box culverts, etc. Expansion joints are required
around junction boxes, inlets, etc. See Figure ST-3 and Figure ST-4.[64]
[64]
Editor's Note: These figures are included as an attachment to this chapter.
(13)
Contraction Joints. Contraction joints in concrete
paving shall be placed as shown on standard drawings at intervals
of not more than twenty (20) feet and not more than twenty (20) feet
from any expansion joint.
(14)
Longitudinal Joints. Longitudinal joints shall
be placed as shown on the Standard Drawings.
(15)
Manholes. Manhole designation and elevation of
top of manhole must be given when located within right-of-way.
(16)
Storm Sewers. Flow line elevations must be given
for storm sewers within right-of-way.
(17)
Approaches Existing Streets. All approaches to
existing curb and gutter streets shall be Portland cement concrete
to radius point.
|
Street Right-Of-Way And Construction Requirements
| ||||||
|---|---|---|---|---|---|---|
|
Boulevard
(feet)
|
Primary Arterial
(feet)
|
Secondary Arterial
(feet)
|
Collector
(feet)
|
Non-Residential Local
(feet)
|
Residential Local
(feet)
| |
|
Right-of-way - normal
|
120
|
110
|
80
|
65
|
60
|
50
|
|
Pavement width - normal (feet)
|
68
|
68
|
46
|
35
|
35
|
32
|
|
Sidewalk requirements**
|
As needed
|
Both sides
|
Both sides
|
Both sides
|
1 side
|
1 side
|
|
Minimum centerline radius
|
To be designed
|
To be designed
|
600
|
400
|
300
|
175
|
|
*
|
Widening flared to the leaving side of opposite approaches.
| |||||
|
**
|
Except in certain zoning districts, see Subdivision Regulations.
| |||||
|
Right-Of-Way Triangle Requirements
| |||||||
|---|---|---|---|---|---|---|---|
|
Intersection Of/With
|
Expressway
|
Primary Arterial
|
Secondary Arterial
|
Collector
|
Non-Residential Local
|
Residential Local
|
Marginal Access
|
|
Expressway
|
A
|
A
|
A
|
B
|
B
|
B
|
B
|
|
Primary arterial
|
A
|
A
|
A
|
B
|
B
|
C
|
C
|
|
Secondary arterial
|
A
|
A
|
B
|
B
|
C
|
D
|
D
|
|
Collector
|
B
|
B
|
B
|
C
|
C
|
D
|
D
|
|
Non-residential local
|
B
|
B
|
C
|
C
|
C
|
D
|
E
|
|
Residential
|
B
|
C
|
D
|
D
|
D
|
E
|
E
|
|
Marginal access
|
B
|
C
|
D
|
D
|
E
|
E
|
E
|
|
KEY:
| |||||||
|
A: 100' X 100' ROW triangle w/separate right turn
lanes
| |||||||
|
B: 30' X 30' ROW triangle w/50' corner radii
| |||||||
|
C: 10' X 10' ROW triangle w/30' corner radii
(or 15' ROW radius)
| |||||||
|
D: 10' X 10' ROW triangle w/20' corner radii
(or 15' ROW radius)
| |||||||
|
E: No ROW triangle w/15' corner radii
|
I.
Transportation Impact Study.
1.
General.
a.
The transportation impact study (TIS) will be completed in accordance
with the Ozark Transportation Organization (OTO) Guidelines tiered
approach. The goal of a TIS is to determine the impact of a development
or redevelopment on the transportation system, which includes examining
parking, multi-modal facilities, and the movement of cars, trucks,
bicycles, and pedestrians around a site. Where deficiencies or issues
are discovered, the TIS should identify feasible solutions to the
problem(s).
b.
Transportation Impact Study Tier Descriptions. The OTO's
transportation impact study parameters are subdivided into five (5)
categories; an initial submittal and four (4) study tiers as follows:
|
Study Tiers Thresholds Transportation Impact Study:
| |
|
•
|
Preliminary transportation assessment (Optional).
|
|
•
|
Transportation impact study: Level I - under 100 peak hour trips,
or fewer than 50 new dwelling units.
|
|
•
|
Transportation impact study: Level II - 100 to 499 peak hour
trips.
|
|
•
|
Transportation impact study: Level III - 500 to 999 peak hour
trips, or change in access to primary arterial or higher-class road
(<1,000 peak hour)
|
|
•
|
Transportation impact study: Level IV - 1,000 or more peak hour
trips.
|
c.
The TIS must be prepared by a professional engineer registered
in the State of Missouri, able to demonstrate experience with traffic
impact analysis.
d.
Checklists to assist in completing the study can be found in
the OTO Toolbox for Transportation Impact Study Guidelines Policy
Memo. A checklist is also provided there to assist in the completion
of this study.
J.
Sidewalks, Curb And Gutter, And Driveways.
1.
Sidewalks.
a.
General. Sidewalks are required on at least one (1) side of
residential streets and on both sides of collector and arterial streets.
All newly constructed sidewalks shall meet the requirements of the
most current ADA Standards for Accessible Design and Public Right
of Way Accessibility Guidelines (PROWAG).
b.
Design. Sidewalks are to be constructed using a minimum of four
(4) inches of Class "A" Portland cement concrete with a minimum twenty-eight-day
compressive strength of four thousand (4,000) psi in accordance with
ASTM C39. The walks shall be constructed on four (4) inches of Type
1, Type 5 or Type 7 rolled stone base extended six (6) inches beyond
the edges. Sidewalk sections for curb ramps and across residential
drives shall be constructed with a six-inch thickness, and eight (8)
inches across commercial drives.
(1)
Sidewalk Plan. A plan must be prepared showing
the sidewalk in plan, profile, location of ADA ramp, location and
details of expansion joints, and typical cross section. This plan
may be included as part of the street plan. For sidewalks to be constructed
on unimproved streets, it is necessary to obtain sufficient field
data to determine the probable future grade of the street curb and
design the sidewalk accordingly. Additional right-of-way to accommodate
the roadside drainage may have to be provided.
c.
Location. The outside edge of the sidewalk shall be placed one
(1) foot inside the street right-of-way line. The green space between
the sidewalk and back of curb shall be no less than two (2) feet in
width. In areas where two (2) feet of green space cannot be achieved,
sidewalk shall be placed adjacent to the back of curb.
d.
Width. Sidewalks shall be a minimum width of five (5) feet unless
sidewalk is directly adjacent to street curb in which case the minimum
width shall be six (6) feet.
e.
Sidewalk Cross-Section Grade. The maximum cross slope for sidewalks
shall be 1:50 [two percent (2%)]. For sidewalks located across a driveway
entrance, the driveway grade may need to be adjusted to meet this
maximum. For commercial and other areas where a wide sidewalk creates
grade problems for access drives, it should be noted that only the
minimum sidewalk width of four (4) feet must be constructed at a maximum
two percent (2%) cross slope across the entrance. The remaining width
of the sidewalk may be constructed at a grade closer to that of the
drive. For commercial entrances, joint lines should delineate the
portion of the sidewalk that crosses the driveway, so it is clear
where the sidewalk crosses the entrance.
f.
Longitudinal Grade. The grade of the sidewalk shall not exceed
five percent (5%), or the grade established for the adjacent roadway
within the right-of-way.
g.
Parkway And Drainage. The parkway cross sectional grade (the
area between the sidewalk and the street) shall be a minimum of two
percent (2%).
(1)
Drainage from properties adjacent to the sidewalk
shall not drain across the surface of the sidewalk nor shall the grade
of the sidewalk be constructed so that water would pond on the surface
of the walk.
h.
Obstructions. All obstructions are to be removed or relocated
to provide a clear minimum horizontal width of forty-eight (48) inches
and a clear vertical height of eighty (80) inches. In the case where
the sidewalk must be shifted a 5:1 taper to and away from the obstruction
with a straight section adjacent to the obstruction should be followed.
i.
Retaining Walls. When the sidewalk construction requires the
installation of retaining walls to maintain or support adjacent improvements,
the detailed plans shall include the wall design. Unless otherwise
approved by the City, all retaining walls should be located on private
property.
j.
Joints. The sidewalk shall be constructed such that panels are
formed using control joints that are cut such that the resulting panel
lengths are not less than four (4) feet nor greater than six (6) feet.
Edges of the slab shall be edged with an edging tool that has a 1/4-inch
radius.
(1)
Expansion joints shall be placed, between the sidewalk
and all structures such as light standards, traffic light standards,
traffic poles, columns, on each side of driveways, intersecting walks,
utility covers, or other locations when against a substantial structure.
Expansion joints should also be placed as close to each property line
as reasonable and at intervals not greater than one hundred (100)
feet. Preformed isolation joint material shall be installed and left
one-half (1/2) inch below the surface to allow for the application
of joint sealer.
(2)
Construction joints shall be installed at the end
of each day's work and at other times when the process of depositing
concrete is stopped for thirty (30) minutes or more.
k.
Ramps. Curb ramps are to be installed at all intersections and
at certain mid-block locations on all new or reconstruction projects.
(1)
Running Slope. The running slope of curb ramps
shall be 1:12 [eight and thirty-three hundreths percent (8.33%)] maximum.
(2)
Cross Slope. The cross slope of curb ramps shall
be 1:50 [two percent (2%)] maximum.
(3)
Landing. A minimum landing of sixty (60) inches
by sixty (60) inches shall be provided at the top of the curb ramp.
Running and cross slopes shall be a maximum of 1:50 [two percent (2.0%)].
(4)
Flares. Flared sides with a maximum slope of 1:10
[ten percent (10.0%)] measured along the curb line, shall be provided
where a circulation path crosses the curb ramp.
(5)
Surfaces. Storm sewer intakes, grates, access covers,
or other appurtenances shall not be located on curb ramps, landings,
and gutter areas within the pedestrian access routes. All ramps shall
have a textured, non-skid surface.
(6)
Grade Breaks. Grade breaks shall not be permitted
on curb ramps, landings or gutter areas within the pedestrian access
route. The grade break between the gutter area and street at the foot
of a curb ramp shall not exceed thirteen percent (13%).
(7)
Drainage. Drainage from properties adjacent to
the sidewalk shall not discharge a concentrated flow across the surface
of the sidewalk nor shall the grade of the landing or sidewalk be
constructed that water would pond on the surface of the ramp.
(8)
Islands. Any raised islands in crossings shall
be cut through level with the street or have curb ramps at both sides
and a level area at least forty (40) inches long between the curb
ramps in the part of the island intersected by the crossings.
l.
Detectable Warning Surfaces. Detectable warning surfaces consisting
of truncated domes aligned in a square grid pattern shall be provided
where a curb ramp or landing connects to a crosswalk.
(1)
Location. The detectable warning surfaces shall
be located so that the nearest edge is six (6) inches minimum to eight
(8) inches maximum from the face of the curb line and the far edge
is no more than five (5) feet from the back of curb line. The detectable
warning surface shall extend a minimum of twenty-four (24) inches
in the direction of travel and the full width of the curb ramp.
(2)
Dome Size. Truncated domes shall have a diameter
of nine-tenths (0.9) inch at the bottom, a diameter of four-tenths
(0.4) inch at the top, a height of two-tenths (0.2) inch and a center-to-center
spacing of two and thirty-five-hundredths (2.35) inches measured along
diagonal of a square arrangement.
(3)
Visual Contrast. There shall be a minimum of seventy
percent (70%) contrast in light reflectance between the detectable
warning and the adjoining surface. The coloring shall be red and homogeneous
and made an integral part of the detectable warning surface.
m.
Design Checklist For Sidewalks.
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Sidewalks shown in plan and profile on at least one (1) side
of residential streets and on both sides of collector and arterial
streets (Check Subdivision Regulations for exceptions).
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_____
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Sufficient field data is shown for unimproved streets to determine
probable future grade of street curb and sidewalks are designed accordingly.
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Typical cross sections shown with plan and profile.
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Outside edge of sidewalk is placed one (1) foot inside of right-of-way
line.
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1/2-inch expansion joints are indicated on the plans.
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Sidewalk minimum width - sixty (60) inches minimum thickness
of four (4) inch [or six (6) inch when sidewalk crosses a residential
driveway or eight (8) inch when sidewalk crosses a commercial driveway
or alleys] placed on four (4) inches of compacted base stone extending
six (6) inches beyond the edges of the walk.
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Sidewalk cross slope not greater than 1:50 [two percent (2%)].
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All ramp slopes are a maximum of 1:12.
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Maximum rise for any length of run is thirty (30) inches.
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Level landing areas provided at top and bottom of each run.
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Detectable warning system indicated on all curb ramps.
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Curb ramps provided wherever sidewalk crosses a curb.
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Minimum width of curb ramp is sixty (60) inches.
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Accessible crossing area indicated on any raised island crossing.
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Hand railing indicated where elevation change between sidewalk
and adjacent grade is thirty (30) inches or more.
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Drainage from properties adjacent to the sidewalk does not discharge
a concentrated flow across the surface of the sidewalk and the grades
of the sidewalk ramps do not allow areas of surface ponding.
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2.
Curb And Gutter.
a.
General. Curb and gutter are required on all public improvement
street projects.
(1)
Design. Curb and gutter are to be constructed from
Class "A" Portland cement concrete with a minimum twenty-eight-day
compressive strength of 4,000 psi. The curb and gutter shall be constructed
on four (4) inches of Type 1, Type 5, or Type 7 rolled stone base
extending a minimum of one (1) foot behind the back of the curb section.
The width of the curb and gutter is to be two feet six (6) inches.
The curb height is to be six (6) inches, and the gutter cross slope
is to be two (2) inches in two (2) feet. The thickness of the gutter
shall be six (6) inches for residential streets and eight (8) inches
for collector streets and above. At driveway locations shown on the
plans, the gutter profile is to be carried across the drive while
the curb is depressed to match the driveway slope. If driveway locations
are not shown on the plans, curbs cannot be depressed. See Figure
ST-2.[65]
[65]
Editor's Note: This figure is included as an attachment to this chapter.
(2)
Expansion Joints. Bituminous preformed expansion
joints, one-half (1/2) inch thick and precut to the exact cross section
of the curb and gutter shall be placed at all driveway and intersection
radii and at intervals of not more than two hundred (200) feet.
(3)
Design Checklist for Curb and Gutter.
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Curb and gutter is provided for on all improved streets.
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Street profile shows centerline elevations.
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_____
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Curb cross section shows curb height and width six (6) inches.
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Gutter thickness is shown as six (6) inches for local residential
streets.
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Gutter thickness is shown as eight (8) inches for non-residential
local streets and collector residential streets.
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Curb and gutter are constructed on four (4) inches Type I rolled
stone base extending a minimum of one (1) foot behind the curb.
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Total curb and gutter width are shown as two (2) feet six (6)
inches.
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Gutter cross slope is one (1) inch/ft (except at ramp areas).
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One-half (1/2) inch expansion joints indicated at all driveways
and at intervals of not more than (200) two hundred feet.
|
3.
Driveways.
a.
General. Driveway approaches are located to serve the operation
of automobiles and other vehicles from the street pavement to a garage,
parking area, building entrance, structure, or other approved use
located on the property.
b.
Residential Design.
(1)
Residential driveway approaches shall be constructed
using Class "A" Portland cement concrete with a minimum twenty-eight-day
compressive strength of 4,000 psi. All driveway pavement shall be
constructed on four (4) inches of Type 1, Type 5, or Type 7 rolled
stone base. When a driveway approach intersects an existing four-inch-thick
sidewalk, the area of the sidewalk within the driveway area including
both sides of the sidewalk transition sections to meet the drive elevation
or eighteen (18) inches, whichever is greater, shall be removed and
reconstructed with six-inch-thick concrete. The cross slope of the
sidewalk area is not to exceed 1:50 [two percent (2%)]. The grade
of the driveway approach from the gutter line shall rise on a constant
grade to the front edge (street side) of the sidewalk area. The slope
of the driveway approach shall be at least 1:50 and not to exceed
1:8.
(2)
The width of residential driveway approaches shall
not exceed thirty-two (32) feet without permission from the City Administrator
or designee and shall not be less than fourteen (14) feet for new
construction. The width of a driveway is measured at the right-of-way
line. See Figure ST-8.[66]
[66]
Editor's Note: This figure is included as an attachment to this chapter.
c.
Commercial Design. Commercial/non-residential driveway approaches
shall be constructed eight (8) inches thick using Class "A" Portland
cement concrete with a minimum twenty eight-day compressive strength
of four thousand (4,000) psi. All driveway pavement shall be constructed
on four (4) inches Type 1, Type 5, or Type 7 rolled stone base. When
a driveway approach intersects an existing four-inch-thick sidewalk,
the area of the sidewalk within the driveway area, including both
sides of the sidewalk transition sections to meet the drive elevation
or a minimum of eighteen (18) inches shall be removed and reconstructed
with eight-inch concrete. The cross slope of the sidewalk area is
not to exceed 1:50 [two percent (2%)]. The grade of the driveway approach
from the gutter line shall rise on a constant grade to the front edge
(street side) of the sidewalk area. The slope of the driveway approach
shall be at least 1:50 and not to exceed grade shown in the following
table for various street classifications. The width of commercial
driveway approaches shall not exceed forty-five (45) feet and shall
not be less than twenty-six (26) feet wide. The width of driveways
is measured along the right-of-way line. One-way driveways shall be
a minimum of fourteen (14) feet and a maximum of twenty-two (22) feet
wide. See Figure ST-9.[67]
(1)
|
Table for determining the driveway grade for various street
classifications.
| |||
|---|---|---|---|
|
Street Classification
|
Approach Grade
|
Maximum Grade Back of Sidewalk
|
Slope 10 feet of R/W
|
|
Major arterial
|
2% to 4%
|
4%
|
-2% to 6%
|
|
Secondary arterial
|
2% to 5%
|
5%
|
-3% to 7%
|
|
Collector
|
2% to 6%
|
6%
|
-4% to 8%
|
|
Non-resident local
|
2% to 8%
|
8%
|
-6% to 10%
|
[67]
Editor's Note: This figure is included as an attachment to this chapter.
d.
Approach Location. Driveway spacing is restricted by the Battlefield
Subdivision Regulations and the Battlefield City Code.
(1)
No driveway approach shall be permitted which will
interfere with any existing parking meters, signs, traffic control
devices, planting, cables, poles, guys, water mains, gas mains, or
other public utilities.
(2)
No part of any driveway approach may be located
within four (4) feet of a drop inlet or other drainage structure or
a pedestrian ramp.
(3)
No part of any driveway approach shall be located
within forty (40) feet of a point on the right-of-way opposite the
end of a raised median.
(4)
Joint driveway approaches shall be permitted only
if there is a perpetual mutual access agreement approved by the City
Attorney and filed of record in the Greene County Recorder's
office.
(5)
All driveway approaches shall be located to meet
the spacing shown in the following table and provide the following
minimum clearances: nearest edge of the driveway to nearest right-of-way
line of alleys, ten (10) feet; nearest edge of the driveway to property
line, five (5) feet; on corner lots, nearest edge of the driveway
to nearest right-of-way line of an intersecting street, twenty (20)
feet, but in no case shall the driveway return extend closer than
fifteen (15) feet to the intersection right-of-way line extended.
Where sight distance triangles exist, the nearest edge of the driveway
to nearest corner of triangle shall be at least twenty (20) feet.
|
Access on Street
|
Expressway
(feet)
|
Primary Arterial
(feet)
|
Secondary Arterial
(feet)
|
Collector
(feet)
|
Residential Local
(feet)
|
Driveway
(feet)
| |
|---|---|---|---|---|---|---|---|
|
Expressway
|
Approach
|
Not permitted
|
Not permitted
|
Not permitted
|
Not permitted
|
Not permitted
|
Not permitted
|
|
Exit
|
Not permitted
|
Not permitted
|
Not permitted
|
Not permitted
|
Not permitted
|
Not permitted
| |
|
Primary arterial
|
Approach
|
350*
|
300*
|
250*
|
200
|
200
|
440
|
|
Exit
|
250
|
200
|
200
|
200
|
200
|
200
| |
|
Secondary arterial
|
Approach
|
300*
|
250*
|
200*
|
150
|
150
|
220
|
|
Exit
|
150
|
150
|
150
|
150
|
150
|
220
| |
|
Collector
|
Approach
|
250*
|
200*
|
150*
|
100
|
100
|
100
|
|
Exit
|
100
|
100
|
100
|
100
|
100
|
100
| |
|
Residential local
|
Approach
|
150
|
100
|
70
|
50
|
20
|
20
|
|
Exit
|
70
|
50
|
30
|
30
|
20
|
20
| |
|
*
|
Where a median is on the street, the recommended access restrictions
for the approach side are the same as for the exit side.
| ||||||
(6)
Edges of the driveway approach may be skewed so
that the angle between the street right-of-way line and the edge of
the driveway approach is not less than sixty degrees (60°).
(7)
Radius of the driveway approach shall not, in any
case, extend beyond the projection of the adjacent property line,
extended perpendicularly to the right-of-way line.
(8)
The radius of a driveway return shall not extend
beyond the right-of-way line or fifteen (15) feet, whichever is smaller.
e.
Expansion Joints. The plans shall show bituminous one-half-inch
thick preformed expansion joints to be placed at the right-of-way
and sidewalk connections.
f.
Existing Curb And Gutter. The plans shall show the existing
curb and gutter section in front of a driveway (radius point to radius
point) shall be saw cut full depth and removed before the driveway
is constructed. The entire curb and gutter section would then be reconstructed
with the same concrete and depth as the driveway approach.
g.
Design Checklist For Driveways.
|
_____
|
Existing and proposed driveway locations must be indicated on
the plans.
|
|
_____
|
All driveway dimensions including slope and elevations/contours
are shown.
|
|
_____
|
Locations of access drives, alleys, and intersections within
two hundred fifty (250) feet of site and across the street are shown.
|
|
_____
|
Driveway approach is located forty (40) feet beyond the end
of a raised median.
|
|
_____
|
Show that driveway approaches do not interfere with any existing
parking meters, signs, traffic control devices, plantings, cables,
poles, guys, water mains, gas mains, or other public utilities.
|
|
_____
|
Show that all landscaping within five (5) feet of the street
does not affect sight distance at the driveway.
|
|
_____
|
Copy of approved joint driveway approach agreement filed in
the Greene County Recorder's office.
|
|
_____
|
Width of residential driveway approach at right-of-way line
is not less than twelve (12) feet or more than twenty-two (22) feet.
The width of commercial driveway approach at the right-of-way line
is not less than twenty-six (26) feet or more than forty-five (45)
feet.
|
|
_____
|
Approach not within four (4) feet of a drop inlet or other drainage
structure or pedestrian ramp.
|
|
_____
|
Approach grade of driveway does not exceed the maximum allowed
per the street classification.
|
|
_____
|
Nearest right-of-way of alley: ten (10) feet.
|
|
_____
|
Nearest edge to property line: five (5) feet.
|
|
_____
|
If corner lot, nearest edge to nearest right-of-way of intersecting
street: twenty (20) feet.
|
|
_____
|
Approach skewed to not less than sixty (60°) between street
right-of-way line and the edge of the driveway approach.
|
|
_____
|
Radius of driveway approach not extended beyond the projection
of the adjacent property line.
|
|
_____
|
Radius of driveway return is designed for the classification
of street and type of vehicle use.
|
|
_____
|
Expansion joints indicated.
|
|
_____
|
Cross slope of sidewalk area within the driveway must not exceed
1:50 [two percent (2%)].
|
