[Ord. No. 257, 7-13-2010]
The purpose of this Article is to lessen or avoid hazards to
persons and property caused by uncontrolled stormwater runoff or by
obstructions to drainage and to lessen the degradation of the quality
of surface runoff.
[Ord. No. 257, 7-13-2010]
A.
Any person or entity shall, prior to commencement of any work, construction
or development activity which is subject to the regulations contained
in this Article:
B.
A stormwater management plan shall be required of any subdivision
which has been platted, but for which no development work or construction
has yet been done, unless the developer of such subdivision has already
submitted to the City and received prior approval of its stormwater
improvement plans.
C.
Detention requirements are directly related to permitted land use in this Chapter 405, Zoning Regulations, of the Code of the City of Leadington. The permitted densities and minimum lot areas are important factors in the anticipated runoff. Table 1 lists the zoning districts with major permitted use category, minimum lot area and the corresponding percent of imperviousness.
D.
For permitted land uses other than those listed in Table 1, such
as schools, churches, fire station, etc., the rate of imperviousness
shall be determined by the same method as for commercial uses listed
in Table 1. For conditional land use in any zoning district, the same
ratio determination criteria shall apply.
|
Table 1
Stormwater Data by Zoning Districts
| |||
|---|---|---|---|
|
Zone
|
Major Permitted Areas
|
Minimum Lot Area
(square feet)
|
Percent of Impervious
Area for Design
|
|
R-1
|
Single-Family Dwellings
|
7,500
|
70
|
|
R-2
|
General Residential
|
12,500
|
60 to 70
|
|
MH
|
Mobile Home Park District
|
3,500 to 4,000
|
30
|
|
C-1
|
Commercial District
|
7,500 to 12,500
|
60 to 70
|
|
A
|
Agricultural District
|
43,560 (1 acre)
|
70
|
|
I
|
Industrial District
| ||
[Ord. No. 257, 7-13-2010]
A.
A development permit shall be required for any of the following.
1.
Land Disturbance. Any land disturbance that impacts two thousand
five hundred (2,500) square feet or more.
a.
Any construction activity, including, but not limited to, grubbing,
grading, excavation or otherwise destroying the root zone on a land
area two thousand five hundred (2,500) square feet or greater.
b.
The land area considered shall include all of the land disturbance
activities that are a part of a common plan and the total land area
to be disturbed over the life of the project.
2.
Land Disturbance Within Valuable Water Resource Areas. Any land
disturbance activities that impact one (1) acre or more, near valuable
water resources. For purposes of this Article, "valuable water resources"
are defined as follows:
a.
Within one thousand (1,000) feet of a lake used primarily as
a public water supply.
b.
Outstanding waters, such as cold water trout streams.
c.
Lakes participating in EPA's "Clean Lakes Program," at or within
one hundred (100) feet of major reservoirs or permanent streams.
d.
Sinkholes, losing streams or other direct conduits to groundwater.
3.
Stormwater Point Sources. The operation, use or maintenance
of existing stormwater point sources or disturbing land which would
result in a stormwater point source.
4.
Waivers. The Administrative Officer may waive specific information
from time to time as deemed appropriate, subject to the following
requirements:
a.
Sufficient documentation shall be provided to the Administrative
Officer to determine whether a waiver is appropriate.
b.
A statement from a registered design professional certifying
that the differential runoff shall result in no adverse impact.
c.
The Administrative Officer may require a review and written
supportive recommendation from City Engineer or other persons having
specialized technical knowledge prior to waiving such information
whenever necessary.
d.
No waiver on the part of the Administrative Officer shall have
the effect of a variance or relieve any person from complying with
all other applicable provisions of this Article.
5.
Plan Adherence. The owner or authorized agent of the applicant
shall be required to adhere strictly to the stormwater management
plan as approved. Any changes or amendments to the plan must be approved
by the Administrative Officer in accordance with the procedures set
forth in this Article.
[Ord. No. 257, 7-13-2010]
A.
Purpose. The purpose of the stormwater management plan review process
is to provide an organized framework for evaluating and acting upon
proposals for development as they relate to stormwater management
issues.
B.
Required Information.
1.
It is the responsibility of an applicant to include sufficient
information in the stormwater management plan to enable evaluation
of the environmental quality of the affected area, the potential and
predicted impacts of the proposed activity on affected waters, and
the effectiveness and acceptability of the measures proposed by the
applicant for preventing or reducing adverse impacts. The applicant
shall furnish the Administrative Officer with three (3) copies of
the stormwater management plan application form and stormwater management
plan, sealed by a professional engineer or architect registered in
the State.
2.
The owner or an authorized agent of the owner shall submit an
application and obtain a permit prior to commencement of any work
requiring a permit.
C.
Applications. A complete application shall consist of the following:
1.
Application Form. The application form shall contain information
including, but not limited to, the following.
2.
At least three (3) copies of a Stormwater Pollution Prevention
Plan (SWPPP) complying with this Article.
3.
At least three (3) copies of a Stormwater Management Plan complying
with this Article.
4.
Any required fees.
D.
Process. The Administrative Officer shall review all applications
to determine if they are complete.
1.
Complete application shall be submitted to an Engineer appointed
by City or other persons with special technical expertise as needed.
2.
The application shall be approved, denied or conditionally approved
within a reasonable time.
3.
All reasons for denial or conditions of approval shall be clearly
stated with the denied application or permit as applicable.
[Ord. No. 257, 7-13-2010]
A.
A Stormwater Pollution Prevention Plan shall be submitted as a part
of any application for a development permit for a land disturbance
activity. A Stormwater Pollution Prevention Plan shall be prepared
by a registered design professional.
1.
General. Drawn and written descriptive materials shall be provided
which contain information including, but not limited to, the following:
a.
A site and physical condition description.
b.
How the drainage area will be protected.
c.
Description of Best Management Practices (BMP) that will be
used.
d.
How the drainage area will be protected from erosion.
e.
Locations at the site where BMP will be installed.
f.
A description of the types of temporary and permanent non-structural
BMP that will be used.
g.
A description of the types of temporary and permanent structural
BMP that will be used.
h.
Location of the sedimentation basin for each drainage area with
ten (10) or more acres disturbed at one (1) time.
i.
Additional site management BMP to be used, such as solid and
hazardous waste management, provision of portable toilets, proper
storage of construction materials, installation of containment berms
and use of drip pans at petroleum product and liquid storage tanks
and containers.
2.
Drawings. The drawn portion of the overall plan shall also conform
to the following requirements:
a.
Shall be of sufficient clarity to clearly indicate proposed
buildings, structures or uses or other features shown on the plan.
b.
Shall be drawn to scale not greater than one (1) inch equals
twenty (20) feet nor less than one (1) inch equals two hundred (200)
feet.
c.
Shall identify property by lot lines and location, including
dimensions, angles and size, correlated with the legal description
of said property.
d.
Shall show the scale, North point, boundary dimensions, natural
features such as woods, streams, rivers, lakes, drains, topography
(at least five-foot contour intervals; when terrain is irregular or
drainage critical, contour interval shall be two-foot) and similar
features.
e.
Shall show existing man-made features such as buildings, structures,
easements, high tension towers, pipelines, existing utilities such
as water and sewer lines, etc., excavations, bridges, culverts and
drains and shall identify adjacent properties within one hundred (100)
yards and their existing uses.
f.
Shall show the location, proposed finished floor and grade line
elevations, size of proposed main and accessory buildings, their relation
one (1) to another and to any existing structures to remain on the
site and the height of all buildings and structures, as well as building
elevations and materials proposed for the structures under consideration.
g.
Shall show the proposed streets, driveways, sidewalks and other
vehicular and pedestrian circulation features within and adjacent
to the site; also the location, size and number of parking spaces
in the off-street parking areas and identification of service lands,
service parking and loading zones in conformance with the requirements
set forth in this Article.
h.
Shall show the location and size of all existing utilities serving
the property as well as the location and size of all proposed utilities
to serve the property.
i.
Shall show any proposed alterations to the topography and other
natural features shall be indicated.
j.
Shall show the pre-development or pre-development activity site
information.
k.
Shall show the location of any adjacent streets or roads.
l.
Shall show the location of vegetative cover and soil types and
characteristics representative of the design conditions, where percolation
or exfiltration systems are proposed.
m.
Shall show the location of farm drains, inlets and outfalls,
storm, sanitary and combined sewers and outfalls, septic tank systems
and outlets, if any, and seeps, springs and flowing and other wells.
n.
Shall show the location and description of nearby existing off-site
water management facilities such as wells, lakes, drainageways and
other similar features which are potentially directly affected by
the proposed construction or development.
o.
Shall show all existing drainage facilities which are to be
maintained, altered or enlarged as part of the stormwater management
system; provide information as to their size, slopes, depths, outfalls,
receiving waters, elevations, cross sections, profiles, construction
materials and other design details as applicable.
p.
Shall show the location of all new drainage facilities, including
detention basins, to be constructed and provide design details on
each as applicable.
q.
Shall show the location and extent of right-of-way and easements
for the stormwater management system, including all areas to be dedicated
for water management purposes.
r.
Shall identify and describe any special or required maintenance
procedures for the project to continue to function as designed.
s.
Shall include provisions for any off-site development activity
related to the project. All land within the City on which development
activity related to a project is proposed shall be identified and
included in the plan. All owners of property where development activity
related to the project is proposed shall be identified and included
in the application.
t.
Shall include any other information required by the Administrative
Officer to determine compliance with this Article.
3.
Construction Details. Detailed construction drawings clearly
indicating the proposed locations, materials and specifications of
any structural BMP shall be submitted.
4.
Additional Requirements. Additional requirements pertaining
to the Stormwater Pollution Prevention Plan shall be as follows.
a.
After a permit is approved, a copy of the Stormwater Pollution
Prevention Plan shall be kept on site during the entire term of the
land disturbance activity and shall be made available to all local,
State and Federal authorities having jurisdiction upon request.
b.
The SWPPP shall be amended or updated as appropriate during
the term of the land disturbance activity.
c.
Amendments or updates shall be also be submitted to the Administrative
Officer to be included in the permit record.
[Ord. No. 257, 7-13-2010]
A.
A stormwater management plan is designed to safely manage the stormwater
runoff following the rainstorms which exceed the maximum allowable
release rate and the capacity of the stormwater drainage system and/or
the storm sewer system by detention of the excess stormwater runoff.
The plan shall provide or be accompanied by maps at a minimum scale
of the (1) inch less than or equal to two hundred (200) feet and other
descriptive material, including the basis of computation, showing
the following:
1.
Required pre-development site information (map scales are minimums):
a.
Detailed location sketch showing the parcel and major adjacent
roads.
b.
Topographic map of the site at a scale of one (1) inch less
than or equal to two hundred (200) feet with maximum five-foot contour
intervals, except in floodplains or other area of low relief where
a smaller interval may be required.
c.
Where percolation or infiltration systems are proposed, information
as to the location and type or vegetative cover and soil types and
characteristics representative of the design condition mapped at a
scale of one (1) inch less than or equal to two hundred (200) feet.
d.
Location of streams and other floodwater runoff channels, their
normal channels, and the extent of the floodplains at the established
high water elevations, and the limits of the floodway mapped at a
scale of one (1) inch less than or equal to two hundred (200) feet.
e.
Location of lakes, ponds, swamps and detention basins indicating
their normal shorelines, floodplains and lines of inflow and outflow
mapped at a scale of one (1) inch less than or equal to two hundred
(200) feet.
f.
Location of farm drains, inlet and outfalls, storm and sanitary
sewers and outfalls, septic tank systems, and outlets, if any, and
seeps, springs, and flowing and other wells mapped at a scale of one
(1) inch less than or equal to two hundred (200) feet.
g.
Location and description of nearby existing off-site water management
facilities such as wells, lakes, drainage ways, etc., which are potentially
directly affected by the proposed construction or development, mapped
at a scale of one (1) inch less than or equal to two hundred (200)
feet.
2.
For all existing drainage facilities which are to be maintained,
altered or enlarged as part of the stormwater management system, provide
information as to their size, slopes, depths, outfalls, receiving
waters, elevations, cross-sections, profiles, construction materials
and other design details as applicable.
3.
Location of all new drainage facilities, including detention
basins, to be constructed. Provide design details on each facility
as applicable.
4.
Location and extent of existing and proposed impervious surfaces
(roads, parking lots, building, etc.) and their elevations. Provide
grading and paving plans and specifications.
5.
Location and extent of right-of-way and easements for the stormwater
management system, including all areas to be dedicated for water management
purposes.
6.
Identification and description of any special or required maintenance
procedures to keep the project functioning as designed.
7.
Provide stormwater management system design calculations as
follows:
a.
Design storms used.
b.
Calculated hydrographs of inflow and outflow of design storm
runoff for the project site under natural and undeveloped conditions.
c.
Hydrographs of the runoff from the design storm runoff under
developed conditions.
d.
For all detention basins, a plot or tabulation of storage volumes
with corresponding water surface elevations and of the basin outflow
rates for those water surface elevations.
f.
Runoff routing calculations showing discharge, elevations and
volumes retained and/or detained during applicable storm event.
g.
Calculations required for determination of minimum building
floor and road elevations.
8.
Identify the entity responsible for operation and maintenance
of the system.
9.
The requirements for specific plan elements cited above may
be waived by the Administrative Officer upon written supportive recommendation
of the City appointed Engineer. The stormwater management plan for
minor development activities may consist of a certification from a
professional engineer or architect that the differential runoff is
not significant.
10.
The Administrative Officer will ascertain the completeness of
the stormwater management plan application. The Administrative Officer
will return incomplete applications to the applicant for completion
and resubmission. After determining that the application is complete,
the Administrative Officer will distribute copies of the application
for review and comment to other persons with special technical expertise
as deemed appropriate by the Administrative Officer. Within a reasonable
period after submission of the complete stormwater management plan
application by the applicant, the Administrative Officer shall approve,
approve with specified conditions, or deny the application and shall
notify the applicant accordingly. If the stormwater management plan
is denied or approved with conditions, the Administrative Officer
shall state the reasons for denial or the specified conditions. Any
applicant aggrieved by the denial or conditions may appeal the decision
to the Board of Adjustment.
[Ord. No. 257, 7-13-2010]
A.
Subject to the exception provided in Subsection (A)(1) herein below, all applications shall be accompanied by payment of a fee based on ten dollars ($10.00) per acre or a fee in the amount of two hundred fifty dollars ($250.00), whichever is greater.
1.
Applications that do not require complete stormwater management
plan review requiring special technical expertise shall be accompanied
by a fee of twenty-five dollars ($25.00).
B.
The effective acreage for a project is not limited to a fractional
part of the total concept; rather, if a project is developed in phases
or small plots, the total acreage of the conceptual project will be
considered.
[Ord. No. 257, 7-13-2010]
A.
A stormwater management system shall be provided for protecting lots,
roads, streets and buildings in the project area from the potential
adverse impacts of stormwater runoff. Streets, blocks, depths of lots,
parks and other public grounds, and ultimate land usage shall be determined,
located and laid out in such a manner as to reduce the velocity of
overland flow and allow the maximum opportunity for infiltration of
stormwaters into the ground and to preserve and utilize natural streams,
channels and detention basins and, wherever possible, to include streams
and floodplains within parks or other public grounds.
B.
The maximum allowable release rate of stormwater after development
shall not exceed the before-development rate based on a fifteen-year
frequency storm. The total drainage area must be used in calculating
the allowable release rate. The required storage volume will be based
on the project area only, with extraneous flows from upland areas
being bypassed or discharged via overflow spillway or other devices.
C.
The increased stormwater runoff resulting from the proposed development
shall be detained on site by appropriate detention basins; by storage
on flat roofs, parking lots or streets; or by other acceptable techniques.
The minimum volume of storage shall be sufficient to store the volume
from a twenty-five-year storm (under developed conditions). Control
devices shall limit the discharge from storage to a rate no greater
than that prescribed by this Chapter. Downstream property, watercourses,
channels or conduits shall not receive stormwater runoff from proposed
development at a higher peak flow rate than that which existed prior
to the development.
D.
Generally acceptable locations of the stormwater runoff channels
in the design of the project area may include the following:
1.
In a depressed median of a double roadway, street or parkway,
provided the median is wide enough to permit required roadway shoulders.
2.
Centered on the rear lot lines in a block or entirely within
the rear yards of a single row of lots or parcels, provided that in
either case the lots are deep enough to permit side slopes in the
runoff channel and a building site of the elevation required by other
Sections of this Article.
3.
In a depressed area long roadway, street or parkway, provided
the area is wide enough to permit side slopes as required in other
Sections of this Article.
4.
Alternative systems such as curb and gutter and storm sewers
that discharge into an appropriate detention basin may be incorporated
into the stormwater management plan.
5.
The smaller, uppermost reaches of drainage channels and swales
forming the natural drainage system near a watershed divided may be
relocated or eliminated and incorporated into the planned system of
storm sewers and open channels designed consistent with the requirements
of this Article.
E.
A continuous easement may be provided abutting rear lot lines as
shown in the stormwater management plan within which utility lines
and open drainage facilities may be located and maintained, but on
which no accessory buildings may be constructed. The utility-drainage
easement shall be at least twenty (20) feet wide. Within the area
so designed for the passage or storage of waters, no structure may
be erected, no fences, shrubbery or trees planted, or changes made
to the prescribed grades and contours of the specified floodwater
or stormwater runoff channels.
F.
All storm sewer outfalls shall be so designed, by reason of elevation
of the invert, by a flap gate or by other features that when the receiving
stream is in full flood, the storm sewers will continue to drain the
areas they are designed to serve unless the provision is made for
sewer backups into planned storage locations.
G.
All sanitary sewer manholes constructed in a floodplain, in a street
designed for detention, or in an area designed for the storage or
passage of floodwater or stormwater shall be provided with either
a water-tight bolted manhole cover, a water-tight concealed pick-hole
cover, or be constructed with a rim elevation at or above the high-water
elevation of the one-hundred-year flood or the high-water elevation
of the design storm, whichever is applicable to the specific area.
H.
Projects that are to be developed in phases will normally require
the submission of a master plan of the applicant's contiguous land
holdings. Applications for individual project phases may be considered
only when the phases are totally independent of, or make sufficient
provisions for, adjacent lands.
I.
The plan shall include provisions for any off-site development activity
related to the project. All land within the City on which development
activity related to a project is proposed shall be identified and
included in the plan. All owners of property where development activity
related to the project is proposed shall be identified and included
in the application.
[Ord. No. 257, 7-13-2010]
A.
Stormwater systems will be designed with sufficient hydraulic capacity
as a minimum for the following frequencies and durations:
|
Type of Facility
|
Design Frequency
|
|---|---|
|
Detention basins
|
25-year
|
|
Primary drainage systems
|
25-year
|
|
Bridges
|
50-year
|
|
Secondary drainage systems, i.e., crossdrains and ditches for
internal subdivision drainage.
|
15-year
|
B.
The Administrative Officer may require alternative designs or features
to reduce the cost of long-term maintenance.
C.
In critical areas, the Administrative Officer may require additional
hydraulic capacity above the minimum set forth above, up to the one-hundred-year
frequency design.
[Ord. No. 257, 7-13-2010]
A.
Method Of Evaluation. Differential runoff evaluation consists of
the determination of rates of runoff before and after development,
the determination of required volume of detention and verification
of adequacy of discharge and control structures.
B.
Differential Runoff Rates. Differential runoff rates for all three (3) size classes of projects shall be evaluated by the rational formula. The runoff coefficients in Table 2, in Subsection (R) of this Section, shall be used. Differential runoff rates shall be evaluated by equation:
|
Equation 1
|
|
R = (Rd-Ru)
|
|
Where:
| |||
|
R
|
=
|
Differential runoff rate
| |
|
Rd
|
=
|
C.I. factor for developed conditions
| |
|
Ru
|
=
|
C.I. factor for undeveloped conditions
| |
C.
Volume Detention. Volumes of detention for the three (3) classes
of projects shall be evaluated according to the following methods:
1.
Volume of detention for projects of less than twenty-five (25)
acres shall be evaluated by the "Simplified Volume Formula."
2.
Volume of detention for projects of twenty-five (25) acres or
greater but less than two hundred (200) acres may be evaluated either
by the "Simplified Volume Formula" or the "Modified Hydrograph Method."
3.
For projects larger than two hundred (200) acres, the owner's
engineer shall submit his/her proposed method of evaluation for the
sizing of the detention basin to the Administrative Officer. The method
will be evaluated for professional acceptance, applicability and reliability.
No detail review for projects larger than two hundred (200) acres
will be rendered before the method of evaluation of the detention
is approved.
4.
Other analytical methods of evaluation of volume of detention
will be considered, provided that reliability, professional acceptance
and proper application are approved by the Administrative Officer.
D.
Calculation Methods. Any of the following methods may be used for
calculating detention volume as applicable:
1.
Simplified Volume Formula. Total volume of detention shall be
computed by the equation:
|
Equation 2
|
|
V = R x A x 30 (min) x 60 (sec/min)
|
|
Where:
| |||
|
V
|
=
|
Total volume of detention
| |
|
R
|
=
|
Differential runoff rate
| |
|
A
|
=
|
Area of project in acres
| |
2.
Graphic Representation. For purposes of further analysis, the
simplified volume formula may be represented by a triangular synthetic
hydrograph as shown in Figure III (in the Seeley Data Book for civil
engineers) with the following elements:
|
Tb = Base time of hydrograph for developed project without detention
|
|
Tb = sixty (60) minutes
|
|
Tp = Time for peak runoff of developed project
|
|
Tp = twenty (20) minutes
|
|
Qd = Total peak runoff of developed project in cfs
|
|
Qd = A x Rd (see Equation 1)
|
|
Qu = Total peak runoff of unimproved project in cfs
|
|
Qu = A x Ru (see Equation 1)
|
|
A = Total area of project in acres
|
|
Tq = Assumed time of peak differential for unimproved project
|
|
Tq = Qu/Qd x 40
|
|
Tr = Assumed recedence time differential for discharge at rates
no greater than unimproved condition
|
|
Tr = (30 Qd/Qu) - 60
|
|
V = Volume of detention
|
|
V = (Qd - Qu) x 30 (min) x 60 (sec/min)
|
3.
Modified Rational Hydrograph Method. This is a modification
of the "Unit Hydrograph Method" of hydrologic evaluation simplified
to reflect features of present practice and some elements of topographic
characteristics, concentration patterns and routing. Figure III from
above illustrates the elements of the modified hydrograph. Steps to
develop the hydrograph are as follows:
a.
Determine the time of concentration for the project by use of Chart IV or similar reference manual adopted by the City Engineer. Chart IV is based on overland flow time from Seeley Data Book for Civil Engineers. Enter chart with overland travel distance, follow horizontally to slope curve then vertically down to C or P factor listed in Table 2, in Subsection (R) of this Section, and obtain Tc. For analysis of large improved channels, time of travel for overland flow and channel are to be analyzed to determine reasonable (Tc) time of concentration.
b.
Determine time of peaking by equation:
|
Equation 3
|
|
T p = D/2 + .6Tc
|
|
Where:
| |||
|
T p
|
=
|
Time of peak discharge of developed project in minutes
| |
|
D
|
=
|
20 min = storm duration in minutes
| |
c.
Determine the base time of the hydrograph without detention
by equation:
|
Equation 4
|
|
Tb = 2.67 T p
|
d.
Determine the base time of the hydrograph with detention by
equation:
|
Equation 5
|
|
(Qd
Tr = Tb _____ -1)
(Qu
|
|
Where:
| |||
|
Tr
|
=
|
Additional time required for discharge at a rate no greater
than that of the undeveloped condition
| |
|
Qd
|
=
|
Total peak runoff of improved project in cfs
| |
|
Equation 6
|
|
Qd = A x Rd (See Equation 1)
Qu = Total runoff of unimproved project in cfs
|
|
Equation 7
|
|
Qu = A x Ru (see Equation 1)
|
e.
Determine the required volume of detention by equation:
|
Equation 8
|
|
V = 1/2 (Qd - Qu) Tb
|
E.
Control Structures. Detention facilities shall be provided with obvious
and effective control structures. Plan view and sections of the structure
with adequate detail shall be included in plans.
1.
The design discharge (Q) for the low-flow weir shall not exceed
the fifteen-year (frequency) with a duration equal to the time of
concentration for the watershed, runoff from the tributary area for
five percent (5%) imperviousness [one and seven-tenths (1.7) cfs per
acre]. The maximum discharge shall be designed to take place under
total anticipated design-head conditions.
2.
Sizing of the low-flow weir shall be by the appropriate weir
formulas.
3.
The overflow opening or spillway shall be designed to accept
the total peak runoff of the improved tributary area.
4.
The low-flow channel invert through dry detention facilities
on other than permanently flowing streams shall be paved.
F.
Detention Design Criteria. Detention in the overall system, including
swales, lakes, canals, greenways, etc., shall be provided as follows.
G.
General.
1.
Storage Volumes. The minimum volume of storage provided in detention
basins, together with such storage as may be authorized in other on-site
facilities, shall be sufficient to store the volume from a twenty-five-year
storm (under developed conditions) with a discharge no greater than
the rate of flow from a fifteen-year storm (under undeveloped conditions).
2.
Outlet Control Structures. Outlet control structures shall be
designed to operate simply and automatically. They will limit discharges
into existing or planned downstream channels or conduits so as not
to exceed predetermined maximum authorized peak flow rates.
3.
Emergency Spillway. Emergency overflow facilities must be provided
in all instances so that stored waters will not exceed the safe capacity
of the basin. At a minimum, the emergency spillway must be able to
pass without damage the one-hundred-year storm.
4.
Appearance. Designs should result in aesthetically pleasing
configurations which will enhance public acceptability.
H.
Dry-Detention Facilities.
1.
Perimeter maintenance easements of fifteen (15) feet (minimum)
width at slopes no steeper than 3:1 (horizontal to vertical) shall
be provided.
2.
Side slopes of the facility shall not be steeper than 3:1 (horizontal
to vertical).
3.
Provisions must be incorporated to facilitate complete interior
drainage to dry-bottom basins, to include the provision of natural
grades to outlet structures, longitudinal and transverse grades to
perimeter drainage facilities, or the installation of sub-surface
drains.
4.
Multi-purpose features may be designed to serve secondary purposes
for recreation, open space or other types of use which will not be
adversely affected by occasional or intermittent flooding.
5.
The entire reservoir area shall be seeded, fertilized and mulched,
sodded or paved.
I.
Wet-Detention Facilities.
1.
Perimeter maintenance and operation easements of fifteen (15)
feet (minimum preferable) width at slopes no steeper than 3:1 (horizontal
to vertical) shall be provided.
2.
Control elevations should be no higher than two and one-half
(2 1/2) feet below the minimum road centerline elevation in the
area served by the control device in order to protect the road subgrade
when structures are constructed near roads.
3.
Side slopes shall not be steeper than 3:1 (horizontal to vertical)
out to a depth of two (2) feet below the control elevation, then as
steep as soils stability will allow.
4.
If fish are to be used to help keep the basin clean, at least
one-fourth (1/4) of an area of the permanent pool must be a minimum
depth of ten (10) feet.
5.
For emergency purposes, cleaning or shoreline maintenance, facilities
shall be provided or plans prepared for the use of auxiliary equipment
to permit emptying and drainage.
6.
The limits of maximum ponding elevations are to be no closer
than twenty-five (25) feet horizontally from any building and no less
than two (2) feet below the lowest sill elevation of any building.
J.
Impervious Areas. Paved parking lots may be designed to provide detention
storage of stormwaters on all or a portion of their surfaces. Outlets
will be designed so as to slowly empty the stored waters, and depths
of storage must be limited to a maximum depth of twelve (12) inches
so as to prevent damage to parked vehicles. Ponding should be regulated
to those positions of the parking lots farthest from the area served.
K.
Rooftop Storage. Detention storage requirements may be met in total
or in part by detention on flat roofs. Details of such designs to
be included in the stormwater management plan application shall include
the depth and volume of storage, details of outlet devices and down-drains,
elevations of overflow scuppers, design loadings for the roof-structure
and emergency overflow provisions.
L.
Underground Storage. All or a portion of the detention storage may
also be provided for in underground facilities, as long as all applicable
requirements of this Chapter are met. Details of such designs are
to include the type of facility, depth and volume of storage, details
of inlet and outlet devices and locations, emergency overflow provisions,
and measures to be used for surface water and groundwater pollution
control.
M.
Design Alternatives. The above listing of design criteria is not
intended to preclude the use of other known state-of-the-art methods
and available best management practices and should not be construed
as a mechanism to discourage innovative design concepts.
N.
Development Adjoining A Floodplain. Where a development adjoins or
encompasses a portion of a floodplain for a one-hundred-year flood,
the following shall apply:
1.
The applicant shall show the floodplain and floodway on the
stormwater management plan.
2.
The applicant shall include in the stormwater management plan
all other plans, plats, specifications, etc., required by Federal,
State, County and/or municipal laws or regulations detailing such
provisions or restrictions as are necessary to comply with the following:
O.
Channel Flow. The applicant shall not alter any channel in such a
way that would prohibit any section of the channel from conveying,
in its post-development state, the same amount of flow at the same
or lower maximum water elevation that is conveyed in its pre-development
state.
P.
Modifications Of Channel. The applicant shall furnish, for the Administrative
Officer's review and approval, the following information pertaining
to proposed channel modifications:
1.
Typical cross sections of the existing and proposed channel.
2.
Plan view of the channel showing the location of existing constrictions,
obstructions and other non-typical areas.
3.
Hydrographs and/or flood routing calculations and backwater
curve profiles of the proposed waterway corresponding to a storm recurrence
interval of one hundred (100) years.
4.
Engineering evaluation of all potential increases in flood hazards
to the adjacent upstream or downstream private or public lands and
facilities located thereon, showing provisions for eliminating any
and all adverse impacts on such land and facilities at no public cost.
5.
Minimum finished floor elevations which shall be set at or above
the maximum water surface elevation as determined by either or both
of the following:
6.
Designation on the final plan of all areas reserved for flood
routing, detention or storage, together with the required wording
pertaining to restrictions, dedications and maintenance responsibilities
of such areas.
Q.
Detention Storage. If detention storage is provided within a floodplain,
only the net increase in storage volume above that which naturally
existed on the floodplain shall be credited to the development. No
credit will be granted for volumes below the elevation of the regulatory
flood at that location unless compensatory storage is also provided.
R.
Verification Of Adequacy.
1.
Analysis of all elements of design is to be verified by the
engineer of record submitting the plan. The following outline is provided
to ascertain that certain critical elements are in workable compliance
with the aims of this Chapter. For projects less than fifty (50) acres
in area, there is no need for submittal of routing calculations or
tabulated proof of adequacy of tributary runoff for detention; however,
it is recommended that verification be made of:
a.
Volume of detention for the total project.
b.
Tributary (Q) peak runoff to basin.
c.
Balanced maximum outflow rate from the low-flow structure.
d.
Ratios of inflow to outflow rates.
e.
Sizing of the overflow facilities.
f.
Stability of detention dikes.
g.
Safety features.
h.
Maintenance features.
2.
For projects of fifty (50) acres or greater but less than two
hundred (200), routing calculations shall be submitted in legible
tabulated form. Proof of adequacy of volume of detention and sizing
computations for low-flow structure shall also be submitted. Features
of stability and safety may also need to be documented if the scope
of the project requires special attention in this area of design.
3.
Projects over two hundred (200) acres in area shall provide
documented verification of adequacy according to scope and complexity
of design.
|
Table 2
Average C.I. (P.I.) Factors in CFS Per Acre 20 Min. Inlet Time
| |||||
|---|---|---|---|---|---|
|
% Impervious Area
|
C or P (Factor)
|
15 Years
|
25 Years
|
50 Years
|
100 Years
|
|
5
|
0.37
|
1.7
|
2.00
|
2.18
|
2.37
|
|
10
|
0.39
|
1.79
|
2.11
|
2.30
|
2.50
|
|
15
|
0.41
|
1.89
|
2.21
|
2.42
|
2.62
|
|
20
|
0.435
|
2.0
|
2.35
|
2.57
|
2.78
|
|
25
|
0.455
|
2.09
|
2.46
|
2.68
|
2.91
|
|
30
|
0.475
|
2.10
|
2.57
|
2.80
|
3.04
|
|
35
|
0.495
|
2.28
|
2.68
|
2.92
|
3.17
|
|
40
|
0.52
|
2.39
|
2.81
|
3.07
|
3.33
|
|
45
|
0.54
|
2.48
|
2.92
|
3.19
|
3.46
|
|
50
|
0.56
|
2.58
|
3.02
|
3.30
|
3.58
|
|
55
|
0.58
|
2.68
|
3.13
|
3.42
|
3.71
|
|
60
|
0.60
|
2.76
|
3.24
|
3.54
|
3.84
|
|
65
|
0.625
|
2.88
|
3.38
|
3.69
|
4.00
|
|
70
|
0.645
|
2.97
|
3.48
|
3.81
|
4.13
|
|
75
|
0.665
|
3.06
|
3.59
|
3.92
|
4.26
|
|
80
|
0.685
|
3.15
|
3.70
|
4.04
|
4.38
|
|
85
|
0.705
|
3.24
|
3.81
|
4.16
|
4.51
|
|
90
|
0.73
|
3.36
|
3.94
|
4.31
|
4.67
|
|
95
|
0.75
|
3.45
|
4.05
|
4.43
|
4.80
|
|
100
|
0.77
|
3.54
|
4.16
|
4.54
|
4.93
|
|
Rainfall
|
4.60
|
5.40
|
5.90
|
6.40
| |
|
From U.S. Weather Bureau Technical Paper No. 40: "Rainfall Frequency
Atlas of the United States for durations from thirty (30) minutes
to twenty-four (24) hours and Return Periods from one (1) year to
one hundred (100) years."
|
S.
Installation Of Stormwater Runoff Control Measures. Positive stormwater
runoff control shall be provided for during development. Stormwater
management plans shall include a schedule for the installation, construction
or modification of all drainage facilities. Erosion control measures
and a schedule for their installation shall be shown on the stormwater
management plan. Installation of drainage facilities and erosion control
measures shall proceed as scheduled in the approved stormwater management
plan.
T.
Best Management Practices.
1.
Best management practices to prevent erosion, sedimentation
and other contamination of the municipal storm sewer system or the
waters of the State shall be incorporated into the Stormwater Pollution
Prevention Plan. Such measures shall be implemented from the time
the land is disturbed until final stabilization of the land is achieved.
Permitted best management practices may include, but are not limited
to, the following.
2.
The best management practices utilized shall be in accordance
with the publication "Protecting Water Quality" as published by the
Missouri Department of Natural Resources. Use of other State-approved
standard specifications or methods which offer a higher level of protection
may also be incorporated by the design professional.
[Ord. No. 257, 7-13-2010]
A.
All stormwater management facilities shall be constructed within
an easement of right-of-way dedicated for stormwater management use
and connected to a public road or other location from which operation
and maintenance is legally available. Minimum rights-of-way and maintenance
easements shall be provided by instrument or plat dedication for all
waterways used to convey or detain runoff. Where permanent maintenance
will be provided by the property owner, maintenance easements or rights-of-way
may not be required. The minimum widths of rights-of-way and easements
shall be as follows:
|
Facility
|
Maintenance Access Width
|
|---|---|
|
Open drainage channel or facility
|
30 feet, 15 feet each side
|
|
Greenways
|
Width of greenway
|
|
Pipes and culverts
|
15 feet, centered
|
|
Detention areas
|
15 feet continuous around total area
|
|
Connecting access
|
15 feet
|
B.
Easements must include the "top of the bank width" and the maintenance
access width.
C.
The maintenance access width begins at the point of the bank or slope
of the facility.
D.
Additional maintenance access width may be required by the Administrative
Officer in special circumstances where more width on one (1) or both
sides is necessary for maintenance purposes.
[Ord. No. 257, 7-13-2010]
A.
General. The Administrative Officer and other officials of the City
charged with the enforcement of this Chapter are hereby granted inspection
rights and right-of-entry privileges in order to ensure compliance
with the requirements of this Article.
B.
Inspections During Construction. The owner or authorized agent shall
employ a registered design professional to inspect all stormwater
improvements during construction. The Administrative Officer or other
officials may conduct inspections from time to time as necessary to
ensure compliance with the provisions of this Article.
C.
After Construction. The following procedures shall apply after construction
activity is completed.
1.
Upon completion of any stormwater improvements, the owner or
authorized agent shall also submit a certification letter signed by
a registered design professional to the Administrative Officer which
states that the improvements have been completed in accordance with
the project specifications and all ordinances and specifications of
the City of Leadington.
2.
The inspection and completion of construction of public stormwater
improvements shall comply with the City's subdivision ordinance(s).
3.
After final stabilization of the site is achieved, the owner
or authorized agent shall submit a written notice of termination for
the Administrative Officer to terminate the permit. The notice shall
contain the following information:
4.
The Administrative Officer shall terminate the permit after
determining that final stabilization has been achieved.
[Ord. No. 257, 7-13-2010]
A.
General. The owner or authorized agent shall utilize methods, approaches
and techniques in the design and construction stormwater management
improvements that will allow for the improvements to be properly maintained.
B.
Responsibility. The responsibility for maintenance of stormwater
management facilities shall be as follows.
1.
The owner or authorized agent shall be responsible for all stormwater
management improvements not officially accepted by the City.
2.
The owner or authorized agent shall be responsible for all stormwater
management improvements on any lot that is not a part of a common
promotional plan.
3.
The owner or authorized agent shall be responsible for the stormwater
management improvements on property that is part of a common promotional
plan until the improvements are either accepted by the City or the
improvements are accepted by a board, association or other permanent
maintenance organization.
C.
Maintenance Arrangements. Any maintenance arrangements shall conform
to the following.
1.
No detention basin shall be considered accepted by the City
unless specifically expressed, written approval and acceptance is
made by the Board of Alderman.
2.
The maintenance of stormwater management improvements by a board,
association or other permanent maintenance organization shall be arranged
through appropriate legal means such as agreements, indentures or
covenants. Any such documents shall be submitted to the Administrative
Officer for review and approval.
3.
The owner or authorized agent shall dedicate all necessary easements
to the City for all stormwater management improvements to be accepted
by the City in accordance with the requirements of this Article and
the City's subdivision ordinance(s).
D.
Minimum Standards. Stormwater management improvements shall be maintained
in a clean, safe, sanitary condition complying with all applicable
provisions of this Article and shall not cause a public nuisance as
defined by the Municipal ordinance(s) of the City.
E.
Periodic Inspections. The Administrative Officer may inspect existing
stormwater management improvements from time to time in order to ensure
compliance with the provisions of this Section.
[Ord. No. 257, 7-13-2010]
A.
Approved Projects. The Administrative Officer or his/her designated representative shall carry out periodic inspections of the project site to ensure the applicant's compliance with this Article. If it is determined that the project is not being carried out in accordance with the approved stormwater management plan, the Administrative Officer is authorized to take the following action(s), in addition to any other actions or remedies which are otherwise authorized under Article XIX, Violations and Penalties, of the this chapter of the Code of the City of Leadington.
1.
Written Notice. Issue written notice to the applicant or owner,
specifying the nature and location of the alleged non-compliance,
with a description of the remedial actions necessary to bring the
project into compliance within a reasonable specified time.
2.
Stop Work Order. Issue a stop work order directing the applicant
or owner to cease and desist all or any portion of the work which
violates the provisions of this Article, if the remedial work identified
in the "written notice" is not completed within the specified time.
3.
Revocation Of Approval. Should the applicant or owner fail to timely bring the project into compliance with the written notice and stop work order, he/she shall then be subject to immediate revocation of his/her stormwater management plan approval and to the penalties described in Article XIX, Violations and Penalties.
4.
Appeals. The Board of Adjustment shall serve as the means of
appeal or variance in accordance with the zoning regulation of the
City.
B.
Unapproved Project. With respect to any development activity determined
by the Administrative Officer or his/her designated representative
to be subject to this Chapter and being carried out without approval,
the Administrative Officer is authorized to:
1.
Written Notice. Issue written notice to the owner specifying
the nature and location of the alleged non-compliance, with a description
of the remedial actions necessary to bring the project into compliance
within a reasonable specified time.
2.
Stop-Work Order. Issue a stop-work order directing the owner
to cease and desist all or any portion of the work which violates
the provisions of this Chapter, if the remedial work identified in
the "written notice" is not completed within the specified time.
3.
Non-Compliance With Stop-Work Order. Should the owner not bring the project into compliance with the written notice and stop-work order, he/she shall then be subject to the penalties described in Article XIX, Violations and Penalties.
4.
Appeals. The Board of Adjustment shall serve as the means of
appeal or variance in accordance with the zoning regulation of the
City.
[Ord. No. 257, 7-13-2010]
This Article shall not in any way limit or modify the vested
rights of any person to complete any development or improvement to
lands based upon prior law where a previous permit or authorization
has been granted or applied for and where such previous permit or
authorization remains in effect. The City may acknowledge vested rights
in other circumstances where it is equitable and just.
[Ord. No. 257, 7-13-2010]
A.
Before starting any work regulated by this Article, an applicant
shall comply with the requirements set forth in all other applicable
ordinances with respect to the submission and approval of preliminary
and final subdivision plats, site plans for construction and rezoning
improvement plans and building, grading and zoning permits, along
with those set forth in this Chapter and as may be required by State
statutes and the regulations of any department of the State.
B.
A discharge permit from the State of Missouri shall be obtained individually
or under the applicable general permit for any activity regulated
under the Department of Natural Resources Clean Water Commission (10
CSR 20) Stormwater.
[Ord. No. 257, 7-13-2010]
In the interpretation and application of this Article, the provisions
expressed herein shall be held to be the minimum requirements and
shall be liberally construed in favor of the City and shall not be
deemed a limitation or repeal of any other powers granted by State
statutes.
[Ord. No. 257, 7-13-2010]
It is not intended by this Article to repeal, abrogate or impair
any existing casements, covenants or deed restrictions. However, where
this Article imposes greater restrictions, the provision of this Article
shall prevail.
[Ord. No. 257, 7-13-2010]
The performance standards and design criteria set forth herein
establish minimum requirements which must be implemented with good
engineering practice and workmanship. Use of the requirements contained
herein shall not constitute a representation, guarantee or warranty
of any kind by the municipality or its officers and employees of the
adequacy or safety of any drainage management structure or use of
land. Nor shall the approval of a stormwater management plan and the
issuance of a permit imply that land use permitted will be free from
damages caused by stormwater runoff. The degree of protection required
by these regulations is considered reasonable for regulatory purposes
and is based on historical records, engineering and scientific methods
of study. Larger storms may occur or stormwater runoff heights may
be increased by man-made or natural causes. Enforcement of these provisions,
therefore, shall not create liability on the part of the municipality
or any officer of the municipality with respect to any legislative
or administrative decision lawfully made hereunder, nor shall compliance
relieve an owner, developer and/or permittee from responsibility under
any circumstances where liability would otherwise exist.
[Ord. No. 257, 7-13-2010]
|
