[R.O. 1997 §405.070; Ord. No. 1088 §3, 12-9-1991]
A.
The area of the lots shall be determined by zoning district
regulations, subject to the availability of public sewer and a public
water supply. Prior to the submission of a preliminary plat, the subdivider
shall obtain a determination from the engineer having jurisdiction
as to whether adequate public sewer and water supply are available.
B.
If the proposed subdivision is serviced by a public water
supply and a public sewer system, the minimum lot area requirements
shall be subject to those set forth herein and in the Zoning Regulations.
C.
If the proposed subdivision is serviced with a public water
supply, but not with a public sewer system, or is serviced with a
public sewer system, but not a public water supply, the preliminary
plat shall be prepared on the basis of minimum three-acre lots; provided,
however, that additional lot area may be required if the area has
or is suspected of having a high water table or if soil conditions
prove to be unsuitable based on percolation tests.
D.
All proposed private water and sewer systems shall be reviewed
for approval by the Barry County Health Department.
[R.O. 1997 §405.080; Ord. No. 1088 §3, 12-9-1991]
A.
Length. Intersecting streets (which determine
block length) shall be provided at such intervals as to serve cross
traffic adequately and to meet existing streets in the neighborhood.
In residential districts where no existing plats are recorded, the
blocks shall not exceed one thousand two hundred (1,200) feet in length,
except that a greater length may be permitted where topography or
other conditions justify a departure from this maximum. In blocks
longer than eight hundred (800) feet, pedestrianways and/or easements
through the block may be required near the center of the block. Such
pedestrianways or easements shall have a minimum width of ten (10)
feet. Blocks for business use should normally not exceed six hundred
(600) feet in length.
B.
Width. In residential development, the
block width shall normally be sufficient to allow two (2) tiers of
lots of appropriate depth. Blocks intended for business or industrial
use shall be of such width and depth as may be considered most suitable
for the prospective use.
[R.O. 1997 §405.090; Ord. No. 1088 §3, 12-9-1991; Ord. No. 2001-1352 §1, 12-3-2001]
A.
Relations To Adjoining Street System. The
arrangement of streets in new subdivisions shall make provisions for
the continuation of the principal existing streets in adjoining additions
(or their proper projection where adjoining property is not subdivided),
insofar as they may be necessary for public requirements. The width
of such streets in new subdivisions shall not be less than the minimum
street widths established herein. Alleys, when required, and street
arrangement must also be such as to cause no hardship to owners of
adjoining property when they plat their land and seek to provide for
convenient access to it. Whenever there exists a dedicated or platted
half street or alley adjacent to the tract to be subdivided, the other
half of the street or alley shall be platted and dedicated as a public
way.
B.
Street Names. Streets that are obviously
in alignment with others already existing and named shall bear the
same alphanumeric designation adopted by the Board of Aldermen.
C.
Arterial And Collector Streets. Major
streets through subdivisions shall conform to the Major Street Plan
as adopted by the Planning and Zoning Commission and the Board of
Aldermen.
D.
Local Streets. Minor streets shall be
so designed to discourage through or non-local traffic.
E.
Culs-De-Sac. An adequate turnaround of
not less than a fifty-foot-radius right-of-way shall be provided at
the closed end of a dead-end street longer than one (1) lot in length.
Such local street segment shall not exceed five hundred (500) feet
in length from the centerline of an intersection of a cross street
to the center of the cul-de-sac; except for suburban, large-lot development,
which shall not exceed one thousand two hundred (1,200) feet.
F.
Right-Angle Intersections. Under normal
conditions, streets shall be laid out to intersect, as nearly as possible,
at right angles. Where topography or other conditions justify a variation
from the right-angle intersection, the minimum angle shall be sixty
degrees (60°).
G.
Streets Adjacent To A Limited Access Freeway Or
Principal Highway. Where lots front or side, but do not back,
on limited-access freeways, or principal highways, a marginal access
street or frontage road may be required parallel and adjacent to the
boundary of such rights-of-way. The distance from said rights-of-way
shall be determined, with due consideration, to minimum distance required
for approach connections to future grade separation.
H.
Half Streets. Dedication of half streets
will not be approved, except where it is essential to the reasonable
development of the subdivision and in conformity with the Major Street
Plan and other requirements of this Chapter.
I.
Alleys. Alleys may be required in commercial
and industrial districts. Dead-end alleys shall be avoided wherever
possible. Alleys may be required in certain residential areas.
J.
Minimum Requirements. The right-of-way
grades, horizontal curves, and vertical curves for streets and alleys
dedicated and accepted shall not be less than the minimum for each
classification, as follows:
K.
Additional Requirements. When existing
or anticipated traffic on arterial and collector streets warrants
greater widths of rights-of-way, the additional width shall be dedicated.
L.
Street Alignment. On streets with reverse
curves, an appropriate tangent shall be provided between curves to
permit a smooth flow of traffic.
M.
Intersections. Local nonaligned intersections
shall be spaced at a minimum of one hundred fifty (150) feet (centerline
to centerline). Collector intersections shall be spaced at a minimum
of five hundred (500) feet (centerline to centerline).
N.
Drainage Easements. Drainage easements
may be required, in addition to street rights-of-way, where the street
or streets adjoin or are parallel with streams or drainage areas or
where lots back on where said drainage exist. The width of such drainage
easement shall be determined by the engineer having jurisdiction who
shall notify the Planning and Zoning Commission of his/her recommendation
in writing.
O.
Sight Triangle. A sight triangle is a
triangular area at the intersection of two (2) streets in which nothing
shall be erected, placed, planted or allowed to grow high enough above
the elevation of the adjacent roadway to constitute a sight obstruction.
The area included in a sight triangle shall be bounded on two (2)
sides by the center lines of each street, and on the third side by
a line connecting the two (2) lines. The unobstructed sight distance
must be sufficient to allow the operators of vehicles approaching
the intersection simultaneously to see each other in time to prevent
collisions. The sight distance must be related to vehicle speeds and
to the resultant distances traversed during perception, reaction time
and braking. (See the Transportation and Traffic Engineering Handbook,
Second Edition, Institute of Transportation Engineers, 1986, or most
recent edition.)
[R.O. 1997 §405.100; Ord. No. 1088 §3, 12-9-1991]
A.
Minimum lot width shall be as specified in the district
regulations of the City of Cassville Zoning Code; however, corner
lots shall be twenty (20) feet wider than that required in those regulations.
Lot width shall be measured at the building setback line.
B.
Minimum depth shall be one hundred (100) feet. Lot depth
shall be measured through the center of the lot and shall be perpendicular
to the property line or radial to the property line on curved streets.
C.
Minimum lot area shall be subject to the Zoning Regulations
of the district in which the subdivision is located.
D.
In subdivisions where septic tanks or other individual sewage disposal devices are to be installed, the size of all lots included in the subdivision shall be subject to regulations as set out in Section 405.070, Water and Sewer.
E.
In subdivisions where private water supply is by well or other means, the size of all lots included in the subdivision shall be subject to regulations as set out in Section 405.070, Water and Sewer.
F.
All side lot lines shall bear sixty degrees (60°) to
ninety degrees (90°) from the street right-of-way line on a straight
street or from the tangent of a curved street.
G.
Corner lots, in residential subdivisions, shall observe
the same setback on both streets.
H.
Double-frontage lots shall be avoided unless, in the opinion
of the Planning and Zoning Commission, a variation to this rule will
give better street alignment and lot arrangement.
I.
Every lot shall abut on a street other than an alley.
J.
Building or setback lines shall be shown on the final plat
for all lots in the subdivision and shall not be less than the setback
required by the Zoning Regulations.
K.
The subdivision or re-subdivision of a tract or lot shall
not be permitted where said subdivision or re-subdivision places an
existing permanent structure in violation of the requirements of the
Zoning Regulations.
L.
The depth of the lot shall not exceed three (3) times its
width.
[R.O. 1997 §405.110; Ord. No. 1088 §3, 12-9-1991]
A.
Where alleys are not provided, permanent, continuous easements
of not less than seven and one-half (7 1/2) feet in width shall
be provided on each side of all rear lot lines, and on side lot lines,
where necessary, for utility poles, wires, conduits, storm and sanitary
sewers, gas, water, and heat mains, and other public utilities.
B.
An additional twelve-foot temporary construction easement
[six (6) feet on each side of the lot line] shall be provided for
initial construction of water, sewer, and other utility lines.
[R.O. 1997 §405.120; Ord. No. 1088 §3, 12-9-1991]
In subdividing land or re-subdividing an existing plat, due
consideration should be given by the subdivider to the dedication
or reservation of suitable sites for schools, parks, playgrounds,
or other public recreational areas or open spaces. Any areas so dedicated
or reserved shall conform as nearly as possible to the Comprehensive
Plan. All areas to be reserved for, or dedicated to, public use shall
be indicated on the preliminary plat in order that it may be determined
when and in what manner such areas will be dedicated to or acquired
by the appropriate agency. A written statement from the Board of Education
may be required to be submitted by the subdivider indicating whether
or not a school site in the proposed subdivision is desired.
[R.O. 1997 §405.130; Ord. No. 1088 §3, 12-9-1991]
In the interest of public safety and for the preservation of
the traffic-carrying capacity of the street system, the Planning and
Zoning Commission shall have the right to restrict and regulate points
of access to all property from the public street system. Such restrictions
shall be indicated on the final plat.
[R.O. 1997 §405.140; Ord. No. 1088 §3, 12-9-1991]
The design of the subdivision shall provide for efficient traffic
flow, proper mixing of land uses, and a logical link between surrounding
existing development and the proposed layout. The Comprehensive Plan
should be used as a guide in determining if the design of the proposed
subdivision is proper. The Planning and Zoning Commission shall have
the authority to deny a plat or request redesign if, in its opinion,
the layout is not suitable for the site.
[R.O. 1997 §405.143; Ord. No. 2001-1328 §1, 4-2-2001]
A.
Current And Enforceable Municipal Ordinances, Regulations
And Statutory Requirements Notwithstanding.
1.
The applicant for a building permit shall submit with the application, plan, drawings and any other such information required by Sections 405.140 to 405.160 of this Article for the management and control of surface water runoff from the tract or tracts for which the permit is requested and to provide that temporary flooding does not occur to other properties during the construction.
2.
Any person or party submitting a final subdivision plat for consideration and approval under the subdivision and zoning ordinance in effect at the time of submittal shall submit plans, drawings, and any other such information required by Sections 405.140 to 405.160 of this Article for the management and control of surface water runoff from the tract or tracts to be subdivided and to provide that temporary flooding does not occur to other properties during construction.
3.
Any person or parties prior to grading, excavating, ditching or otherwise implementing activities that would alter the topography of an area or contiguous areas greater than ten thousand (10,000) square feet or alter, channelize, rechannel or modify a natural or man-made watercourse shall first submit to the City plans, drawings, calculations and other information required by Sections 405.140 to 405.160 of this Article for the management and control of surface water runoff from the area to be altered, or surface water conveyed by any natural or man-made watercourse and to provide that temporary flooding does not occur to other properties during construction.
B.
Surface Water Runoff Management And Control.
1.
The applicant or the person or party submitting
a final subdivision plat shall retain the services of a professional
engineer, registered in the State of Missouri, to provide under his/her
professional seal and signature the surface water runoff management
and control plans, drawings, calculations and information required
under Appendix A to these stormwater provisions, which is on file
in the City offices.
2.
All facilities constructed or required to be constructed
for approval of a final subdivision plat for the management and control
of surface water runoff shall, during and upon completion of construction,
be inspected by a professional engineer licensed in the State of Missouri.
Upon completion of construction of the surface water runoff management
and control facilities, the City shall receive from the professional
engineer certification that said facilities have been completed and
constructed in accordance with the intent of the plans, drawings and
calculations upon which permits or approval were issued.
3.
Upon written request by the building permittee or person or parties submitting a subdivision plat, the City shall retain the services of a professional engineer licensed in the State of Missouri to perform the inspection and provide certification requirements of Subsection (B)(2).
4.
In the event certification of completion and compliance
with plans, drawings and calculations are not received by the City,
or should the City determine the improvements facilities as described
in the approved plans are not being constructed to meet minimum standards
set forth in Appendix A of these stormwater provisions, which is on
file in the City offices, the City shall so notify the permittee and
may issue an order revoking the building permit or recommend to the
Governing Body to discontinue provision of municipal utilities until
the deficiencies are corrected.
C.
Obstruction Of Watercourses Prohibited.
1.
It shall be unlawful for any person to block,
obstruct, destroy, cover, fill or alter in any way a watercourse or
any part thereof so as to cause damage to the property of the other
persons from surface water.
2.
A watercourse is land which has a conformation
so as to give to surface water flowing from one tract of land to another
tract of land, a fixed and determinate course so as to uniformly discharge
it upon the servient tract at a fixed and definite point. It shall
include, but not be limited to, ravines, swales, sinkholes or depressions
of greater or less depth extending from one tract and so situated
as to gather up the surface water flowing upon the dominant tract
and to conduct along a definite course to a definite point of discharge
upon the servient tract. It shall not be deemed to be important that
the force of water flowing from one tract of land to another has not
been sufficient to wear out a channel or canal having definite or
well marked sides or banks. If the surface water, in fact, uniformly
or habitually flows over a given course having reasonable limits as
to the width of the line of its flow, it shall be considered to have
a definite course.
3.
A violation of Subsection (C)(1) shall be deemed to be a public nuisance. Whenever the City has determined that a person has blocked, obstructed, destroyed, covered, filled or altered in any way a watercourse so as to cause surface water damage to the property of others, the City Administrator is authorized to proceed in accordance with the Municipal Code of the City of Cassville so as to abate the public nuisance.
4.
In reviewing applications for building permits, the City shall further determine if the work interferes with the use and operation of existing watercourses. If the City has reason to believe that the work may interfere with the use and operation of existing watercourses, then the City shall notify the applicant and request information or revisions to the plans and drawings stipulated in Subsection (A). When determined by the City to be necessary, the applicant shall comply with the provision set forth in Subsection (B) of this Section.
D.
Wastewater Discharge.
1.
Stormwater and all other unpolluted waters shall
be discharged to storm sewers or waters of the State.
2.
It shall be unlawful to discharge into any storm
sewers and/or waters of the State within the City or in any area where
there is an availability of sanitary sewers any waste water or pollutant,
except where suitable treatment has been provided and approved by
the City and the State of Missouri under the National Pollution Discharge
Elimination Systems (NPDES).
3.
Violations of this Section shall be subject to
the enforcement procedures contained in the Municipal Code of the
City of Cassville.
E.
Maintenance Of Surface Water Runoff Control Facilities.
1.
When any surface water runoff control facility
(hereafter called "facility") is located on the same lot or tract
it is intended to serve, the facilities shall be maintained at all
times by the owner of the lot or tract. Unless otherwise approved
by the City, such facility shall not be constructed on separate lots
and no building permit shall be issued for any such facility if it
is located on a lot or tract of land other than the lot or tract of
land it is intended to serve.
2.
When the facility is designed to serve more than
one (1) lot or tract, the City may permit the construction of such
facilities on a lot other than the lot or tract the facility is intended
to serve, if it is determined that there are sufficient easements
and covenants filed on record with the County Recorder of Deeds imposing
the duty and responsibility to maintain the facilities, together with
the liability for the costs of such maintenance upon the owners of
each of the lots served by the facility, and further covenanting the
assessed costs of any repairs and maintenance work done by the City
shall be in lien enforceable against each of the lots so served. The
City shall require as a precondition to the issuance of a building
permit that the owner of the property file such covenants and easements
with the County Recorder of Deeds allocating such obligations and
liabilities for the cost of the maintenance of the facility, which
covenants and easements shall secure the right of the City to execute
remedies and the power to assess the costs thereof against each lot
served by the facility.
3.
In the event the owners of the lots or tracts
served by the facility fail to maintain the facility, then the City,
upon ten (10) days' written notice, may revoke the occupancy permit
issued for such premises, and in addition thereto, or in the alternative,
may order utilities disconnected. Any aggrieved owner shall have the
right to an administrative hearing prior to revocation of the occupancy
permit or disconnect of utilities to determine whether the stormwater
detention facility has been maintained so as to meet the standards
set forth, provided the owner has filed a written demand for hearing
with the City within ten (10) days after notice was given. The hearing
shall be conducted before the City Board of Adjustment within twenty
(20) days of receipt of the owner's demand for hearing. The hearing
officer shall prepare a written decision setting forth his/her findings
of fact and conclusions.
4.
Failure To Maintain Declared A Nuisance
— Assessment Of Costs As A Lien. If the owners of the
lots or tracts served by the facility fail to adequately maintain
the facility, the same is hereby declared to be a nuisance, and the
City may require abatement of the nuisance under the procedures set
forth in the City of Cassville Code. In addition to the procedures
set forth above, or in the alternative, upon determining that a nuisance
exists, the City may refuse to issue or renew licenses for any business
on any lot or tract served by the facility.
F.
Development In Areas Of Karst Geological Characteristics
And Sinkholes.
1.
No person shall engage in the altering of topography, grading, excavating or the development of land in a sinkhole area without first securing a permit from the City. To obtain a permit, the owner of the property or person having an interest therein shall submit an application for a permit to the City with a plan set out in Subsection (C), which shall contain the following additional information:
a.
The plan shall show the location of the sinkhole,
the immediate sinkhole drainage area, a sinkhole cluster area or portions
of such items, along with ground contours, a stormwater analysis of
the sinkhole and significant physical features on the property.
b.
Upon review of the information presented by the
applicant, the site, and such other information as may be available,
the City may issue a permit for work to be performed in the sinkhole
area. All work shall be performed in accordance with the permit. The
City may designate certain areas where grading or construction equipment
is not permitted or is otherwise limited.
2.
In addition to establishing a plan for grading
and use of construction equipment, the City may, based upon the topography,
geology, soils and history of the sinkhole (such as past filling)
and the stormwater analysis and plan of the developer's engineer,
establish sinkhole-related non-buildable areas. No building, parking
areas, grading or other structures shall be permitted within the sinkhole-related
non-buildable area unless otherwise authorized by the City. This non-buildable
area shall follow the limits of the sinkhole in most cases. However,
the non-buildable area may be expanded or contracted by action of
the City where warranted, due to the nature of the specific sinkhole,
the underlying geology, soils, drainage and any related information,
such as depth to bedrock. In sinkhole cluster areas, the City may
require the owner or developer to provide recommendations from a consulting
engineer and a consulting hydrogeologist, based upon substantial and
state-of-the-art field studies and evaluation of the specific sinkhole
system. Such studies shall be submitted to the City's authorized representative
for review.
3.
Development may occur in the immediate sinkhole
drainage area if the developer provides alternative surface drainage
away from the sinkhole, while keeping the water in the same surface
drainage basin; and provided further, that the water shall not go
into another stream of known flooding problems. The immediate sinkhole
drainage area (or portion thereof) which cannot be provided with an
alternative drainage system can be deleted from the development area
and can be used to meet open space requirements. The developer may
request the Planning and Zoning Commission and the City that the density
on the remainder of the developable area be increased, with the total
resulting density no greater than if the entire area were developed
to the permitted density under the Zoning Ordinance.
G.
Enforcement And Liability.
1.
In enforcing the provisions of the aforesaid Sections,
in addition to the various remedies provided therein, the City shall
have all other rights, powers and authority granted to it by Missouri
law, including, without limitation, the right to file civil suit against
any person who violates or fails to comply with the aforesaid Sections.
In the event of civil suit, the City any recover reasonable attorney's
fees, court cost and other expenses of litigation.
2.
No person issued a permit under the terms of the
aforesaid Section shall have any recourse whatsoever against the City
for any loss, cost or expense or damage arising out of any of the
provisions or requirements of these Sections, or because of the provisions
or requirements of these Sections, or because of the enforcement thereof
by the City. These Sections shall not cease liability on the part
of the City, its officers, agents or employees as the result of reliance
on any permits issued hereunder or as the result of any administrative
decision lawfully made hereunder.
[R.O. 1997 §405.145; Ord. No. 2001-1328 §1, 4-2-2001]
A.
Minimum Requirements For Storm Sewer And Drainage
Design.
1.
Drainage Area Plan: a plan of the drainage area
at a scale of one (1) inch equals one hundred (100) feet with two-foot
contour internals using USGS datum for areas less than one hundred
(100) acres or a plan of the drainage area at a scale of one (1) inch
equals three hundred (300) feet with five-foot contour intervals for
larger areas. This plan shall include all proposed streets, drainage
and grading improvements with flow quantities and direction of flow
at all critical points. All areas and sub-areas for drainage calculations
shall be clearly distinguished.
2.
Hydraulic data: Complete hydraulic data showing
all calculations shall be submitted.
3.
Plan and profile: A plan and profile of all proposed
improvements at a scale of one (1) inch equals forty (40) feet horizontal
and one (1) inch equals four (4) feet vertical shall be submitted.
This plan shall include the following:
a.
Locations, size, flow line elevations and grades,
type of pipe, channels, boxes, manholes, and other structures drawn
on standard plan-profile sheets;
b.
Existing and proposed ground line profiles along
centerline of the drainage improvement;
c.
A list of the kind and quantity of material;
d.
Typical sections and reinforcement of all boxes
and channels;
e.
Location of property lines, street paving, sanitary
sewers and other utilities, both public and private.
4.
Field study: A field study of the downstream capacity
of all drainage facilities and the effect of additional flow from
the area to be improved shall be submitted. If the effect is to endanger
property or life, the problems must be solved before the plan will
be given approval.
5.
Stormwater flow quantities: Stormwater flow quantities
in the street shall be shown at all street intersections, all inlet
openings and at locations where flow is removed from the streets.
This shall include the hydraulic calculations for all inlet openings
and street capacities. Street flow shall be limited according to Table
1 at the end of this Section.
6.
Sinkholes or karst areas: Sinkhole or karst areas
shall be clearly defined. If any portion of the stormwater from an
area is to be drained into a sinkhole, all information available shall
be obtained and the capacity of the sinkhole shall be studied, and
this study shall be submitted to determine the effect of the drainage
and pollution on groundwater and streams.
7.
Additional information: Any additional information
deemed necessary by the City for an adequate consideration of the
storm drainage effect on the City of Cassville and surrounding areas
must be submitted.
B.
Requirements Relating To Improvements.
1.
General Design Requirements.
a.
All bridges shall be designed to accommodate a
one-hundred-year frequency rain. Box culverts, pipe culverts, channels
and ditches shall be designed to accommodate a one-hundred-year frequency
rain at all locations having a drainage area in excess of one (1)
square mile. Locations having
a drainage area of less than or equal to one (1) square mile shall
be designed to accommodate a twenty-five-year frequency rain.
2.
Specific Requirements For Various Improvements.
a.
Bridges and culverts: Bridges, box culverts or
concrete pipe culverts shall be provided where continuous streets
or alleys cross watercourses. The structure shall be designed in accordance
with City specifications for material and to carry HS-20 loadings
in all cases.
b.
Closed storm sewers: Closed storm sewers shall
either be reinforced concrete box or pipe of approved type designed
for HS-20 loadings. Reinforced concrete pipe or reinforced concrete
boxes must be used within two (2) feet of the back of the street curb
and under paved areas. All storm sewers having trench walls within
two (2) feet of the back of the street curb shall be backfilled with
granular material. The use of corrugated steel, zinc-coated pipe and
extra-strength clay pipe will not be permitted within two (2) feet
of the curb or under pavement areas. All pipe material shall meet
the requirements of the latest revision of the City of Cassville standard
general conditions and technical specifications for public works construction.
Grades for closed storm sewers shall be designed so that the velocity
shall not be less than three (3) feet per second nor exceed twelve
(12) feet per second. All other structures such as junction boxes
or inlets shall be in accordance with the standard drawings adopted
by the City of Cassville. Closed storm sewers shall extend to the
furthest downstream point of the development with consideration given
to velocities and to providing discharge energy dissipaters to prevent
erosion and scouring along down- stream properties.
c.
Open paved concrete channels: Grades for open
paved channels shall be designed so that the velocity shall not be
less than three (3) feet per second nor exceed twelve (12) feet per
second. Such concrete channels may be of different shapes according
to existing conditions; however, a channel with a flat bottom and
4:1 to 5:1 side slopes is the most desirable type and shall be used
whenever possible. The thickness of channel paving shall depend on
conditions at site and size of channel; however, a minimum thickness
of six (6) inches is required. A six-inch freeboard must be provided.
An eighteen-inch toe wall is required at both the outlet and inlet
ends of the channel.
d.
Open ditches (earth channels): Ditches shall have
a gradient that limits the velocity within one and one-half (1 1/2)
to five (5) feet per second, depending on existing soil conditions.
Such ditches shall have a minimum side slope ratio of 3:1.
C.
Runoff Calculations.
1.
The rate of runoff concentrated at any point shall
be determined by the Rational Formula:
|
Q
|
=
|
CIA, in which:
| |
|
Q
|
=
|
Runoff in cubic feet per second
| |
|
C
|
=
|
The runoff coefficient for the area
| |
|
I
|
=
|
Design rainfall intensity in inches per hour over the area based
on the time of concentration and rainfall
|
|
Intensity curves included as a part of this Section.
| |
|
A five-minute time of concentration is the minimum permitted.
| |
|
A = Drainage area in acres.
|
2.
Runoff Coefficient. The runoff
coefficient "C" is the variable in the rational formula least susceptible
to precise determination and the one that requires the greatest exercise
of engineering judgment because of the many area characteristics which
affect the coefficient. Among the factors to be considered in influencing
the runoff coefficients are the following: present and future zoning,
terrain, local ponding or depressions, the amount of pavement, roofs,
turf and other areas having different degrees of imperviousness. The
selection of a coefficient should take into consideration the probable
ultimate development of presently undeveloped areas. Suggested values
of runoff coefficients are included in the following table:
|
Suggested Runoff Coefficients "C"
| ||
|---|---|---|
|
"C" Value
|
Surface Conditions
| |
|
0.10 to 0.15
|
Tall grass, brush
| |
|
0.15 to 0.20
|
Parks, golf courses, farms and one-acre single-family residences
| |
|
0.35
|
Single-family residences on lots of not less than 15,000 square
feet
| |
|
0.45
|
Single-family residences on lots of not less than 10,000 square
feet
| |
|
0.47
|
Single-family residences on lots of not less than 7,500 square
feet
| |
|
0.51
|
Single-family residences on lots of not less than 6,000 square
feet
| |
|
0.90
|
Gravel surfaces
| |
|
0.95
|
Asphalt and concrete surfaces
| |
|
1.00
|
Buildings and other structures
| |
3.
Rainfall Intensity. The average
frequency of rainfall occurrence used for design determines the degree
of protection afforded by a drainage system. Maximum intensity of
rainfall of a given expectancy is greater for a short period of the
time than for longer periods. Therefore, it is assumed that the maximum
runoff will occur as soon as all parts of the drainage area under
consideration are contributing. The length of time from the beginning
of rainfall until runoff from the most remote point in the drainage
area reaches the point under consideration is a channel or gutter
flow time. Nomographs which may be used for determining time of concentration
are reproduced and on file in the City offices. Once the time of concentration
is known, the design intensity rainfall may be determined from the
rainfall intensity curves developed from United States Weather Bureau
data.
D.
Sizing Of Storm Sewers And Drainage Structures.
1.
The size of closed storm sewers, open channels,
culverts and bridges shall be designed so that their capacity will
not be less than the runoff computed by using the Manning Formula:
|
Q
|
=
|
1.486 (a)(r)2/3(s)(1/2)
| |
|
N
| |||
|
Q
|
=
|
Capacity = Discharge in cubic feet per second
| |
|
a
|
=
|
Cross-sectional area of water in conduit or channel in square
feet
| |
|
r
|
=
|
Hydraulic radius of water in conduit or channel equals area/wetted
perimeter
| |
|
s
|
=
|
Mean slope of hydraulic gradient in feet per foot
| |
|
n
|
=
|
Roughness coefficient based on condition and type of material
of conduit or channel lining
|
|
Values of "n" for various kinds of pipe for use in Manning Formula:
| |||
|---|---|---|---|
|
Concrete pipe
|
0.013
| ||
|
Corrugated metal pipe
|
0.024
| ||
|
Concrete lined channel
|
0.015
| ||
|
Earth channels
|
0.030 to 0.050
| ||
2.
Design Tabulations. For systems
of storm sewers with inlets in various locations, the time of concentration
at any point will be time of concentration at the most remote inlet
upstream, plus the flow time in the storm sewer to the point under
consideration. Computations for systems lend themselves readily to
tabulation showing the drainage area, time of concentration runoff
and capacity of each inlet and section of sewer under consideration.
This data is to accompany the improvement plans.
|
Table 1 — Street Flow
| ||
|---|---|---|
|
Street flow shall be limited by pavement encroachment and depth
of flow as follows:
| ||
|
Street classification (minor)
|
Maximum encroachment of a two-year storm, no curb overtopping.
Flow may spread to crown of street.
| |
|
Collector
|
No curb overtopping. Flow spread must leave the equivalency
of one (1) ten-foot driving lane clear of water.
| |
|
Arterials (thoroughfares)
|
No curb overtopping. Flow spread must have the equivalent of
two (2) ten-foot driving lanes clear of water. One lane in each direction.
Where no curbing exists, encroachment shall not extend past property
lines.
| |
3.
The storm sewer system shall commence at the
point where the volume of flow equals five (5) cfs.
[R.O. 1997 §405.147; Ord. No. 2001-1328 §1, 4-2-2001]
A.
General.
1.
Stormwater runoff and the velocity of discharge
are considerably increased through development and growth of the City.
2.
Prior to the development of the land, surface
conditions provide a higher percentage of permeability and longer
time of concentration. With the construction of buildings, parking
lots, etc., permeability and the time of concentrations are significantly
decreased, resulting in an increase in both the rate and volume of
runoff.
3.
These modifications may create harmful effects
on properties downstream. Therefore, to minimize these effects, the
following minimum stormwater detention requirements have been established.
B.
Stormwater Detention Plans.
1.
A complete set of stormwater detention plans and
calculations shall be provided for all construction projects that
increase stormwater runoff.
2.
Plans for the construction of public improvements
shall be submitted to and approved by the City.
3.
The required stormwater detention plans for private
improvements shall be submitted, along with the building plans, to
the City for review and approval. An escrow for stormwater detention
will not be accepted.
C.
Method Of Evaluation.
1.
Differential runoff evaluation consists of the
determination of the rates of runoff, before and after development,
determination of required volume of detention and verification of
adequacy of discharge and control structures. The one-hundred-year
(frequency) runoff coefficients shall be used. Differential runoff
rates shall be evaluated by equation:
|
R = (Cd x I-100) - (Cu x I-100)
|
|
Where:
| ||||
|
R
|
=
|
Differential runoff rate
| ||
|
Cd
|
=
|
Runoff coefficient for development conditions
| ||
|
Cu
|
=
|
Runoff coefficient for underdeveloped conditions
| ||
|
I-100
|
=
|
Intensity for one-hundred-year storm
| ||
2.
"C" values shall be determined from the following
table:
|
Suggested Runoff Coefficients
| ||
|---|---|---|
|
"C" Value
|
Surface Conditions
| |
|
0.10 to 0.15
|
Tall grass, brush
| |
|
0.15 to 0.20
|
Parks, golf courses, farms and one-acre single-family residences
| |
|
0.35
|
Single-family residences on lots of not less than fifteen thousand
(15,000) square feet
| |
|
0.45
|
Single-family residences on lots of not less than ten thousand
(10,000) square feet
| |
|
0.47
|
Single-family residences on lots of not less than seven thousand
five hundred (7,500) square feet
| |
|
0.51
|
Single-family residences on lots of not less than six thousand
(6,000) square feet
| |
|
0.90
|
Gravel surfaces
| |
|
0.95
|
Asphalt and concrete surfaces
| |
|
1.00
|
Buildings and other structures
| |
3.
Use the Chart A (on file in the City offices)
to find time of concentration (tc), then use Chart B (on file in the
City offices) to determine intensity (I). A five-minute time of concentration
is the minimum permitted.
D.
Volume Of Detention.
1.
Volume of detention for areas less than twenty
(20) acres shall be evaluated according to the "Simplified Volume
Formula." For areas larger than twenty (20) acres, other methods may
be used upon the approval of the City of Cassville. The Rational Formula
method will generally be accepted for areas greater than twenty (20)
acres.
a.
Total volume of detention shall be computed by
the equation:
|
V
|
=
|
R x A x tc (min) x 60 (seconds/minute)
| |
|
V
|
=
|
Total volume of detention (cubic feet)
| |
|
R
|
=
|
Differential runoff rate
| |
|
A
|
=
|
Area of project in acres
| |
|
tc
|
=
|
Time of concentration as determined for use with differential
runoff rates
|
b.
The design volume of detention shall be determined
from the following table:
|
Calculated Volume
(cubic feet)
|
Design Volume
(cubic feet)
| |
|---|---|---|
|
1 through 500
|
500
| |
|
501 through 4,999
|
Round up to nearest 500
| |
|
5,000 through 9,999
|
Round up to nearest 1,000
| |
|
10,000 through 49,999
|
Round up to nearest 5,000
| |
|
50,000 through 99,999
|
Round up to nearest 10,000
| |
|
100,000 and above
|
Round up to nearest 25,000
|
2.
Clearing Of Vegetation. Silt
and debris connected with early construction shall be removed periodically
from the detention area and control structure in order to maintain
full storage capacity.
E.
Temporary Detention. It may be advantageous
in some situations to delay the building of the permanent detention
facilities until after the completion of the other improvements. In
these situations, temporary detention facilities must be provided.
The permanent or temporary detention facilities must be constructed
and be functional before proceeding with any other construction.
F.
Off-Site And Regional Detention Concepts.
1.
Off-Site Detention. Stormwater
detention facilities designed and constructed off site or outside
the limits of the proposed development will be considered for approval.
This approval is contingent upon documentation being furnished to
verify that drainage easements have been obtained for the channel
area from the proposed development to the detention facility and including
the detention area. The drainage easements must clearly set out provisions
for maintenance.
2.
Regional Detention. Detention
facilities designed and located to provide detention on major drainage
channels will be considered as a regional detention facility and must
be one hundred sixty (160) acres or greater. The facility must provide
a detention volume for a one-hundred-year storm for the entire drainage
area and must be designed with a variable control outlet structure
that has one-year maximum outlet opening. The regional detention facility
must be designed with a low-flow concrete channel through the limits
of the basin. Upon conceptual approval of the location and final approval
of the design and construction, the City of Cassville may accept the
responsibility for the maintenance of the regional facility. Drainage
and access easements will be required giving the City of Cassville
the authority to gain vehicular access to the facility from the public
street.
3.
As additional development occurs upstream of the
regional facility, on-site detention requirements may be waived, provided
the regional detention basin has been designed for full development
of the basin, or if modifications are made to the regional facility
by the developer to provide for the additional volume of detention
required for the new development. Easements must be provided along
the drainage channel from the new development to the regional facility,
and the channel must be constructed to carry the peak rate of runoff
from the one-hundred-year storm for the entire basin upstream from
the regional facility.
