HomeMy WebLinkAboutOrd.675.03-06-1989BILL NO. 89-3
ORDINANCE NO.
AN ORDINANCE ENACTING STORMWATER
MANAGEMENT REGULATIONS
BE IT ORDAINED BY THE COUNCIL OF THE CITY OF CAPE GIRARDEAU, MISSOURI, AS
FOLLOWS:
SECTION 1.
An ordinance enacting a new chapter to be known as Chapter 25A, entitled Stormwater
Management Regulations, to read as follows:
SECTION 2.
PURPOSE: The purpose of this ordinance 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.
SECTION 3.
DEFINITIONS: Unless specifically defined, words or phrases shall be interpreted so as to give
them the meaning they have in common usage and to give this ordinance its most reasonable
application. The term "shall" is always mandatory and not discretionary; the word "may" is
permissive.
Administrative Officer: The duly appointed City Manager of the City of Cape Girardeau, or
his designated representative.
Adverse Impact: Any modifications, alterations, or effects on a feature or characteristic of
surface waters including their quality, quantity, hydrodynamics, surface area, species
composition, living resources, aesthetics or usefulness for human or natural uses which are or
may potentially be harmful or injurious to human health, welfare, safety or property, to
biological productivity, diversity, or stability, or which unreasonably interfere with the
enjoyment of life or property, including outdoor recreation. The term includes secondary and
cumulative, as well as direct impacts.
Applicant: The record owner, or his authorized representative, of a tract of land that is the
site of development, or development activity within the scope of this ordinance.
Base Flood Elevation: The elevation at any location delineating high waters having a
one -percent probability of being equaled or exceeded in any given year (also known as the
100 -year flood).
Buildin Any structure built for the support, shelter or enclosure of persons, animals,
chattels, or movable property of any kind.
Capacity of a. Storm Drainage Facility: The maximum ability of a storm drainage facility to
convey, detain or retain stormwater flows without causing substantial damage to public or
private property, and in the case of a pipe, without surcharging.
Channel: A natural or artificial open watercourse with definite bed and banks which
periodically or continuously contains moving water or which forms a connecting link between
two bodies of water.
Com: The City of Cape Girardeau, Missouri.
Conduit: Any channel, pipe, sewer or culvert used for the conveyance or movement of water,
whether open or closed.
Control Device: An element of a discharge structure which allows the gradual release of
water under controlled conditions.
Control Elevation: Design elevation of a discharge structure at which, or below which, water
is contained behind the structure.
Council: The City Council of Cape Girardeau, Missouri.
Detention: The delay of storm runoff prior to discharge into receiving waters.
Detention Basin: a facility constructed or modified to restrict the discharge of stormwater to
a prescribed maximum rate, and to concurrently detain the excess waters that accumulate
behind the outlet. A wet bottom detention basin is a structure designed to retain a permanent
pool of water after having provided its planned detention of runoff during a storm event. A
dry bottom detention basin is designed to be completely dewatered after having provided its
planned detention of runoff during a storm event.
Detention Storage: The temporary detaining or storage of stormwater in storage basins, or
rooftops, in streets, parking lots, school yards, parks, open space, or other areas under
predetermined and controlled conditions, with the rate of drainage therefrom regulated by
appropriately installed devices.
Detention Volume: The volume of water eaual to the difference between the control elevation
of a discharge structure and the maximum level at which water can be accumulated prior to
discharge times the average area of open surface storage (between the control elevation and
maximum level) behind the discharge structure.
Developer: Any individual, firm, corporation, association, partnership, or other entity involved
in commencing proceedings under this ordinance to effect the development of land for himself
or another.
Development or Development Activity: Any man-made change to improved or unimproved
land, including but not limited to buildings or other structures, mining, dredging, filling,
grading, paving, excavation, or drilling operation. Any subdivision of land as defined in the
City's subdivision regulations, excluding minor subdivisions.
Differential Runoff: The difference in rate and volume of stormwater runoff from a parcel or
project in its undeveloped natural condition and its developed condition is known as the
Differential Runoff.
Discharge: The rate of outflow of water from detention storage.
Discharge Structure: Structural device, usually of concrete, metal, timber, etc., through
which water is discharged from a project to the receiving water.
WA
Drainage Area: The area from which water is carried off by a drainage system; a watershed or
catchment area.
Drainage Facility: An element in a drainage system which includes, but is not limited to any
of the following: conduits and appurtenant features, canals, channels, detention basins,
ditches, streams, culverts, streets and pumping stations.
Drainage System: The surface or subsurface system which conveys water from or over the
land including all watercourses, water bodies and wetlands (also referred to as the Stormwater
Management System).
Easement: a grant by a property owner to the public, a corporation, or a person of the use of
land for a specific purpose.
Elevation: Height in feet above mean sea level according to National Geodetic Vertical
Datum( GVD).
Emergency Spillway: Saddle or low point facility located around the rim of a dammed
impoundment such as a detention or retention basin for providing an efficient and safe means
of conveying the maximum design flood discharge through the impoundment, without
overtopping the dam.
Excess Stormwater Runoff: The volume and rate of flow of stormwater discharged from a
drainage area which is or will be in excess of that volume and rate which is specified in this
ordinance.
Fifteen Year Storm: Rainstorms of varying duration and intensity having a 6.67 percent
probability of being equaled or exceeded in any given year.
Floodplain: The special flood hazard land adjoining a watercourse, the surface elevation of
which is equal to or lower than the Base Flood Elevation (the 100 year flood), which is subject
to periodic inundation during floods.
Floodway: The channel of a watercourse and those portions of the adjoining floodplain which
are reasonably required to carry and discharge the base flood.
Flood Fringe: The higher portion of the floodplain, immediately adjacent to and on either side
of the floodway, occupied by quiescent or slow moving waters during floods.
High Water Elevation: The elevation of floodwaters of a flood of specified frequency or
occurrence at any given point.
Impervious Surface: A surface which has been compacted or covered with a layer of materials
so that it is highly resistant to infiltration of water; the term includes most conventionally
surfaced streets, roofs, sidewalks, parking lots and similar structures.
Improvement: A structure on, or other alteration of land on a given site, including but not
limited to grading, street paving, storm sewers, sanitary sewers and utilities.
Off -Site Detention Basin: A feature or structure for temporarily storing excess stormwater
originating at two or more sites having devices for controlling the rate of release of the stored
water, and located downstream of all sites where the runoff originates.
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On -Site Detention Basin: A feature or structure for temporarily storing excess stormwaters,
having devices for controlling the rate of release of the stored waters, and located within the
sites where the runoff originates.
One Hundred -Year Storm: Rainstorm of varying duration and intensity having a one percent
probability of recurring in any one year.
Overflow Elevation: Design elevation of a discharge structure at which point, or above which
point, water leaks out, or bleeds out, through a control device down to the control elevation.
Peak Flow: The maximum rate of flow of water at a given point in a channel or conduit
resulting from a predetermined storm or flood.
Post -Development Conditions: Those conditions which are expected to exist, or do exist, after
alteration, resulting from human activity, of the natural topography, vegetation and rate,
volume or direction of surface or subsurface flow.
Pre -Development Conditions:. Those conditions which existed at the time this ordinance
becomes effective in terms of topography, vegetation and rate, volume or direction of surface
or subsurface flow, as indicated by the best available historical data.
Primary Drainage (Water Management) Systems: Includes major waterways and appurtenant
structures or systems whose total tributary area from origin to outfall exceeds or equals 50
acres.
Professional Engineer or Architect: An engineer or architect duly registered or otherwise
authorized by the State of Missouri to practice engineering.
Rational Method: An empirical formula for calculating peak rates of runoff resulting from
rainfall. Expressed mathematically, the formula is:
Q = CIA
Where Q = peak flow in cubic feet per second (cfs)
C = runoff coefficient, or fraction of runoff to rainfall, dependent on
.type of surface cover and topography
I = rainfall intensity, in inches per hour, for a specific storm and duration
A = watershed area, in acres
Receiving Bodies of Water: Any water body or stream into which surface waters flow.
Site Plan: The plan, usually in map form, prepared pursuant to the governing body's zoning or
other land development ordinances as a requirement for the development of property.
Stormwater Runoff: The waters derived from rain falling or snow melting within a tributary
drainage basin, flowing over the surface of the ground or collected in a stormwater drainage
system, storm sewer, or water course.
Subdivision: As defined in Chapter 25, Subdivisions, of the Code of Ordinances of the City of
Cape Girardeau, Missouri.
Twenty -Five Year Storm: Rainstorms of varying duration and intensities having a four percent
probability of being equaled or exceeded in any given year.
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Time of Concentration: The elapsed time for stormwater to flow from the most distant point
in a drainage basin to the outlet or point in question.
Watercourse: Any stream, creek, brook, branch, natural or artificial depression, slough, gulch,
reservoir, lake, pond or natural or man-made drainageway in or into which stormwater runoff
and flood waters flow either regularly or intermittently.
SECTION 4.
APPLICABILITY. Any person, firm, corporation or business or government entity within the
municipality shall apply to the Administrative Officer for approval of a Stormwater
Management Plan and obtain a permit before commencing any development or development
activity as defined herein.
A stormwater management plan shall be required of any platted subdivision for which no
improvement plans have been submitted at the time this ordinance takes effect.
Detention requirements are directly related to permitted land use in the Zoning Ordinance of
the City of Cape Girardeau. The permitted densities and minimum lot areas are important
factors in the anticipated runoff. Table I lists the Zoning Districts with the major permitted
use category, minimum lot area and the corresponding percent of imperviousness.
For permitted land uses other than those listed in Table I, such as schools, churches, fire
stations, etc., the rate of imperviousness shall be determined by the same method as for
commercial uses listed in Table I.
For conditional land use in any zoning district, the same ratio determination criteria shall
apply.
TABLE I
SECTION 5.
EXEMPTIONS. Development within a subdivision shall not require approval of a Stormwater
Management Plan if each of the following conditions have been met:
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STORM WATER DATA BY ZONING DISTRICTS
PERCENT OF IMPERVIOUS
MAJOR PERMITTED
MINIMUM
AREA FOR DESIGN STANDARDS
ZONE
AREAS
LOT AREA
IN TABLE II
MH -1
Residential
45
R-1
Residential
10,000
35
R-2
Residential
7,000
35
R-3
Residential
7,000
45
R-4
Residential
7,000
[ Determine ]
[ Percentage ]
C-1
Commercial
[ of ]
C-2
Commercial
[ Impervious ]
C-3
Commercial
[ Area by ]
C-4
Commercial
( Ratio of ]
( Impervious ]
M-1
Industrial
[ Surface ]
M-2
Industrial
[Area to Total ]
[ Area ]
SECTION 5.
EXEMPTIONS. Development within a subdivision shall not require approval of a Stormwater
Management Plan if each of the following conditions have been met:
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A. Drainage provisions for the project were previously approved and remain valid as part of a
final plat;
B. The development is conducted in substantial accordance with the Stormwater Management
provisions contained in the development plan submitted with the final plat as approved.
Development on isolated lots of record for single-family and two-family dwelling purposes
shall not require approval of a Stormwater Management Plan, nor a grading permit, unless the
development involves altering, rerouting, deepening, widening, obstructing or changing in any
way existing drainage facilities, degrades the quality of water, adversely affects any wetland
or adversely affects any sinkhole, watercourse or waterbody.
Stormwater Management Plans may be waived for building construction which will not
increase the amount of impervious area on the site and will not adversely impact an existing
drainage area or drainage on adjoining properties.
Written notice of intent to commence development shall be delivered to the Administrative
Officer prior to undertaking any development activity, whether exempt from plan provisions or
not. Application for a building permit may constitute notice of intent.
SECTION 6.
STORMWATER MANAGEMENT PLAN APPLICATION.
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: 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 of Missouri.
C. The application form requires the following minimum information:
1. The name, address, and telephone number of the Applicant, and the Owner if different
from the Applicant.
2. Name and address of the Professional Engineer or Architect.
3. The legal description of the property.
SECTION 7.
STORMWATER MANAGEMENT PLAN. 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 1" < 200' and other descriptive material,
including the basis of computation, showing the following:
A. Required Pre -Development Site Information (Map scales are minimums)
1. Detailed location sketch showing the parcel and major adjacent roads.
M
2. Topographic map of the site at a scale of 1" < 200' with maximum five feet countour
intervals, except in floodplains or other areas of low relief where a smaller interval
may be required..
3. Where percolation or exfiltration systems are proposed, information as to the location
and type of vegetative cover and soil types and characteristics representative of the
design condition mapped at a scale of 1" ,- 2001.
4. Location of streams and other flood water 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 1" < 2001.
5. Location of lakes, ponds, swamps and detention basins indicating their normal
shorelines, floodplains and lines of inflow and outflow mapped at a scale of 1" < 2001.
6. 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 mapped at a scale of 1" < 2001.
7. 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 1" < 2001.
B. 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.
C. Location of all new drainage facilities, including detention basins, to be constructed.
Provide design details on each facility as applicable.
D. Location and extent of existing and proposed impervious surfaces (roads, parking lots,
buildings, etc.) and their elevations. Provide grading and paving plans and specifications.
E. Location and extent of rights-of-way and easements for the stormwater management
system, including all areas to be dedicated for water management purposes.
F. Identification and description of any special or required maintenance procedures to keep
the project functioning as designed.
G. Provide stormwater management system design calculations as follows:
1. Design storms used.
2. Calculated hydrographs of inflow and outflow of design storms runoff for the project
site under natural and undeveloped conditions.
3. Hydrographs of the runoff from the design storm for the project site under developed
conditions.
4. 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.
5. Acreages and percentage of property proposed as:
impervious surfaces
pervious surfaces (green areas)
lakes, canals, detention areas, etc.
bA
total acreage of project
other
6. Runoff routing calculation showing discharge, elevations, and volumes retained and/or
detained during applicable storm event.
7. Calculations required for determination of minimum building floor and road elevations.
H. Identify entity responsible for operation and maintenance of the system.
I. The requirements for specific plan elements cited above may be waived by the
Administrative Officer, upon written supportive recommendation of the City Engineer.
The Stormwater Management Plan for minor development activities may consist of a
certification from a professional engineer or architect that the differential run-off equals
zero.
J. 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 City Manager. Within a reasonable period after submission of the
completed 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 Application is
denied or approved with conditions, the Administrative Officer shall state the reasons for
denial or the specified conditions. If the Applicant feels aggrieved due to the denial or
conditions, he may appeal the decision to the City Council.
SECTION 8.
PROJECT CLASSIFICATION AND FEES: For purposes of evaluation, projects will be
classified in three categories according to acreage:
Class Review Fee
A. Less than 25 acres $ 25
B. 25 acres to 200 acres $ 50
C. Over 200 acres $100
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.
The review fee shall be collected at the time the Stormwater Management Plan Application is
submitted by the Applicant to the Administrative Officer, and will reflect the cost of the
administration and management of the review process. These fees may be adjusted from time
to time by the City Council to reflect actual costs of adminstration and review.
SECTION 9.
GENERAL DESIGN REQUIREMENTS FOR STORMWATER MANAGEMENT PLANS.
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
5:19
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 15 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 25 year storm (under developed conditions). Control
devices shall limit the discharge from storage to a rate no greater than that prescribed by
this ordinance. 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 the ordinance.
3. In a depressed area along roadway, street or parkway, provided the area is wide enough
to permit side slopes as required in other sections of this ordinance.
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 divide may be relocated or eliminated and
incorporated into the planned system of storm sewers and open channels designed
consistent with the requirements of this ordinance.
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 flood
water 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 flood or stormwater, shall be provided
W
with either a. watertight bolted manhole cover, a watertight concealed pick -hole cover, or
be constructed with a rim elevation at or above the high water elevation of the 100 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.
SECTION 10.
HYDRAULIC DESIGN CONSIDERATIONS.
A. Design Storms. Stormwater systems will be designed with sufficient hydraulic capacity as
a minimum for the following frequencies and durations.
TYPE OF FACILITY DESIGN FREQUENCY
1. Detention Basins 25 year
2. Primary Drainage Systems 25 year
3. Bridges 50 year
4. Secondary Drainage Systems, i.e., Crossdrains 15 year
and Ditches for Internal Subdivision Drainage
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 minimums set forth above, up to the 100 year frequency design.
SECTION 11.
STORMWATER MANAGEMENT SYSTEM DESIGN REQUIREMENTS.
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 size classes of projects
shall be evaluated by the Rational Formula. The runoff coefficients in Table II shall be
used. Differential Runoff rates shall be evaluated by equation:
R = (Rd -Ru) [EQUATION 11
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 3 classes of projects shall be evaluated
according to the following methods:
1. Volume of detention for projects of less than 25 acres shall be evaluated by the
"Simplified Volume Formula."
2. Volume of detention for projects of 25 acres or greater but less than 200 acres may be
evaluated either by the "Simplified Volume Formula" or the "Modified Rational
Hydrograph Method."
3. For projects larger than 200 acres the owners' Engineer shall submit his 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 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. 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:
V = R x A x 30 (min) x 60 (sec/min) [EQUATION 21
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
with the following elements:
Tb = Base time of hydrograph for developed project without detention
Tb 60 minutes
Tp Time of peak runoff of developed project
Tp = 20 minutes
Qd = Total peak runoff of developed project in c.f.s.
Qd A x Rd (See Equation 1)
Qu = Total peak runoff of unimproved project in c.f.s
Qu = A x RU (See Equation 1)
A = Total area of project in acres
To = 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 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 II 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:
Tp
where Tp
D
D/2 + .6 Tc
[EQUATION 31
Time of peak discharge of developed project in minutes
20 min = storm duration in minutes
c. Determine the base time of the Hydrograph without detention, by equation:
Tb = 2.67 Tp [EQUATION 41
d. Determine the base time of the Hydrograph with detention by equation:
Tr = Tb �Q - 1) [EQUATION 51
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 c.f.s.
Qd = A X Rd (See Equation 1) [EQUATION 61
Qu = Total runoff of unimproved project in c.f.s.
Qu = A X Ru (See Equation 1) [EQUATION 71
e. Determine the required volume of detention by equation:
V = 1/2 (Qd - Qu) Tb [EQUATION 81
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.
The design discharge (Q) for the low -flow weir shall not exceed the 15 year (frequency)
with a duration equal to the time of concentration for the watershed, runoff from the
tributary area for five percent (5%) imperviousness (1.7 c.f.s. per acre). The maximum
discharge shall be designed to take place under total anticipated design -head conditions.
Sizing of the low -flow weir shall be by the appropriate weir formulas.
The overflow opening or spillway shall be designed to accept the total peak runoff of the
improved tributary area.
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 25 year storm (under developed conditions) with a
discharge no greater than the rate of flow from a 15 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 100 year storm.
4. Designs should result in aesthetically pleasing configurations which will enhance public
acceptability.
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H. Dry -Detention Facilities.
1. Perimeter maintenance easements of 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 subsurface
drains.
4. Multipurpose 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. In no case shall the limits of maximum ponding elevation be closer than twenty-five (25)
feet horizontally from any building and less than two (2) feet vertically below the
lowest sill elevation. The entire reservoir area shall be seeded, fertilized and mulched,
sodded or paved.
I. Wet -Detention Facilities.
1. Perimeter maintenance and operation easements of 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 2.5 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: vertical) out to a depth of two feet
(21) 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-quarter of an area of the
permanent pool must be a minimum depth of 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 12
inches so as to prevent damage to parked vehicles. Ponding should be relegated 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 ordinance are met.
Details of such designs are to include 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 and groundwater pollution control.
-13-
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. Developments Adjoining a Floodplain - where a development adjoins or encompasses a
portion of a floodplain for a 100 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., reauired by federal, state, county and/or municipal law or
regulations detailing such provisions or restrictions as are necessary to comply with the
following:
a. All applicable zoning and subdivision requirements.
b. All applicable building code reeuirements.
c. All reeuirements of other federal, state or local agencies exercising jurisdiction
over the area..
O. 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 it conveyed in its pre -development state.
P. 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 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 said 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:
"Flood Insurance Rate Map" published by the Federal Emergency Management Agency.
Backwater Curve Profiles of the proposed waterway due to a. 100 year storm recurrence
interval.
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. 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 Adeouacy. 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
-14-
certain critical elements are in workable compliance with the aims of this ordinance. For
projects less than 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:
1. volume of detention for the total project
2. tributary (Q) peak runoff to basin
3. balanced maximum outflow rate from the low -flow structure
4. ratios of inflow to outflow rates
5. sizing of the overflow facilities
6. stability of detention dikes
7. safety features
8. maintenance features
For projects of 50 acres or greater but less than 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 reouires special
attention in this area of design.
Projects over 200 acres in area shall provide documented verification of adequacy
according to scope and complexity of design.
Rainfall 4.60 5.40 5.90 6.40
From U.S. Weather Bureau Technical Paper No. 40: "Rainfall Freauency Atlas of the United
States for durations from 30 minutes to 24 hours and Return Periods from 1 to 100 Years."
-15-
TABLE 11
AVERAGE C.I. (P.I.)
FACTORS IN C.F.S. PER
ACRE
20 Min. INLET TIME
% Impervious Area
C or P (Factor)
15 Yr.
25 Yr.
50 Yr.
100 Yr.
5
.37
1.7
2.00
2.18
2.37
10
.39
1.79
2.11
2.30
2.50
15
.41
1.89
2.21
2.42
2.62
20
.435
2.0
2.35
2.57
2.78
25
.455
2.09
2.46
2.68
2.91
30
.475
2.10
2.57
2.80
3.04
35
.495
2.28
2.68
2.92
3.17
40
.52
2.39
2.81
3.07
3.33
45
.54
2.48
2.92
3.19
3.46
50
.56
2.58
3.02
3.30
3.58
55
.58
2.68
3.13
3.42
3.71
60
.60
2.76
3.24
3.54
3.84
65
.625
2.88
3.38
3.69
4.00
70
.645
2.97
3.48
3.81
4.13
75
.665
3.06
3.59
3.92
4.26
80
.685
3.15
3.70
4.04
4.38
85
.705
3.24
3.81
4.16
4.51
90
.73
3.36
3.94
4.31
4.67
95
.75
3.45
4.05
4.43
4.80
100
.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 Freauency Atlas of the United
States for durations from 30 minutes to 24 hours and Return Periods from 1 to 100 Years."
-15-
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.
SECTION 12.
RIGHTS-OF-WAY AND EASEMENTS.
A. All stormwater management facilities shall be constructed within an easement or
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
Open Drainage Channel or Facility
Greenways
Pipes and Culverts
Detention Areas
Connecting Access
Maintenance Access Width
30 feet, 15 feet each side
Width of Greenway
15 feet, centered
15 feet continuous around total area
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 or both sides is necessary for maintenance
purposes.
SECTION 13.
MAINTENANCE RESPONSIBILITIES FOR STORMWATER MANAGEMENT FACILITIES.
A. Purpose: The purpose of this section is to establish maintenance standards to ensure that
after stormwater management facilities have been properly designed and constructed, they
continue to function properly. Continued proper functioning is highly dependent upon the
proper maintenance of the facilities.
B. Design of Facilities: Maintenance costs over a period of years will generally surpass the
costs of initially constructing water management facilities. The Applicant and the
Administrative Officer should utilize all appropriate methods, approaches and techniques
to design and construct these facilities in such a manner that fulfills the requirements of
this ordinance, facilitates their inspection, and minimizes future maintenance costs.
C. Maintenance Responsibilities: The growth of noxious weeds, the creation of conditions
which support the growth of mosquitoes and other insects, and the decrease in available
storage by accumulated sediments shall be controlled. The cleanup of accumulated debris,
flotsam and other materials after runoff events have subsided shall be assured.
-16-
Detention facilities, when mandatory, are to be built in conjunction with the storm sewer
installation and/or grading. Since these facilities are intended to control increased runoff,
they must be partially or fully operational soon after the clearing of the vegetation. Silt
and debris connected with early construction shall be removed periodically from the
detention area and control structure in order to maintain close to full storage capacity.
The responsibility for maintenance of stormwater management facilities in single -lot
development projects shall remain with the owner, developer and general contractor until
final inspection of the development is performed and approved, and a legal occupancy
permit, where applicable, is issued. After legal occupancy of the project, the maintenance
of stormwater management facilities shall be vested with the owner of the project.
The responsibility for maintenance of stormwater management facilities in subdivision
projects shall remain with the developer until such time as responsibility is transferred,
under appropriate legal arrangements, to the private individual owners in the subdivision,
the trustees of the subdivision, the City of Cape Girardeau or such other maintenance
entity or authority as may be proposed and approved by the City Council.
If responsibility is to be transferred to the private individual owners in the subdivision, the
developer shall assure perpetual maintenance of the drainage management facilities,
including detention systems, if any are included, through the adoption of maintenance
agreements or covenants for any facilities that remain in private ownership. Such
agreements or covenants shall be subject to the approval of the Administrative Officer.
If the responsibility is to be transferred to the trustees of the subdivision, the developer
shall establish a suitable indenture of trust. Upon release of escrows required for the
subdivision development, the responsibility for maintenance shall be vested in the trustees
of the subdivision by virtue of the trust indenture. The indenture of trust shall clearly
indicate resident responsibility for maintenance and shall be subject to the approval of the
Administrative Officer.
If responsibility for maintenance is to be transferred to the City of Cape Girardeau, the
system(s) to be maintained by the City shall have adequate easements, dedicated to the
public for stormwater management use, to permit the City to inspect and enter upon the
property, as necessary, to maintain the system(s).
D. Performance and maintenance security: Security against defects in workmanship shall be
required for any portion of the drainage management facilities dedicated to the public.
The terms of the performance security shall apply to any repairs needed and maintenance
needed during the two-year period following completion. Inspection and repair of defects
shall be required as a condition of release of the posted security.
SECTION 14.
PLAN ADHERENCE. 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 ordinance for
obtaining Stormwater Management Plan approval. Enforcement officials shall be, and are
herein, granted inspection rights and right -of -entry privileges in order to ensure compliance
with the requirements of this ordinance.
-17-
SECTION 15.
ENFORCEMENT.
A. Approved Projects: The Administrative Officer or his designated representative shall carry
out periodic inspections of the project site to insure the Applicant's compliance with this
ordinance. 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:
1. Written Notice: Issue written notice to the Applicant or owner, specifying the nature
and location of the alleged noncompliance, 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 ordinance,
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, not bring the project into
compliance with the written notice and stop -work order, he shall then be subject to
immediate revocation of his Stormwater Management Plan approval and to the
penalties described in Section 16.
4. Appeal: Any notice, order or revocation issued pursuant to subparagraphs A(1), A(2) or
AN above shall become final unless the person or persons named therein requests, in
writing, no later than ten (10) days after the date such notice, order or revocation is
served, a hearing before the City Council.
B. Unapproved Projects: With respect to any development or development activity
determined by the Administrative Officer or his designated representative to be subject to
this ordinance, and being carried out without approval, the Administrative Officer is
authorized to:
I. Written Notice: issue written notice to the owner specifying the nature and location of
the alleged noncompliance, 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 ordinance, 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 shall then be subject to the
penalties described in Section 16.
4. Appeal: Any notice, order or revocation issued pursuant to subparagraphs B(l), B(2) or
B(3) above shall become final unless the person or persons named therein requests, in
writing, no later than ten (10) days after the date such notice, order or revocation is
served, a hearing before the City Council.
M
SECTION 16.
PENALTIES FOR VIOLATION.
A. General: Violation of the provisions of this ordinance or failure to comply with any of its
requirements, including conditions and safeguards established in connection with variances
or special use permits, shall constitute a misdemeanor. Any person who violates this
ordinance or fails to comply with any of its requirements shall upon conviction thereof be
fined not more than Five Hundred Dollars ($500.00) or imprisoned for not more than three
(3) months, or both, and in addition, shall pay all costs and expenses involved in the case.
Each day such violation continues shall be considered a separate offense.
B. Corrective Actions: Nothing herein contained shall prevent the City of Cape Girardeau
from taking such other lawful action as is necessary to prevent or remedy any violation.
All such costs connected therewith shall accrue to the person or persons responsible.
SECTION 17.
VESTED RIGHTS. This ordinance shall not in any way limit or modify the vested rights of any
person to complete any development or improvements 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.
SECTION 18.
CONFLICT WITH OTHER ORDINANCES AND CODES. In case of conflicts within this
ordinance or any part thereof, and the whole or part of any other existing or future ordinance
or code of the City of Cape Girardeau, the most restrictive in each case shall apply.
SECTION 19.
OTHER PERMITS. Before starting any work regulated by this ordinance, 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 ordinance and as may be required by State statutes and the regulations of any
department of the State of Missouri.
SECTION 20.
INTERPRETATION. In the interpretation and application of this ordinance, the provisions
expressed herein shall be held to be the minimum requirements and shall be liberally construed
in favor of the City of Cape Girardeau and shall not be deemed a limitation or repeal of any
other powers granted by State statutes.
SECTION 21.
SAVINGS CLAUSES.
A. Separability: If 'any part of this ordinance is held to be unconstitutional, it shall be
construed to have been the legislative intent to pass this ordinance without such
unconstitutional part and the remainder of this ordinance, as to the exclusion of such part,
shall be deemed and held to be valid as if such part had not been included herein. If this
owls
ordinance or any provision hereof is held to be inapplicable to any persons, group of
persons, property, kind of property, circumstances or set of circumstances, such holding
shall not affect the applicability hereof to any other person, property or circumstances.
B. Abrogation and Greater Restrictions: It is not intended by this ordinance to repeal,
abrogate or impair any existing easements, covenants or deed restrictions. However,
where this ordinance imposes greater restrictions, the provision of this ordinance shall
prevail.
SECTION 22.
LIABILITY DISCLAIMER. 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 uses 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.
SECTION 23.
It is the intention of the governing body and it is hereby ordained that the provisions of this
ordinance shall become and be made a part of the Code of Ordinances of the City of Cape
Girardeau, Missouri, and the sections of this Code may be renumbered to accomplish such
intention.
SECTION 24.
This ordinance shall be in full force/and effect ten days after its passage and approval.
PASSED AND APPROVED THIS (O(�fc , DAY OF , 1989.
Francis I-. Rhodes,
Evelyn , City Clerk
ATTESTED AND FILED in my office this `tri. day of �� ���-'� �,�'L/ , 1989, and
published as provided by law this day of (,��t ���' , 1989.
� 7
velyn G eGrand, City Clerk
-20-
STORMWATER MANAGEMENT PLAN
APPLICATION FORM
Project
Name
Date of
Submission
Date of
Return
Date of
Approval _
Signature of Administrative Officer
APPLICANT:
Name:
Firm:
Address:
Phone Number:
PROFESSIONAL ENGINEER:
Name:
Firm:
Address:
Phone Number:
LEGAL DESCRIPTION OF PROPERTY:
OWNER (if different):
Name:
Firm:
Address:
Phone Number:
[Attached]
OVERLAND FLOW TIME
FROM SEELEY'S DATA BOOK FOR CIVIL ENGINEERS
100
900
35
800
700
600
30-
500
.80-
400
2
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300
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