[Ord. No. 1437 §I(435.010), 6-21-2004]
Unless specifically defined, words or phrases shall be interpreted
so as to give them the meanings they have in common usage and to give
this Chapter its most reasonable application:
Rainstorms of varying duration and intensity having a six
and sixty-seven hundredths (6.67%) percent probability of being equaled
or exceeded in any given year.
Rainstorms of varying duration and intensities having a four
percent (4%) probability of being equaled or exceeded in any given
year.
A rainstorm of varying duration and intensity having a one
percent (1%) probability of recurring in any one (1) year.
The duly appointed City Administrator or their designated
representative.
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 use 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.
The record owner or his/her authorized representative of
a tract of land that is the site of development or development activity
within the scope of this Chapter.
The elevation at any location delineating high waters having
a one percent (1%) probability of being equaled or exceeded in any
given year (also known as the 100-year flood).
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.
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 (2) bodies of water.
Any channel, pipe, sewer or culvert used for the conveyance
or movement of water, whether open or closed.
An element of a discharge structure that allows the gradual
release of water under controlled conditions.
Design elevation of a discharge structure at which, or below
which, water is contained behind the structure.
The delay of storm runoff prior to discharge into receiving
waters.
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.
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 rage of drainage therefrom regulated by appropriately installed
devices.
The volume of water equal 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.
Any individual, firm, corporation, association, partnership
or other entity involved in commencing proceedings under this Chapter
to effect the development of land for him/her or another.
Any manmade 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.
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.
The rate of outflow of water from detention storage.
Structural device, usually of concrete, metal, timber, etc.,
through which water is discharged from a project to the receiving
water.
The area from which water is carried off by a drainage system,
a watershed or catchment area.
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.
The surface or subsurface system that conveys water from
over the land including all watercourses, water bodies and wetlands
(also referred to as the stormwater management system).
A grant by a property owner to the public, a corporation
or a person of the use of land for a specific purpose.
Height in feet above mean sea level according to national
geodetic vertical datum (NGVD).
Saddle or low point facility located around the rim of 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.
The wearing away of the land surface by the action of the
wind, water, ice, gravity or any combination thereof.
The volume and rate of flow of stormwater discharged from
a drainage area that is or will be in excess of that volume and rate
that is specified in this Chapter.
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.
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.
The channel of a watercourse and those portions of the adjoining
floodplain that are reasonably required to carry and discharge the
base flood.
The elevation of floodwaters of a flood of specified frequency
or occurrence at any given point.
A surface that 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.
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.
A feature or structure for temporarily storing excess stormwater
originating at two (2) 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.
A feature or structure for temporarily storing excess stormwater,
having devices for controlling the rate of release of the stored waters
and located within the sites where the runoff originates.
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.
The maximum rate of flow of water at a given point in a channel
or conduit resulting from a predetermined storm or flood.
Those conditions that 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.
Those conditions that existed at the time this Section 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.
Includes major waterways and appurtenant structures or systems
whose total tributary area from origin to outfall exceeds or equals
fifty (50) acres.
An engineer or architect duly registered or otherwise authorized
by the State to practice engineering.
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 (c.f.s.)
|
|
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.
|
Any water body or stream into which surface waters flow.
The process by which suspended solids from erosion are transported
and deposited.
The plan, usually in map form, prepared pursuant to the City
Council's zoning or other land development ordinances as requirement
for the development of property.
The waters derived from rain falling or snow melting within
a tributary drainage basis, flowing over the surface of the ground
or collected in a stormwater drainage system, storm sewer or watercourse.
Elapsed time for stormwater to flow from the most distant
point in a drainage basin to the outlet or point in question.
Any stream, creek, brook, branch, natural or artificial depression,
slough, gulch, reservoir, lake pond or natural or manmade drainage
way in or into which stormwater runoff and floodwaters flow either
regularly or intermittently.
[Ord. No. 1437 §I(435.020), 6-21-2004]
The purpose for this Chapter is to lessen or avoid hazards to
persons and property caused by uncontrolled stormwater runoff or by
obstructions to drainage and to lessen the degradation of the quality
of surface runoff.
[Ord. No. 1437 §I(435.030), 6-21-2004]
A.
Any
person or government entity within the City shall apply to the Administrative
Officer for approval of a stormwater management plan and obtain a
permit before commencing any development or development activity.
B.
A stormwater
management plan shall be required of any platted subdivision for which
no improvement plans have been submitted at the time this Section
takes effect.
C.
Detention
requirements are directly related to permitted land use in the zoning
ordinance of the City. 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.
D.
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.
E.
For
conditional land use in any zoning district, the same ration determination
criteria shall apply
|
Table I
Stormwater Data By Zoning District
| |||
|---|---|---|---|
|
Zone
|
Major Permitted Areas
|
Minimum Lot Area
|
Percent of Impervious Area for Design Standards in Table
II
|
|
"R-1"
|
Residential single-family
|
7,200
|
35
|
|
"R-2"
|
Residential two-family
|
10,000
|
35
|
|
"R-3"
|
Medium density multi-family
|
7,500
|
45
|
|
"R-4"
|
High density multi-family
|
7,000
|
*
|
|
"RMH"
|
Residential manufactured home
|
45
| |
|
"BR"
|
Business-residential overlay
|
*
| |
|
"B-1"
|
Highway business district
|
*
| |
|
"B-2"
|
Central business district
|
10,000
|
*
|
|
*
|
For these classifications, the percent impervious area shall
be the actual proposed ration of impervious area to total area for
the lot. Also, any lot in any district greater than ten thousand (10,000)
square feet shall use an actual ration for determining the percent
impervious area.
|
[Ord. No. 1437 §I(435.040), 6-21-2004]
A.
Development
within a subdivision shall not require approval of a stormwater management
plan if each of the following conditions has been met:
B.
Development
on isolated lots or 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; or unless
said lot is one (1) acre or more in size as State law now requires
a land disturbance permit for any construction that disturbs more
than one (1) acre.
C.
Stormwater
management plans may be waived for building construction or other
development that will not increase the amount of impervious area on
the site and will not adversely impact an existing area or drainage
on adjoining properties.
D.
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.
[Ord. No. 1437 §I(435.050), 6-21-2004]
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 environment quality of the affected area,
the potential and predicted impacts of the proposed activity of 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 sealed by a registered professional
engineer or architect.
[Ord. No. 1437 §I(435.060), 6-21-2004]
A.
A stormwater
management plan is designed to safely manage the stormwater runoff
following the rainstorms that exceed the maximum allowable release
rate and the capacity of the stormwater drainage system and/or the
storm sewer by detention of the excess stormwater runoff. It is also
designed to manage the quality of stormwater runoff during development
through erosion and sedimentation controls. The plan shall provide
or be accompanied by maps at a minimum scale of one (1) inch is less
than or equal to two hundred (200) feet and other descriptive material,
including the basis of computation, showing the following:
1.
Required pre-development site information (map scales are minimums):
a.
Detailed location sketch showing the parcel and major adjacent roads.
b.
Topographic map of the site at a scale of one (1) inch is less than
or equal to one hundred (100) feet with maximum two (2) foot contour
intervals, except in floodplain or other areas of low relief where
a smaller interval may be required.
c.
Where percolation or infiltration systems are proposed, information
as to the location and type of vegetative cover and soil types and
characteristics representative of the design condition mapped at a
scale of one (1) inch is less than or equal to one hundred (100) feet.
d.
Location of streams and other floodwater runoff channels, their normal
channels and the extent of the floodplains at the established high
water elevations and the limits of the floodway mapped at a scale
of one (1) inch is less than or equal to one hundred (100) feet.
e.
Location of lakes, ponds, swamps and detention basins indicating
their normal shorelines, floodplains and lines of inflow and outflow
mapped at a scale of one (1) inch is less than or equal to one hundred
(100) feet.
f.
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 one (1) inch is less than or equal to one hundred (100) feet.
g.
Location and description of nearby existing off-site water management
facilities such as wells, lakes, drainage ways, etc., that are potentially
directly affected by the proposed construction or development, mapped
at a scale of one (1) inch is less than or equal to one hundred (100)
feet.
2.
For all existing drainage facilities that are to be maintained, altered
or enlarged as part of the stormwater management system; provide information
as to their size, slopes, depths, outfalls, receiving waters, elevations,
cross sections, profiles, construction materials and other design
details as applicable.
3.
Location of all new drainage facilities, including detention basins,
to be constructed. Provide design details on each facility as applicable.
4.
Location and extent of existing and proposed impervious surfaces
(roads, parking lots, buildings, etc.) and their elevations. Provide
grading and paving plans and specifications.
5.
Location and extent of rights-of-way and easements for the stormwater
management system, including all areas to be dedicated for water management
purposes.
6.
Identification and description of any special or required maintenance
procedures to keep the project functioning as designed.
7.
Provide stormwater management system design calculations as follows:
a.
Design storms used.
b.
Calculated hydrographs of inflow and outflow of design storms for
the project site under natural and undeveloped conditions.
c.
Hydrographs of the runoff from the design storm for the project site
under developed conditions.
d.
For all detention basins, a plot or tabulation of storage volumes
with corresponding water surface elevations and of the basin overflow
rates for those water surface elevations.
f.
Runoff routing calculation showing discharge, elevations and volumes
retained and/or detained during applicable storm event.
g.
Calculations required for determination of minimum building floor
and road elevations.
8.
Identify entity responsible for operation and maintenance of the
system.
9.
The requirements for specific plan elements cited above may be waived
by the Administrative Officer upon written supportive recommendation
of the City Engineer. The stormwater management plans for minor development
activities may consist of a certification from a professional engineer
or architect that the differential runoff equals zero.
10.
The Administrative Officer will ascertain the completeness of the
stormwater management plan application. The Administrative Officer
will return incomplete applications to the applicant for completion
and resubmission. After determining that the application is complete,
the Administrative Officer will distribute copies of the application
for review and comment to other persons with special technical expertise
as deemed appropriate by the City Administrator. 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/she may appeal the decision to the Board of Aldermen.
[Ord. No. 1437 §I(435.070), 6-21-2004; Ord. No. 1614 §§I — II, 10-20-2008]
A.
For
the purpose of evaluation, projects will be classified into three
(3) categories.
|
|
Class
|
Permit Fee
|
|---|---|---|
|
|
"R-1" and "R-2"
|
Lot square footage x .004
|
|
|
"R-3" and "R-4"/Residential Subdivision
|
Land square footage x .006
|
|
|
Commercial/Industrial
|
Land square footage x .006
|
B.
The
effective acreage for a project is not limited to a fractional part
of the total concept, rather if a project is developed in phases or
small plots, the total acreage of the conceptual project will be considered.
C.
The
stormwater permit fee will be collected before the stormwater management
permit is issued to the applicant and will reflect the cost based
on the land square footage of the project. These fees may be adjusted
from time to time by the Board of Aldermen to reflect cost changes.
[Ord. No. 1437 §I(435.080), 6-21-2004]
A.
A stormwater
management system shall be provided for protecting lots, roads, streets
and buildings in the project area from the potential adverse impacts
of stormwater runoff. Streets, blocks, depths of lots, parks and other
public grounds and ultimate land usage shall be determined, located
and laid out in such a manner as to reduce the velocity of overland
flow and allow the maximum opportunity for infiltration of stormwater
into the ground and to preserve and utilize natural streams, channels
and detention basins and, wherever possible, to include streams and
floodplains within parks and 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 by-passed
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 Section. 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 lines in a block or entirely within the rear
yards of a single row of lots or parcels, provided that in either
case the lots are deep enough to permit side slopes in the runoff
channel and a building site of the elevation required by other Sections
of this Section.
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 Section.
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
Chapter.
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 areas so designed for the passage
or storage of waters, no structure may be erected, no fences, shrubbery
or trees planted or changes made to the prescribed grades and contours
of the specified floodwater or stormwater runoff channels.
F.
All
storm sewer outfalls shall be so designed, by reason of elevation
of the invert, by a flap gate or by other features, that when the
receiving stream is in full flood, the storm sewers will continue
to drain the areas they are designed to serve unless the provision
is made for sewer back-ups into planned storage locations.
G.
All
sanitary sewer manholes constructed in a floodplain, in street designed
for detention or in an area designed for the storage or passage of
floodwater or stormwater shall be provided with either a watertight
bolted manhole cover, a watertight concealed pick-hole cover or be
constructed with a rim elevation at least one (1) foot higher than
the high water elevation of the 100-year flood or the high water elevation
of the design storm, whichever is applicable to the specified area.
H.
Projects
that are to be developed in phases will normally require the submission
of a master plan of the applicant's contiguous land holdings. Applications
for individual project phases may be considered only when the phases
are totally independent of, or make sufficient provisions for, adjacent
lands.
I.
Systems
such as curb and gutter, drop inlets and storm sewers shall discharge
into closed conduits into a detention basin or natural drainage way.
Suitable methods of erosion control shall be provided at the discharge
of such enclosed conduits.
J.
Flow Towards Streets. Any concentration of surface flow
in excess of two (2) cubic feet per second (cfs) for the 10-year frequency
rain shall be intercepted before reaching the street right-of-way
and shall be carried by an enclosed storm drain to connect with a
drainage structure at the low point in the street right-of-way or
to discharge to a watercourse.
K.
Detention
facilities shall release stormwater at a non-erosive velocity. Protected
channels receiving detention discharge shall incorporate features
to reduce velocity to non-erosive levels at the point where such discharge
enters the unprotected channel. If release is into a subsurface conduit,
the energy gradient in the receiving facility shall not be increased
beyond the slope of the conduit.
[Ord. No. 1437 §I(435.090), 6-21-2004]
A.
Stormwater
systems will be designed with sufficient hydraulic capacity as a minimum
for the following frequencies and durations:
|
Type of Facility
|
Design Frequency
| |
|---|---|---|
|
Detention basins
|
25-year
| |
|
Primary drainage systems
|
25-year
| |
|
Bridges
|
50-year
| |
|
Secondary drainage systems, i.e., cross drains and ditches for
interval subdivision drainage
|
15-year
|
B.
The
Administrative Officer may require alternative designs or features
to reduce the cost of long-term maintenance.
C.
In
critical areas, the Administrative Officer may require additional
hydraulic capacity above the minimums set forth above, up to the 100-year
frequency design.
[Ord. No. 1437 §I(435.100), 6-21-2004]
A.
Method Of Evaluation. Differential runoff evaluation consists
of the determination or 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 for all three
(3) 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 equations:
|
|
Equation 1
| |||
|---|---|---|---|---|
|
|
R
|
=
|
(Rd-Rd)
| |
|
|
Where
|
R
|
=
|
Differential runoff rate
|
|
|
Rd
|
=
|
C.I. factor for developed conditions
| |
|
|
Ru
|
=
|
C.I. factor for undeveloped conditions
| |
C.
Volume Detention. Volumes of detention for the three (3)
classes of projects shall be evaluated according to the following
methods:
1.
Volume of detention for projects of less than twenty-five (25) acres
shall be evaluated by the "simplified volume formula".
2.
Volume of detention for projects of twenty-five (25) acres or greater
but less than two hundred (200) acres may be evaluated either by the
"simplified volume formula" or the "modified rational hydrograph method".
3.
For projects larger than two hundred (200) acres, the owner's engineer
shall submit his/her proposed method of evaluation for the sizing
of the detention basin to the Administrative Officer. The method will
be evaluated for professional acceptance, applicability and reliability.
No detail review for projects larger than two hundred (200) areas
will be rendered before the method of evaluation of the detention
is approved.
4.
Other analytical methods of evaluation of volume of detention will
be considered, provided that reliability, professional acceptance
and proper application are approved by the Administrative Officer.
D.
Calculation Methods. Any of the following methods may be
used for calculating detention volume as applicable:
1.
Simplified volume formula. Total volume of detention
shall be computed by the equation:
|
|
Equation 2
| |||
|---|---|---|---|---|
|
|
V
|
=
|
R x A x 30 x 60 (sec/min)
| |
|
|
Where
|
V
|
=
|
Total volume of detention
|
|
|
R
|
=
|
Differential runoff rate
| |
|
|
A
|
=
|
Area of project in acres
| |
2.
Graphic representation. For purposes of further
analysis, the simplified volume formula may be represented by a triangular
synthetic hydrograph 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
|
|
|
Tq
|
=
|
Assumed time of peak differential for unimproved project
|
|
|
Tq
|
=
|
Qu/Qd x 40
|
|
|
Tr
|
=
|
Assumed recedence time differential for discharge at rates no
greater than unimproved condition
|
|
|
Tr
|
=
|
(30 Qd/Qu) - 60
|
|
|
V
|
=
|
(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.
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.
b.
Determine time of peaking by equation:
|
|
Equation 3
| |||
|---|---|---|---|---|
|
|
Tp
|
=
|
D/2 = .6 Tc
| |
|
|
Where
|
Tp
|
=
|
Time of peak discharge of developed project in minutes
|
|
|
D
|
=
|
20 min - storm duration in minutes
| |
c.
Determine the base time of hydrograph without detention by equation:
|
|
Equation 4
| |||
|---|---|---|---|---|
|
|
Tb
|
=
|
2.67Tp
| |
d.
Determine the base time of the hydrograph with detention by equation:
|
|
Equation 5
| ||||
|---|---|---|---|---|---|
|
|
Tr
|
=
|
Tb
|
(Qd
(Qu- 1)
| |
|
|
Where
|
Tr
|
=
|
Additional time required for discharge at a rate no greater
than that of undeveloped condition
| |
|
|
Equation 6
| |||
|---|---|---|---|---|
|
|
Qd
|
=
|
A x Rd (See Equation 1)
| |
|
|
Qu
|
=
|
Total runoff of unimproved project in c.f.s.
| |
|
|
Equation 7
| |||
|---|---|---|---|---|
|
|
Qu
|
=
|
A x Ru (See Equation 1)
| |
e.
Determine the required volume of detention by equation.
|
|
Equation 8
| |||
|---|---|---|---|---|
|
|
V
|
=
|
½(Qd - Qu) Tb
| |
E.
Control Structures. Detention facilities shall be provided
with obvious and effective control structures. Plan view and sections
of the structure with adequate detail shall be included in plans.
1.
The design discharge (Q) for the low-flow weir shall not exceed the
15-year (frequency) with 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.
2.
Sizing of the low-flow weir shall be by the appropriate weir formulas.
3.
The overflow opening or spillway shall be designed to accept the
total peak runoff of the improved tributary area.
4.
The low-flow channel invert through dry detention facilities on other
than permanently flowing streams shall be paved.
F.
Detention design criteria. Detention in the overall system,
including swales, lakes, canals, greenways, etc., shall be provided
as follows:
G.
General.
1.
Storage volumes. The minimum volume of storage provided
in detention basins, together with such storage as may be authorized
in other on-site facilities, shall be sufficient to store the volume
from a 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.
Appearance. Designs should result in aesthetically
pleasing configurations that will enhance public acceptability.
H.
Dry Detention Facilities.
1.
Perimeter maintenance easements of fifteen (15) feet (minimum) width
at slopes no steeper than 3:1 (horizontal to vertical) shall be provided.
2.
Side slopes of the facility shall not be steeper than 3:1 (horizontal
to vertical).
3.
Provisions must be incorporated to facilitate complete interior drainage
to dry bottom basins, to include the provision of natural grades to
outlet structures, longitudinal and transverse grades to perimeter
drainage facilities or the installation of subsurface drains.
4.
Multi-purpose features may be designed to serve secondary purposes
for recreation, open space or other types of use which will not be
adversely affected by occasional or intermittent flooding.
5.
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 fifteen (15) feet
(minimum preferable) width at slopes no steeper than 3:1 (horizontal
to vertical) shall be provided.
2.
Control elevations should be no higher than two and one-half (2½)
feet below the minimum road centerline elevation in the area served
by the control device in order to protect the road subgrade when structures
are constructed near roads.
3.
Side slopes shall not be steeper than 3:1 (horizontal to vertical)
out to a depth of two (2) feet below the control elevation, then as
steep as soils stability will allow.
4.
If fish are to be used to help keep the basin clean, at least one-quarter
(¼) of an area of the permanent pool must be a minimum depth
of ten (10) feet.
5.
For emergency purposes, cleaning or shore line 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.
7.
Any wet detention facility that is to be turned over to the City
for operation and maintenance shall be secured by means of fencing.
Fencing plans shall be detailed in the overall stormwater management
plan and shall include at a minimum a lockable access point for maintenance
personnel and equipment.
J.
Impervious Areas. Paved parking lots may be designed to
provide detention storage of stormwater on all or a portion of their
surfaces. Outlets will be designed so as to slowly empty the stored
waters and depths of storage must be limited to a maximum depth of
twelve (12) inches so as to prevent damage to parked vehicles. Ponding
should be relegated to 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 downdrains, elevations of overflow scuppers, design loadings for
the roof structure and emergency overflow provisions.
L.
Underground Storage. All or a portion of the detention storage
may also be provided for in underground facilities, as long as all
applicable requirements of this Chapter are met. Details of such designs
are to include type of facility, depth and volume or storage, details
of inlet and outlet devices and locations, emergency overflow provisions
and measurers to be used for surface water and ground water pollution
control.
M.
Design Alternatives. The above listing of design criteria
is not intended to preclude the use of other know 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, specification, etc., required by Federal, State,
County and/or municipal laws or regulations detailing such provisions
or restrictions as are necessary to comply with the following:
O.
Channel Flow. The applicant shall not alter any channel
in such a way that would prohibit any section of the channel from
conveying, in its post-development state, the same amount of flow
at the same or lower maximum water elevation which it conveyed in
its pre-development state.
P.
Modifications Of Channel. The applicant shall furnish, for
the Administrative Officer's review and approval, the following information
pertaining to proposed channel modifications:
1.
Typical cross sections of the existing and proposed channel.
2.
Plan view of the channel showing the location of existing constrictions,
obstructions and other non-typical areas.
3.
Hydrographs and/or flood routing calculations and backwater curve
profiles of the proposed waterway corresponding to a storm recurrence
interval of one hundred (100) years.
4.
Engineering evaluation of all potential increases in flood hazards
to the adjacent upstream or downstream private or public lands and
facilities located thereon, showing provisions for eliminating any
and all adverse impacts on such land and facilities at no public cost.
5.
Minimum finished floor elevations that shall be set at or equal to
an elevation one (1) foot higher than surface elevation as determined
by either or both of the following:
6.
Designation on the final plan of all areas reserved for flood routing,
detention or storage, together with the required wording pertaining
to restrictions, dedications and maintenance responsibilities of such
areas.
Q.
Detention Storage. If detention storage is provided within
a floodplain, only the net increase in storage volume above that which
naturally existed on the floodplain shall be credited to the development.
No credit will be granted for volumes below the elevation of the regulatory
flood at that location unless compensatory storage is also provided.
R.
Verification Of Adequacy. Analysis of all elements of design
is to be verified by the engineer of record submitting the plan. The
following outline is provided to ascertain that certain critical elements
are in workable compliance with the aims of this Section. For projects
less than fifty (50) acres in area, there is no need for submittal
of routing calculations or tabulated proof of adequacy of tributary
runoff for detention; however, it is recommended that verification
be made of:
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 fifty (50) acres or greater but less than two
hundred (200), routing calculations shall be submitted in legible
tabulated form. Proof of adequacy of volume of detention and sizing
computations for low-flow structure shall also be submitted. Features
of stability and safety may also need to be documented if the scope
of the project requires special attention in this area of design.
|
|
|
Projects over two hundred (200) acres in area shall provide
documented verification of adequacy according to scope and complexity
of design.
|
|
Table II
Average C.I. (P.I.) Factors in CFS/Acre
20 Minute Inlet Time
| ||||||
|---|---|---|---|---|---|---|
|
% Impervious Area
|
C or P (Factor)
|
15-year
|
25-year
|
50-year
|
100-year
| |
|
5
|
0.37
|
1.74
|
1.85
|
2.23
|
2.48
| |
|
10
|
0.39
|
1.83
|
1.95
|
2.35
|
2.61
| |
|
15
|
0.41
|
1.93
|
2.05
|
2.47
|
2.75
| |
|
20
|
0.44
|
2.07
|
2.20
|
2.65
|
2.95
| |
|
25
|
0.46
|
2.16
|
2.30
|
2.77
|
3.08
| |
|
30
|
0.48
|
2.26
|
2.40
|
2.89
|
3.22
| |
|
35
|
0.50
|
2.35
|
2.50
|
3.02
|
3.35
| |
|
40
|
0.52
|
2.44
|
2.60
|
3.14
|
3.48
| |
|
45
|
0.54
|
2.54
|
2.70
|
3.26
|
3.26
| |
|
50
|
0.56
|
2.63
|
2.80
|
3.38
|
3.75
| |
|
55
|
0.58
|
2.73
|
2.90
|
3.50
|
3.89
| |
|
60
|
0.60
|
2.82
|
3.00
|
3.62
|
4.02
| |
|
65
|
0.63
|
2.96
|
3.15
|
3.80
|
4.22
| |
|
70
|
0.65
|
3.06
|
3.25
|
3.92
|
4.36
| |
|
75
|
0.67
|
3.15
|
3.35
|
4.04
|
4.49
| |
|
80
|
0.69
|
3.24
|
3.45
|
4.16
|
4.62
| |
|
85
|
0.71
|
3.34
|
3.55
|
4.28
|
4.76
| |
|
90
|
0.73
|
3.43
|
3.65
|
4.40
|
4.89
| |
|
95
|
0.75
|
3.53
|
3.75
|
4.52
|
5.03
| |
|
100
|
0.77
|
3.62
|
3.85
|
4.64
|
5.16
| |
|
Rainfall
|
4.60
|
5.40
|
5.90
|
6.40
| ||
S.
Installation Of Stormwater Runoff Control Measures. Positive
stormwater runoff control shall be provided for during development.
Stormwater management plans shall include a schedule for the installation,
construction or modification of all drainage facilities. Erosion control
measures and a schedule for their installation shall be shown on the
stormwater management plan. Installation of drainage facilities and
erosion control measures shall proceed as scheduled in the approved
stormwater management plan.
T.
Erosion And Sedimentation Control Criteria. The Best Management
Practices to control the occurrence of erosion and sedimentation are
to be incorporated into the plan for the time land is disturbed by
development activity. Permanent controls and practices shall also
be identified where they are necessary to control an ongoing potential
for erosion and sedimentation. Types of Best Management Practices
include, but are not limited:
1.
Use of State approved standard specifications of the City.
2.
Tree, topsoil and vegetative cover preservation and restoration.
3.
Surface stabilization with various natural or manmade materials.
4.
Runoff control measures such as berms, dikes, sediment traps and
barriers.
5.
Inlet and outlet protection.
6.
Streambank protection.
7.
Scheduling of development activities and protection measures for
minimal impact.
[Ord. No. 1437 §I(435.110), 6-21-2004]
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 easement or rights-of-way
shall not be required. The minimum widths of rights-of-way and easements
shall be as follows:
|
Facility
|
Maintenance Access Width
| |
|---|---|---|
|
Open drainage channel or facility
|
30 feet, 15 feet each side
| |
|
Greenways
|
Width of greenway
| |
|
Pipes and culverts
|
15 feet, centered
| |
|
Detention areas
|
15 feet continuous around total area
| |
|
Connecting access
|
15 feet
|
B.
Easements
must include the "top of the bank width" and the maintenance access
width.
C.
The
maintenance access width begins at the point of the bank or slope
of the facility.
D.
Additional
maintenance access width may be required by the Administrative Officer
in special circumstances where more width on one (1) or both sides
is necessary for maintenance purposes.
[Ord. No. 1437 §I(435.120), 6-21-2004]
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 Section, facilitates their inspection and
minimizes future maintenance costs.
C.
Maintenance Responsibility. The growth of noxious weeds,
the creation of conditions that 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.
1.
Detention facilities, when mandatory, are to be 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.
2.
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.
3.
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 or such other maintenance entity or authority
as may be proposed and approved by the Board of Aldermen.
4.
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.
5.
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.
6.
If responsibility for maintenance is to be transferred to the City,
the system 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.
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 (2) year period following completion. Inspection and repair of
defects shall be required as a condition of release of the posted
security.
[Ord. No. 1437 §I(435.130), 6-21-2004]
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 Chapter obtaining stormwater management
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 Section.
[Ord. No. 1437 §I(435.140), 6-21-2004]
A.
Approved Projects. The Administrative Officer or his/her
designated representative shall carry out periodic inspections of
the project site to insure the applicant's compliance with this Section.
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 non-compliance,
with a description of the remedial actions necessary to bring the
project into compliance within a reasonable specified time.
2.
Stop work order. Issue a stop work order directing
the applicant or owner to cease and desist all or any portion of the
work that violates the provisions of this Section, 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/she shall then be subject to immediate revocation
of his/her stormwater management plan approval and to the penalties
described in penalties for violation.
4.
Appeal. Any notice order or revocation issued pursuant to Subsections (A)(1), (A)(2) or (A)(3) above shall become final unless the person named therein requests, in writing, not later than ten (10) days after the date such notice order or revocation is served, a hearing before the Board of Aldermen.
B.
Unapproved Projects. With respect to any development or
development activity determined by the Administrative Officer or his/her
designated representative subject to this Chapter and being carried
out without approval, the Administrative Officer is authorized to:
1.
Written notice. Issue written notice to the owner,
specifying the nature and location of the alleged non-compliance,
with a description of the remedial actions necessary to bring the
project into compliance within a reasonable specified time.
2.
Stop work order. Issue a stop work order directing
the owner to cease and desist all or any portion of the work that
violates the provisions of this Section, if the remedial work identified
in the written notice is not completed within the specified time.
3.
Non-compliance with stop work order. Should the
owner not bring the project into compliance with the written notice
and stop work order, he/she shall then be subject to the penalties
described in penalties for violation.
4.
Appeal. Any notice, order or revocation issued pursuant to Subsections (B)(1), (B)(2) or (B)(3) above shall become final unless the person 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 Board of Aldermen.
[Ord. No. 1437 §I(435.150), 6-21-2004]
A.
General. Violation of the provisions of this Section 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 Section 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 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 responsible.
[Ord. No. 1437 §I(435.160), 6-21-2004]
This Section shall not in any way limit or modify the vested
rights of any person to complete any development or improvement to
lands based upon prior law, where a previous permit or authorization
has been granted or applied for and where such previous permit or
authorization remains in effect. The City may acknowledge vested rights
in other circumstances where it is equitable and just.
[Ord. No. 1437 §I(435.170), 6-21-2004]
In case of conflicts within this Section or any part thereof
and the whole part of any other existing or future ordinance or code
of the City, the most restrictive in each case shall apply.
[Ord. No. 1437 §I(435.180), 6-21-2004]
A.
Before
starting any work regulated by this Section, 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 Section and as may be required by State Statutes and
the regulations of any department of State.
B.
A discharge
permit from the State of Missouri shall be obtained individually or
under the applicable general permit for any activity regulated under
the Department of Natural Resources Clean Water Commission (10 CSR
20) Stormwater.
[Ord. No. 1437 §I(435.190), 6-21-2004]
In the interpretation and application of this Chapter, the provisions
expressed herein shall be held to be the minimum requirements and
shall be liberally construed in favor of the City and shall not be
deemed a limitation or repeal of any other powers granted by State
Statutes.
[Ord. No. 1437 §I(435.200), 6-21-2004]
It is not intended by this Chapter to repeal, abrogate or impair
any existing easements, covenants or deed restriction. However, where
this Section imposes greater restrictions, the provision of this Chapter
shall prevail.
[Ord. No. 1437 §I(435.210), 6-21-2004]
The performance standards and design criteria set forth herein
establish minimum requirements that 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. Larger storms may occur or stormwater
runoff heights may be increased by manmade or natural causes. Enforcement
of these provisions, therefore, shall not create liability on the
part of the municipality with respect to any legislative or administrative
decision lawfully made hereunder, nor shall compliance relieve an
owner, developer and/or committee from responsibility under any circumstances
where liability would otherwise exist.
[Ord. No. 1437 §I(435.220), 6-21-2004]
A.
Any
stormwater management facility for which a permit has been issued
as a part of a subdivision improvement plan must be included with
as-built drawings and certified to have been constructed accordingly.
B.
Any
stormwater management facility for which a permit has been issued
individually or as a part of a site development plan must be certified
to have been constructed in conformance with the approved drawings
prior to issuance of an occupancy permit.
