HomeMy WebLinkAboutORD.3753.11-06-2006BILL NO. 06-227 ORDINANCE NO.
AN ORDINANCE AMENDING CHAPTER 23 OF THE CITY
CODE RELATING TO STORMWATER REGULATIONS
BE IT ORDAINED BY THE COUNCIL OF THE CITY OF CAPE
GIRARDEAU, MISSOURI, AS FOLLOWS:
ARTICLE (1). Section 23-4, of the Code of Ordinances of
the City of Cape Girardeau, Missouri, relating to "Exemptions",
reading as follows:
Sec. 23-4. Exemptions.
(a) Development within a subdivision shall not
require approval of a stormwater management plan
if each of the following conditions have been
met:
(1) Drainage provisions for the project
were previously approved and remain
valid as part of a final plat.
(2) The development is conducted in
substantial accordance with the
stormwater management provisions
contained in the development plan
submitted with the final plat as
approved.
(b) 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; or unless said lot is
five (5) acres or more in size.
I
(c) Stormwater management plans may be waived for
building construction or other development which
will not adversely impact an existing drainage
area or drainage on adjoining properties.
(d) Written notice of intent tc
shall be delivered to the
prior to undertaking any
whether exempt from plan
Application for a building
notice of intent.
D commence development
administrative officer
development activity,
provisions or not.
permit may constitute
is hereby, repealed in its entirety, and a new Section 23-4
relating to "Exemptions", is hereby enacted in lieu, in words
and figures, to read as follows:
Sec. 23-4. Exemptions.
(a) Development within a subdivision shall not
require approval of a stormwater management plan
if each of the following conditions have been
met:
(1) Drainage provisions for the project
were previously approved and remain
valid as part of a final plat.
(2) The development is conducted in
substantial accordance with the
stormwater management provisions
contained in the development plan
submitted with the final plat as
approved.
(b) Development on isolated lots of reeera for
single-family and two-family dwelling purposes
shall not require approval of a separate
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
five (5) acres or more in size. Also, in order
to qualify for exemption the lot must provide the
following prptetion.
2
3
(c) Stormwater management plans may be waived for
building construction or other development which
will not adversely impact an existing drainage
area or drainage on adjoining properties.
(d) Written notice of intent t(
shall be delivered to the
prior to undertaking any
whether exempt from plan
Application for a building
notice of intent.
:) commence development
administrative officer
development activity,
provisions or not.
permit may constitute
ARTICLE (2). Section 23-6 of the Code of Ordinances of the
City of Cape Girardeau, Missouri, relating to "Stormwater
management plan", reading as follows:
Section 23-6. 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. 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 predevelopment
scales are minimums):
4
site information (map
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 two hundred (200) feet with maximum
five-foot contour intervals, except in
floodplains or other areas of low
relief where a smaller interval may be
required.
C. 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
one (1) inch is less than or equal to
two hundred (200) feet.
d. Location of streams and other
floodwater runoff channels, their
normal channels, and the extent of the
floodplains at the established high
water elevations, and the limits of the
floodway mapped at a scale of one (1)
inch is less than or equal to two
hundred (200) feet.
e. Location of lakes, ponds, swamps and
detention basins indicating their
normal shorelines, floodplains and
lines of inflow and outflow mapped at a
scale of one (1) inch is less than or
equal to two hundred (200) 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 two hundred ( 2 0 0 )
feet.
g. Location and description of nearby
existing off-site water management
5
facilities such as wells, lakes,
drainageways, etc., which are
potentially directly affected by the
proposed construction or development,
mapped at a scale of one (1) inch is
less than or equal to two hundred (200)
feet.
(2) For all existing drainage facilities which are to
be maintained, altered, or enlarged as part of
the stormwater management system; provide
information as to their size, slopes, depths,
outfalls, receiving waters, elevations, cross
sections, profiles, construction materials and
other design details as applicable.
(3) Location of all new drainage facilities,
including detention basins, to be constructed.
Provide design details on each facility as
applicable.
(4) Location and extent of existing and proposed
impervious surfaces (roads, parking lots,
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 storm's runoff for
the project site under natural and
undeveloped conditions.
6
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 outflow rates for
those water surface elevations.
e. Acreages and percentage of property
proposed as:
1. Impervious surfaces.
2. Pervious surfaces (green
areas) .
3. Lakes, canals, detention
areas, etc.
4. Total acreage of project.
5. Other.
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
plan 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
7
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.
is hereby r pealed in its entirety, and a new Section 23-6,
relating to "Stormwater management plan", is hereby enacted in
lieu, in words and figures, to read as follows:
Section 23-6. 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. 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 predevelopment 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
8
to two hundred (200) feet with maximum
five-foot contour intervals, except in
floodplains or other areas of low
relief where a smaller interval may be
required.
C. 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
one (1) inch is less than or equal to
two hundred (200) feet.
d. Location of streams and other
floodwater runoff channels, their
normal channels, and the extent of the
floodplains at the established high
water elevations, and the limits of the
floodway mapped at a scale of one (1)
inch is less than or equal to two
hundred (200) feet.
e. Location of lakes, ponds, swamps and
detention basins indicating their
normal shorelines, floodplains and
lines of inflow and outflow mapped at a
scale of one (1) inch is less than or
equal to two hundred (200) 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 two hundred ( 2 0 0 )
feet.
g. Location and description of nearby
existing off-site water management
facilities such as wells, lakes,
drainageways, etc., which are
potentially directly affected by the
proposed construction or development,
mapped at a scale of one (1) inch is
9
less than or equal to two hundred (200)
feet .
(2) For all existing drainage facilities which are to
be maintained, altered, or enlarged as part of
the stormwater management system; provide
information as to their size, slopes, depths,
outfalls, receiving waters, elevations, cross
sections, profiles, construction materials and
other design details as applicable.
(3) Location of all new drainage facilities,
including detention basins, to be constructed.
Provide design details on each facility as
applicable.
(4) Location and extent of existing and proposed
impervious surfaces (roads, parking lots,
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 storm's runoff 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
10
and of the basin outflow rates for
those water surface elevations.
e. Acreages and percentage of property
proposed as:
1. Impervious surfaces.
2. Pervious surfaces (green
areas).
3. Lakes, canals, detention
areas, etc.
4. Total acreage of project.
5. Other.
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.
h. Calculations for all iniets, pipes, and
ditches shall be submitted for review.
(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
plan 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
11
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.
ARTICLE (3). Section 23-8 of the Code of Ordinances of the
City of Cape Girardeau, Missouri, relating to "General design
requirements for stormwater management plans" reading as
follows:
Sec. 23-8. 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 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 flood plains within parks or other public
grounds.
(b) The maximum allowable release rate of stormwater
after development shall not exceed the before -
development rate based on a fifteen -year
frequency storm. The total drainage area must be
used in calculating the allowable release rate.
The required storage volume will be based on the
project area only, with extraneous flows from
upland areas being bypassed or discharged via
overflow spillway or other devices.
12
(c) The increased stormwater runoff resulting from
the proposed development shall be detained on-
site by appropriate detention basins; by storage
on flat roofs, parking lots or streets; or by
other acceptable techniques. The minimum volume
of storage shall be sufficient to store the
volume from a twenty -five-year storm (under
developed conditions). Control devices shall
limit the discharge from storage to a rate no
greater than that prescribed by this chapter.
Downstream property, watercourses, channels or
conduits shall not receive stormwater runoff from
proposed development at a higher peak flow rate
than that which existed prior to the development.
(d) Generally acceptable locations of the stormwater
runoff channels in the design of the project area
may include the following:
(1) In a depressed median of a double
roadway, street or parkway, provided
the median is wide enough to permit
required roadway shoulders.
(2) Centered on the rear lot lines in a
block, or entirely within the rear
yards of a single row of lots or
parcels, provided that in either case
the lots are deep enough to permit side
slopes in the runoff channel and a
building site of the elevation required
by other sections of this chapter.
(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
chapter.
(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
13
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 area so designed for the passage or storage
of waters, no structure may be erected, no
fences, shrubbery or trees planted, or changes
made to the prescribed grades and contours of the
specified floodwater or stormwater runoff
channels.
(f) All storm sewer outfalls shall be so designed, by
reason of elevation of the invert, by a flap gate
or by other features, that when the receiving
stream is in full flood, the storm sewers will
continue to drain the areas they are designed to
serve unless the provision is made for sewer
backups into planned storage locations.
(g) All sanitary sewer manholes constructed in a
floodplain, in a street designed for detention,
or in an area designed for the storage or passage
of floodwater or stormwater, shall be provided
with either a 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 one -hundred -year
flood or the high water elevation of the design
storm, whichever is applicable to the specific
area.
(h) Projects that are to be developed in phases will
normally require the submission of a master plan
of the applicant's contiguous land holdings.
Applications for individual project phases may be
considered only when the phases are totally
independent of, or make sufficient provisions
for, adjacent lands.
14
is herby repealed in its entirety, and a new Section 23-8,
relating to "General design requirements for stormwater
management plans", is hereby enacted in lieu, in words and
figures, to read as follows:
Sec. 23-8. 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 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 flood plains within parks or other public
grounds.
(b) The maximum allowable release rate of stormwater
after development shall not exceed the before -
development rate based. --en a fifteen ear for a.` 2
year and 10 -year frequency storm and the 2`5 -year
storm shall have the release rate of 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; ge
en— flat reefs, parking lets r streets,- or by
other acceptable techniques. The minimum volume
of storage shall be sufficient to store the
volume from a twenty -five-year storm (under
developed conditions). Control devices shall
limit the discharge from storage to a rate no
greater than that prescribed by this chapter.
Downstream property, watercourses, channels or
15
conduits shall not receive stormwater runoff from
proposed development at a higher peak flow rate
than that which existed prior to the development.
(d) Generally acceptable locations of the stormwater
runoff channels in the design of the project area
may include the following:
(1) In a depressed median of a double
roadway, street or parkway, provided
the median is wide enough to permit
required roadway shoulders.
(2) Centered on the rear lot lines in a
block, or entirely within the rear
yards of a single row of lots or
parcels, provided that in either case
the lots are deep enough to permit side
slopes in the runoff channel and a
building site of the elevation required
by other sections of this chapter.
(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
chapter.
(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
16
maintained, but on which no accessory buildings
may be constructed. The utility -drainage easement
shall be at least twenty (20) feet wide. Within
the area so designed for the passage or storage
of waters, no structure may be erected, no
fences, shrubbery or trees planted, or changes
made to the prescribed grades and contours of the
specified floodwater or stormwater runoff
channels.
(f) All storm sewer outfalls shall be so designed, by
reason of elevation of the invert, by a flap gate
or by other features, that when the receiving
stream is in full flood, the storm sewers will
continue to drain the areas they are designed to
serve unless the provision is made for sewer
backups into planned storage locations.
(g) All sanitary sewer manholes constructed in a
floodplain, in a street designed for detention,
or in an area designed for the storage or passage
of floodwater or stormwater, shall be provided
with either a 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 one -hundred -year
flood or the high water elevation of the design
storm, whichever is applicable to the specific
area.
17
18
! r I r);
rc:u vva
resp(
,pment, along
natural I watercourses shall
have
imum thirty
(30)
font geneial maintenance
Irainage easement
from the top of
the
.ng stream
bank.
Development shall
not
.ch on said
thirty
() foot easement.
The
:ourse shall be
maintained and made
the
Permanent vegetat o:
�e appropriate legal entity.
x should be left intact
lude designed stream: bank
zres and shall be approved by
ENA guidelines and shall be
.pplicable regarding site
plains.
�eeded and mulched or sodded
,ermit shall be issued.
ARTICLE (4). Section 23-10 of the Code of Ordinances of
the City of Cape Girardeau, Missouri, relating to "Stormwater
management system design requirements" reading as follows:
Sec. 23-10. 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 (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
equation:
Equation 1
TABLE INSET:
R = (Rd -Ru)
where R = Differential runoff rate
19
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 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
two hundred (200) acres will be
rendered before the method of
evaluation of the detention is
approved.
(4) Other analytical methods of evaluation
of volume of detention will be
considered provided that reliability,
professional acceptance and proper
application are approved by the
administrative officer.
(d) Calculation methods. Any of the following
methods may be used for calculating detention
volume as applicable:
20
(1) Simplified volume formula. Total
volume of detention shall be computed
by the equation:
Equation 2
TABLE INSET:
(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:
TABLE INSET:
Th
V
=
R X A X 30 (min) X 60 (sec/min)
where
V
=
Total volume of detention
Time of peak runoff of developed project
R
=
Differential runoff rate
Qd
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:
TABLE INSET:
Th
Base time of hydrograph for developed project without detention
Th
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)
21
A
Total area of project in acres
Tq
Assumed time of peak differential for unimproved project
Tq
Qu/Qd X 40
Tr
=
Assumed recedence time differential for discharge at rates no greater
than unimproved condition
Tr
=
(30 Qd/Qu) - 60
V
Volume of detention
V
(Qd - Qu) X 30 (min) X 60 (sec/min)
(3) Modified rational hydrograph method.
This is a modification of the "Unit
Hydrograph Method" of hydrologic
evaluation simplified to reflect
features of present practice and some
elements of topographic
characteristics, concentration patterns
and routing. Figure III 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.
22
For analysis of large
improved channels time of
travel for overland flow and
channel are to be analyzed to
determine reasonable (Tc)
time of concentration.
b. Determine time of peaking by
equation:
Equation 3
TABLE INSET:
C. Determine the base time of the Hydrograph
without detention, by equation:
Equation 4
Tb = 2.67 Tp
d. Determine the base time of the Hydrograph
with detention by equation:
Equation 5
TABLE INSET:
Tr
T p
=
D/2 +.6 Tc
where
T p
=
Time of peak discharge of developed project in
minutes
Tb
D
=
20 min = storm duration in minutes
C. Determine the base time of the Hydrograph
without detention, by equation:
Equation 4
Tb = 2.67 Tp
d. Determine the base time of the Hydrograph
with detention by equation:
Equation 5
TABLE INSET:
Tr
Tr
=
(Qd
1)
=
Tb
Qd
_
Total peak runoff of improved project in c.f.s.
(Qu
TABLE INSET:
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.
23
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 = 1/2 (Qd - Qu) Tb
(e) Control structures. Detention facilities shall
be provided with obvious and effective control
structures. Plan view and sections of the
structure with adequate detail shall be included
in plans.
(1) The design discharge (Q) for the low -
flow weir shall not exceed the fifteen -
year (frequency) with a duration equal
to the time of concentration for the
watershed, runoff from the tributary
area for five (5) percent
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.
24
(f) Detention design criteria. Detention in the
overall system, including swales, lakes, canals,
greenways, etc., shall be provided as follows.
(g) General.
(1) Storage volumes. The minimum volume of
storage provided in detention basins,
together with such storage as may be
authorized in other on-site facilities,
shall be sufficient to store the volume
from a twenty -five-year storm (under
developed conditions) with a discharge
no greater than the rate of flow from a
fifteen -year storm (under undeveloped
conditions).
(2) Outlet control structures. Outlet
control structures shall be designed to
operate simply and automatically. They
will limit discharges into existing or
planned downstream channels or conduits
so as not to exceed predetermined
maximum authorized peak flow rates.
(3) Emergency spillway. Emergency overflow
facilities must be provided in all
instances so that stored waters will
not exceed the safe capacity of the
basin. At a minimum, the emergency
spillway must be able to pass without
damage the one -hundred -year storm.
(4) Appearance. Designs should result in
aesthetically pleasing configurations
which will enhance public
acceptability.
(h) Dry -detention facilities.
(1) Perimeter maintenance easements of
fifteen (15) feet (minimum) width at
slopes no steeper than 3:1 (horizontal
to vertical) shall be provided.
25
(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 fifteen (15) feet (minimum
preferable) width at slopes no steeper
than 3:1 (horizontal to vertical) shall
be provided.
(2) Control elevations should be no higher
than two and one-half (2 1/2) feet
below the minimum road centerline
elevation in the area served by the
control device in order to protect the
road subgrade when structures are
constructed near roads.
(3) Side slopes shall not be steeper than
3:1 (horizontal:vertical) out to a
26
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 of an
area of the permanent pool must be a
minimum depth of ten (10) feet.
(5) For emergency purposes, cleaning or
shoreline maintenance, facilities shall
be provided or plans prepared for the
use of auxiliary equipment to permit
emptying and drainage.
(6) The limits of maximum ponding
elevations are to be no closer than
twenty-five (25) feet horizontally from
any building and no less than two (2)
feet below the lowest sill elevation of
any building.
(j) Impervious areas. Paved parking lots may be
designed to provide detention storage of
stormwaters on all or a portion of their
surfaces. Outlets will be designed so as to
slowly empty the stored waters, and depths of
storage must be limited to a maximum depth of
twelve (12) inches so as to prevent damage to
parked vehicles. Ponding should be 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.
(1) 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
27
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
water and groundwater pollution control.
(m) Design alternatives. The above listing of design
criteria is not intended to preclude the use of
other known state -of -the art methods and
available best management practices and should
not be construed as a mechanism to discourage
innovative design concepts.
(n) Developments adjoining a floodplain. Where a
development adjoins or encompasses a portion of a
floodplain for a one -hundred -year flood, the
following shall apply:
(1) The applicant shall show the floodplain
and floodway on the stormwater
management plan.
(2) The applicant shall include in the
stormwater management plan all other
plans, plats, specifications, etc.,
required by federal, state, county
and/or municipal laws or regulations
detailing such provisions or
restrictions as are necessary to comply
with the following:
a. All applicable zoning and
subdivision requirements.
b. All applicable building code
requirements.
C. All requirements of other,
state or local agencies
exercising jurisdiction over
the area.
(o) Channel flow. The applicant shall not alter any
channel in such a way that would prohibit any
section of the channel from conveying, in its
post -development state, the same amount of flow
at the same or lower maximum water elevation,
that it conveyed in its predevelopment state.
28
(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 nontypical
areas.
(3) Hydrographs and/or flood routing
calculations and backwater curve
profiles of the proposed waterway
corresponding to a storm recurrence
interval of one hundred (100) years.
(4) Engineering evaluation of all potential
increases in flood hazards to the
adjacent upstream or downstream private
or public lands and facilities located
thereon, showing provisions for
eliminating any and all adverse impacts
on such land and facilities at no
public cost.
(5) Minimum finished floor elevations which
shall be set at or above the maximum
water surface elevation as determined
by either or both of the following:
a. "Flood Insurance Rate Map"
published by the Federal
Emergency Management Agency.
b. Backwater curve profiles of
the proposed waterway due to
a one -hundred -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.
29
(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 chapter. For
projects less than fifty ( 50 ) acres in area there
is no need for submittal of routing calculations
or tabulated proof of adequacy of tributary
runoff for detention; however, it is recommended
that verification be made of:
(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.
30
TABLE II
Average C.I. (P.I.) Factors In C.F.S. Per Acre
20 Min. Inlet Time
TABLE INSET:
% Impervious
C or P (Factor)
15 Yr.
25 Yr.
50 Yr.
100
Area
Yr.
5
.37
1.7
2.00
2.18
2.37
10
.39
1.79
2.11
2.30
2.50
2.62
15
.41
1.89
2.21
2.42
2.78
20
.435
2.0
2.35
2.57
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
3.33
40
.52
2.39
2.81
3.07
45
.54
2.48
2.92
3.19
3.46
3.58
50
.56
2.58
3.02
3.30
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
31
From U.S. Weather Bureau Technical Paper No. 40:
"Rainfall Frequency Atlas of the United States for
durations from 30 minutes to 24 hours and Return
Periods from 1 to 100 Years."
(s) Installation of stormwater runoff control
measures. Positive stormwater runoff control
shall be provided for during development.
Stormwater management plans shall include a
schedule for the installation, construction or
modification of all drainage facilities. Erosion
control measures and a schedule for their
installation shall be shown on the stormwater
management plan. Installation of drainage
facilities and erosion control measures shall
proceed as scheduled in the approved stormwater
management plan.
(t) 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 to:
32
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 Frequency Atlas of the United States for
durations from 30 minutes to 24 hours and Return
Periods from 1 to 100 Years."
(s) Installation of stormwater runoff control
measures. Positive stormwater runoff control
shall be provided for during development.
Stormwater management plans shall include a
schedule for the installation, construction or
modification of all drainage facilities. Erosion
control measures and a schedule for their
installation shall be shown on the stormwater
management plan. Installation of drainage
facilities and erosion control measures shall
proceed as scheduled in the approved stormwater
management plan.
(t) 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 to:
32
(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
and protection
impact.
development activities
measures for minimal
is here epealed in its entirety, and a new Section 23-10,
relating to "General design requirements for stormwater
management plans", is hereby enacted in lieu, in words and
figures, to read as follows:
Sec. 23-10. Stormwater management system design
requirements.
33
==Mw! ME e 'A n�
34
OEM .. .....
�m
T -b-
Base t me of hydr-ogr-aph for- developed pr-ejeet Mtheut detention
Tb--
60 mincutes—
T -p-
Time of peak ,, „ff of developed pr-sjeet
28 nin-utes—
Totalpeak funeg e f developed pfejea in e.f s.
"Ctf-
TO+nTR1 peak fC uneff of unl' impr-e ed pr-ej eet in e. fl. s-
35
013
A X RU (See Equation
A—
T-etal area of pr-ojeet in aer-es
T -q-
Assumed time of peak diff-erential for- unimpreved prejeet
T -r-
Assumed f-eeedenee time differential for disehar-ge a4 rates no grea4e
than unimproved raondition
V—
Veli ne „f ao+onto„
Eng—ehart with everl-an
t= rave I d3� �c-e, red -lei
he r i z entally te—s-1 e
then vertieally—dam teGe-
36
OWN
-T-P-
37
37
MI=ME furms,
38
prop
engi
sdeg
Tutu
Prot
prow
Alai
from
thin:
Line
Perm
elev
design of the stor water
ccord.ance with the,,City of
L Drainage Design Manual (.f
available, the development;
based on the minimum of one
:)d shall be as identified, in
Transportation Design Manual
d Drainage current edition.
ease 55 (TR -y5)', shall be as
3rban Hydrology for Small Water
39
40
dra
pon<
tel,; a backwater
:nt from the affected
:ty owner(s) shall be
or _ to final. plan.
N reduction in the
requirement may be
e city engineer when
:f-site,downstream
upstream
(e) Detention design criteria. Detention in the
overall system, including swales, lakes, canals,
greenways, etc., shall be provided as follows.
(f) General.
(1) Storage volumes. The minimum volume of
storage provided in detention basins,
together with such storage as may be
authorized in other on-site facilities,
shall be sufficient to store the volume
from a twenty -five-year storm (under
developed conditions) with a disc Barg
negreater than -the rate
ef f lewTfre�
a
fifteen tesa,---(under _ R e. e i e e a
eenditiens) .
(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) Release Rate. A release rate shall be
calculated for a two (2), ten (10)
twenty-five (25) year storm for the
proposed development in the condition
prion to the proposed development.
sten-m water- release races als net
41
(4) Emergency spillway. Emergency overflow
facilities must be provided in all
instances so that stored waters will
not exceed the safe capacity of the
basin. At a minimum, the emergency
spillway must be able to pass without
damage the one -hundred -year storm.
(,5`) Appearance. Designs should result in
aesthetically pleasing configurations
which will enhance public
acceptability.
(g) 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) 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.
42
(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.
(h)'' Wet -detention facilities.
(1) Perimeter maintenance and operation
easements of fifteen (15) feet (minimum
preferable) width at slopes no steeper
than 3:1 (horizontal to vertical) shall
be provided.
(2) Control elevations should be no higher
than two and one-half (2 1/2) feet
below the minimum road centerline
elevation in the area served by the
control device in order to protect the
road subgrade when structures are
constructed near roads.
(3) Side slopes shall not be steeper than
3:1 (horizontal: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 of an
area of the permanent pool must be a
minimum depth of ten (10) feet.
(5) For emergency purposes, cleaning or
shoreline maintenance, facilities shall
be provided or plans prepared for the
use of auxiliary equipment to permit
emptying and drainage.
(6) The limits of maximum ponding
elevations are to be no closer than
twenty five (25T thirty (30) feet
horizontally from any building and no
43
less than two (2) feet below the lowest
sill elevation of any building.
( )- 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 of storage, details of inlet and
outlet devices and locations, emergency overflow
provisions, and measures to be used for surface
water and groundwater pollution control.
(j)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.
(k):` Developments adjoining a floodplain. Where a
development adjoins or encompasses a portion of a
floodplain for a one -hundred -year flood, the
following shall apply:
44
(1) The applicant shall show the floodplain
and floodway on the stormwater
management plan.
(2) The applicant shall include in the
stormwater management plan all other
plans, plats, specifications, etc.,
required by federal, state, county
and/or municipal laws or regulations
detailing such provisions or
restrictions as are necessary to comply
with the following:
a. All applicable zoning and
subdivision requirements.
b. All applicable building code
requirements.
C. All requirements of other
federal, state or local
agencies exercising juris-
diction over the area.
O Channel flow. The applicant shall not alter any
channel in such a way that would prohibit any
section of the channel from conveying, in its
post -development state, the same amount of flow
at the same or lower maximum water elevation,
that it conveyed in its predevelopment state.
(m) 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 nontypical
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.
45
(4) Engineering evaluation of all potential
increases in flood hazards to the
adjacent upstream or downstream private
or public lands and facilities located
thereon, showing provisions for
eliminating any and all adverse impacts
on such land and facilities at no
public cost.
(5) Minimum finished floor elevations which
shall be set at or above the maximum
water surface elevation as determined
by either or both of the following:
a. "Flood Insurance Rate Map"
published by the Federal
Emergency Management Agency.
b. Backwater curve profiles of
the proposed waterway due to
a one -hundred -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.
(n) 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.
('c)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 chapter. For
46
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.
imper-views
1 c�
25 Yn-
50 ynArea
99
--A--
9--
'9
2i
2.30
2-.50-
4-5--
:4-
1.89--
2 -
2.42
2-.62-
-
120--
•435
2,0-
1 X35--
1-557-
$-
47
48
2L.94-
-
•455-
2.09
2.46
2.68
3-.04--
3-0-
.47-5
2.10 r0
2..57
2.80
3-.1-7-
35-
:495-
22-
2.68
2.92
_
40-
32-
2.39--
2.81-
34
3-.46-
45-
34--
2.48
2.92
3.19
�-
58-
.56-
2.58-
3.92-
3.30
3-.74-
55-
-.59-
268-
3.13-
3.42
3,84-
60-
-.68-
2.76
33.24 --
3.54
4 A8
6-5--
:625-
2.88
3.38-
369
44-3-
79--
:645--
2.97-
3.48-
33.81
4,26-
-75-
:665--
33.96-
3-59-
3.92
4-.38-
84-
:-585--
345-
33.8-
4.04-
8-5-
.705-
3.24
3.81-
4.16
4 Fri
99--
-.73-
3Z�
3-94-
4.31-
95-
-.75-
33..45--
405-
4.43
i 0o -
.7-7-
3.54-
4.16
4.54-
4 -.9 -3 -
Rainfall
-
4-60
5:48-
5.90
6-.40-
48
(p)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.
(q)>, 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 to:
(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.
49
(7) Scheduling of
and protection
impact.
development activities
measures for minimal
ARTICLE (5). Section 23-11(a) of the Code of Ordinances of
the City of Cape Girardeau, Missouri, relating to "Rights-of-way
and easements" reading as follows:
Section 23-11. 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:
TABLE INSET:
50
Maintenance
Facility
Access Width
Open
drainage
30 feet, 15 feet
channel or
each side
facility
Greenways
Width of greenway
Pipes and
15 feet, centered
culverts
Detention
15 feet continuous
around total area
areas
Connecting
15 feet
access
50
i .rby,repelel in its entirety, and a new Section 23-11(a)
relating to "Rights-of-way and easements", is hereby enacted in
lieu, in words and figures, to read as follows:
Section 23-11. 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:
TABLE INSET:
51
Maintenance
Facility
Access
Width
Open
drainage
30 feet,
5feet
channel or
eaeh side
from trap
facility
of bank
Greenways
Width of
greenway
Pipes and
15 feet,
centered
culverts
15 feet
continuous
Detention
around total
area
areas
Connecting
15 feet
access
51
ARTICLE (6). Section 23-12 of the Code of Ordinances of
the City of Cape Girardeau, Missouri, relating to "Maintenance
responsibilities for stormwater management facilities" reading
as follows:
Sec. 23-12. 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 chapter, 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.
(1) 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
52
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 city
council.
(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
53
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-year period following completion. Inspection
and repair of defects shall be required as a
condition of release of the posted security.
is hereby ':rep a od in its entirety, and a new Section 23-12
relating to "Maintenance responsibilities for stormwater
management facilities", is hereby enacted in lieu, in words and
figures, to read as follows:
Sec. 23-12. 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.
54
(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 chapter, 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.
(1) 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.
(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.
55
(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 city
council.
(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.
56
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-year period following completion. Inspection
and repair of defects shall be required as a
condition of release of the posted security.
ARTICLE (7). There is hereby enacted a new Section 23-13
of the Code of Ordinances of the City of Cape Girardeau,
Missouri, entitled "Illicit discharges" reading as follows:
Section 23-13. Illicit discharges.
(a) Prohibition of Illicit Discharges.
(1) Pursuant to the National Pollutant
Discharge Elimination System (NPDES)
Municipal Separate Storm Sewer System
(MS4) program illicit discharges to the
MS4 are being defined as illegal. This
is accomplished by identifying
allowable non-stormwater discharges
into the MS4 in the best interest of
the City of Cape Girardeau, Missouri.
(2) Non-stormwater discharge means any
discharge to the Municipal Separate
Storm Sewer System.
(3) Except as hereinafter provided, all
non-stormwater discharges into the
Municipal Separate Storm Sewer System
are prohibited and declared to be
unlawful.
(b) Allowable storm discharges.
(1) Unless the city of Cape Girardeau,
MoDNR, EPA or other regulatory agency
has identified them as a source of
57
pollutants to the "Waters of the State
of Missouri", the following non-
stormwater discharges into the
Municipal Separate Storm Sewer System
are lawful:
a. Water line flushing or other
potable water sources.
b. Landscape irrigation or lawn
watering with potable water.
C. Diverted stream flows.
d. Rising ground water.
e. Groundwater infiltration to storm
drains.
f. Pumped groundwater.
g. Foundation or footing drains.
h. Crawl space pumps.
i. Air conditioning condensation.
j. Springs.
k. Non commercial washing of
vehicles.
1. Natural riparian habitat or wet-
land flows.
M. Swimming pools (if dechlorinated).
n. Fire fighting activities.
o. Discharges specified in writing
by the City of Cape Girardeau as
being necessary to protect public
health and safety.
ARTICLE (8). If any section, subsection, sentence, clause,
phrase or portion of this Ordinance is for any reason held
invalid or unconstitutional by any court of competent
jurisdiction, such portion shall be deemed a separate, distinct
and independent provision and such holding shall not affect the
validity of the remaining portions hereof.
ARTICLE (9). 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.
ARTICLE (10). This Ordinance shall be in full force and
effect from and after its passage and approval.
58
PASSED AND APPROVED this day of
Gayle L. C
d, City Clerk
Jay Knudtson, Mayor
59
I
BILL NO. 06-227 ORDINANCE NO. ,3_763
AN ORDINANCE AMENDING CHAPTER 23 OF THE CITY
CODE RELATING TO STORMWATER REGULATIONS
BE IT ORDAINED BY THE COUNCIL OF THE CITY OF CAPE
GIRARDEAU, MISSOURI, AS FOLLOWS:
ARTICLE (1). Section 23-4, of the Code of Ordinances of
the City of Cape Girardeau, Missouri, relating to "Exemptions",
reading as follows:
Sec. 23-4. Exemptions.
(a) Development within a subdivision shall not
require approval of a stormwater management plan
if each of the following conditions have been
met:
(1) Drainage provisions for the project
were previously approved and remain
valid as part of a final plat.
(2) The development is conducted in
substantial accordance with the
stormwater management provisions
contained in the development plan
submitted with the final plat as
approved.
(b) 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; or unless said lot is
five (5) acres or more in size.
(c) Stormwater management plans may be waived for
building construction or other development which
will not adversely impact an existing drainage
area or drainage on adjoining properties.
(d) Written notice of intent t4
shall be delivered to the
prior to undertaking any
whether exempt from plan
Application for a building
notice of intent.
:> commence development
administrative officer
development activity,
provisions or not.
permit may constitute
is hereby repealed in its entirety, and a new Section 23-4
relating to "Exemptions", is hereby enacted in lieu, in words
and figures, to read as follows:
Sec. 23-4. Exemptions.
(a) Development within a subdivision shall not
require approval of a stormwater management plan
if each of the following conditions have been
met:
(1) Drainage provisions for the project
were previously approved and remain
valid as part of a final plat.
(2) The development is conducted in
substantial accordance with the
stormwater management provisions
contained in the development plan
submitted with the final plat as
approved.
(b) Development on isolated lots for single-family
and two-family dwelling purposes shall not
require approval of a separate 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
five (5) acres or more in size. Also, in order
to qualify for exemption the lot must provide the
following protection:
2
I
(1) Waste and Material Disposal. All waste
and unused building materials
(including garbage, debris, cleaning
wastes, wastewater, toxic materials, or
hazardous materials) shall be properly
disposed of and not allowed to go
offsite or in storm sewers.
(2) Tracking. Each site shall have
graveled roads, access drives and
parking areas of sufficient width and
length to prevent sediment from being
tracked onto public or private
roadways. Any sediment reaching a
public or private road shall be removed
by street cleaning (not flushing) by
those responsible before the end of
each workday.
(3) All excavations, grading, or filling
shall have a finished grade not to
exceed 3:1.
(4) Sediment shall be controlled and
contained onsite.
(5) For vacant land held for development,
grass and other vegetative ground cover
is required.
(6) All erosion control measures must be
installed before land disturbing
activity can take place and shall be
installed according to the city
engineer's standard details.
(7) Disturbed areas which are at a finished
grade with installed utilities shall be
permanently seeded and mulched or
sodded within seven (7) days.
(8) Single-family lots that remain inactive
for thirty (30) days or more shall be
established with temporary vegetation.
This requirement may be waived if the
3
landowner has sold the lot and
construction activity is scheduled to
begin within thirty (30) days of being
sold.
(9) Slopes over 5 to 1 which are disturbed
and are at final grade with installed
utilities shall be covered immediately
with seeding, mulch, or other covering
appropriate for the season.
(c) Stormwater management plans may be waived for
building construction or other development which
will not adversely impact an existing drainage
area or drainage on adjoining properties.
(d) Written notice of intent ti
shall be delivered to the
prior to undertaking any
whether exempt from plan
Application for a building
notice of intent.
:) commence development
administrative officer
development activity,
provisions or not.
permit may constitute
ARTICLE (2). Section 23-6 of the Code of Ordinances of the
City of Cape Girardeau, Missouri, relating to "Stormwater
management plan", reading as follows:
Section 23-6. 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. 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 predevelopment
scales are minimums):
4
site information (map
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 two hundred (200) feet with maximum
five-foot contour intervals, except in
floodplains or other areas of low
relief where a smaller interval may be
required.
C. 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
one (1) inch is less than or equal to
two hundred (200) feet.
d. Location of streams and other
floodwater runoff channels, their
normal channels, and the extent of the
floodplains at the established high
water elevations, and the limits of the
floodway mapped at a scale of one (1)
inch is less than or equal to two
hundred (200) feet.
e. Location of lakes, ponds, swamps and
detention basins indicating their
normal shorelines, floodplains and
lines of inflow and outflow mapped at a
scale of one (1) inch is less than or
equal to two hundred (200) 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 two hundred (200)
feet.
g. Location and description of nearby
existing off-site water management
5
facilities such as wells, lakes,
drainageways, etc., which are
potentially directly affected by the
proposed construction or development,
mapped at a scale of one (1) inch is
less than or equal to two hundred (200)
feet.
(2) For all existing drainage facilities which are to
be maintained, altered, or enlarged as part of
the stormwater management system; provide
information as to their size, slopes, depths,
outfalls, receiving waters, elevations, cross
sections, profiles, construction materials and
other design details as applicable.
(3) Location of all new drainage facilities,
including detention basins, to be constructed.
Provide design details on each facility as
applicable.
(4) Location and extent of existing and proposed
impervious surfaces (roads, parking lots,
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 storm's runoff for
the project site under natural and
undeveloped conditions.
6
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 outflow rates for
those water surface elevations.
e. Acreages and percentage of property
proposed as:
1. Impervious surfaces.
2. Pervious surfaces (green
areas) .
3. Lakes, canals, detention
areas, etc.
4. Total acreage of project.
S. Other.
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
plan 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
7
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.
is 'hereby repealed in its entirety, and a new Section 23-6,
relating to "Stormwater management plan", is hereby enacted in
lieu, in words and figures, to read as follows:
Section 23-6. 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. 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 predevelopment 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
8
to two hundred (200) feet with maximum
five-foot contour intervals, except in
floodplains or other areas of low
relief where a smaller interval may be
required.
C. 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
one (1) inch is less than or equal to
two hundred (200) feet.
d. Location of streams and other
floodwater runoff channels, their
normal channels, and the extent of the
floodplains at the established high
water elevations, and the limits of the
floodway mapped at a scale of one (1)
inch is less than or equal to two
hundred (200) feet.
e. Location of lakes, ponds, swamps and
detention basins indicating their
normal shorelines, floodplains and
lines of inflow and outflow mapped at a
scale of one (1) inch is less than or
equal to two hundred (200) 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 two hundred (200)
feet.
g. Location and description of nearby
existing off-site water management
facilities such as wells, lakes,
drainageways, etc., which are
potentially directly affected by the
proposed construction or development,
mapped at a scale of one (1) inch is
E
less than or equal to two hundred (200)
feet .
(2) For all existing drainage facilities which are to
be maintained, altered, or enlarged as part of
the stormwater management system; provide
information as to their size, slopes, depths,
outfalls, receiving waters, elevations, cross
sections, profiles, construction materials and
other design details as applicable.
(3) Location of all new drainage facilities,
including detention basins, to be constructed.
Provide design details on each facility as
applicable.
(4) Location and extent of existing and proposed
impervious surfaces (roads, parking lots,
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 storm's runoff 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
10
and of the basin outflow rates for
those water surface elevations.
e. Acreages and percentage of property
proposed as:
1. Impervious surfaces.
2. Pervious surfaces (green
areas).
3. Lakes, canals, detention
areas, etc.
4. Total acreage of project.
5. Other.
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.
h. Calculations for all inlets, pipes, and
ditches shall be submitted for review.
(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
plan 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
11
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.
ARTICLE (3). Section 23-8 of the Code of Ordinances of the
City of Cape Girardeau, Missouri, relating to "General design
requirements for stormwater management plans" reading as
follows:
Sec. 23-8. 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 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 flood plains within parks or other public
grounds.
(b) The maximum allowable release rate of stormwater
after development shall not exceed the before -
development rate based on a fifteen -year
frequency storm. The total drainage area must be
used in calculating the allowable release rate.
The required storage volume will be based on the
project area only, with extraneous flows from
upland areas being bypassed or discharged via
overflow spillway or other devices.
12
(c) The increased stormwater runoff resulting from
the proposed development shall be detained on-
site by appropriate detention basins; by storage
on flat roofs, parking lots or streets; or by
other acceptable techniques. The minimum volume
of storage shall be sufficient to store the
volume from a twenty -five-year storm (under
developed conditions). Control devices shall
limit the discharge from storage to a rate no
greater than that prescribed by this chapter.
Downstream property, watercourses, channels or
conduits shall not receive stormwater runoff from
proposed development at a higher peak flow rate
than that which existed prior to the development.
(d) Generally acceptable locations of the stormwater
runoff channels in the design of the project area
may include the following:
(1) In a depressed median of a double
roadway, street or parkway, provided
the median is wide enough to permit
required roadway shoulders.
(2) Centered on the rear lot lines in a
block, or entirely within the rear
yards of a single row of lots or
parcels, provided that in either case
the lots are deep enough to permit side
slopes in the runoff channel and a
building site of the elevation required
by other sections of this chapter.
(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
chapter.
(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
13
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 b
rear lot lines as shown
management plan within whicl
open drainage facilities m
maintained, but on which no
may be constructed. The utili
shall be at least twenty (2C
the area so designed for the
of waters, no structure m
fences, shrubbery or trees
made to the prescribed grades
specified floodwater or
channels.
provided abutting
in the stormwater
utility lines and
y be located and
accessory buildings
:y -drainage easement
feet wide. Within
passage or storage
y be erected, no
)lanted, or changes
and contours of the
stormwater runoff
(f) All storm sewer outfalls shall be so designed, by
reason of elevation of the invert, by a flap gate
or by other features, that when the receiving
stream is in full flood, the storm sewers will
continue to drain the areas they are designed to
serve unless the provision is made for sewer
backups into planned storage locations.
(g) All sanitary sewer manholes constructed in a
floodplain, in a street designed for detention,
or in an area designed for the storage or passage
of floodwater or stormwater, shall be provided
with either a 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 one -hundred -year
flood or the high water elevation of the design
storm, whichever is applicable to the specific
area.
(h) Projects that are to be developed in phases will
normally require the submission of a master plan
of the applicant's contiguous land holdings.
Applications for individual project phases may be
considered only when the phases are totally
independent of, or make sufficient provisions
for, adjacent lands.
14
is'hereby repealed in its entirety, and a new Section 23-8,
relating to "General design requirements for stormwater
management plans", is hereby enacted in lieu, in words and
figures, to read as follows:
Sec. 23-8. 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 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 flood plains within parks or other public
grounds.
(b) The maximum allowable release rate of stormwater
after development shall not exceed the before -
development rate for a 2 -year and 10 -year
frequency storm and the 25 -year storm shall have
the release rate of 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; or by other
acceptable techniques. The minimum volume of
storage shall be sufficient to store the volume
from a twenty -five-year storm (under developed
conditions). Control devices shall limit the
discharge from storage to a rate no greater than
that prescribed by this chapter. Downstream
property, watercourses, channels or conduits
shall not receive stormwater runoff from proposed
15
development at a higher peak flow rate than that
which existed prior to the development.
(d) Generally acceptable locations of the stormwater
runoff channels in the design of the project area
may include the following:
(1) In a depressed median of a double
roadway, street or parkway, provided
the median is wide enough to permit
required roadway shoulders.
(2) Centered on the rear lot lines in a
block, or entirely within the rear
yards of a single row of lots or
parcels, provided that in either case
the lots are deep enough to permit side
slopes in the runoff channel and a
building site of the elevation required
by other sections of this chapter.
(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
chapter.
(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
16
may be constructed. The utility -drainage easement
shall be at least twenty (20) feet wide. Within
the area so designed for the passage or storage
of waters, no structure may be erected, no
fences, shrubbery or trees planted, or changes
made to the prescribed grades and contours of the
specified floodwater or stormwater runoff
channels.
(f) All storm sewer outfalls shall be so designed, by
reason of elevation of the invert, by a flap gate
or by other features, that when the receiving
stream is in full flood, the storm sewers will
continue to drain the areas they are designed to
serve unless the provision is made for sewer
backups into planned storage locations.
(g) All sanitary sewer manholes constructed in a
floodplain, in a street designed for detention,
or in an area designed for the storage or passage
of floodwater or stormwater, shall be provided
with either a 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 one -hundred -year
flood or the high water elevation of the design
storm, whichever is applicable to the specific
area.
(h) Projects that are to be developed in phases will
normally require the submission of a master plan
of the applicant's contiguous land holdings.
Applications for individual project phases may be
considered only when the phases are totally
independent of, or make sufficient provisions
for, adjacent lands.
(i) All excavations, grading or filling shall have a
finished grade not to exceed a 3:1 (three (3)
horizontal to one (1) vertical) slope. Steeper
grades may be approved by the city engineer if
the excavation is through rock or the excavation
or fill is protected (a designed head wall or toe
wall may be required). Retaining walls that
exceed a height of four (4) feet shall require
the construction of safety guards as identified
in the 2003 International Building Code or
17
subsequent amendments thereto. Permanent safety
guards will be constructed in accordance with the
2003 International Building code.
(j) Grading plans for sites that exceed one (1) acre
shall provide for sediment or debris basins, silt
traps or filters, staked straw bales, a
combination of these measures or other measures
approved by the city engineer to remove sediment
from runoff waters. The design to be approved by
the public works director. Temporary siltation
control measures (structural) shall be maintained
until vegetative cover is established at a
sufficient density to provide erosion control on
the site.
(k) Where natural vegetation is removed during
grading, vegetation shall be re-established in
such a density as to prevent erosion. Permanent
type grasses shall be established as soon as
possible during the next seeding period after
grading has been completed.
(1) When grading operations are completed or
suspended for more than thirty (30) days between
permanent grass seeding periods, temporary cover
shall be provided. All finished grades (areas
not to be disturbed by future improvements)
between 3:1 and 5:1 shall be sodded, hydro
seeded, or have erosion control fabric installed
less than (5:1) slopes (five (5) horizontal to
one (1) vertical) shall be mulched at the rate of
one hundred (100) pounds per one thousand (1,000)
square feet when seeded.
(m) Ground adjoining development sites (lots) shall
be provided with protection from accelerated and
increased surface water, silt from erosion, and
any other consequences of erosion. Runoff water
from developed areas (parking lots, paved sites,
and buildings) above the area to be developed
shall be directed to diversions, detention
basins, concrete gutters, and/or underground
outlet systems. Sufficiently anchored straw
bales may be substituted with the approval of the
city engineer.
18
P_
(n) Development along natural watercourses shall have
a minimum thirty (30) foot general maintenance
and drainage easement from the top of the
existing stream bank. Development shall not
encroach on said thirty (30) foot easement. The
watercourse shall be maintained and made the
responsibility of the appropriate legal entity.
Permanent vegetation should be left intact.
Variances will include designed stream bank
erosion control measures and shall be approved by
the city engineer FEMA guidelines and shall be
followed where applicable regarding site
development in flood plains.
(o) All lots shall be seeded and mulched or sodded
before an occupancy permit shall be issued.
ARTICLE (4). Section 23-10 of the Code of Ordinances of
the City of Cape Girardeau, Missouri, relating to "Stormwater
management system design requirements" reading as follows:
Sec. 23-10. 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 (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
equation:
Equation 1
TABLE INSET:
19
R
=
(Rd -Ru)
where
R
=
Differential runoff rate
Rd
=
C.I. factor for developed conditions
19
Ru I = I 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 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
two hundred (200) acres will be
rendered before the method of
evaluation of the detention is
approved.
(4) Other analytical methods of evaluation
of volume of detention will be
considered provided that reliability,
professional acceptance and proper
application are approved by the
administrative officer.
(d) Calculation methods. Any of the following
methods may be used for calculating detention
volume as applicable:
(1) Simplified volume formula. Total
volume of detention shall be computed
by the equation:
20
Equation 2
TABLE INSET:
(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:
TABLE INSET:
Tb
V
=
R X A X 30 (min) X 60 (sec/min)
where
V
=
Total volume of detention
Time of peak runoff of developed project
R
=
Differential runoff rate
Qd
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:
TABLE INSET:
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
21
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
22
determine reasonable (Tc)
time of concentration.
b. Determine time of peaking by
equation:
Equation 3
TABLE INSET:
C. Determine the base time of the Hydrograph
without detention, by equation:
Equation 4
Tb = 2.67 Tp
d. Determine the base time of the Hydrograph
with detention by equation:
Equation 5
TABLE INSET:
Tr
T p
=
D/2 +.6 Tc
where
1)
Time of peak discharge of developed project in
Tb
T p
=
minutes
Equation 6
D
=
20 min = storm duration in minutes
C. Determine the base time of the Hydrograph
without detention, by equation:
Equation 4
Tb = 2.67 Tp
d. Determine the base time of the Hydrograph
with detention by equation:
Equation 5
TABLE INSET:
Tr
Tr
=
(Qd
1)
=
Tb
Qd
_
Total peak runoff of improved project in c.f.s.
Equation 6
(Qu
=
A X Rd (See Equation 1)
TABLE INSET:
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.
Equation 6
Qd
=
A X Rd (See Equation 1)
Qu
=
Total runoff of unimproved project in c.f.s.
23
Equation 7
Qu = I A X Ru (See Equation 1)
e. Determine the required volume of detention
by equation:
Equation 8
V = 1/2 (Qd - Qu) Tb
(e) Control structures. Detention facilities shall
be provided with obvious and effective control
structures. Plan view and sections of the
structure with adequate detail shall be included
in plans.
(1) The design discharge (Q) for the low -
flow weir shall not exceed the fifteen -
year (frequency) with a duration equal
to the time of concentration for the
watershed, runoff from the tributary
area for five (5) percent
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.
24
(1) Storage volumes. The minimum volume of
storage provided in detention basins,
together with such storage as may be
authorized in other on-site facilities,
shall be sufficient to store the volume
from a twenty -five-year storm (under
developed conditions) with a discharge
no greater than the rate of flow from a
fifteen -year storm (under undeveloped
conditions) .
(2) Outlet control structures. Outlet
control structures shall be designed to
operate simply and automatically. They
will limit discharges into existing or
planned downstream channels or conduits
so as not to exceed predetermined
maximum authorized peak flow rates.
(3) Emergency spillway. Emergency overflow
facilities must be provided in all
instances so that stored waters will
not exceed the safe capacity of the
basin. At a minimum, the emergency
spillway must be able to pass without
damage the one -hundred -year storm.
(4) Appearance. Designs should result in
aesthetically pleasing configurations
which will enhance public
acceptability.
(h) Dry -detention facilities.
(1) Perimeter maintenance easements of
fifteen (15) feet (minimum) width at
slopes no steeper than 3:1 (horizontal
to vertical) shall be provided.
(2) Side slopes of the facility shall not
be steeper than 3:1 (horizontal to
vertical).
(3) Provisions must be incorporated to
facilitate complete interior drainage
to dry bottom basins, to include the
25
8
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 fifteen (15) feet (minimum
preferable) width at slopes no steeper
than 3:1 (horizontal to vertical) shall
be provided.
(2) Control elevations should be no higher
than two and one-half (2 1/2) feet
below the minimum road centerline
elevation in the area served by the
control device in order to protect the
road subgrade when structures are
constructed near roads.
(3) Side slopes shall not be steeper than
3:1 (horizontal: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 of an
26
area of the permanent pool must be a
minimum depth of ten (10) feet.
(5) For emergency purposes, cleaning or
shoreline maintenance, facilities shall
be provided or plans prepared for the
use of auxiliary equipment to permit
emptying and drainage.
(6) The limits of maximum ponding
elevations are to be no closer than
twenty-five (25) feet horizontally from
any building and no less than two (2)
feet below the lowest sill elevation of
any building.
(j) Impervious areas. Paved parking lots may be
designed to provide detention storage of
stormwaters on all or a portion of their
surfaces. Outlets will be designed so as to
slowly empty the stored waters, and depths of
storage must be limited to a maximum depth of
twelve (12) inches so as to prevent damage to
parked vehicles. Ponding should be 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.
(1) 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 of storage, details of inlet and
outlet devices and locations, emergency overflow
provisions, and measures to be used for surface
water and groundwater pollution control.
27
(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 one -hundred -year flood, the
following shall apply:
(1) The applicant shall show the floodplain
and floodway on the stormwater
management plan.
(2) The applicant shall include in the
stormwater management plan all other
plans, plats, specifications, etc.,
required by federal, state, county
and/or municipal laws or regulations
detailing such provisions or
restrictions as are necessary to comply
with the following:
a. All applicable zoning and
subdivision requirements.
b. All applicable building code
requirements.
C. All requirements of other,
state or local agencies
exercising jurisdiction over
the area.
(o) Channel flow. Z
channel in such
section of the
post -development
at the same or
that it conveyed
ie applicant shall not alter any
a way that would prohibit any
channel from conveying, in its
state, the same amount of flow
lower maximum water elevation,
in its predevelopment 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:
28
t
(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 nontypical
areas.
(3) Hydrographs and/or flood routing
calculations and backwater curve
profiles of the proposed waterway
corresponding to a storm recurrence
interval of one hundred (100) years.
(4) Engineering evaluation of all potential
increases in flood hazards to the
adjacent upstream or downstream private
or public lands and facilities located
thereon, showing provisions for
eliminating any and all adverse impacts
on such land and facilities at no
public cost.
(5) Minimum finished floor elevations which
shall be set at or above the maximum
water surface elevation as determined
by either or both of the following:
a. "Flood Insurance Rate Map"
published by the Federal
Emergency Management Agency.
b. Backwater curve profiles of
the proposed waterway due to
a one -hundred -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) 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
29
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 chapter. For
projects less than fifty ( 5 0 ) 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. 1. (P. 1.) Factors In C.F.S. Per Acre
20 Min. Inlet Time
TABLE INSET:
Impervious C or P (Factor) 15 Yr. 25 Yr. 50 Yr. 100
30
Area
Yr.
2.37
5
.37
1.7
2.00
2.18
10
.39
1.79
2.11
2.30
2.50
2.62
15
.41
1.89
2.21
2.42
20
.435
2.0
2.35
2.57
2.78
25
.455
2.09
2.46
2.68
2.91
3.04
30
.475
2.10
2.57
2.80
3.17
35
.495
2.28
2.68
2.92
3.33
40
.52
2.39
2.81
3.07
3.46
45
.54
2.48
2.92
3.19
3.58
50
.56
2.58
3.02
3.30
3.71
55
.58
2.68
3.13
3.42
3.84
60
.60
2.76
3.24
3.54
4.00
65
.625
2.88
3.38
3.69
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
31
t
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 Frequency Atlas of the United States for
durations from 30 minutes to 24 hours and Return
Periods from 1 to 100 Years."
(s) Installation of stormwater runoff control
measures. Positive stormwater runoff control
shall be provided for during development.
Stormwater management plans shall include a
schedule for the installation, construction or
modification of all drainage facilities. Erosion
control measures and a schedule for their
installation shall be shown on the stormwater
management plan. Installation of drainage
facilities and erosion control measures shall
proceed as scheduled in the approved stormwater
management plan.
(t) 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 to:
(1) Use of state approved standard
specifications of the city.
(2) Tree, topsoil and vegetative cover
preservation and restoration.
32
(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.
. hereby repeaied in its entirety, and a new Section 23-10,
relating to "General design requirements for stormwater
management plans", is hereby enacted in lieu, in words and
figures, to read as follows:
Sec. 23-10. Stormwater management system design
requirements.
(a) Calculations. The design of the stormwater
system shall be in accordance with the City of
Cape Girardeau's Storm Drainage Design Manual (if
available). If not available, the development
calculations shall be based on the minimum of one
(1) fifteen (15) minute rainfall using the
following:
Watershed Area
Method
(acres)
0-25
Rational (See Note
1)
> 25
Technical Release 55
(TR -55) (see Note 2)
Note l: Rational method shall be as identified in
Missouri Department of Transportation Design Manual
Chapter IX -Hydraulics and Drainage current edition.
33
I
Note 2: Technical release 55 (TR -55) shall be as
identified in the NRCS Urban Hydrology for Small Water
Sheds.
(b) Open channels.
(1) Open channels, natural or improved, may
be placed at the rear or side of
properties upon approval of the city
engineer where the design provides
adequate protection to the existing and
future property and structures. Such
protection shall be through the
provision of a fifty (50) year flood
plain setback and a minimum distance
from the to of bank to the setback of
thirty (30) feet. This drainage setback
line shall be shown on the final plat.
Permanent vegetation, existing ground
elevation, and grades within the thirty
(30) foot setback area shall be left
intact and undisturbed on channels with
watersheds of one hundred (100) acres
or more unless modification is approved
in writing by the director or his
designee.
(2) Area inlets shall be required behind
the curbs to intercept overland flows
greater than one (1) cfs to prevent
flows from crossing sidewalks and/or
curbs.
(c) Inlets, junctions boxes and inlet spacing shall
be per the city's standard details and as
approved by the city engineer. When locating
inlets in sump locations consideration must be
made with respect to the major drainage system.
A one hundred (100) year design event shall not
cause buildings to flood in the event that a
single inlet becomes blocked. In new
developments the one hundred (100) year design
storm elevation shall be mapped on the final plat
as a building set back. Overland relief to
another inlet or surface channel shall be
provided to protect property.
34
(d) Enclosed Systems.
(1) The outlet of an enclosed system
shall have sufficient energy
dissipation provided to negate the
increases posed by development as
approved by the city engineer.
(2) Building gutter drainage systems
may not be discharged directly
into the city's enclosed system.
(3) If development plans call for the
enclosure of an existing, natural
drainage way which carries greater
than fifty (50) cfs during the
design storm event, the enclosure
shall be sized for a fifty (50)
year twenty (20) minute storm
event. Upstream inundation shall
be checked. Where inundation
extends beyond the site property
line and exceeds the design water
surface elevation of the natural
drainway/channel, a backwater
ponding easement from the affected
offsite property owner(s) shall be
required prior to final plan
approval. A reduction in the
design storm requirement may be
granted by the city engineer when
existing off-site, downstream
storm sewer would be smaller than
the required on-site, upstream
sewer and the downstream storm
sewer are not designed to
intercept/pass the fifty (50) year
twenty (20) minute storm event.
(e) Detention design criteria. Detention in the
overall system, including swales, lakes, canals,
greenways, etc., shall be provided as follows.
(f) General.
35
(1) Storage volumes. The minimum volume of
storage provided in detention basins,
together with such storage as may be
authorized in other on-site facilities,
shall be sufficient to store the volume
from a twenty -five-year storm (under
developed conditions).
(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) Release Rate. A release rate shall be
calculated for a two (2), ten (10)
twenty-five (25) year storm for the
proposed development in the condition
prior to the proposed development.
(4) Emergency spillway. Emergency overflow
facilities must be provided in all
instances so that stored waters will
not exceed the safe capacity of the
basin. At a minimum, the emergency
spillway must be able to pass without
damage the one -hundred -year storm.
(5) Appearance. Designs should result in
aesthetically pleasing configurations
which will enhance public
acceptability.
(g) 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).
36
(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.
(h) Wet -detention facilities.
(1) Perimeter maintenance and operation
easements of fifteen (15) feet (minimum
preferable) width at slopes no steeper
than 3:1 (horizontal to vertical) shall
be provided.
(2) Control elevations should be no higher
than two and one-half (2 1/2) feet
below the minimum road centerline
elevation in the area served by the
control device in order to protect the
road subgrade when structures are
constructed near roads.
(3) Side slopes shall not be steeper than
3:1 (horizontal:vertical) out to a
depth of two (2) feet below the control
elevation, then as steep as soils
stability will allow.
37
(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 ten (10) feet.
(5) For emergency purposes, cleaning or
shoreline maintenance, facilities shall
be provided or plans prepared for the
use of auxiliary equipment to permit
emptying and drainage.
(6) The limits of maximum ponding
elevations are to be no closer than
thirty (30) feet horizontally from any
building and no less than two (2) feet
below the lowest sill elevation of any
building.
(i) 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 of storage, details of inlet and
outlet devices and locations, emergency overflow
provisions, and measures to be used for surface
water and groundwater pollution control.
(j) 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.
(k) Developments adjoining a floodplain. Where a
development adjoins or encompasses a portion of a
floodplain for a one -hundred -year flood, the
following shall apply:
(1) The applicant shall show the floodplain
and floodway on the stormwater
management plan.
(2) The applicant shall include in the
stormwater management plan all other
plans, plats, specifications, etc.,
38
M
required by federal, state, county
and/or municipal laws 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
requirements.
C. All requirements of other
federal, state or local
agencies exercising juris-
diction over the area.
(1) Channel flow. The applicant shall not alter any
channel in such a way that would prohibit any
section of the channel from conveying, in its
post -development state, the same amount of flow
at the same or lower maximum water elevation,
that it conveyed in its predevelopment state.
(m) 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 nontypical
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
39
on such land and facilities at no
public cost.
(5) Minimum finished floor elevations which
shall be set at or above the maximum
water surface elevation as determined
by either or both of the following:
a. "Flood Insurance Rate Map"
published by the Federal
Emergency Management Agency.
b. Backwater curve profiles of
the proposed waterway due to
a one -hundred -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.
(n) 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.
(o) 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 chapter. For
projects less than fifty (50) acres in area there
is no need for submittal of routing calculations
or tabulated proof of adequacy of tributary
runoff for detention; however, it is recommended
that verification be made of:
40
0
(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.
(p) 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.
(q) 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
41
i
best management practices include, but are not
limited to:
(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
and protection
impact.
development activities
measures for minimal
ARTICLE (5). Section 23-11(a) of the Code of Ordinances of
the City of Cape Girardeau, Missouri, relating to "Rights-of-way
and easements" reading as follows:
Section 23-11. 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:
42
TABLE INSET:
is hereby repealed in its entirety, and a new Section 23-11(a)
relating to "Rights-of-way and easements", is hereby enacted in
lieu, in words and figures, to read as follows:
Section 23-11. 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:
43
Maintenance
Facility
Access Width
Open
drainage
30 feet, 15 feet
channel or
each side
facility
Greenways
Width of greenway
Pipes and
15 feet, centered
culverts
15 feet continuous
Detention
around total area
areas
Connecting
15 feet
access
is hereby repealed in its entirety, and a new Section 23-11(a)
relating to "Rights-of-way and easements", is hereby enacted in
lieu, in words and figures, to read as follows:
Section 23-11. 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:
43
s
TABLE INSET:
ARTICLE (6). Section 23-12 of the Code of Ordinances of
the City of Cape Girardeau, Missouri, relating to "Maintenance
responsibilities for stormwater management facilities" reading
as follows:
Sec. 23-12. 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,
44
Maintenance
Facility
Access Width
Open
drainage
30 feet from top of
channel or
bank
facility
Greenways
Width of greenway
Pipes and
15 feet, centered
culverts
15 feet continuous
Detention
around total area
areas
Connecting
15 feet
access
ARTICLE (6). Section 23-12 of the Code of Ordinances of
the City of Cape Girardeau, Missouri, relating to "Maintenance
responsibilities for stormwater management facilities" reading
as follows:
Sec. 23-12. 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,
44
P
approaches and techniques to design and construct
these facilities in such a manner that fulfills
the requirements of this chapter, 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.
(1) 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.
(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
45
f
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 city
council.
(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-year period following completion. Inspection
and repair of defects shall be required as a
condition of release of the posted security.
is hereby 'epeled in its entirety, and a new Section 23-12
relating to "Maintenance responsibilities for stormwater
management facilities", is hereby enacted in lieu, in words and
figures, to read as follows:
Sec. 23-12. 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 chapter, 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.
(1) Detention facilities, when mandatory,
are to be built in conjunction with the
47
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 city
council.
(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
48
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.
(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.
ARTICLE (7). There is hereby enacted a new Section 23-13
of the Code of Ordinances of the City of Cape Girardeau,
Missouri, entitled "Illicit discharges" reading as follows:
Section 23-13. Illicit discharges.
(a) Prohibition of Illicit Discharges.
(1) Pursuant to the National Pollutant
Discharge Elimination System (NPDES)
Municipal Separate Storm Sewer System
(MS4) program illicit discharges to the
MS4 are being defined as illegal. This
is accomplished by identifying
allowable non-stormwater discharges
into the MS4 in the best interest of
the City of Cape Girardeau, Missouri.
49
w r
(2) Non-stormwater discharge means any
discharge to the Municipal Separate
Storm Sewer System.
(3) Except as hereinafter provided, all
non-stormwater discharges into the
Municipal Separate Storm Sewer System
are prohibited and declared to be
unlawful.
(b) Allowable storm discharges.
(1) Unless the city of Cape Girardeau,
MoDNR, EPA or other regulatory agency
has identified them as a source of
pollutants to the "Waters of the State
of Missouri", the following non-
stormwater discharges into the
Municipal Separate Storm Sewer System
are lawful:
a. Water line flushing or other
potable water sources.
b. Landscape irrigation or lawn
watering with potable water.
C. Diverted stream flows.
d. Rising ground water.
e. Groundwater infiltration to storm
drains.
f. Pumped groundwater.
g. Foundation or footing drains.
h. Crawl space pumps.
i. Air conditioning condensation.
j. Springs.
k. Non commercial washing of
vehicles.
1. Natural riparian habitat or wet-
land flows.
M. Swimming pools (if dechlorinated).
n. Fire fighting activities.
o. Discharges specified in writing
by the City of Cape Girardeau as
being necessary to protect public
health and safety.
ARTICLE (8). If any section, subsection, sentence, clause,
50
phrase or portion of this Ordinance is for any reason held
invalid or unconstitutional by any court of competent
jurisdiction, such portion shall be deemed a separate, distinct
and independent provision and such holding shall not affect the
validity of the remaining portions hereof.
ARTICLE (9). 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.
ARTICLE (10). This Ordinance shall be in full force and
effect from and after its passage and approval.
PASSED AND APPROVED this -#(( day of aflAe,pt1,� ,
2006.
ATTEST:
A
Gayle L. onrad, City Clerk
Jay Knudtson, Mayor
51