[Ord. No. 1623, 5-22-2017]
A.
With continued growth and development the community has been confronted
with issues of increased stormwater runoff and its impact upon streams,
the environment and quality of life. Increased stormwater runoff causes
more frequent and intense flooding problems as well as erosion, rechannelization,
and sedimentation of the natural watercourses and creeks. In addition,
changing and proposed new water quality regulations impact the City's
ability to meet the requirements of the community's Municipal Separate
Storm Sewer System (MS4) discharge permit.
B.
The natural condition of the land before development is in relative
balance with the natural capacity of the receiving streams. Undeveloped
conditions provide natural absorption of water into the ground and
longer periods of concentration. Modification of the ground surface
from its natural vegetated state to solid paved surfaces and buildings
causes water to runoff site at faster rates. The solid surfaces do
not allow absorption and filtering of the stormwater, and all the
other benefits that vegetated ground cover provides. It is the policy
of the City of Cottleville to protect and promote the public health,
safety and general welfare by the management of stormwater. The management
of stormwater will reduce the possibility of damage to public and
private property, will reduce the erosion on land and creek channels,
will assist in the attainment and maintenance of water quality standards,
and will preserve and enhance the environmental quality of the watercourses
in the City of Cottleville.
[Ord. No. 1623, 5-22-2017]
For the purposes of this Article, the following terms, phrases,
words, and their derivations shall have the meanings given herein.
Unless the context clearly indicates to the contrary, words used in
the present tense include the future tense; words used in the singular
shall include the plural, and vice-versa; the words "these regulations"
mean "this Article IV"; and the word "shall" is always mandatory.
The pre-development or existing condition peak flow corresponding
to a selected rainfall frequency event.
The specific person applying for the permit for an approved
stormwater management system.
The flood having a one percent (1%) probability of being
equaled or exceeded in any given year, i.e., the one-hundred-year
flood. (The base flood, adopted by the Federal Emergency Management
Agency, FEMA, is the one-hundred-year flood).
Shall have the same meaning as set forth in Section 510.290 of this Code.
A closed conduit for the free passage of surface drainage
water under a highway, railroad, or other embankment.
The process by which the owner gives approved storm sewers
and facilities to the City for public use and maintenance.
The design water surface elevation is the upper limit of
the capacity of the stormwater facility. The design water surface
elevation can be relative to the final discharge point, a known actual
elevation on-site, or can be set to zero.
Any man-made area or facility designed to detain (hold) stormwater
temporarily during and immediately after a runoff event.
The temporary detaining or storage of stormwater in reservoirs,
on rooftops, on parking lots and other areas under pre-determined
conditions.
The peak flow corresponding to a selected rainfall event
as a result of developed site conditions.
Any subdivision of land as herein defined or any material change in the use or appearance of any parcel of land subject to provisions of Chapter 405 of this Code or the act of building structures and/or installing site improvements.
Any plan for the development of a site, including, but not
limited to, a preliminary plat, site plan, area plan or final plan.
The difference between the calculated developed runoff rate,
and the calculated pre-developed runoff rate.
The Director of Public Works or any other person or persons
designated by the City Administrator.
Any system of artificially constructed drains, including
open channels and sewers used to convey stormwater, surface or groundwater
either continuously or intermittently to natural watercourses.
A facility designed for the temporary storage of stormwater
runoff.
A form of security to guarantee the completion or performance
of a stormwater management plan or the maintenance of drainage improvements,
established as a cash or letter of credit escrow deposit in an amount
and form satisfactory to the governing body.
A geographic area susceptible to periodic inundation from
the overflow of natural waterways during the base (one-hundred-year)
flood.
The channel of a river or other watercourse and the adjacent
land areas that must be reserved in order to discharge the base flood
without cumulatively increasing the water surface elevation more than
one (1) foot and so delineated in the Federal Emergency Management
Agency (FEMA) Flood Insurance Study.
An area or device to trap silt before it enters a detention
pond.
The difference in elevation between the hydraulic grade line
elevation and: (1) the inlet sill elevation; or (2) the top of structure
elevation; or (3) the top of channel bank elevation; or (4) the top
of wall elevation.
A line coinciding with the level of flowing water at any
given point along an open channel; or the level to which water would
rise in a vertical tube connected to any point along a pipe or closed
conduit flowing under pressure.
A surface that prevents the infiltration of water.
Percolation of water into the ground.
Any activity which affects the ground surface and/or vegetation
(i.e., clearing and grubbing, grading, excavating, etc.)
The level of water quality protection recommended for a development
or provided by a post-development stormwater management system. The
LS requirement for the development is determined by the change in
runoff from the predevelopment condition. The LS provided by the stormwater
management system is determined by a combination of detention and
water quality treatment.
The act of maintaining or preserving, including, but not
limited to, operation, construction, and re-construction.
Municipal Separate Storm Sewer System.
The peak rate of flow of water at a given point in a channel,
watercourse, or conduit resulting from the base flood.
Rainstorms of a specific duration having a one percent (1%)
probability of occurrence in any given year.
The point location or structure where drainage discharges.
A permit granted by the City to a person to construct a stormwater
management system.
Any person to whom a permit has been granted by the City
under this Article.
An individual, corporation, partnership, and/or unincorporated
association of persons.
The amount of flow from an existing site prior to new development
or improvements as computed using the Rational Method.
This term shall have the same meaning as set forth in the Manual of Best Management Practices for Stormwater Quality adopted pursuant to Section 510.520 of this Code.
An empirical formula for calculating peak rates of runoff
resulting from rainfall.
A pond, lake or basin used for the permanent storage of water
runoff without release except by means of evaporation, infiltration
or emergency by-pass.
Shall have the same meaning as set forth in Section 510.290 of this Code.
A technique for calculating stormwater runoff volume and
peak flow described in Soil Conservation Service (SCS) Technical Release
55.
Monies reserved for funding improvements to stormwater management
systems owned and maintained by the City of Cottleville.
The drawings, computations, data, reports, etc., which identify how stormwater runoff is to be managed required to be submitted pursuant to Section 510.490 of this Code.
All means, natural or man-made, used for conducting stormwater
runoff to, through, or from a drainage area to the point of outlet.
See escrow.
A management plan, the purpose of which is to ensure the
design, implementation, management and maintenance of Best Management
Practices (BMPs) in order to reduce the amount of sediment and other
pollutants in stormwater discharges associated with land disturbance
activities.
Water that results from precipitation which is not absorbed
by the soil, evaporated into the atmosphere, or entrapped by ground
surface depressions and vegetation.
A pipe or closed conduit that carries surface runoff and
subsurface waters.
Any object constructed above or below ground.
A broad, shallow watercourse.
Consists of inlet time plus the travel time in the sewer
or channel from the most remote point in the watershed to the point
under consideration.
All of the area that contributes stormwater runoff to a given
point.
A flood having a four-percent (4%) probability of occurrence
in a given year.
The peak rate of flow of water at a given point in a channel,
watercourse, or conduit resulting from the twenty-five-year flood.
Rainstorms of a specific duration having a four percent (4%)
probability of occurrence in any given year.
The assumed water quality improvement value of a cover type
or BMP, based on its ability to improve water quality and mitigate
runoff volume.
The chemical, physical, and biological characteristics of
water. This term also can refer to regulatory concerns about water's
suitability for swimming, drinking, agriculture, industrial activity,
and healthy aquatic ecosystems.
The storm event that produces less than or equal to ninety
percent (90%) stormwater runoff volume of all twenty-four-hour storms
on an annual basis. In the Cottleville area this is the one and fourteen
hundredths (1.14) inch storm.
The storage needed to capture and treat ninety percent (90%)
of the average annual stormwater runoff volume. It is calculated by
multiplying the Water Quality Storm times the volumetric runoff coefficient
and site area.
Any natural or artificial stream, river, creek, channel,
ditch, canal, culvert, drain, waterway, gully, ravine, street, roadway,
swale, or wash in which water flows, either continuously or intermittently,
and which has a definite channel, bed or bank.
All the land that drains to a given point (also described
as a basin, catchment, and drainage area).
A detention basin intended to have a permanent pool.
[Ord. No. 1623, 5-22-2017]
A.
A City-wide stormwater management program plan (SWMP) was prepared
in 2013. This plan shall serve as a guide for public policies to protect
the watersheds and for the selection and scheduling of specific activities
that will protect and promote the public health, safety and welfare.
The basic goal of stormwater management is to align water quantity
and water quality management techniques in such a way as to prevent
further deterioration and to begin improving the quality of the City's
watersheds.
B.
Changing City-Approved Drainage Patterns. Stormwater drainage patterns
that have been approved by the City shall not be changed without approval
of the Director.
[Ord. No. 1623, 5-22-2017]
A.
Any development or area which is to be paved, expanded, redeveloped
or otherwise improved shall be required to provide on-site stormwater
management unless the Director waives such requirement for the reasons
contained below:
1.
Off-Site Or Regional Facility, Two (2) Or More Developments.
If two (2) or more developments, including that of the applicant,
have provided for a common system. Such a Stormwater Agreement shall
be developed and signed by all developments or properties contributing
to a common system that clearly defines maintenance responsibilities
between all parties.
2.
Off-Site Or Regional Facility By City. If an off-site stormwater
management system has been either constructed or programmed or identified
for construction by the City, and the applicant has agreed to contribute
to, or participate in, the construction thereof.
3.
Contribution In Lieu Of On-Site Detention. A financial contribution may be considered in lieu of on-site detention if the increased amount or velocity of stormwater generated by the development will have minor detrimental effect on the receiving watercourse and there are no known downstream flooding, erosion or water quality issues, and the applicant has agreed to contribute to the Stormwater Management Improvements Fund an amount equal to the cost of the otherwise required on-site stormwater management system. Reference Section 510.480, Subsection (A)(5) of this code for criteria to qualify for this option.
a.
For the purpose of establishing an amount to be contributed,
the developer shall prepare an estimate of cost for a detention basin,
including, but not limited to, the land value for the detention basin
area, and construction costs (including grading and vegetation) which
shall be reviewed and approved by the Director.
b.
Contributions to the Stormwater Management Improvements Fund
shall only be required if the amount of runoff is increased.
4.
Other Management Techniques. Management techniques other than
detention facilities may be utilized by the development provided the
proposed techniques meet the intent of this Article and provide a
benefit to the watershed that equals or exceeds the benefit that a
detention facility would provide.
[Ord. No. 1623, 5-22-2017]
A Stormwater Management Improvements Fund shall be and is created by the adoption of this Article. The Stormwater Management Improvements Fund shall be reserved for funding improvements to stormwater systems owned and maintained by the City, and for no other purposes unless authorized in this Article. All contributions made by parties developing within the City in accordance with Section 510.430 of this Article shall be deposited to said fund. Said fund shall be maintained in an interest bearing account.
[Ord. No. 1623, 5-22-2017]
When the Director determines that additional storage capacity
beyond that required by the applicant for on-site stormwater management
is necessary in order to correct an existing problem, or to provide
protection in a more desirable method for future development, or to
complete improvements as outlined in the City's Stormwater Improvement
Plan, the City may acquire from the applicant or owner, by purchase
or dedication, the construction of stormwater management systems to
the extent that it exceeds the required on-site stormwater management.
[1]
Editor's Note: Former Section 510.460, Inspection, Maintenance,
Acceptance By City, was repealed 3-15-2023 by Ord. No. 2069. Prior
history includes Ord. No. 1623.
[Ord. No. 1623, 5-22-2017]
Upon approval of the final stormwater management plan for any
stormwater management system, but before the issuance of any permits,
the Director shall require the applicant to post an escrow in the
form of a Letter of Credit, cash escrow, or certified check, for the
amount of the work to be done pursuant to the approved stormwater
management plan. This performance security shall not be fully released
by the Director until a final inspection has been made and the facility
has been found to be in compliance with the approved plans, and in
the event the facility is to remain privately owned, provisions have
been made to assure perpetual maintenance. An eighteen (18) month
maintenance guarantee against defects in workmanship will be required
by the Director for any system dedicated to the City.
[Ord. No. 1623, 5-22-2017]
A.
Applicabilty. The requirements of stormwater management outlined
in this Article shall apply to all developments within the corporate
limits of the City of Cottleville, Missouri. Stormwater management
plans shall be provided and designed in accordance with the requirements
of this Article and all design and construction specifications adopted
by this Article. Each development is to strive to maintain or improve
predevelopment peak flows, runoff volumes and water quality. Stormwater
quality and quantity management requirements will be evaluated for
all developments, and specifically, will be required for developments
including:
1.
All new development and redevelopment projects that disturb
greater than or equal to one (1) acre, including developments less
than one (1) acre that are part of a larger common parcel or development
that is greater than one (1) acre.
2.
All developments that have a differential runoff of one (1)
cubic feet per second (cfs) or greater for the fifteen-year, twenty-minute
storm event. The differential runoff is calculated by the Rational
Method using PI factors.
3.
Development or redevelopment of sites without prior stormwater
detention shall provide detention or retention, when the cumulative
differential increase equals one (1) cfs or greater. Developments
with prior detention shall provide additional detention or retention
for all increased runoff.
4.
When existing stormwater management (detention or retention)
facilities are going to be used to accommodate additional runoff,
the facilities shall be retrofitted to meet the current stormwater
management requirements. Developments which cannot meet this requirement
due to physical constraints will be evaluated for alternatives on
a case by case basis.
B.
Affadavit Of Disclosure Of Property Interest. The effective acreage
for a site is not limited to a fractional part of the total. If a
development is developed in phases or small plats, the total acreage
of the development site will be considered. At the time of submittal
of a development plan, the owner shall also submit an affidavit to
the Director, identifying all contiguous property or property in the
watershed in which the owner of the property depicted on the development
plan has an interest.
[Ord. No. 1623, 5-22-2017]
A.
Stormwater Management Plans. Concurrent with the filing of a development
plan, a stormwater management plan shall be prepared for each phase
of the proposed development as each phase is developed. The stormwater
management plan shall contain the following:
1.
A topographic map of the site and adjacent areas, of suitable
scale and contour interval, which shall define the location of watercourses,
streams and other flood water run-off channels, the extent of floodplains,
the limits of the floodway, if pertinent, and calculated high water
elevations, the shoreline and elevation of lakes, ponds, swamps, and
detention basins including their floodplains and their inflow and
outflow structures.
2.
The location and flowline elevation of all existing sanitary
and storm sewers.
3.
Detailed determination of runoff anticipated for the site following
development, indicating design volumes and rates of proposed runoff
for each portion of the watershed, the calculations used to determine
said runoff volumes and rates, and restatement of the criteria which
have been used.
4.
A layout of the proposed stormwater management system including
the location and size of all drainage structures, storm sewers, channels
and channel sections, detention basins, water quality BMPs, and other
stormwater improvements, and analysis regarding the effect said improvements
will have upon the receiving channel and its high water elevation.
5.
Specific information regarding the type and characteristics
of soils which will be encountered within the development, and the
locations of any sinkholes on the site.
6.
A planting palette and seeding rates for vegetated water quality
BMPs.
7.
The location and calculated flow rates of other existing storm
drains, inlets and outfalls.
8.
The location and calculated flow rates of any existing storm
sewers which occur within the site, or adjacent thereto within a distance
of approximately one hundred (100) feet from the perimeter of said
site; or as conditions warrant.
9.
The location and observed flow rates of any flowing springs,
existing wells or any existing seepage areas as determined by means
of a field inspection of the property.
10.
The slope, type, size, and flow calculations for all existing
and proposed storm sewers and other waterways.
11.
For any stormwater basins (retention, detention or rain gardens),
a detention analysis report for each basin, including, but not limited
to, a plot or tabulation of storage volumes with corresponding water
surface elevations and the basin outflow rates for those water surface
elevations.
12.
For any stormwater basins (retention, detention or rain gardens),
design hydrographs of inflow and outflow for the two-year storm and
twenty-five-year storm differential runoff rates from the site under
proposed development conditions.
13.
A refined grading plan for the entire development site drawn
at a suitable scale and contour interval, or the terrain within the
proposed development site including contours of the existing terrain,
along with contours indicating final grades which will be established
during completion of the development. The grading plan shall also
include a plot of the line defining the high water elevation to be
expected under the one-hundred-year peak flow conditions produced
by the projected development of the contributing watershed based on
the best available land use information.
14.
Profile and cross-section drawings of all existing and proposed
channels or other open drainage facilities, showing existing and proposed
conditions, flow volume (Q) and velocity, together with the high water
elevations expected from stormwater runoff under the controlled conditions
called for by these regulations and the relationship of structures,
streets, and other utilities to such channels.
15.
Calculations supporting the method and capacity needed for the
safe and temporary storage of increased runoff resulting from the
proposed development, if temporary storage is needed.
16.
Calculations for Water Quality Volume (WQv) to determine the
amount of storage needed to capture and treat ninety percent (90%)
of the average annual stormwater runoff volume.
17.
Calculations for Flood Protection Volume (Qp) to protect downstream
areas from flooding.
18.
Calculations for the Level of Service (LS) and Value Rating
(VR) to determine the level of water quality protection needed for
a development.
19.
Basic information regarding the receiving watercourse into which
the proposed stormwater system will discharge including the watercourse
location, general cross section, existing downstream culverts and
bridges and other waterway openings within a reasonable distance;
any existing detention basins or lakes and other information required
to determine, in final form, the effect which the proposed development
will have on downstream drainage conditions.
20.
A Stormwater Pollution Prevention Plan (SWPPP) pursuant to the requirements of Section 510.280 of this Code.
21.
All computations, plans, and specifications must be prepared
and sealed by a professional engineer registered in the State of Missouri.
22.
The Director, or his/her designee, shall review final stormwater
management plans.
a.
If it is determined that the proposed development will provide
stormwater quantity and quality control in accordance with the purposes,
design criteria and performance standards of these regulations and
will not be detrimental to the public health, safety, and general
welfare, the Director shall approve the final stormwater management
plan or conditionally approve such final stormwater management plan,
setting forth the conditions thereof.
b.
If it is determined that the proposed development will not manage
stormwater quantity and quality in accordance with these regulations
the Director shall disapprove the final stormwater management plan.
[Ord. No. 2069, 3-15-2023]
A.
Stormwater drainage systems shall be equipped with adequate basins,
inlets and outlets and shall be constructed in accordance with the
applicable provisions in the stormwater management plan. The stormwater
drainage system shall be separate and independent of the sanitary
sewer system. The plans and specifications for the disposing of stormwater
shall be approved by the Director.
B.
General. All design, construction details and specifications pertaining
to stormwater drainage shall be in accordance with the St. Charles
County Highway Department Standard Construction Specifications, latest
version, and the City's requirements, unless otherwise noted
herein. A registered engineer's seal is required on all drainage
plans submitted for approval.
1.
Design Criteria. All stormwater design is to be by the Rational
Method, except that in certain large developments, the use of other
methods of analysis such as the Unit Hydrograph will be considered
for stormwater design. However, prior approval must be obtained from
the Director at the preliminary design stage, where use of the Unit
Hydrograph or other methods of analysis are requested.
2.
Runoff factors shall be per St. Charles County Highway Department
requirements.
C.
Drainage Structures. All structures shall be designed for HS20-44
loading.
1.
Bridges. Bridges shall be designed for the 100-year storm frequency
and provide two (2) feet of freeboard between the bottom of superstructure
and high water elevations.
2.
Culverts.
a.
Crossroad culverts, not at low points, shall be designed on
a storm frequency of fifteen (15) years with entrance control and
two (2) feet of freeboard at the shoulder line.
b.
Culverts, at or near low points in floodplains, shall be designed
on a storm frequency of one hundred (100) years with entrance control
and two (2) feet of freeboard at the shoulder line.
c.
Culverts, at or near low points not in floodplains, shall be
designed on a storm frequency of fifty (50) years with entrance control
and two (2) feet of freeboard at the shoulder line.
3.
Roadways. Whenever a watercourse is proposed or exists within
proximity of and is approximately parallel to an existing or proposed
roadway, the low shoulder elevation of the roadway shall be established
from the high water elevation with one (1) foot of freeboard in non-floodplain
areas and two (2) feet of freeboard in floodplain areas.
4.
Street Inlets. In certain cases, where steep grades or other
unusual conditions are encountered, a grated trough may be required
in lieu of multiple inlet structures upstream in order to eliminate
excessive bypass.
5.
Pipes.
a.
Pipes within the public right-of-way or easement shall be reinforced
concrete pipe ("RCP") ASTM C-76, Class III, and a minimum of twelve
(12) inches diameter. Design calculations may be submitted allowing
a lower class of RCP.
b.
The use of high-density polyethylene ("HDPE") shall be allowed
following St. Charles Highway Department requirements.
c.
The use of polypropylene ("PP") shall be allowed following St.
Charles County Highway Department requirements.
d.
The use of corrugated steel pipe should only be considered when
all options for reinforced concrete pipe are deemed not feasible.
Corrugated steel shall be M-36, minimum sixteen-gauge asphalt polymer,
or aluminized coating, a minimum of eighteen (18) CSP, will be allowed
with these conditions. This pipe material may be used for private
driveway culverts or private road culverts, as the maintenance shall
be with the property owner, even though the pipe is in the right-of-way.
e.
Additional general pipe requirements.
f.
The required stormwater hydraulics shall be submitted with all
types of pipes.
g.
Pipe reduction will not be allowed.
h.
In situations where storm pipe cover is less than three (3)
feet, calculations will be required to determine the class or gauge
of pipe.
i.
All concrete pipe shall be installed with O-ring rubber-type
gaskets per St. Charles County Highway Department Standard Construction
Specifications. Connections at all structures are to be made with
rubber, watertight A-lock joints or approved equals.
j.
Pipes normally should be sized using the partial flow design;
however, under special circumstances, full flow design will be allowed,
provided hydraulic grade line information is shown indicating adequate
freeboard. This additional information will be supplied for the 2-,
15-, 25-, and 100-year storms.
k.
Freeboard requirements will be two (2) feet from the inlet sill
or manhole top.
D.
Plans And Calculations.
1.
General. Plans shall be any scale from one (1) inch equals ten
(10) feet through one (1) inch equals one hundred (100) feet so long
as the scale is an increment of ten (10) feet. Plans shall be prepared
on exhibits nominally twenty-four (24) inches by thirty-six (36) inches.
All calculations submitted shall include the following information:
a.
Site Drainage Map. A drainage map is required and should be
developed from a base reproduction of the site plan or grading plan.
Plans and calculation shall be prepared in accordance to the checklist
pertinent for the type of development.
b.
Supplemental Drainage Map. A supplemental map may be required
and should be developed from a portion of USGS Quadrangle Map. This
map must include the site boundary and the watershed tributary to
the project area.
c.
Surface Drainage. The following information shall be provided
by the developer:
(1)
No sheet flow over one (1) cubic foot per second
("cfs") will be allowed over terraces with slopes that are and/or
greater than five (5) feet in height. Berms and/or swales shall be
provided to collect the flow at the top of the terrace and carry it
to a drainage structure. Total accumulation inside berm and/or swales
shall be a maximum of three (3) cubic feet per second.
(2)
Excluding existing creeks and swales not being
modified by the proposed development, the developer's engineer
shall provide critical cross sections, profiles and hydraulic computations
for ditches and swales with flows in excess of one (1) cfs and creeks
with flows in excess of three (3) cfs.
(3)
Overland Flow Swale. All emergency/overland flow
swales shall be designed on the plans. At all low points on streets,
the flow-line elevation of the swale at the right-of-way line shall
not exceed eight (8) inches higher than the top of the curb inlet
(at said low point). The alternative to this depth is to install a
larger storm pipe, capable of handling the 100-year twenty-minute
storm.
d.
Location Of Drainage Structures. The lateral location of all
drainage structures shall be shown by street center line stationing
and perpendicular offset distance, and in large lot subdivisions,
by referencing to rear lot line, in addition to the following requirements:
(1)
Inlets shall be appropriately sized and spaced,
taking into consideration by pass, depth of flow and width of spread
of flow in gutters.
(2)
For inlets in vertical sag curves, the center of
the main chambers shall be placed within one (1) foot of the exact
mathematical low point.
(3)
All manholes shall be located outside of the proposed
roadway pavements.
(5)
Bypass shall be minimized at inlet structures and
shall be shown on the hydraulic computations and site drainage map.
No greater than one (1) cfs of stormwater shall be allowed to cross
an intersection.
(6)
Where termination of pavement occurs, erosion protection
in the form of asphalt curb, gutters, additional structures, paving
and/or revetment may be required.
(7)
Data required on plans and/or profiles shall include:
(a)
Type of drainage structure (single, double, grated,
etc.).
(b)
Flow line and top elevations.
(c)
"Q" in upstream gutter line or drainage swale.
(d)
The hydraulic grade line of the structure may be
shown on the plan, profile or computation sheets.
(e)
Attach hydraulic computations.
(f)
Label All Pipe Runs As Public Or Private. For detention
basins, the flared end section and pipe leading up to the next upstream
structure shall be labeled as private. The outfall structure and section
of pipe down to the next structure shall be labeled as private. Pipe
runs crossing non-City-maintained roadways shall be labeled as private.
(8)
For non-standard structures (for example, cast-in-place
or severe modifications to standard structures), construction details
shall be included on the plan sheets.
e.
Pipes.
(1)
The following information shall be shown on the
plans and/or profiles:
(a)
Location and length of pipes;
(b)
Grade;
(c)
Curve data for radius pipes.
|
Note: On intake structures, such as flared end section or headwalls,
entrance control shall be applied. Two (2) foot minimum freeboard
is required based on the 15-year, twenty-minute storm. Check for inundation
upstream. Toe walls are required to be two (2) feet deep on headwalls
upstream, three (3) feet deep on headwalls downstream.
|
(2)
Outfall termination shall conform to the following:
(a)
All outfall pipes shall be concrete and have a
reinforced concrete headwall or flared end section with cutoff wall
and revetment to protect from scour.
(b)
If discharge is at a property line, discharge easements
will be acquired on affected adjacent properties prior to approval
of the Director. A guarantee will be required for future extension
of the outfall to the property line. Open trenching of roadway pavements
will normally be permitted on minor residential streets only.
[1]
Editor's Note: Former Section 510.500, Design Criteria —
Adopted, was repealed 3-15-2023 by Ord. No. 2069. Prior history includes
Ord. No. 1623.
[Ord. No. 2069, 3-15-2023]
A.
Policy. It is the policy of the City of Cottleville, Missouri, to
protect and promote the public health, safety, and general welfare.
The criteria for stormwater detention will:
1.
Reduce the possibility of damage to public and private property;
2.
Reduce the erosion of land and creek channels;
3.
Assist in the attainment and maintenance of water quality standards;
4.
Preserve and enhance the environmental quality of the watercourses
in the City. This criteria provides uniform procedures for designing
and checking the design of storm drainage detention systems.
B.
General Guidelines.
1.
Applicability. This shall apply to all development within the
corporate limits of the City. Residential developments having a total
area of less than five (5) acres and commercial or industrial developments
having a total area of less than one (1) acre may be given a waiver
by the City subject to the following conditions:
a.
The City retains the right to reacquire detention storage in
all cases in which the proposed development will generate excess runoff
that adversely affects the carrying capacity of the receiving watercourse.
b.
Developments less than one (1) acre with less than thirty percent (30%) of the area paved and developments generating less than one (1) cubic foot per second per acre ("cfs/acre") increased runoff shall not be required to provide detention storage unless the condition in Subsection (B)(1)(a) above is applicable.
2.
Affidavit Of Disclosure Of Property Interest. The effective
acreage for a site is not limited to a fractional part of the total.
If a project is developed in phases or small plats, the total acreage
of the project site must be considered.
3.
Method Of Evaluation. The storage capacity and discharge rate
shall be based upon the calculated volume and peak flow of the stormwater
runoff, respectively. The calculations for sites having an area of
one hundred (100) acres or less shall be made using either the Soil
Conservation Service Method or the Rational Method. If the site is
larger than one hundred (100) acres, then the engineer shall use the
Soil Conservation Service Method. If another method is desired to
be used, the engineer shall submit a proposed method of evaluation
for the calculations for review and approval. The permitted discharge
rate of stormwater runoff shall be determined by calculating the rate
of runoff for the site's pre- and post-development conditions.
The engineer shall determine the most critical storm looking at three
(3) different time periods:
4.
Detention Of Differential Runoff. All new developments shall
provide a stormwater detention facility that insures that the rate
of flow of stormwater runoff discharge from the site after development
for a 2-year, 15-year, 25-year, and 100-year, twenty-minute storm,
unless given a waiver by the Director. Data shall be submitted for
the 2-, 15-, 25-, and 100-year frequency twenty-minute storms.
a.
The maximum ponding elevation shall be calculated based on a
routing of the design storm [100-year, twenty-minute] assuming the
lowest outlet is blocked with the water ponded to its maximum elevation.
A minimum of one (1) foot of freeboard shall be provided from the
top of the basin to the maximum ponding elevation.
5.
Flows From Upstream Areas. Flows from upstream areas outside
the site should be based upon the assumption that those areas are
fully developed under forecast land use patterns. The required storage
volume will be based upon the site only, with flows from upstream
areas being bypassed or discharged via overflow spillways or other
devices for the 100-year storm.
6.
Facilities In Floodplains. 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 unless approved by the Director. No credit will be
granted for volumes below the elevation of the base flood at that
location unless compensatory storage is also provided. Where encroachments
in the existing floodplain fill the valley storage areas, an equal
amount of detention volume shall be provided.
C.
Design Criteria.
1.
General Requirements. The design shall be accomplished under
the direction of a Missouri-registered professional engineer. The
design shall also be based on land use in the tributary area as zoned,
actually developed or indicated by an adopted future land use plan,
whichever basis produces the greatest runoff.
2.
Other References. Other agencies have criteria and regulations
pertaining to drainage systems which may complement this criteria.
When conflicts are encountered, the most rigorous criteria shall govern.
a.
FEMA: floodplain regulations and implementing ordinances adopted
by municipalities. Drainage systems designed within the limits of
the designated 100-year floodplain on the principal stream shall be
designed to convey the flood as defined by applicable published floodplain
information studies. For areas located in FIRM Zone "A" outside the
detailed study, the developer shall prepare studies and calculations
establishing the floodplain, elevation and width. These calculations
shall be submitted to the reviewing agencies for approval.
b.
Missouri Department Of Natural Resources. Rules and regulations
of the Dam and Reservoir Safety Council shall apply to those Missouri
structures classified as dams thereunder.
3.
Stormwater Runoff. The design criteria used in determining the amount of runoff shall be the same as set out in Section 510.500 of this Chapter.
4.
Hydraulic Considerations For Detention Storage.
a.
Principal spillways shall be designed to meet the following
requirements:
(1)
The principal spillway shall be designed to function
without requiring attendance or operation of any kind or requiring
use of equipment or tools.
(2)
All discharge from the detention facility when
inflow is equal to or less than the 100-year inflow shall be via the
principal spillway(s).
(3)
The design shall allow for discharge of at least
eighty percent (80%) of the detention storage volume within twenty-four
(24) hours after the peak or center of mass of the inflow has entered
the detention basin. On basins less than one hundred (100) acres,
this shall not apply.
(4)
The design discharge rate via the spillway shall
continuously increase with increasing head and shall have hydraulic
characteristics similar to weirs, orifices or pipes.
b.
Emergency Spillways. The emergency spillway shall be provided
to pass a 100-year storm without damaging any property and, where
applicable, designed to the Department of Natural Resources ("DNR")
dam safety requirements. Overland flow route will be required to be
depicted on the plan for emergency spillways.
c.
Outlet Works. Detention facilities shall have an outlet works
consisting of valves, gates, pipes and other devices as necessary
to completely drain the facility in seventy-two (72) hours or less
when required for maintenance or inspection on normally wet basins.
d.
Sediment Storage. All detention facilities shall provide storage
for two (2) years of sediment accumulation, except for those using
roofs of buildings, paved parking areas, or other facilities designed
to preclude the deposition or accumulation of sediment. Sediment storage
volume shall be in addition to the volume required for temporary storage
of stormwater to properly size the detention facility on normally
wet basins.
e.
Erosion Control. Principal spillways and outlet works shall
be designed to prevent erosion and, if necessary, equipped with energy-dissipating
devices to slow the water to normal velocity. Special measures shall
be taken by the developer to not permit sediment from filling the
proposed detention basin during all construction of the proposed development
unless a design is provided and approved to use the detention basin
as a temporary silt basin until such time as the stormwater improvements
are completed and the site vegetated.
f.
Private detention facilities shall be designed requiring the
same criteria as the public detention facilities. The amount of easement
shall be equal to the land occupied by the facility, plus a twenty-foot-wide
strip around the perimeter of the highest elevation attained by the
design storage volume, plus an access easement twenty (20) feet in
width between the facility and the public street. This easement shall
be shown as common ground and be dedicated to the trustees of the
subdivision or owner of the multi-family, commercial, or industrial
property for the purpose of maintenance of the stormwater detention
facility, and shall not be part of a residential lot. The easements
as described above shall also be dedicated to the City for emergency
access or periodic inspection. The following items shall be addressed.
(1)
A plan for perpetual maintenance and designating
responsibility for the maintenance shall be provided for its continuing
performance to the standards established by these criteria.
(2)
Underground detention facilities shall also have
the above-mentioned easements provided. Easements shall be labeled
properly on the record plat or by separate document.
g.
Plan Requirements. The plan requirements shall be the same as set out in Section 510.500 of this Chapter with the following additions:
(1)
Elevation-area-capacity curves for the detention
facility, including notation of the storage volumes allocated to runoff
and permanent residual water storage for other uses (wet basins only).
(2)
Inflow hydrograph (detention volumes for Rational
Method) for the 2-, 15-, 25-, and 100-year recurrence interval design
storms.
(3)
Stage-discharge rating curves for each spillway
and for combined spillway discharges.
(5)
A ten-foot minimum depth for all retention (wet
detention) basins shall be required (per DNR recommendation for healthy
aquatic environment). This will be required until the five percent
(5%) escrow release has been established.
(6)
All storm sewer pipes shall be labeled as either
"public" or "private" on the storm sewer profile sheets. The transition
structure from public to private shall also be labeled accordingly.
Pipes are not allowed to have said transition outside of a structure.
(7)
For all underground detention facilities, a manhole
(or similar accessible structure) shall be provided both upstream
and downstream [within ten (10) feet or as approved by the Director],
for access. Access lids shall be labeled with the words "underground
basin" or similar on each structure. Labels shall be cast into the
lid and be of the same material that is required under storm sewer
design.
(8)
No planting of trees or extensive landscaping shall
be permitted over the top of the underground detention facility, within
the limits of the encompassing easement.
D.
Construction Alternates. The developer shall build as part of his/her
development a detention facility as required by this Section unless
the following Subsections apply:
1.
If requested by the developer or by the City, the City, at its option, may waive the construction of a detention facility as for the development. The developer shall seek approval from the Director for the basin to be waived. If the waiver is granted, the developer shall pay an amount equal to the cost of detention for the site as determined by the unit cost as published and updated by St. Louis County. This money is to be used in a stormwater fund for future City stormwater projects. A contractor's bid may be submitted in lieu of using the published data although the bid must be reviewed and approved by the Director prior to acceptance. This option may only be considered if the requirements set out in Subsection (B) above are applicable.
2.
Off-Site/Regional Detention. All detention facilities shall
be on the individual site being developed. The exception to this requirement
is if there is either a regional detention facility identified that
accounts for the subject property being developed, or if the subject
property is a lot within a subdivision plat that accounts for detention.
In any case, if the off-site or regional detention facility does not
fully account for the City's requirements at the time of development,
then supplemental detention may be needed.
a.
On-site detention will be required whenever increased runoff
from the proposed development creates a hazard downstream.
b.
Supplemental detention may be provided by means of modifications
to the off-site or regional basin if feasible. If it is not feasible,
then supplemental detention on-site shall be provided.
c.
If the off-site/regional detention facility is existing at the
time of development, then the developer of the subject property shall
provide approval for use of the detention facility (that also addresses
maintenance responsibility) for said facility, prior to approval.
E.
Inspection, Maintenance, And Acceptance By The City.
1.
The Director shall inspect or cause to be inspected all stormwater
detention facilities constructed within the City. Through such inspections
the Director shall ensure that the facilities under construction are
being constructed in accordance with the approved plans for such development.
2.
Each owner of the property being developed or has been developed,
whose property has caused the increase in runoff that has necessitated
the need for detention, has the responsibility and duty to properly
operate and maintain any stormwater management system and/or detention
facility, which has not been accepted for maintenance by the City.
The responsibility of maintenance of the system and subdivision projects
shall remain with the developer until such time as the stormwater
management system escrow for such development has been released and
turned over to the homeowners' association or property owner(s)
of record. If there is no active homeowners' association, all
properties listed as part of the subdivision and/or development will
become responsible for maintenance. This will include all underground
detention facilities.
3.
Maintenance responsibility shall remain with the property owner(s)
whose said property or development necessitated the need for detention.
Regardless of ownership of said basin, should the developer, owner(s),
association, or other entity responsible for maintenance choose to
sell, abandon, or otherwise vacate their interest or ownership of
the basin, this will in no way eliminate their maintenance responsibility
of said basin unless they have provided for perpetual future maintenance
separately.
4.
All such privately owned and maintained stormwater systems and/or
detention facilities shall be subject to periodic inspections by the
City Engineer and/or his/her designee. After an inspection by the
City Engineer and/or his/her designee, he/she determines whether or
not the conditions of the privately owned stormwater system and/or
detention facilities are safe and operating and functioning per the
approved plans.
a.
For underground detention facilities, the owner(s) shall be
required to submit an annual maintenance report to the City Engineer
verifying its condition and that it is operating and functioning per
the approved plans. Said inspection shall be performed by a competent
professional who is experienced in this type of work.
5.
If the privately owned stormwater systems and/or detention facility is found to be deficient and in need of compliance measures or maintenance, the property owner(s) will be notified and connection of such requested. Any connections will be the responsibility as identified in Subsection (E)(3) above. Any cost incurred by the City, as a result of the City Engineer's actions, shall be assessed against the owner(s) of the system. Initially, the stormwater funds as set up in Subsection (D)(2) above may be used to pay for any such emergency authorized by the City.
6.
After notification is provided to the owner(s) of any deficiencies
discovered from an inspection of a privately owned stormwater system
and/or detention facility, the owner(s) shall have thirty (30) days
or other time frame mutually agreed to between the City and the owner(s)
to correct the deficiencies. The City shall then conduct a subsequent
inspection to ensure completion of the repairs. If repairs are not
undertaken or not found to be done properly, then enforcement procedures
following this Section shall be followed.
7.
If, after inspection by the City, the condition of a privately
owned stormwater system and/or detention facility presents an immediate
danger to the public health or safety, because of an unsafe condition
or improper maintenance, the City shall take such action as may be
necessary to protect the public and make the facility safe. Any cost
incurred by the City, as a result of the City Engineer's actions,
shall be assessed against the owner(s) of the system.
8.
Native Vegetation/Natural Basins. Should the owner(s) of a privately
owned stormwater system and/or detention facility want to alter original
construction to convert the system to provide increased water quality
benefits and have a more natural appearance, such alternatives must
be submitted by permit process to the City Engineer or his/her designee
for review of detention facility functionality and approval.
a.
Conversion examples include, but are not limited to, native
grasses, wildflowers, removal of concrete swales, or alteration of
outfall structures.
b.
If approved, the owner(s) shall prepare and submit a maintenance
schedule for the conversion. Modifications will be subject to inspection
during conversion and continue after acceptance.
c.
If approved, converted areas shall be excluded from mowing requirements as stated in Section 215.090 of this Code, Weeds, but an alternative mowing/maintenance schedule shall be submitted and followed.
(1)
Annual mowing will be required in efforts to prevent the vegetation from becoming excessive and basins from getting overgrown. All conversion- permitted basins shall be mowed by November 1 of each year. Failure to meet this requirement will result in enforcement in accordance with Section 215.090.
e.
Under no circumstances does the altercation from a detention
facility to a native vegetation area waive the requirements for detention.
9.
Upon acceptance of public detention facilities by the Board
of Aldermen, the stormwater detention facility may be dedicated to
the City for perpetual maintenance. Any such system shall include
adequate perpetual access and sufficient area for maintenance by the
City personnel and vehicles.
[Ord. No. 1623, 5-22-2017]
The Mid-America Regional Council (MARC) "MANUAL OF BEST MANAGEMENT
PRACTICES FOR STORMWATER QUALITY," August 2009, is hereby adopted
as the design requirements for stormwater quality for the City and
made a part thereof, as if fully set out in this Article with the
additions, insertions, deletions, and changes prescribed in this Article.
[Ord. No. 2069, 3-15-2023]
Throughout the Manual of Best Management Practices for Stormwater Quality adopted in Section 510.520, whenever the terms "Kansas City, Kansas City Metropolitan Area, Kansas City Region or MARC Region" appears, it shall be deemed to mean the City of Cottleville, Missouri.
[1]
Editor's Note: Former Section 510.530, Design Criteria And
Manual Of Best Management Practices For Stormwater Quality Jurisdictional
Titles, was repealed 3-15-2023 by Ord. No. 2069. Prior history includes
Ord. No. 1623.
[Ord. No. 1623, 5-22-2017; Ord. No. 2069, 3-15-2023]
Throughout the Manual of Best Management Practices for Stormwater Quality adopted in Section 510.520, wherever the term "Director" or "Engineer" appears, it shall be deemed to mean the Director.
[Ord. No. 1623, 5-22-2017]
A.
Compliance With Laws. Each applicant shall comply with all applicable
Federal and State laws as well as City ordinances, resolutions, rules
and regulations heretofore and hereafter adopted or established.
B.
Appeals. Any party shall have the right to appeal decisions of the
Director to the Board of Adjustment of the City.
C.
Penalties For Violations.
1.
General. Violation of the provisions of this Article for failure
to comply with any of its requirements, including conditions and safeguards
established shall constitute an offense. Each day such violation continues
shall be considered a separate offense.
2.
Corrective Action. Nothing herein contained shall prevent the City of Cottleville from taking such other lawful action as is necessary to prevent or remedy any violation, including, but not necessarily limited to abatement of public nuisances pursuant to Chapter 215 of this Code. All such costs connected therewith shall accrue to the person or persons responsible.
D.
Calculation Of Time. Unless otherwise indicated, when the performance
or doing of any act, duty, matter, or payment is required under this
Article or any permit, and a period of time is prescribed and is fixed
herein, the time shall be computed to as to exclude the first and
include the last day of the prescribed or fixed period of time.
E.
Design Criteria Applicable To The City. The Design Criteria outlined
herein and adopted by this Article relating to storm water drainage
facilities shall be fully applicable to work performed by the City
and its departments.
F.
Implementation. The Design Criteria and the Manual of Best Management
Practices for Stormwater Quality adopted by this Article shall be
enforced for all developments for which the preliminary plat is considered
by the Planning and Zoning Commission after the effective date of
this Article, and for all single lot developments for which the site
plan is considered by the Planning and Zoning Commission after the
effective date of this Article. Sites previously approved that are
requesting an extension of time or a minor modification to the previously
approved plan shall be exempted from the new code requirements and
shall comply with the codes intact at the time of their initial approval.
Previously approved sites that have no infrastructure constructed
and/or for which a new configuration of the site or new configuration
of the storm water detention facilities are proposed shall comply
with the codes adopted herein.
