[Ord. No. 1684 §11, 5-15-2013]
A.
With
continued growth and development the community has been confronted
with issues of increased storm water runoff and its impact upon streams,
the environment and quality of life. Increased storm water 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 run off site at faster rates. The solid surfaces do not allow absorption
and filtering of the storm water, and all the other benefits that
vegetated ground cover provides. It is the policy of the City of Dardenne
Prairie to protect and promote the public health, safety and general
welfare by the management of storm water. The management of storm
water 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 Dardenne Prairie.
[Ord. No. 1684 §11, 5-15-2013]
For the purposes of this Chapter, 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 Chapter"; and the
word "shall" is always mandatory.
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 25-year flood.
Rainstorms of a specific duration having a four percent (4%)
probability of occurrence in any given year.
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 pre-development or existing condition peak flow corresponding
to a selected rainfall frequency event.
The specific person applying for the permit for an approved
storm water management system.
The flood having a one percent (1%) probability of being
equaled or exceeded in any given year, i.e., the 100-year flood. (The
base flood, adopted by the Federal Emergency Management Agency, FEMA,
is the 100-year flood.)
Practices, procedures or a schedule of activities to reduce
the amount of sediment and other pollutants in storm water discharges
associated with construction and land disturbance activities.
The City Engineer or his/her designee.
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 storm water 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 (0).
Any man-made area or facility designed to detain (hold) storm
water temporarily during and immediately after a runoff event.
The temporary detaining or storage of storm water 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.
Any system of artificially constructed drains, including
open channels and sewers, used to convey storm water, surface or ground
water either continuously or intermittently to natural watercourses.
A facility designed for the temporary storage of storm water
runoff.
A form of security to guarantee the completion or performance
of a storm water 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 (100-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
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 storm water management system. The
LS requirement for the development is determined by the change in
runoff from the pre-development condition. The LS provided by the
storm water 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 reconstruction.
Municipal Separate Storm Sewer System.
The point location or structure where drainage discharges.
A permit granted by the City to a person to construct a storm
water management system.
Any person to whom a permit has been granted by the City
under this Chapter.
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.
An empirical formula for calculating peak rates of runoff
resulting from rainfall.
The area to be developed or improved.
A technique for calculating storm water runoff volume and
peak flow described in Soil Conservation Service (SCS) Technical Release
55.
Monies reserved for funding improvements to storm water management
systems owned and maintained by the City of Dardenne Prairie.
The drawings, computations, data, reports, etc., which identify
how storm water runoff is to be managed.
All means, natural or man-made, used for conducting storm
water 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 storm water 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 storm water runoff to a
given point.
The assumed water quality improvement value of a cover type
or BMP, based on its ability to improve water quality and mitigate
runoff volume.
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.
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%) storm water runoff volume of all twenty-four (24) hour
storms on an annual basis. In the Dardenne Prairie 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 storm water runoff volume. It is calculated
by multiplying the water quality storm times the volumetric runoff
coefficient and site area.
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. 1684 §11, 5-15-2013]
A.
The
City Engineer shall prepare for review and approval by the Board of
Aldermen a City-wide storm water management plan (SWMP). The SWMP
shall include an assessment of stability, habitat, flooding, and water
quality for streams and detention basins within the City of Dardenne
Prairie, Missouri. The SWMP shall contain recommendations for future
locations of capital improvements and retrofits to provide for improved
stabilization, storage capacity, and water quality best management
practices. 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 goals of storm water 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 streams and watersheds. The three (3) basic methods
for addressing these goals include maintaining existing conditions,
decreasing peak flows and reducing or removing pollutants. These goals
will be achieved by preserving and protecting quality stream corridors,
renovating and improving degraded stream sections, and retrofitting
detention basins for water quality benefits.
Until such time as the SWMP has been prepared and approved by
the Board of Aldermen, the City Engineer is authorized to make such
determinations to implement the intent and purpose of the City's ordinances.
After the approval of the SWMP by the Board of Aldermen, the construction
of all storm water management systems shall be in substantial compliance
with the SWMP.
B.
Changing City-Approved Drainage Patterns. Storm water drainage
patterns that have been approved by the City shall not be changed
without approval of the City Engineer.
[Ord. No. 1886, 10-18-2017]
A.
The construction of any structure or the performing of any activity
which affects the ground surface and/or vegetation that is within
or upon any area of a stormwater management system, including, but
not limited to, swales on private property, shall be prohibited except
as approved by permit.
B.
Applications for permits required pursuant to this Section shall
be submitted to the City Engineer for approval on forms created by
the City Engineer. Applicants for permits must submit the following:
1.
The name, address and phone number of the applicant;
2.
The name, address and phone number of the owner(s) of the subject
property;
3.
The name, address, phone number and contact person for any contractor
hired by the applicant to perform the construction or activity requiring
the permit required pursuant to this Subsection;
4.
The address of the subject property;
5.
Such information as may be required by the City Engineer to
evidence the provision of adequate facilities to carry surface waters
to the nearest practical storm drain, natural watercourse, street
or other suitable place to deposit and receive such waters, which
may include, but is not necessarily limited to:
6.
The application fee of four hundred dollars ($400.00) plus one
hundred dollars ($100.00) per acre of land affected.
C.
Nothing contained in this Section shall prohibit the performance
of routine maintenance of landscaped areas or other existing vegetation.
[Ord. No. 1684 §11, 5-15-2013]
A.
Any
development or area which is to be paved, expanded, redeveloped or
otherwise improved shall be required to provide on-site storm water
management unless the City Engineer 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 storm water 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
storm water management system has been either constructed or programmed
or identified for construction by the City, and 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 storm water 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 Storm Water Management Improvements Fund an amount equal to the cost of the otherwise required on-site storm water management system. Reference Section 550.090(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 City Engineer.
b.
Contributions to the Storm Water 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 Chapter and
provide a benefit to the watershed that equals or exceeds the benefit
that a detention facility would provide.
[Ord. No. 1684 §11, 5-15-2013]
A Storm Water Management Improvements Fund shall be and is created by the adoption of this Chapter. The Storm Water Management Improvements Fund shall be reserved for funding improvements to storm water systems owned and maintained by the City, and for no other purposes unless authorized in this Chapter. All contributions made by parties developing within the City in accordance with Section 550.040 of this Chapter shall be deposited to said fund. Said fund shall be maintained in an interest-bearing account.
[Ord. No. 1684 §11, 5-15-2013]
When the City Engineer determines that additional storage capacity
beyond that required by the applicant for on-site storm water 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 Storm Water Improvement
Plan, the City may acquire from the applicant or owner, by purchase
or dedication, the construction of storm water management systems
to the extent that it exceeds the required on-site storm water management.
[Ord. No. 1684 §11, 5-15-2013]
A.
The
City Engineer shall inspect, or cause to be inspected, all storm water
management systems constructed within the City of Dardenne Prairie,
Missouri. Through such inspections, the City Engineer shall ensure
that the facilities under construction are being constructed in accordance
with the approved plans for such development.
B.
If
it is determined that construction is not in accordance with the approved
plans, the City Engineer shall immediately issue written notice to
the permittee and the surety, of the nature and location of the non-compliance,
specifying what remedial work is necessary to bring the construction
into compliance. The notified permittee shall immediately, unless
weather conditions or other factors beyond the control of the permittee
prevent immediate remedial action, commence the remedial action and
shall complete the remedial work within seventy-two (72) hours, or
within a reasonable time, not to exceed seven (7) calendar days, after
receipt of said notice. Upon satisfactory completion of the remedial
work, the City Engineer shall issue a notice of compliance.
C.
In
the event that the remedial action is not taken, the City Engineer
may then issue a stop work order, which stop work order shall direct
all parties involved to cease and desist all or any portion of the
work on the development except such work necessary to bring the development
into compliance. If such stop work order is ignored, the parties shall
be in violation of this Chapter and subject to the penalties contained
herein.
D.
Each
owner of the property being developed has the responsibility and duty
to properly operate and maintain any storm water management system,
which has not been accepted for maintenance by the City. The responsibility
of maintenance of the system in subdivision developments shall remain
with the developer until such time as the storm water management system
escrow for such development has been released. Upon release of escrow
the maintenance responsibility shall be vested in the trustees of
the subdivision by virtue of a trust indenture. The indenture of trust
shall clearly indicate resident responsibility for maintenance. The
responsibility for maintenance in a single lot development shall remain
with the general contractor and owner until final inspection of the
development is approved, and an occupancy permit is issued. After
occupancy, the maintenance of the management system shall be vested
in the owner of the development. All such privately-owned and maintained
systems and BMPs shall be subject to periodic inspection by the City
Engineer or his representative.
E.
If,
after an inspection by the City Engineer, the City Engineer determines
that the condition of a privately-owned storm water management system
is an immediate danger to the public health or safety because of an
unsafe condition, or if the trustees or owner fail to provide a reasonable
degree of maintenance, the City Engineer shall take such action as
may be necessary to protect the public health and safety and make
the system safe and correct. Any costs incurred by the City, as a
result of the City Engineer's actions, shall be assessed against the
owner(s) of the system.
F.
Upon
acceptance by the Board of Aldermen, a storm water management system
may be dedicated to the City for perpetual maintenance. Any such system
shall include adequate perpetual access and sufficient area for maintenance
by City personnel and vehicles.
[Ord. No. 1684 §11, 5-15-2013]
Upon approval of the final storm water management plan for any
storm water management system, but before the issuance of any permits,
the City Engineer 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 storm water
management plan. This performance security shall not be fully released
by the City Engineer 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. A one (1) year maintenance
escrow against defects in workmanship will be required by the City
Engineer for any system dedicated to the City.
[Ord. No. 1684 §11, 5-15-2013]
A.
Applicability. The requirements of storm water management
outlined in this Chapter shall apply to all developments within the
corporate limits of the City of Dardenne Prairie, Missouri. Storm
water management plans shall be provided and designed in accordance
with the requirements of this Chapter and all design and construction
specifications adopted by this Chapter. Each development is to strive
to maintain or improve pre-development peak flows, runoff volumes
and water quality. Storm water 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 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 two (2) cubic
feet per second (cfs) or greater for the 15-year, twenty (20) minute
storm event. The differential runoff is calculated by the Rational
Method using PI factors.
3.
Development or redevelopment of sites without prior storm water detention
shall provide detention or retention, when the cumulative differential
increase equals two (2) cfs or greater. Developments with prior detention
shall provide additional detention or retention for all increased
runoff.
4.
When existing storm water management (detention or retention) facilities
are going to be used to accommodate additional runoff, the facilities
shall be retrofitted to meet the current storm water management requirements.
Developments which cannot meet this requirement due to physical constraints
will be evaluated for alternatives on a case-by-case basis.
B.
Affidavit 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 City Engineer, 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. 1684 §11, 5-15-2013]
A.
Preliminary Storm Water Management Plans. Concurrent with
the filing of a development plan, the following information shall
be submitted to the City Engineer:
1.
Topographic map outlining the limits of the contributing watershed.
Topographic maps should be the best available. Topographic maps with
two (2) foot contour intervals will be accepted as a minimal requirement.
2.
A map of the property being of suitable scale and contour interval,
showing the land to be developed and such adjoining land whose topography
may affect the layout or drainage patterns for the site.
3.
The location of streams and other floodwater runoff channels, the
extent of floodplains, the limits of the floodway, if pertinent, and
any additional information, all of which shall be properly identified.
4.
The normal elevation and shoreline of lakes, ponds, swamps, and detention
basins including their floodplains and inflow and outflow structures,
if such structures exist.
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.
Concepts that will be considered within the site to handle the quantity
of storm water runoff, including the methods for detention or control
of increased storm water runoff generated by the development, and
how storm water quality will be addressed.
7.
A general plan showing the extent and nature of the storm water management
system planned to serve the site including preliminary calculations
indicating the runoff which must be handled by such systems, the methods
and criteria which have been utilized in calculating such runoff,
and basic information regarding the receiving watercourse into which
such system will discharge.
8.
A general plan indicating the exterior perimeter of the site, the
general development proposed for the site, and an indication by means
of rough contours showing the terrain after grading of the site.
9.
All computations, plans, and specifications must be prepared and
sealed by a professional engineer registered in the State of Missouri.
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Following receipt of a preliminary storm water management plan,
and the information to be included with such plan, the general concepts
and planning proposals will be reviewed by the City Engineer. The
City Engineer will schedule a review meeting with representatives
of the developer, including, but not limited to, the developer's engineer,
to review the overall concepts included in the preliminary storm water
management plan. The purpose of this review shall be to jointly agree
upon an overall storm water management plan for the proposed development
and to review criteria and design parameters which shall apply to
the final design for the development of the site.
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B.
Final Storm Water Management Plans. Following review of
the preliminary storm water management plan and after the concept
review meeting and approval of the preliminary plan by the City Engineer,
a final storm water management plan shall be prepared for each phase
of the proposed development as each phase is developed. The final
storm water management plan shall constitute a refinement of the concepts
approved in the preliminary storm water management plan with preparation
and submittal of the following additional detailed information unless
specifically excluded during the preliminary concept review meeting:
1.
A topographic map of the site and adjacent areas, of suitable scale
and contour interval, which shall define the location of watercourses,
the extent of floodplains and calculated high water elevations, the
shoreline and elevation of lakes, ponds, swamps, and detention basins
including 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 storm water management system including
the location and size of all drainage structures, storm sewers, channels
and channel sections, detention basins, water quality BMPs, and other
storm water improvements, and analysis regarding the effect said improvements
will have upon the receiving channel and its high water elevation.
5.
A planting palette and seeding rates for vegetated water quality
BMPs.
6.
The location and calculated flow rates of other existing storm drains,
inlets and outfalls.
7.
The location and calculated flow rates of any existing storm sewers
which occur within the site or adjacent thereto within a distance
of approximately two hundred (200) feet from the perimeter of said
site; or as conditions warrant.
8.
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.
9.
The slope, type, size, and flow calculations for all existing and
proposed storm sewers and other waterways.
10.
For all detention basins, 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.
11.
For all detention basins, design hydrographs of inflow and outflow
for the 2-year storm and 25-year storm differential runoff rates from
the site under proposed development conditions.
12.
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 100-year peak flow conditions produced by the projected
development of the contributing watershed based on the best available
land use information.
13.
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 storm water runoff under the controlled conditions called
for by these regulations and the relationship of structures, streets,
and other utilities to such channels.
14.
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.
15.
Calculations for water quality volume (WQv) to determine the amount
of storage needed to capture and treat ninety percent (90%) of the
average annual storm water runoff volume.
16.
Calculations for flood protection volume (Qp) to protect downstream
areas from flooding.
17.
Calculations for the level of service (LS) and value rating (VR)
to determine the level of water quality protection needed for a development.
18.
Basic information regarding the receiving watercourse into which
the proposed storm water 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.
19.
A Storm Water Pollution Prevention Plan (SWPPP) pursuant to the requirements of Chapter 412 of this Code.
20.
All computations, plans, and specifications must be prepared and
sealed by a professional engineer registered in the State of Missouri.
21.
The City Engineer, or his/her designee, shall review final storm
water management plans.
a.
If it is determined that the proposed development will provide storm
water 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 City Engineer shall approve the final storm water management
plan or conditionally approve such final storm water management plan
setting forth the conditions thereof.
b.
If it is determined that the proposed development will not manage
storm water quantity and quality in accordance with these regulations,
the City Engineer shall disapprove the final storm water management
plan.
[Ord. No. 1684 §11, 5-15-2013]
The "Standard Construction Specifications for Sewers and Drainage
Facilities of the Metropolitan St. Louis Sewer District", 2009, as
published by Metropolitan St. Louis Sewer District, is hereby adopted
as the Standard Construction Specifications for the City and made
a part hereof, as if fully set out in this Chapter, with the additions,
insertions, deletions, and changes prescribed in this Chapter.
[Ord. No. 1684 §11, 5-15-2013]
Chapter 4 of "The Metropolitan St. Louis Sewer District —
Rules and Regulations and Engineering Design Requirements for Sanitary
Sewage and Storm Water Drainage Facilities", February 2006, is hereby
adopted as the design requirements for storm drainage facilities for
the City and made a part thereof, as if fully set out in this Chapter,
with the additions, insertions, deletions, and changes prescribed
in this Chapter.
[Ord. No. 1684 §11, 5-15-2013]
The Mid-America Regional Council (MARC) "Manual of Best Management
Practices for Storm Water Quality", August 2009, is hereby adopted
as the design requirements for storm water quality for the City and
made a part thereof, as if fully set out in this Chapter, with the
additions, insertions, deletions, and changes prescribed in this Chapter.
[Ord. No. 1684 §11, 5-15-2013]
Throughout the Standard Construction Specifications adopted in Section 550.110 and the Rules and Regulations and Engineering Design Requirements for Storm Water Drainage Facilities adopted in Section 550.120, whenever the term "District" appears, it
shall be deemed to mean the City of Dardenne Prairie, Missouri. Wherever
the phrase "St. Louis County" appears in the Standard Construction Specifications or the Rules and Regulations and Engineering Design Requirements for Storm Water Drainage Facilities, the phrase shall be replaced with the phrase "St. Charles County". Throughout the Manual of Best Management Practices for Storm Water Quality adopted in Section 550.125, 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 Dardenne Prairie,
Missouri.
[Ord. No. 1684 §11, 5-15-2013]
Throughout the Standard Construction Specifications adopted in Section 550.110, the Rules and Regulations and Engineering Design Requirements for Storm Water Drainage Facilities adopted in Section 550.120, and the Manual of Best Management Practices for Storm Water Quality adopted in Section 550.125, wherever the term "Director" or "Engineer" appears, it shall be deemed to mean
the City Engineer.
[Ord. No. 1684 §11, 5-15-2013]
A.
Standard Construction Specifications. The Standard Construction Specifications adopted in Section 550.110 are amended as follows:
1.
Delete: Materials of Construction, Part 2, Section (G)(1)(e): Fiberglass pipe (RPM).
2.
Delete: Materials of Construction, Part 2, Section (G)(2)(a): Vitrified clay pipe — 12 inch and larger.
3.
Delete: Materials of Construction, Part 2, Section (G)(2)(e): Fiberglass pipe (RPM) — 12 inch and larger.
4.
Delete: Materials of Construction, Part 2, Section (G)(2)(f)
High density polyethylene: 12 — 24 inch, and replace
with: 12 — 48 inch.
5.
Delete: Materials of Construction, Part 2, Section (G)(11)
High Density Polyethylene (HDP E) Corrugated Pipe in its entirety
and replace with: The use of HDPE corrugated pipe with an
integrally formed smooth waterway is approved for use, with the exception
that HDPE pipe cannot be used under or through existing street right-of-way
or through an area where potential future right-of-way may occur.
Reinforced concrete pipe shall be installed to the next structure
outside of the right-of-way. The HDPE corrugated pipe shall be installed,
inspected and tested according to manufacturer specifications or in
accordance with ASTM 2390, D2321, C969, C924, and C1103. Nominal sized
HDPE pipe 12 to 36 inches in diameter shall conform to the AASHTO
M294 classification "Type S"; and 42 inch to 48 inch diameter HDPE
corrugated pipe shall conform to AASHTO MP6-95 classification "Type
D".
6.
Add: Materials of Construction, Part 2, Section (G)(11)(a): All HDPE corrugated pipe joints shall consist of bell and spigot
joining system with the bell covering two pipe corrugations as recommended
in AASHTO M294. Pipe joints with rubber O-Ring gaskets meeting ASTM
F477 shall be installed on the spigot end of the pipe. Both the bell
and spigot (with O-Ring gasket) ends of each pipe shall be lubricated
as recommended by the manufacturer and inserted to the homing mark
on the spigot end of the pipe.
7.
Add: Materials of Construction, Part 2, Section (G)(11)(b): HDPE corrugated pipefittings may be either molded or fabricated
and shall conform to the requirements of AASHTO M252 and M294. The
fittings shall not reduce or impair the overall integrity or function
of the pipeline. Only fittings supplied or recommended by the pipe
manufacturer shall be used.
8.
Delete: Materials of Construction, Part 2, Section (G)(13)
Fiberglass Pipe: delete this Section in its entirety.
9.
Delete: Materials of Construction, Part 2, Section (H)(1)(a)
Sanitary and Combined Sewers: Vitrified Clay Pipe (VCP) and
Fiberglass Pipe (RPM).
10.
Delete: Materials of Construction, Part 2, Section (H)(1)(a)
Storm Water Sewers: Vitrified Clay Pipe (VCP) and Fiberglass
Pipe (RPM).
11.
Delete: Materials of Construction, Part 2, Section (H)(7)
Type F Joints.
12.
Delete: Excavation, Part 3, Sections (F)(2)(b and c) in their entirety.
13.
Add: Pipe Sewer Construction, Part 4, Section (B)(5): HDPE corrugated pipe manufactured for this specification shall comply
with the requirements for test methods, dimensions, and markings found
in AASHTO designations M252 and M294. HDPE corrugated pipe and fittings
shall be made from virgin PE compounds which conform with the requirements
of cell class 335420C as defined and described in ASTM D3350.
14.
Amend: Pipe Sewer Construction, Part 4, Section (G)(4)(a): The use of precast concrete inlet covers (Detail Sheet 46) is prohibited.
Where precast concrete structures are permitted or required by the
project plans, they will be manufactured in accordance to Part 2 of
this specification and to the sizes and shapes detailed in the drawings
for this specification.
15.
Amend: Pipe Sewer Construction, Part 4, Section (I)(2) Pipe
Sewers: Any reference to locator disks shall be changed to
locator balls.
16.
Delete: Channel Construction, Part 6, Section (C)(1)(c) and
replace with: The rock shall be neatly placed, and shall
not be less than one foot thick on the sides and on the bottom. The
surface shall be reasonable regular and uniform.
17.
Delete: Detail Sheet 48, Steel Grates.
18.
Delete: Detail Sheet 49, Steel Vane Grate.
19.
Delete: Detail Sheet 71, Signs.
[Ord. No. 1684 §11, 5-15-2013]
A.
Rules And Regulations. The Rules and Regulations and Engineering Design Requirements for Storm Water Drainage Facilities adopted in Section 550.120 are amended as follows:
1.
Section 4.020 General Requirements of Storm Sewer Construction: Hydraulic Grade Line and Inlet/Flow Capacity Data Computations shall
be submitted on Attachment A ("Hydraulic Data Form") for all projects.
The form may be computerized; however, all information required on
the form shall be included in the computerized version.
Section 4.020.11 Overflow/Design System Paragraph 2: Whenever the phrase "100-year, 20-minute" appears in the design
requirements, the phrase shall be replaced with "15-year, 20-minute".
2.
Section 4.030.01 (1) Rainfall Frequency: This Section
shall be deleted and replaced as follows:
A fifteen (15) year rainfall frequency is to be used in St.
Charles County. In the design of local storm sewer systems, a twenty
(20) minute time of concentration shall be used. Figure 4-1 gives
rainfall curves for 2-5-10-15-20- and 100-year frequencies.
3.
Section 4.030.03 Hydraulic Grade Line Limits, Paragraph 5: This paragraph shall be deleted.
4.
Section 4.030.04 Inlets Paragraph 2: Inlet capacity
should not be less than the quantity flow tributary to the inlet and
bypass flow shall be avoided whenever possible. Inlets at low points
or grade pockets should have extra capacity to compensate for possible
flow bypass of upstream inlets. Figure 4-3 shows inlet capacity/maximum
gutter capacity with a given gutter line grade and flow. The value
for inlet capacity obtained from Figure 4-3 shall be multiplied by
a factor of 0.85 and the result will be used for the capacity of the
inlet. The multiplication factor is to account for clogging of inlets
and bypass around the inlet. An example is presented below.
Example: Street/Gutter at a 3% grade has an
inlet capacity of approximately 1.6 CFS for a single inlet and approximately
5.1 CFS for a double inlet capacity.
1.6 CFS * 0.85 = 1.36 CFS →→→→ single inlet
capacity
5.1 CFS * 0.85 = 4.34 CFS →→→→ double inlet
capacity
The following guidelines shall also apply to inlets:
a.
Inlets shall be appropriately sized and spaced, taking into consideration
bypass, depth of flow and gutter capacity. Inlets shall be required
when the pavement is super elevated or warped causing water to flow
from the gutter line across the roadway.
b.
For inlets in vertical sag curves, the center of the main chamber
shall be placed within one (1) foot of the computed mathematical low
point.
c.
Inlets shall be located so the inlet face is a maximum of two and
one-half (2.5) feet behind the back of the roadway curb in new residential
subdivisions. The sump shall begin two (2) feet in front of the back
of curb. The top elevation of the stone shall remain three (3) inches
above the top of rolled curb and level with the top of vertical curb.
When required, the nearest two (2) sections of sidewalk on each side
of the inlet shall be warped down to the top of the inlet stone elevation.
At intersections, inlets shall be placed so no part of the inlet structure
or sump is in the curb rounding.
d.
Area inlets in roadway ditches shall be compatible with the ultimate
pavement improvements. Rear yard area inlets shall be required when
more than one (1) cubic feet per second (CFS) is concentrated between
buildings and crossing sidewalks or curbs.
e.
Bypass shall be minimized at inlet structures and shall be shown
on the hydraulic computations and site drainage map. Bypass shall
be used in determining gutter flow downstream. Bypass shall not be
considered in sizing of the storm sewer pipe system (i.e., pipe shall
be designed for total tributary "Q" regardless of bypass). Curb inlets
shall be required to intercept runoff when more than one (1) CFS crosses
street intersections.
5.
Section 4.030.06 Culverts: Add Paragraph 3. Crossroad
Culverts — Crossroad culverts not at low points shall be designed
on a storm frequency of fifteen (15) years with entrance control and
a minimum of two (2) feet of freeboard at the shoulder line. Culverts,
functioning as the low point in floodplains shall be designed on a
storm frequency of one hundred (100) years with entrance control and
a minimum of two (2) feet of freeboard at the shoulder line. Culverts
functioning as the low point not in floodplains shall be designed
on a storm frequency of fifty (50) years with entrance control and
a minimum of two (2) feet of freeboard at the shoulder line. Refer
to the U.S. Department of Transportation Hydraulic Engineering Circular
No.5 entitled "Hydraulic Charts for the Selection of Highway Culverts".
6.
Section 4.030.06 Culverts: Add Paragraph 4. Drainage
Pipes (Inlet) — At all intake structures such as flared end
sections or headwalls, entrance control shall be applied. Two (2)
foot minimum freeboard shall be required. Upstream inundation shall
be checked. Where inundation extends beyond the site property line
and exceeds the Design Water Surface Elevation of the natural drainageway/channel,
a backwater ponding easement from the affected off-site property owner
shall be required prior to approval of the improvement plans. Concrete
outfall pipes shall have a reinforced concrete headwall or flared
end section with cut-off wall and properly sized, placed revetment
underlain with a woven geotextile fabric or paved ditch. Cut-off walls
shall be two (2) feet deep on upstream headwalls/end sections.
7.
Section 4.030.06 Culverts: Add Paragraph 5. Drainage
Pipes (Outlet) — Outfall termination shall occur at a natural
drainageway/channel so that the flow does not exceed the natural capacity
of the drainageway/channel. Discharge velocities in an outfall pipe
shall not exceed eight (8) feet per second, where practical. Special
approved methods of energy dissipation will be required when discharge
velocities in outfall pipes exceed five (5) feet per second. Concrete
outfall pipes shall have a reinforced concrete headwall or flared
end section with cut-off wall and properly sized, placed revetment
underlain with a woven geotextile fabric or paved ditch. Revetment
shall be a minimum length of ten (10) feet or ten (10) times the diameter
of the discharge pipe (in feet) whichever is greater when not discharging
to a lake or pond. Revetment in lakes or ponds shall be placed between
the outlet pipe and the low water elevations. Cut-off walls shall
be three (3) feet deep on downstream headwalls/end sections.
8.
Section 4.040.02 Clearance: This Section shall be
deleted and replaced as follows: The lowest point of the bridge superstructure,
not at low points, shall be designed on a storm frequency of fifteen
(15) years with entrance control and a minimum of two (2) feet of
freeboard clearance. Bridges functioning as the low point in floodplains
shall be designed on a storm frequency of one hundred (100) years
with entrance control and a minimum of two (2) feet of freeboard clearance.
Bridges, functioning as the low point not in floodplains, shall be
designed on a storm frequency of fifty (50) years with entrance control
and a minimum of two (2) feet of freeboard clearance.
9.
Section 4.060 Limitations on Areas Draining Across Sidewalks
or Driveways: Delete this Section.
10.
Section 4.070 Impervious Areas — In the City of St.
Louis: This Section shall be renamed "Impervious Areas" and
the second paragraph shall be deleted.
11.
Section 4.080 General Performance Criteria for Storm Water
Management: Wherever the phrase "100-year" appears in the
design requirements, the phrase shall be replaced with "25-year".
Wherever a 24-hour event is specified, Technical Release 55 (TR-55)
shall be used as the method for calculating flows. Wherever a 20-minute
event is specified, flow rates shall be determined using the method
set forth in Section 4.030.01 Flow Quantities.
12.
Section 4.080.01 When Required, Paragraph 1: Paragraph
1 shall be deleted and replaced as follows:
1. The requirements of the storm water quantity and quality
management shall be evaluated for all projects submitted to the City
for review and approval. Storm water management facilities shall be
provided and designed in accordance with the requirements of this
Section and of the Kansas City MARC Manual adopted herein.
13.
Section 4.080.01 When Required, Paragraph 2: Whenever
the phrase "2 cfs" appears, it is to be replaced with "1 cfs".
14.
Section 4.080.02 Unified Storm Water Sizing Criteria: Delete this Section in its entirety and replace with:
Section 4.080.02 Design Considerations.
a. General. This Section presents the summary
for sizing storm water BMPs to meet pollutant removal goals, to prevent
flooding, and to pass extreme floods.
|
Water Quality Volume
(WQv) (acre-feet)
|
WQv
|
=
|
[(P)(Rv)(A)]/12
|
|
P
|
=
|
=rainfall depth in inches= 1.14
| |
|
Rv
|
=
|
volumetric runoff coefficient
| |
|
Rv
|
=
|
0.05 + 0.009(I)
| |
|
Where I= percent impervious cover
| |||
|
A
|
=
|
area in acres
| |
|
Flood Protection Volume
(Q2, Q25 and Q100)
|
The post-developed peak flow from the site must be released
at a rate not to exceed the allowable release rate for the appropriate
rainfall events, as discussed in Section 4.080.03.
| ||
|
|
The following Subsections provide more information on WQv and Flood Protection Volume.
| |||
|
2.
|
Water Quality Volume (WQv)
| |||
|
(a)
|
The Water Quality Volume (denoted WQv) is the storage needed to capture and treat the runoff from ninety
percent (90%) of the recorded daily rainfall events. It is equivalent
to one and fourteen-hundredths (1.14) inches of rainfall multiplied
by the volumetric runoff coefficient (Rv) and
site area. The WQv is directly related to the
amount of impervious cover created at a site. Refer to the MARC Manual
for methods and coefficients.
| |||
|
(b)
|
The following assumptions may be made:
| |||
|
(1)
|
The Water Quality Volume WQv for off-site
areas is not required.
| |||
|
(2)
|
Measuring impervious cover. The measured area
of a site plan that does not have vegetative or permeable cover shall
be considered total impervious cover.
| |||
|
(3)
|
Multiple drainage areas. When a project contains
or is divided by multiple drainage areas, the WQv shall be analyzed for each drainage area. BMPs are not required
to be located within each drainage area, but shall be placed to provide
the greatest impact on water quality (i.e. the placement of BMPs in
drainage areas discharging directly into a creek or body of water
is strongly encouraged, rather than placing BMPs in drainage areas
that have an existing downstream treatment train). Although BMPs are
not required to be placed within each drainage area, the WQv shall be accounted for the overall tract.
| |||
|
(4)
|
Off-site drainage areas. The WQv shall be based on the impervious cover of the proposed site. Off-site
existing impervious areas may be excluded from the calculation of
the WQv.
| |||
|
(5)
|
BMP treatment. The final WQv shall be treated by acceptable BMPs, as provided in the MARC Manual.
| |||
|
3.
|
Flood protection volume.
| |||
|
(a)
|
To protect downstream areas from flooding, storm water shall
be detained on-site or off-site as approved and released at a rate
not to exceed the allowable release rates for the 2-year, 24-hour
storm and 25-year, 24-hour rainfall events for sites larger than ten
(10) acres. For sites less than ten (10) acres, the developed release
rate from the site may not exceed the existing peak flow for the 2-year,
20-minute event and the 25-year, 20-minute event. Note that storm
water pipes, downstream from the control structure, shall be sized
to carry the runoff from the 15-year, 20-minute design storm for the
total tributary upstream watershed. No reduction in outfall pipe size
shall be permitted because of detention.
| |||
|
The outlet structure for the basin shall be sized to pass the
100-year, 24-hour storm event for sites larger than ten (10) acres.
For sites less than ten (10) acres, the 100-year, 20-minute rainfall
event shall be used. The basin shall have a minimum of two (2) feet
of freeboard above the high water elevation for the 100-year storm
event.
| ||||
|
b.
|
The existing and developed peak flows shall be determined by
using Technical Release 55 (TR-55) for sites with a drainage area
of ten (10) acres or more. All assumptions that are required for the
TR-55 method shall be approved, in writing, by the proper agency prior
to commencing grading activities or issuance of a grading permit.
For sites less than ten (10) acres, flow rates shall be determined
using the method set forth in Section 4.030.01 Flow Quantities.
| |||
|
c.
|
The 2-year, 25-year, and 100-year 24-hour inflow hydrographs
shall be determined by using Technical Release 55 (TR-55), "Urban
Hydrology for Small Watersheds" from the Natural Resources Conservation
Service, formerly Soil Conservation Service (SCS). The inflow hydrograph
shall be developed based on the actual flow and timing characteristics
upstream of the detention facility. The rainfall distribution shall
be Type II.
| |||
|
d.
|
The volume of detention may be provided through permanent detention
facilities such as extended dry detention basins, permanent ponds
or lakes, underground storage facilities or parking lots. The engineer
shall make every effort to locate the detention facility at or near
the lowest point of the project such that all of the on-site runoff
will be directed into the detention facility. Multiple use of detention
basins is encouraged. Multiple use may include parking lots, ball
fields, tennis courts, playgrounds, and picnic areas. This is subject
to the approval of the City.
| |||
|
Flows from off-site, upstream areas should be bypassed around
the detention facility to ensure that the proposed detention facility
will function as designed and will provide effective control of downstream
flows with development in place. If off-site flows are directed into
a detention facility, the allowable release rates shall not be modified
without City approval. Modifying the release rate to accommodate off-site
flows may reduce or eliminate the effectiveness of the detention facility,
because it will no longer control the increased volume of runoff during
the critical time period of the watershed.
| ||||
|
The engineer has the option to calculate a site specific release
rate based on the procedures provided by the City's Engineering Department.
The engineer shall provide detailed modeling to prove that the increase
in runoff volume has been limited to existing conditions during the
critical time period of the watershed.
| ||||
|
e.
|
Detention basin volume will be based on routing the post-developed
2-year and 25-year inflow hydrographs through the detention facility
while satisfying the appropriate release rate. The routing computations
shall be based on an application of the continuity principle (i.e.
level pool routing).
| |||
15.
Section 4.080.03 Limits
of Maximum Ponding in Storm Water Ponds, Paragraph 1: Paragraph
1 shall be deleted and replaced with:
1.
For sites larger than ten (10) acres, the maximum ponding elevation
shall be calculated based on a routing of the design storm (100-year,
24-hour event) assuming the low-flow outlet is blocked. For sites
less than ten (10) acres, the 100-year, 20-minute rainfall event shall
be used.
16.
Section 4.080.03 Limits
of Maximum Ponding in Storm Water Ponds, Paragraph 4: Paragraph
4 shall be deleted and replaced with:
4.
A minimum of two (2) feet of freeboard shall be
provided from the top of the basin to the maximum ponding elevation.
17.
Section 4.080.03 Limits of Maximum Ponding in Storm Water
Ponds, Paragraph 5: Paragraph 5 shall be deleted.
18.
Section 4.080.04 General Storm Water Basin Design Requirements,
Paragraph 1(b): Paragraph 1 (b) shall be deleted and replaced
with:
1(b). For sites larger than ten (10) acres,
the basin should have sufficient volume and spillway capacity to pass/contain
the 100-year, 24-hour storm event with the low flow outlet blocked.
For sites less than ten (10) acres, the 100-year, 20-minute rainfall
event shall be used.
19.
Section 4.080.04 General Storm Water Basin Design Requirements,
Paragraph 13: Paragraph 13 shall be deleted and replaced
with:
13. Detention Basin Elevation. If the detention
basin discharges to a piped sewer system, the low elevation of the
detention basin shall be above the 15-year, 20-minute hydraulic elevation
of the receiving storm system.
20.
Section 4.080.04 General Storm Water Basin Design Requirements,
Paragraph 15: Paragraph 15 shall be deleted.
21.
Section 4.080.05 Acceptable Urban BMP Options: This
entire Section shall be deleted and replaced with:
Acceptable Urban BMP Options.
The design and selection of BMPs shall comply with the Mid-America
Regional Council (MARC) "Manual of Best Management Practices for Storm
Water Quality", August 2009, with the additions, insertions, deletions
and changes prescribed by the City.
22.
Section 4.080.06 Storm Water Credits: This entire
Section shall be deleted.
23.
Section 4.080.08 Maintenance Agreement: Delete the
existing paragraphs and insert the following:
Maintenance Agreement. Maintenance of detention
basins shall be the responsibility of the property owner. The detention
basin shall be kept in working order, per the approved plans, at all
times. By submittal of improvement plans, the owner grants the City
of Dardenne Prairie the right to access and inspect the basin at any
time, prior to and after development. The City may submit a list of
deficiencies to the owner, which shall be corrected at the owner's
expense, in a reasonable time.
24.
Section 4.100 Detention Report: Delete Section 6.
25.
Exhibit 4-A: Delete Exhibit 4-A in its entirety.
26.
Table 4-5: Delete Table 4-5.
[Ord. No. 1684 §11, 5-15-2013]
A.
Volume Of Detention Required. The volume of storage required
shall be sufficient to provide enough storage to control the differential
runoff and the water quality storm.
B.
Flows From Upstream Areas.
1.
No materials (fence, shed, landscaping, decorative blocks, etc.)
shall be placed in a manner that blocks or alters the drainage of
adjacent properties.
2.
Flows from upstream areas outside the site should be based upon the
assumption that those areas are fully developed under forecast land
use patterns. For detention sizing, the required storage volume will
be based upon the site only, with the flow from upstream areas being
bypassed or discharged via overflow spillways or other devices.
C.
Early Installation Of Control Systems. Runoff control measures
shall be installed prior to any land disturbance.
1.
Land disturbances that fall under the requirements for a grading
permit, and that are greater than or equal to one (1) acre in size,
are required to have a Storm Water Pollution Prevention Plan.
2.
Land disturbances less than one (1) acre are required to have perimeter
siltation controls that protect off-site properties, road rights-of-way,
storm sewer systems and drainage ways.
D.
Facilities In Floodplains. If detention storage is provided
within a floodplain, only the storage above the 100-year Base Flood
Elevation (BFE) will be credited to the development. No credit will
be granted for detention volumes below the 100-year BFE at that location,
unless compensatory basin storage is provided elsewhere above the
100-year BFE.
E.
Surface Drainage. Sheet flow in excess of one (1) cubic
feet per second (cfs) shall not be allowed over terraces. Berms and/or
vegetated swales shall be provided to collect the flow at the top
or the bottom of the terrace and carry it to a drainage structure.
Total accumulation inside berms and/or swales shall be a maximum of
four (4) cfs. Critical cross sections, profiles, and hydraulic computations
for ditches and swales with flows in excess of one (1) cfs and relocated
or man-made creeks with flows in excess of four (4) cfs shall be provided.
F.
Pipe Slope And Velocity. The minimum grade shall be the
grade establishing a self-cleansing velocity of three (3) feet per
second. Velocities shall not exceed twenty-five (25) feet per second,
where practical.
G.
Drainage Structures. The lateral location of all street
drainage structures shall be shown on the plans by the street centerline
stationing and the perpendicular offset distance.
1.
All manholes shall be located outside of the proposed roadway pavements.
2.
Erosion protection in the form of asphalt curb, gutters, additional
structures, paving and/or revetment may be required at the temporary
termination of pavements.
3.
Subsurface pre-cast storm water structures may be used provided detailed
drawings are submitted and approved prior to construction plan approval.
H.
Open Channel Setback Requirement. Development along natural
watercourses shall have residential lot lines, commercial or industrial
improvements, parking areas or driveways set back a minimum of twenty
five (25) feet from the top of existing stream bank or 15-year, twenty
(20) minute water surface elevation, where no defined bank exists.
The watercourse and twenty-five (25) foot setback area shall be maintained
and made the responsibility of the subdivision trustees. Residential
lots having an area of one (1) acre or greater which shall be exempt
from this regulation if the stream bank is not erosive. In the case
of a site plan, commercial or industrial site, the watercourse and
twenty-five (25) foot setback area shall be maintained and made the
responsibility of the property owner. Permanent native vegetation
and existing ground elevation and grades within the twenty-five (25)
foot setback shall be left intact and undisturbed. Variances will
include designed stream bank erosion control measures and shall be
approved by the appropriate government agency, which has jurisdiction
over the land and/or development in question. FEMA and U.S. Army Corps
of Engineers guidelines shall be followed where applicable regarding
site development areas designated as floodplains and wetlands.
I.
Natural Drainageway Enclosure. Engineered construction plans
and a permit are required for the enclosure of an existing natural
drainageway, or for any channel crossing that causes a restriction
to the natural drainageway, if the channel carries greater than ten
(10) CFS of storm water during a 15-year, twenty (20) minute storm
event. The enclosure shall be sized for a 50-year, twenty (20) minute
storm event for flows equal or greater than one hundred (100) CFS.
The enclosure shall be sized for a 15-year, twenty (20) minute storm
for flows less than one hundred (100) CFS. For flows equal or greater
than one hundred (100) CFS, two (2) foot minimum freeboard shall be
required and upstream inundation shall be checked for the 100-year,
twenty (20) minute storm event. 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 off-site property owner shall be required prior to approval
of the improvement plans.
J.
General Design Features.
1.
Dry detention basins. Basins may be constructed
to temporarily detain the storm water runoff so that the rate at which
it is released is the same rate as before development. In addition
to the design requirements set forth in the MARC Manual, the following
features shall be incorporated into the design of any dry detention
basin:
a.
Storage volume. The volume of storage provided
shall be sufficient to provide enough storage to control the differential
runoff from the 2-year and 25-year storm events.
b.
Freeboard. Detention storage areas shall have adequate
capacity to contain the storage volume of tributary storm water runoff
with at least two (2) feet of freeboard above the water surface.
c.
Outlet control works. Outlet works shall be designed
to limit peak outflow rates from detention storage areas to or below
peak flow rates that would have occurred prior to the proposed development.
Outlet works shall not include any mechanical components or devices
and shall function without requiring attendance or control during
operation, unless specifically approved by the City Engineer.
d.
Spillway. Emergency spillways shall be provided
to permit the safe passage of runoff generated from a 100-year storm.
e.
Multi-purpose basins. If the detention basin is
to have other uses, the design of the basin bottom should include
underdrains to expedite drying of the bottom between runoff events.
f.
Aesthetics. Designs should result in aesthetically
pleasing configurations, which will enhance public acceptability.
2.
Rooftop storage. Detention storage may be met in
total or in part by detention on roofs. Details of such design, which
shall be included in the building permit application, shall include
the depth and volume of storage, details of outlet devices and downdrains,
elevations of overflow scuppers, design loadings for the roof structure
and emergency overflow provisions. Direct connection of roof drains
to sanitary sewers is prohibited.
3.
Parking lot storage. Paved parking lots may be designed
to provide temporary detention storage of storm water 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 so as
to prevent damage to parked vehicles. Maximum depth shall not exceed
eight (8) inches of water.
4.
Other detention methods. All or a portion of the
detention storage may also be provided in underground or surface detention
facilities to include basins, tanks, or swales, etc.
K.
Maintenance Of Storm Water Systems And BMPs. Designs of
storm water systems and BMPs shall incorporate features which facilitate
their inspection and maintenance. The growth of obnoxious weeds, the
creation of conditions which support the growth of mosquitoes and
other insects, and the decrease in available storage by accumulated
sediments must be controlled. The cleanup of accumulated debris, flotsam
and other materials after runoff events have subsided must be assured.
Maintenance of storm water and detention systems and BMPs shall be
the responsibility of the property owner. Assignment of responsibility
for maintaining facilities serving more than one (1) lot or holding
shall be documented by appropriate covenants to property deeds unless
responsibility is formally accepted by the City.
1.
Inspections. All privately-owned detention storage
facilities will be inspected by representatives of the City not less
often than once every three (3) years, and BMPs will be inspected
yearly. A letter will be sent to the owner, with a checklist, notifying
them of the results of the inspection and listing any deficiencies
found that are in need of correction.
2.
Corrective measures. If deficiencies are found by
the inspector, the owner of the detention facility and/or BMP(s) will
be required to take the necessary measures to eliminate nuisances
and correct the deficiencies. If the owner fails to do so, the City
may undertake the work necessary and recover all expenses from the
owner.
L.
Safety Features. Designs of storm water systems shall incorporate
safety features, particularly at outlets, on steep slopes, and at
any attractive nuisances to include, as necessary, fencing, handrails,
lighting, steps, grills, signs, and other protective or warning devices
so as to restrict access during critical periods and to afford some
measure of safety to both authorized and unauthorized persons.
[Ord. No. 1684 §11, 5-15-2013]
A.
Storm Water Quality. The Manual of Best Management Practices for Storm Water Quality adopted in Section 550.125 are amended as follows:
1.
Section 3.2 Water Quality Concepts, Paragraph 6. The last sentence shall be deleted and replaced as follows: In the
Dardenne Prairie area, the water quality storm is the one and fourteen-hundredths
(1.14) inch rain event.
All future references in the manual to the one and thirty-seven
hundredths (1.37) inch water quality storm shall be replaced with
the one and fourteen-hundredths (1.14) inch water quality storm.
2.
Section 4.2.1 Pre-development and Post-development Conditions,
Paragraph 3: The following sentence shall be deleted: Assume
that soils which will be disturbed by development are assigned a HSG
rating one (1) higher than the pre-development condition unless they
are preserved in accordance with the specifications in Appendix A.
3.
Table 4.4 Best Management Practice Value Ratings: Table 4.4 shall be modified to include the following Cover Type
or BMPs and Overall Value Ratings:
|
|
Cover Type or BMP
|
Overall Value Rating
|
|---|---|---|
|
|
Rock Filter Strip
|
3.0
|
|
|
Rock Filter Strip with underdrain system
|
4.0
|
|
|
Amended Soils
|
5.0
|
4.
Add Section 4.5 Storm Water Quality Credits.
Credits toward the weighted Value Rating (VR) or LS can be given
by the City Engineer, if the design features of a site or its BMP(s)
are part of a Treatment Train that includes existing off-site downstream
BMPs that the storm water will filter through before reaching its
ultimate discharge point (creek, drainage way, lake, etc.) or if the
site conditions restrict the ability to meet the VR or LS required.
All sites will be evaluated on a case-by-case basis.
5.
Worksheet 1A on Page 4-17 of the MARC Manual, titled Required Level
of Service — Developed Site, Section 2, Subsection E, shall
be deleted and replaced as follows:
|
|
2.E.
|
Level of Service
|
|
|
Use percent Impervious to Enter Table 4.3
| |
|
|
LS = 3.0 for a Percent Impervious = 0
|
6.
Worksheet 1A on Page 4-17 of the MARC Manual, titled Required Level
of Service — Developed Site, Section 3 shall be deleted and
replaced as follows:
|
3.
|
Minimum Required Total Value Rating of BMP Package
| ||
|
|
Total Value Rating = LS X Required Treatment Area plus "existing
impervious area inside disturbed area that is to remain Impervious
in post development condition" X 1.
| ||
7.
Table 6.1 Volumetric Coefficients for Urban Runoff for Directly
Connected Impervious Areas: Table 6.1 shall be modified to
include the following information for a 1.14 inch storm event:
|
Rainfall
(inches)
|
Flat roofs and unpaved parking lots
|
Pitched roofs and large impervious (parking) areas
|
Small impervious areas and narrow streets
|
Silty soil HSG-B
|
Clayey soils HSG-C and D
|
|---|---|---|---|---|---|
|
1.14
|
0.85
|
0.98
|
0.72
|
0.12
|
0.22
|
8.
Table 6.2 Reduction Factors to Volumetric Runoff Coefficients
for Disconnected Impervious Surfaces: Table 6.2 shall be
modified to include the following information for a 1.14 inch storm
event:
|
Rainfall
(inches)
|
Strip commercial and shopping center
|
Medium to high density residential with paved alleys
|
Medium to high density residential without alleys
|
Low-density residential
|
|---|---|---|---|---|
|
1.14
|
0.99
|
0.44
|
0.22
|
0.22
|
9.
Table 6.3 Rainfall Intensity for Water Quality Rainfall Event
(1.37 inches): Delete Table 6.3.
10.
Appendix A, page A-35, Trees: Delete all Ash trees
(White Ash, Green Ash).
11.
Appendix A: Add
the following supplemental lists of plants and trees to Appendix A:
A.
Plants lists from the St. Louis MSD guidance and Missouri Botanical
Garden resources.
B.
Plant Palette Recommendation, Wet Detention Basin.
|
Botanical Name
|
Common Name
|
Height (ft)
|
Spacing*
|
Water
|
Light
|
Comments
|
|---|---|---|---|---|---|---|
|
Upper 5 Feet
| ||||||
|
Asclepias Incarnata
|
Marsh Milkweed
|
2 to 3
|
18" o.c.
|
moist soil
|
full sun
| |
|
Carex grayi
|
Gray's Sedge
|
2 to 3
|
18" o.c.
|
moist soil
|
full to medium sun
| |
|
Carex muskingumensis
|
Palm Sedge
|
2 to 3
|
18" o.c.
|
moist soil
|
full to medium sun
|
Plant in massings for best foliage effect
|
|
Middle 10 feet
| ||||||
|
Acorus calamus
|
Sweet Flag
|
2 to 4
|
18" o.c.
|
moist soil to shallow water
|
full sun
| |
|
Carex Stricta
|
Tussock Sedge
|
1 to 3
|
18" o.c.
|
moist to wet soil
|
full to medium sun
| |
|
Iris fulva
|
Copper Iris
|
2 to 3
|
18" o.c.
|
moist to wet soil
|
full sun
|
Plant individuals with other plant massings
|
|
Iris Virginica
|
Southern Blue Flag Iris
|
2 to 3
|
18" o.c.
|
moist to wet soil
|
full sun
|
Plant in massings for best flower effect
|
|
Saururus cernus
|
Lizard's Tail
|
2 to 4
|
18" o.c.
|
moist soil to shallow water
|
full to medium sun
| |
|
Lower 5 Feet
| ||||||
|
Juncus effusus
|
Soft Rush
|
2 to 3
|
18" o.c.
|
moist soil to standing water (up to 4" deep)
|
full sun
|
Good for erosion control on moist banks
|
|
Pontederia cordata
|
Pickerel Weed
|
2 to 4
|
18" o.c.
|
standing water (3" to 5" deep)
|
full sun
|
Plant in massings for best folliage/ flower effect
|
|
Sagittaria latifolia
|
Arrowhead
|
1 to 4
|
18" o.c.
|
wet soil to shallow water
|
full sun
| |
|
Scirpus validus
|
Softstem Bulrush
|
1 to 6
|
24" o.c.
|
wet soil to shallow water
|
full sun
| |
C.
Dominant Tree Species.
Silver Maple Acer saccharinum (not recommended for yards and
landscapes)
Sugar Maple Acer saccharum
Cottonwood Populus deltoides
Sycamore Platanus occidentalis
Box Elder Acer negundo
American Elm Ulmus americana
Slippery Elm Ulmus rubra
Hackberry Celtis occidentalis
Sugarberry Celtis laevigata
Black Willow Salix nigra
Bur Oak Quercus macrocarpa
White Oak Quercus alba
Swamp White Oak Quercus bicolor
Black Walnut Juglans nigra
Bitternut Hickory Carya cordiformis
Shellbark Hickory Carya laciniosa
River Birch Betula nigra
Kentucky Coffeetree Gymnocladus dioica
Bald Cypress Taxodium distichum Appendix F-2
D.
Understory Trees and Shrubs
Sandbar Willow Salix exigua
Gray Dogwood Cornus foemina
Swamp Dogwood Cornus amonum
Pawpaw Asimina triloba
Ohio Buckeye Aesculus glabra
Red Buckeye Aesculus pavia
Horse Chestnut Aesculus hippocastanuum
Eastern Witch Hazel Hamamelis virginiana
Vernal Witch Hazel Hamamelis vernalis
Buttonbush Cephalanthus occidentalis
Spicebush Lindera benzoin
Blackhaw Viburnum Viburnum prunifolium
Shrubby St. John's Wort Hypericum prolificum
Deciduous Holly Ilex decidua
Ninebark Physocarpus opulifolius.
[Ord. No. 1684 §11, 5-15-2013; Ord. No. 1689 §3, 7-17-2013]
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 City Engineer to the Board of Adjustment of the City.
C.
Penalties For Violations.
1.
General. Violation of the provisions of this Chapter
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 Dardenne Prairie 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 Chapter 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 (1st) and include the last day of the prescribed or fixed period
of time.
E.
Standard Construction Specifications Applicable To The City. Standard construction specifications outlined herein and adopted
by this Chapter relating to storm water drainage facilities shall
be fully applicable to work performed by the City and its departments.
F.
Implementation. The Standard Construction Specifications,
the Rules and Regulations and Engineering Design Requirements for
Storm Water Drainage Facilities, and the Manual of Best Management
Practices for Storm Water Quality adopted by this Chapter 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 Chapter, 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 Chapter. 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.
G.
Exceptions. Notwithstanding any other provision of this
Chapter to the contrary, the provisions of this Chapter shall not
apply to any development the valid, unexpired area plan for which
was approved on or before January 16, 2013.
