[R.O. 2006 §430.010; Ord. No. 1132 §I, 7-18-2000]
A.
This
Section provides minimum standards, controls and criteria for stormwater
management. The principal objective of this Section is to help minimize
the harmful physical and economic effects of erosion, sedimentation
and flooding from stormwater runoff. This is to be accomplished through
the requirement of special measures to mitigate erosion both during
and after construction, the detention and controlled discharge of
the differential runoff from the development, and a well-designed
stormwater conveyance system.
B.
Stormwater
management planning must be performed on a watershed basis independent
of legal property boundaries. Stormwater management plans must consider
and address each watershed associated with, or impacted by, the proposed
development, construction or site improvement work. Erosion control
plans, cleanup plans, and individual lot stormwater drainage plans
must clearly show how stormwater falling on, entering, crossing and
exiting the subject area(s) will be handled.
C.
All stormwater
management planning shall seek to reduce the velocity of overland
flow and allow the maximum opportunity for infiltration of stormwaters
into the ground, to preserve and utilize natural streams, channels
and detention basins and, wherever possible, to include streams and
floodplains within parks or other public grounds.
[R.O. 2006 §430.020; Ord. No. 1132 §I, 7-18-2000; Ord. No. 1828 §I, 1-20-2009]
For the purposes of this Chapter, the following terms shall
be deemed to have the meaning indicated below:
A storm of varying duration and intensity having a ten percent
(10%) probability of being equaled or exceeded in any given year (a
10-year storm).
A surface water runoff storage facility that is normally
dry but is designed to hold (detain) surface water temporarily during
and immediately after a runoff event.
The difference in peak flow rate of water anticipated to
shed from a parcel of land between the existing and improved surface
condition for each rainfall event.
A plan to clean up the property or any surrounding properties
affected by erosion and stormwater runoff as a result of land disturbance
activities.
A plan to prevent, control and minimize the wearing away of land surface through the action of wind or water. Such practices, procedures or schedule of activities shall comply with sediment and erosion control standards listed in Section 430.030.
The difference in elevation between the top of the detention
basin dam and the design surface water elevation.
Clearing, grading or any related work which results in removal
of the natural site vegetation and destruction of the root zone or
otherwise results in leaving the ground surface exposed to soil erosion
through the action of wind or water.
A storm of varying duration and intensity having a one percent
(1%) probability of being equaled or exceeded in any given year (a
100-year storm).
An empirical formula for calculating peak rates of runoff
resulting from rainfall.
A surface water runoff storage facility that always contains
(retains) a substantial volume of water to serve recreational, aesthetic,
water supply or other functions. Surface water is temporarily stored
above the normal stage during and immediately after runoff events.
The drawings, computations, data, proposed contours, reports,
etc., that identify how stormwater runoff is to be handled.
All means, natural or manmade, used for conducting stormwater
runoff to, through or from a drainage area to the point of outlet.
Water that results from precipitation which is not absorbed
by soil, evaporated into the atmosphere, or entrapped by ground surface
depressions and vegetation.
A calculation of the time of surface water flow from the
hydraulically most remote part of the drainage area to the point in
question.
All of the area that contributes stormwater runoff to a given
point.
[R.O. 2006 §430.030; Ord. No. 1132 §I, 7-18-2000; Ord. No. 1650 §I, 11-7-2006; Ord. No. 1832 §§V — VII, 2-17-2009]
A.
General. Sediment and erosion control shall be accomplished
by applying conservation practices that will reduce the potential
for damage from these hazards. Control practices use trapping, filtering
or diversion techniques to protect adjacent properties from land disturbance
activities.
The application of this Chapter is not limited to cases in which
building permits have been issued for construction work, but it is
the intent of this Chapter that it shall apply to all cases in which
the owner of any real estate in the City permits soil from such real
estate to be eroded onto the public way.
B.
Stormwater Permit. Effective March, 2003 construction sites
where the area to be disturbed is one (1) acre or more must apply
for a stormwater discharge permit from the Missouri Department of
Natural Resources. Prior to beginning any grading or clearing on the
subject parcel, the owner or his/her designee shall file a copy of
said permit with the Building Commissioner.
C.
When Controls Are Required. Standard vegetative and structural
practices, as specified below, that filter, divert or promote the
settlement of sediment particles from stormwater runoff shall be provided
in the following situations:
D.
Types Of Controls. Acceptable sediment and erosion controls
shall be either vegetative or structural as described below.
1.
Vegetative practices.
a.
Topsoiling. Stockpiling of topsoil to enhance final site
stabilization with vegetation shall be done in such a manner that
natural drainage is not obstructed, and no off-site sediment damage
results.
b.
Seeding. Of the rate and type to produce a dense vegetation.
c.
Sodding.
d.
Mulching. The application of grass, hay, wood chips, wood
fibers, straw, gravel, or other suitable material to the soil surface.
Seeded and planted areas where slopes are steeper than 2:1 shall be
stabilized with mulch.
2.
Structural practices.
a.
Construction entrance. Is a rock stabilized pad located
at points of vehicular ingress and egress on a construction site.
b.
Straw bale barrier. Shall be placed on downslope areas to
intercept sediment or to reduce flow velocity. Straw bale barriers
shall not be constructed in streams or swales where there is the possibility
of washout.
c.
Silt fence. Sediment shall be removed when it reaches one-third
(1\3) to one-half (½) the height of the filter fence.
d.
Storm drain inlet protection. May consist of filter fabric,
sandbags, excavated gravel, straw bale, block and gravel, and any
combination of the above.
e.
Diversion swale or dike. These may be used to intercept
runoff and divert to a sediment control device around a disturbed
area or to an area where it can be safely released.
f.
Sediment trap. Is a small storage or detention area used
to detain construction runoff long enough to allow the larger-sized
sediment particles to settle out before the runoff is released to
downstream areas.
g.
Temporary sediment basin. Performs the same function as
a sediment trap, although it has a greater volume and is located below
disturbed areas generally greater than five (5) acres.
h.
Temporary slope drain. May be plastic sheets, metal or
flexible pipe, stone, gutter, fiber mats, concrete or asphalt ditches,
or half round pipe to carry runoff from one elevation to a lower elevation
without excessive erosion of the slope.
i.
Check dam. May be constructed of logs or stone across a
swale or drainage ditch to reduce the water's velocity and to trap
small amounts of sediment.
j.
Level spreader. Is an excavated depression to convert a
concentrated flow to a sheet flow, allowing water to be released at
less erosive levels.
k.
Erosion control fabrics.
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It is not the intent of this Section to stipulate any particular
means of erosion control or cleanup but to allow the owner, developer,
builder or contractor to select the best method for any particular
project, subject to the approval of the City's Building Commissioner.
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3.
Construction plans. A contoured development map must clearly
indicate the pattern of surface water runoff, both upstream and downstream
of the development. The type of sediment and erosion control to be
utilized shall be clearly indicated. The City shall have authority
to require proper controls as specified herein.
4.
Cleanup plan. The cleanup plan shall include a method of
cleanup and a time schedule for the work to be done after the owner,
builder, contractor or developer has been advised by the City's Building
Commissioner or his/her authorized representative that erosion has
occurred or that excessive material has been tracked off-site onto
the public way.
[R.O. 2006 §430.040; Ord. No. 1132 §I, 7-18-2000]
A.
Purpose. A development's stormwater drainage system shall
be designed to:
1.
Protect
natural waterways.
2.
Convey
upstream and on-site stormwater runoff to a natural watercourse or
to a stormwater drainage facility.
3.
Protect
existing stormwater conveyance systems.
4.
Provide
protection from the design storm event and address the major storm
event so as to prevent major property damage and loss of life.
B.
Rainfall Frequency. All facilities shall be designed to
carry a 10-year storm of a duration which produces the maximum peak
flow rate of stormwater runoff without inundation or surcharging.
All hydraulic structures shall be designed to allow for a 100-year
storm to pass through the subdivision without destroying or damaging
property or inundating dwellings. Design information which substantiates
both conditions shall be provided.
Utilize MoDOT published I.D.F. curves for the 2-, 5-, 10-, 25-
and 100-year frequencies.
C.
Calculation Of Runoff. The method of calculating and routing
stormwater runoff shall be a generally accepted stormwater management
practice. The drainage area shall consider all on- and off-site lands
contributing to the proposed development's drainage system. Capacity
for such facilities shall be based on the maximum potential watershed
development permitted.
1.
The
Rational Method for calculating stormwater runoff may be used for
developments up to two hundred (200) acres. The Rational Method may
be modified per MSD standards for developments greater than two hundred
(200) acres. Other common rainfall runoff calculation methods that
may be utilized include Graphical Peak Discharge, Tabular, and the
Synthetic Unit Hydrograph.
2.
The
minimum percentage of imperviousness to be used in design shall be
based on the zoning district as shown in the following table:
|
|
District
|
Minimum % Impervious
| |
|---|---|---|---|
|
|
AG
|
Agricultural Reserve
|
30
|
|
|
R-1
|
Low Density Residential
|
45
|
|
|
R-2
|
Medium Density, Single-Family Residential
|
55
|
|
|
R-3
|
High Density Residential
|
70
|
|
|
RC-1
|
Planned Business District
|
70
|
|
|
RC-2
|
Residential Commercial Planned District
|
55
|
|
|
C-1
|
Neighborhood Commercial
|
70
|
|
|
C-2
|
General Commercial
|
90
|
|
|
C-3
|
Highway Commercial
|
90
|
|
|
C-4
|
Planned Commercial Shopping Center District
|
90
|
|
|
M-1
|
Light Industrial
|
80
|
|
|
M-2
|
General Industrial
|
90
|
|
|
Parking, Streets, Roofs
|
100
| |
3.
Special
uses, such as schools, churches, etc., shall have the differential
runoff computed and approved by the City.
4.
Special
circumstances may dictate that the developed impervious area may differ
from that shown in the above table. Calculations prepared by a registered
professional engineer may be submitted to the City for their evaluation
to determine if a minimum impervious area which differs from that
shown in the above table may be utilized. Likewise, the City may determine
that the percent of impervious area for a particular development differs
from that shown in the above table.
5.
See
Figure "B" at the end of this Chapter for the runoff factor to be
utilized for various impervious conditions and rainfall durations.
D.
Open Channels. Open channels consist of swales, ditches
or depressions, both natural and manmade, that convey water. Channels
shall be protected from scour and erosion by providing a channel lining
adequate to sustain the velocity of the 10-year design storm. If velocities
in channels exceed five (5) feet per second during 10-year design
storms, then erosion control other than vegetation shall be provided
in channel construction. Channels shall have the hydraulic capacity
to carry the 10-year design storm runoff within the channel bed and
banks. Out-of-bank flow may be permitted on land slopes parallel to
the channel where it can be shown that no erosion damage or serious
property damage will result. Channels function as part of the major
drainage system and shall be evaluated for the 100-year design storm
to determine the impacts of runoff on adjacent property. The channel's
hydraulic capacity shall be increased where adjustments to channel
geometry provide significant protection to adjacent properties during
the 100-year event.
E.
Closed Conduit Storm Sewers. Pipe sizes for closed conduit
flow shall be based on the 10-year design storm runoff and minimum
allowable velocities. The system shall provide for the cleaning of
sediment and other deposits by maintaining a minimum velocity of two
(2) fps during the 10-year storm, but in no instance shall be less
than twelve (12) inches in diameter.
1.
Manning's
Equation is the most common method of estimating the capacity and
flow resistance in closed conduits, although the Kutter, HazenWilliams,
and Darcy Weisbach formulas are also acceptable.
2.
Closed
conduit storm sewer systems shall convey the 10-year design storm
to a point of discharge by gravity or pressure flow. In pressure flow
conditions, the hydraulic grade line shall be calculated to reflect
losses in pipes and structures and shall not rise to an elevation
greater than the sewer structure tops during the design storm.
3.
Generally,
gravity flow occurs where the capacity of pipe run exceeds the design
flow and the outfall point does not control discharge. Storm sewer
systems may be designed for pressure flow when the hydraulic grade
line is above the crown of the pipe. The decision to design a pressure
flow system may be based on aesthetics, the need to submerge outfalls,
economics, limitations associated with reduced pipe sizes, or grade
constraints in outfalling the system.
F.
Inlets. Calculations shall be submitted to demonstrate
the capacity of all inlets, such calculations must consider the cross-slope
of the pavement, depth of water at the curb face, size of opening,
and the longitudinal grade of street. Street inlets and inlets in
parking areas shall reduce the spread and depth of flow to acceptable
levels during the 10-year design storm. The acceptable level of flow
for a minor access or local access street would maintain an eight
(8) foot travel lane with a maximum one (1) inch depth. One (1) clear
ten (10) foot travel lane must be maintained for a collector street
and two (2) clear ten (10) foot travel lanes must be maintained for
a major street. Any area inundated by water ponding at an inlet during
the 10-year storm event shall be located within an easement or right-of-way.
The effects of the 100-year storm event shall be analyzed to insure
no property damage or dangerous conditions result. Inlets located
on continuous grades may be designed to permit a portion of flow to
by-pass the structure; however, calculations for the downstream structure
must consider the by-pass.
[R.O. 2006 §430.050; Ord. No. 1132 §I, 7-18-2000; Ord. No. 1669 §§I — II, 12-19-2006; Ord. No. 1954 §I, 3-15-2011]
A.
When Detention And/Or Retention Facilities Are Required. The City retains the right to require detention or retention storage
in all cases in which the proposed development will increase stormwater
runoff (post-development runoff greater than pre-development runoff)
for the design storms given above. Therefore, every development shall
have stormwater detention or retention, except as specified herein.
1.
Off-site
detention facilities shall not be allowed, except that, at the discretion
of the Board of Aldermen, a variance can be granted by the Board of
Aldermen allowing off-site detention subject to reasonable restrictions
and conditions.
2.
Off-site 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.
It is determined that no immediate adverse effects will result to adjacent property, and a contribution is made to the Stormwater Management Improvements Fund (as described in Subsection (D) of this Section).
If immediate on-site or off-site detention is not required as
specified in the above paragraph, the applicant must contribute to
the Stormwater Management Improvements Fund. The minimum contribution
shall be an amount equal to two hundred dollars ($200.00) for every
cubic foot per second or any fraction thereof of differential runoff
generated during the 100-year design storm event or one thousand dollars
($1,000.00), whichever is greater.
4.
Other management techniques. Management techniques other
than detention facilities may be utilized by the development provided
the techniques proposed meet the intent of this Section and provide
a benefit to the watershed that equals or exceeds the benefit that
a detention facility would provide.
5.
If drainage
provisions for the proposed development were previously approved and
remain valid as part of a final plat.
6.
Isolated
lots of record for single-family and two-family dwelling purposes
unless the development involves changing in any way existing drainage
facilities, degrades the quality of water, adversely affects any wetland
or adversely affects any sinkhole, watercourse or waterbody.
7.
Building
construction which will not increase the amount of impervious area
on the site and will not adversely impact an existing drainage area
or drainage on adjoining properties.
B.
Storage Capacity. The rates (pre-developed and post-developed)
of runoff shall be determined for the 10- and 100-year rainfall frequencies.
The minimum storm duration shall be twenty (20) minutes.
1.
Stormwater shall be detained on site, or on adjacent property under agreement, and metered out at the rate of an undeveloped site for the above frequencies and minimum duration to prevent possible flooding and erosion downstream. Design criteria to establish this differential runoff rate shall be as provided in Section 430.040, "Stormwater Drainage System Standards". Note that stormwater pipes shall be sized to carry the total developed tributary upstream watershed. No reduction in pipe size shall be permitted because of detention.
2.
Detention
basin volume will be based on routing each post-developed runoff hydrograph
through the detention facility while satisfying the appropriate allowable
release rate. The routing computation shall be based on an application
of the continuity principle. The discharge rate shall be based on
the maximum head conditions in the detention facility.
C.
General Design Features.
1.
Dry bottom basins. May be constructed to temporarily detain
the stormwater runoff so that the rate at which it is released is
the same rate as before development. The following features shall
be incorporated into the design of any detention basin:
a.
Freeboard. Detention storage areas shall have adequate capacity
to contain the storage volume of tributary stormwater runoff with
at least two (2) feet of freeboard above the water surface.
b.
Outlet control works. Outlet works shall be designed to
limit peak outflow rates from detention storage areas to at 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.
c.
Emergency overflow/spillway. Emergency structure shall be
provided to permit the safe passage of runoff generated in excess
of the design storm event. Antivortex measures shall be provided where
warranted.
d.
Maximum depth. The maximum planned depth of stormwaters
stored shall not normally exceed five (5) feet.
e.
Side slopes. The maximum side slopes for grassed basins
shall not exceed one (1) foot vertical for three (3) feet horizontal.
f.
Limits of ponding. In no case shall the limits of maximum
ponding be closer than thirty (30) feet horizontally from any building
and less than two (2) feet vertically below the lowest sill elevation.
g.
Interior drainage. The basin bottom should be designed to
drain expeditiously. Flows through the detention basin should be handled
by paved ditch from inflow structure to outflow structure to minimize
erosion.
h.
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.
i.
Aesthetics. Designs should result in aesthetically pleasing
configurations which will enhance public acceptability.
2.
Wet bottom basins. Wet bottom basins may also be used to
temporarily detain the differential runoff from the development. In
addition to the general design features enumerated above for dry bottom
basins, the following features should also be incorporated into the
design of any wet bottom basin:
a.
Normal pool depth. In order to minimize weed growth, the
normal pool depth should be four (4) feet minimum.
b.
Depth for fish. If fish are to be kept in the pond, at least
one-quarter (¼) of the area of the permanent pool should have
a minimum depth of ten (10) feet.
c.
Facilities for emptying. In order to ease cleaning of the
pond or shoreline maintenance, the pond design should include provisions
for emptying the pond.
d.
Low flow by-pass. The design of any pond may include a low
flow by-pass channel or pipeline to divert runoff that can be accommodated
by downstream drainageways.
e.
Side slopes below normal pool. The side slopes below the
normal pool elevation may exceed the maximum side slope permitted
above normal pool (3:1 slope). The design shall, however, include
provisions for a safety ledge having a depth of water not greater
than three (3) feet immediately adjacent to the shoreline.
f.
Forbay. In order to minimize siltation of the pond, a forbay
should be included in the design.
3.
Parking lot storage. Paved parking lots may be designed
to provide temporary detention storage of stormwater on all or a portion
of their surfaces. Outlets will be designed so as to slowly empty
the stored waters and depths of storage must be limited so as to prevent
damage to parked vehicles.
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. Emergency overflow conditions
shall be considered in all methods.
D.
Stormwater Management Improvements Fund. A Stormwater Management Improvements Fund shall be and is hereby created. Said fund shall be reserved for funding improvements to stormwater systems owned and maintained by the City and for no other purposes unless authorized in the Chapter. All contributions made by parties developing within the City in accordance with Section 430.050(A) of this Chapter shall be deposited to said fund. Said fund shall be deposited in an interest-bearing account.
[R.O. 2006 §430.060; Ord. No. 1132 §I, 7-18-2000]
A.
Storm
pipes shall be protected from excessive bearing pressures by placing
them outside the forty-five degree (45°) influence zone of building
structures unless an engineering calculation shows the pipe material
or soil condition to be adequate for the subjected land.
B.
Pipes
on twenty percent (20%) slopes or greater shall be anchored securely
with concrete anchors or equal to prevent the pipe from creeping downhill.
C.
Pipes
or structures constructed on fill shall be stable and protected against
settlement by compacting fill material to ninety-five percent (95%)
of the modified proctor maximum dry density.
D.
Pipes
thirty-six (36) inches or larger may be placed on a curved alignment
utilizing alignment radii established by the pipe manufacturer.
E.
The receiving
surface where pipes discharge shall be protected from erosion by evaluating
the discharge velocity for the 10-year design storm. The use of energy-dissipating
devices may be necessary to reduce the velocity to acceptable levels
for the receiving surface. Grouted revetment used shall be a minimum
length of ten (10) times the diameter of the discharge pipe.
F.
A manhole,
inlet or junction box shall be located at changes in pipe size, grade,
alignment or material.
G.
The angle
between influent and effluent pipes shall be not less than ninety
degrees (90°), and the drop between inverts shall be not less
than one-fourth (0.25) foot.
H.
Manhole
and inlet castings located in travelways shall be capable of withstanding
traffic loads and shall be constructed flush with the finished surface.
I.
All materials
and appurtenances for stormwater management systems shall conform
to current standards of the American Society for Testing and Materials
(ASTM).
J.
Manholes
shall be precast or cast-in-place concrete or concrete block with
concrete or brick risers and approved manhole covers.
K.
A new
drainage channel or pipe shall intersect an existing drainage channel
at a maximum angle of sixty degrees (60°).
L.
All trenches
under roadway pavement shall be backfilled with MoDOT Type I aggregate
in six (6) inch layers and compacted to ninety-five percent (95%)
of the modified proctor maximum dry density.
M.
All piping
shall be bedded and backfilled per the manufacturer's requirements.
N.
Grated
inlets will not be allowed without special approval by the City.
O.
All materials
used in the construction of storm sewers shall be subject to inspection
and approval of the City.
P.
Acceptable
pipe material shall be reinforced concrete pipe, corrugated metal
pipe, and corrugated polyethylene pipe.
1.
Reinforced
concrete pipe shall conform to the requirements of the Specifications
for Reinforced Concrete Culvert, Storm Drain and Sewer Pipe, ASTM
C76. Strength class or classes shall be as required per design specifications
of the latest edition of the Concrete Pipe Handbook as published by
the American Pipe Association.
2.
Corrugated
metal pipe shall conform to the requirements of the "Standard Specifications
for AASHTO M196 Corrugated Aluminum Pipe" or the "Standard Specifications
for AASHTO M274 Aluminized Steel Type 2" and ASTM A929. Structural
design requirements shall be per the latest edition of the Handbook
of Steel Drainage and Highway Construction Products" as published
by the American Iron and Steel Institute.
3.
Corrugated
polyethylene pipe shall conform to the requirements of AASHTO M294,
"Standard Specifications for Corrugated Polyethylene Pipe". All polyethylene
pipe should be installed according to ASTM D 2321, "Standard Practice
for Underground Installation of Thermoplastic Pipe for Sewers and
Other Gravity-Flow Applications".
Q.
The City
Engineer may consider for approval a written request to use other
types of pipe.
R.
Reinforced
concrete pipe shall be required under road pavement.
S.
All construction
details pertaining to stormwater drainage shall be in accordance with
the Metropolitan St. Louis Sewer District requirements, unless otherwise
noted herein.
[R.O. 2006 §430.070; Ord. No. 1132 §I, 7-18-2000; Ord. No. 1832 §VIII, 2-17-2009]
A.
Detention
and retention facilities, when required, are to be built in conjunction
with the storm sewer installation and/or grading. Since these facilities
are intended to control increased runoff, they must be partially or
fully operational soon after the clearing of the vegetation. Silt
and debris connected with early construction shall be removed periodically
from the detention area and control structure in order to maintain
close to full storage capacity.
B.
The responsibility
for maintenance of stormwater management facilities in single-lot
development projects shall remain with the owner, developer and general
contractor until final inspection of the development is performed
and approved. After legal occupancy of the project, the maintenance
shall be vested with the owner of the project/property.
C.
The responsibility
for maintenance of stormwater management facilities for subdivision
projects shall remain with the developer until such time as responsibility
is transferred, under appropriate legal arrangements, to the private
individual owners or such other maintenance entity as may be approved
by the City.
D.
If responsibility
is to be transferred to the private individual owners in a subdivision,
the developer shall assure perpetual maintenance of all open watercourses
and detention systems, if any are included, through the adoption of
maintenance agreements or covenants for any facilities that remain
in private ownership. Such agreements or covenants shall be subject
to the approval of the City.
E.
If the
responsibility is to be transferred to the trustees in a subdivision,
the developer shall establish a suitable indenture of trust. Upon
release of escrows required for the subdivision development, the responsibility
for maintenance shall be vested in the trustee of the subdivision
by virtue of the trust indenture. The indenture of trust shall clearly
indicate resident responsibility for maintenance and shall be subject
to the approval of the City.
F.
The growth
of noxious weeds, the creation of conditions which support the growth
of mosquitoes and other insects, and the decrease in available storage
by accumulated sediments shall be controlled. The cleanup of accumulated
debris, flotsam and other materials after runoff events have subsided
shall be assured.
G.
All such
privately owned and maintained facilities shall be subject to the
periodic inspection by the City. If deficiencies are found during
an inspection, the owner of the facility will be required to take
the necessary measures to eliminate nuisances and correct structural
deficiencies. If the owner fails to do so, the City may undertake
the work necessary and recover all expenses from the owner.
H.
Portions
of the stormwater management facilities that are in or on the City's
right of-way (curb inlets, manholes, below grade piping, etc.) may,
at the City's discretion, be accepted as City improvements with maintenance
to be provided by the City. All such proposed improvements must be
clearly shown and identified as such in the final stormwater management
plans and public utility construction plans.
[R.O. 2006 §430.080; Ord. No. 1132 §I, 7-18-2000; Ord. No. 1436 §I, 9-7-2004; Ord. No. 1832 §§IX — X, 2-17-2009]
A.
Land Disturbance Permit. No owner of real property within
the City, and no developer, contractor or builder doing business in
the City, shall conduct any land disturbance activities affecting
a land area of one (1) acre of real estate or more prior to obtaining
a land disturbance permit. No land disturbance permit shall be issued
by the Building Commissioner until such time as the owner, developer,
builder or contractor has provided a complete erosion control plan
and cleanup plan in the event erosion should occur. No land disturbance
permit may be issued until such plan is approved by the City's Public
Works Director and the Building Commissioner. Such erosion control
plan shall be implemented prior to beginning any land disturbance
activity. The City reserves the right to request a more detailed stormwater
analysis, in line with other provisions of this Chapter, if such analysis,
in the opinion of the City, is warranted. The fee for such permit
shall be fifty dollars ($50.00).
B.
Exceptions — Land Disturbance Permits Not Required. Land disturbance permits are not required in the following situations:
C.
Any owner,
developer, contractor or builder doing business in the City planning
to begin construction of any improvements on any property within the
City must submit an individual lot stormwater drainage plan to the
City's Building Commissioner, or his/her authorized representative,
prior to the issuance of a building permit. No building permit may
be issued until such plan has been reviewed and approved by the City's
Building Commissioner or his/her authorized representative.
D.
Each
applicant for an individual lot stormwater drainage plan shall pay
a review fee as hereinafter set forth:
Fee = $125.00 plus engineering deposit of $500.00
E.
As a minimum, plans described herein must include information as set forth in Section 430.030 plus planned first (1st) floor and/or lowest slab elevations. The City reserves the right to request a more detailed stormwater analysis, in line with other provisions of this Chapter, if such analysis, in the opinion of the City, is warranted.
F.
Orders Of City's Building Commissioner, Compliance, Enforcement. No person shall fail to comply with any directions of the City's
Building Commissioner given pursuant to the provisions of this Chapter.
Each day that the violator fails to comply with directions of the
City's Building Commissioner shall constitute a separate offense.
The City's Building Commissioner shall have the authority to revoke
the building permit under which any work is being done until such
time as compliance occurs. If the violation occurs for more than ten
(10) days, the City may, at its option, clean up the eroded material,
and the cost of such cleanup shall be levied against the property
by a special tax bill.
[R.O. 2006 §430.090; Ord. No. 1132 §I, 7-18-2000; Ord. No. 1437 §I, 9-7-2004; Ord. No. 1832 §XI, 2-17-2009]
A.
Any person,
firm, corporation, business or government entity planning development
within the municipality shall submit to Planning and Zoning for approval
a stormwater management plan before commencing any development or
development activity in any existing or proposed platted area. Preliminary
stormwater management plans shall accompany any preliminary plats
submitted to Planning and Zoning for their consideration.
B.
It shall
be the responsibility of the City's Public Works Director and Building
Commissioner, or a professional engineering consultant retained by
the City, to review the stormwater management plan and to submit their
findings and recommendations to Planning and Zoning at the time the
associated plat is to be reviewed and considered by Planning and Zoning.
Evaluation of the submitted plan is to be completed within thirty
(30) days of submittal. The report will recommend approval, conditional
approval, or denial of approval and a listing of deficiencies, concerns,
questions and/or unresolved issues to be addressed prior to consideration
of final approval.
C.
Application And Review Fee. The application and review fee
for stormwater management plans is hereby established as follows:
$300.00 + $50.00/acre of platted subdivision plus engineering
deposit of $500.00
D.
The review
fee shall be collected at the time the preliminary stormwater management
plan is submitted to the appropriate City personnel and will reflect
the cost for the review process. Any costs above this fee shall be
billed to the applicant. These fees may be adjusted from time to time
by the Board of Aldermen to reflect actual costs of administration
and review.
[R.O. 2006 §430.100; Ord. No. 1132 §I, 7-18-2000]
A.
The purpose
of the preliminary stormwater management plan is to provide an organized
framework for evaluating and acting upon proposals for development
as they relate to stormwater management issues.
B.
It is
the responsibility of an applicant to include sufficient information
in the stormwater management plan to enable evaluation of the environmental
quality of the affected area, the potential and predicted impacts
of the proposed activity on affected waters, and the effectiveness
and acceptability of the measures proposed by the applicant for preventing
or reducing adverse impacts of stormwater runoff following the rainstorms
which exceed the maximum allowable release rate and the capacity of
the stormwater drainage system.
C.
The applicant
shall furnish four (4) copies of the preliminary stormwater management
plan sealed by a professional engineer registered in the State of
Missouri. The plan shall include as a preface the following information:
1.
The
name, address and telephone number of the applicant and the owner,
if different from the applicant.
2.
Name
and address of the professional engineer.
3.
The
legal description of the property and its acreage.
|
|
The plan shall also include maps at a minimum scale of one (1)
inch equals one hundred (100) feet and other descriptive materials,
including the basis of computation, showing the following:
|
|
|
Required pre-development site information:
| |
|
1.
|
Detailed location sketch showing the parcel and major adjacent
roads.
| |
|
2.
|
Topographic map of the site outlining the limits of the contributing
watershed with maximum two (2) feet contour intervals, except in floodplains
or other areas of low relief where a smaller interval may be required.
Only USGS datum shall be used.
| |
|
3.
|
Where percolation or exfiltration systems are proposed, information
as to the location and type of vegetative cover and soil types and
characteristics representative of the design condition.
| |
|
4.
|
Location of streams and other floodwater runoff channels, their
normal channels and the extent of the floodplains at the established
high water elevations, and the limits of the floodway.
| |
|
5.
|
Location of lakes, ponds, swamps and detention basins indicating
their normal shorelines, floodplains and lines of inflow and outflow.
| |
|
6.
|
Location of farm drains, inlets and outfalls, storm, sanitary
and combined sewers and outfalls, septic tank systems and outlets,
if any, and seeps, springs and flowing and other wells.
| |
|
7.
|
Location and description of nearby existing off-site water management
facilities such as wells, lakes, drainage ways, etc., which are potentially
directly affected by the proposed construction or development.
| |
|
8.
|
Concepts which will be considered within the site to handle
all stormwater runoff, including the methods for detention or control
of increased stormwater runoff generated by the development.
| |
|
9.
|
A general plan showing the extent and nature of the stormwater
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.
| |
|
10.
|
A general plan indicating the exterior perimeter of the site,
the general development proposed for the project, and an indication
by means of rough contours showing the terrain after grading of the
site.
|
D.
Following
receipt of preliminary stormwater management plan and information
to be included with such plan, the general concepts and planning proposals
will be reviewed by the City's Public Works Director, Planning and
Zoning Officer and/or a professional engineering consultant retained
by the City. The purpose of this review shall be to jointly agree
upon an overall stormwater management concept for the proposed development
and to review criteria and design parameters which shall apply to
final design of the project.
[R.O. 2006 §430.110; Ord. No. 1132 §I, 7-18-2000; Ord. No. 1832 §XII, 2-17-2009]
A.
Following
review and approval of the preliminary plan, a final stormwater management
plan shall be prepared for each phase of the proposed project as each
phase is developed. The final plan shall constitute a refinement of
the concepts approved in the preliminary stormwater management plan
with preparation and submittal of the following additional detailed
information, unless specifically excluded during the preliminary concept
review:
1.
For
all existing drainage facilities which are to be maintained, altered
or enlarged as part of the stormwater management system, provide information
as to their size, slopes, depths, outfalls, receiving waters, elevations,
cross sections, profiles, construction materials and other design
details as applicable. Only USGS datum shall be used to establish
elevations.
2.
Location
of all new drainage facilities, including detention basins, to be
constructed. Provide design details on each facility as applicable.
3.
Location
and extent of existing and proposed impervious surfaces (roads, parking
lots, buildings, etc.) and their elevations. Provide grading and paving
plans and specifications.
4.
Post-development
location of 100-year flood boundary.
5.
Location
and extent of rights-of-way and easements for the stormwater management
system, including all areas to be dedicated for water management purposes.
6.
Identification
and description of any special or required maintenance procedures
to keep the project functioning as designed.
7.
Stormwater
management system design calculations as follows:
a.
Design
storms used.
b.
Calculated
hydrographs of inflow and outflow of design storm runoffs for the
project site under natural and undeveloped conditions.
c.
Hydrographs
of the runoffs from the design storms for the project site under developed
conditions.
d.
For
all detention basins, a plot or tabulation of storage volumes with
corresponding water surface elevations and of the basin outflow rates
for those water surface elevations.
f.
Runoff
routing calculation showing discharge, elevations and volumes retained
and/or detained during applicable storm even. Show individual flows
for each existing and proposed structure and cumulative flows in pipes
and gutters, including "Q" and areas.
g.
Calculation
required for determination of minimum building floor and road elevations.
8.
Identify
entity responsible for operation and maintenance of the system.
9.
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.
10.
Estimate
of expected construction cost for stormwater related improvements.
Estimates should be broken down into enough detail to allow timely
review of each component (inlets, manholes, storm sewer piping, basin
earthwork, control structures, etc.) cost.
11.
The
stormwater management plan for minor development activities may consist
of a certification from a registered professional engineer that the
differential runoff equals zero.
B.
Final
stormwater management plans shall be reviewed by the City's Building
Commissioner, Planning and Zoning Officer and/or a professional engineering
consultant retained by the City. If it is determined that the proposed
development will provide control of stormwater runoff 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's staff shall recommend and the City
will approve the plan or conditionally approve the plan setting forth
the conditions thereof. If it is determined that the proposed development
will not control stormwater runoff in accordance with these regulations,
the City shall deny approval of the final stormwater management plan,
and it shall be returned to the applicant for resubmittal.
[R.O. 2006 §430.120; Ord. No. 1132 §I, 7-18-2000; Ord. No. 1832 §XIII, 2-17-2009]
The applicant requesting approval of a stormwater management
plan shall be required to adhere strictly to the stormwater management
plan as recommended by the City's Building Commissioner, Planning
and Zoning Officer and/or professional engineering consultant charged
with reviewing said plan for conformance with the applicable provisions
of the City's stormwater ordinance. Any changes or amendments to the
plan must be approved by the City in accordance with the general procedures
set forth in the stormwater ordinance as well as the engineer of record
for the stormwater management plan. City staff shall be granted inspection
rights and right-of-entry privileges in order to ensure compliance
with the requirements of the stormwater provisions of the City regulations.
[Ord. No. 1832 §XIV, 2-17-2009]
A.
To insure
completion of the improvements herein required, the Board of Aldermen
shall require the developer to file a surety bond of evidence of an
escrow account or an irrevocable letter of credit with the City Finance
Officer to ensure the actual construction of such improvements according
to the plans and specifications approved by the Board of Aldermen
within a period of time not to exceed two (2) years from the date
of approval of the site plan. Such bond or account shall be in the
amount of one hundred percent (100%) of the estimated cost of the
improvement as determined by the Building Commissioner and with surety
and conditions satisfactory to the Board of Aldermen. No building
construction shall be permitted on any lot that does not comply with
the provisions of these regulations and other applicable elements
of the Comprehensive Plan and no municipal utility service shall be
furnished to such lot.
1.
Completion of construction. The construction of all stormwater
improvements shall be completed within two (2) years of signing of
the site plan by the Mayor of the City of Warrenton. The Board of
Aldermen may grant time extension for those developments showing good
cause as to why the improvements have not been completed. In the event
that an extension is requested and granted, the escrow, surety bond
or irrevocable letter of credit for those developments not completed
shall be extended for the same period of time.
2.
Construction approval. When the Public Works Director or
Building Commissioner approves the completion of each phase of improvement
construction, ninety-five percent (95%) of the appropriate amount
of escrow will be released by the City.
3.
Final approval. Upon completion and approval of all improvements
and receipt of all required documentation, the balance of the escrow
will be released.
4.
Failure of construction of improvements. Upon the default
or failure of the developer to complete such improvements within said
two (2) year period or any extension thereof granted by the Board
of Aldermen, the developer shall be considered in default and the
City will become the owner of the escrow account or may make demand
upon the surety bond or irrevocable letter of credit.
[R.O. 2006 §430.130; Ord. No. 1132 §I, 7-18-2000; Ord. No. 1832 §XV, 2-17-2009]
A.
If it
is determined that the project is not being carried out in accordance
with an approved stormwater management plan or is being carried out
without approval, the City, acting through its Building Commissioner
and/or Planning and Zoning Officer, is authorized to:
1.
Issue
written notice to the applicant or owner specifying the nature and
location of the alleged non-compliance with a description of the remedial
actions necessary to bring the project into compliance within a reasonable
specified time.
2.
Issue
a stop work order directing the applicant or owner to cease and desist
all or any portion of the work which violates the provisions of the
stormwater ordinance if the remedial work identified in the written
notice is not completed within the specified time.
B.
Should
the applicant or owner not bring the project into compliance following
the written notice and stop work order, he/she shall then be subject
to immediate revocation of his/her stormwater management plan approval
and be subject to the penalties provided for elsewhere.
C.
Any notice,
stop work order or revocation issued pursuant to this Section shall
become final unless the person or persons named therein requests,
in writing, no later than ten (10) days after the date such notice,
order or revocation is served, a hearing before the Board of Aldermen.
[R.O. 2006 §430.140; Ord. No. 1132 §I, 7-18-2000]
A.
No subdivisions
of property within the City limits, or approval of proposed subdivision
plats, will be allowed without the submittal and subsequent approval
of an appropriate stormwater management plan in accordance with the
provisions of this Chapter of the City's regulations.
B.
Failure
to comply with the provisions of this Chapter, whether as principal,
agent, employee or otherwise, or any provisions of this or any related
Section of the City's regulations, shall be a misdemeanor and will
be subject to a fine up to five hundred dollars ($500.00) or imprisonment
for a period not to exceed ninety (90) days, or both, and, in addition,
shall pay all costs and expenses involved in the case. Each day of
the continued violation shall constitute a separate additional violation.
If more than one (1) provision is violated, each provision violated
shall be considered a separate misdemeanor, and each shall be liable
to maximum penalties as herein specified. Nothing herein shall limit
any other right or remedy of the City or other person in interest,
including the right to obtain an injunction of any violation from
a court of competent jurisdiction.
|
FIGURE A. RAINFALL INTENSITY — DURATION CURVES
| |
|---|---|
|
|
FIGURE B. P FACTOR FOR RUNOFF
| ||||||
|---|---|---|---|---|---|---|
|
# IMPERVIOUS
|
DURATION OF RAIN IN MINUTES
| |||||
|
15
|
20
|
30
|
60
|
90
|
120
| |
|
0
|
0.30
|
0.35
|
0.41
|
0.51
|
0.56
|
0.60
|
|
5
|
0.32
|
0.37
|
0.43
|
0.53
|
0.58
|
0.62
|
|
10
|
0.34
|
0.39
|
0.46
|
0.56
|
0.60
|
0.64
|
|
15
|
0.36
|
0.41
|
0.48
|
0.58
|
0.62
|
0.66
|
|
20
|
0.38
|
0.44
|
0.50
|
0.60
|
0.64
|
0.67
|
|
25
|
0.40
|
0.46
|
0.52
|
0.62
|
0.66
|
0.69
|
|
30
|
0.42
|
0.48
|
0.54
|
0.64
|
0.68
|
0.71
|
|
35
|
0.44
|
0.50
|
0.57
|
0.66
|
0.70
|
0.73
|
|
40
|
0.46
|
0.52
|
0.59
|
0.68
|
0.72
|
0.74
|
|
45
|
0.48
|
0.54
|
0.61
|
0.71
|
0.74
|
0.75
|
|
50
|
0.50
|
0.56
|
0.63
|
0.73
|
0.75
|
0.78
|
|
55
|
0.52
|
0.58
|
0.65
|
0.75
|
0.77
|
0.80
|
|
60
|
0.54
|
0.60
|
0.68
|
0.77
|
0.79
|
0.81
|
|
65
|
0.56
|
0.63
|
0.70
|
0.79
|
0.81
|
0.83
|
|
70
|
0.58
|
0.65
|
0.72
|
0.81
|
0.83
|
0.85
|
|
75
|
0.60
|
0.67
|
0.74
|
0.84
|
0.85
|
0.87
|
|
80
|
0.62
|
0.69
|
0.76
|
0.86
|
0.87
|
0.88
|
|
85
|
0.64
|
0.71
|
0.79
|
0.88
|
0.89
|
0.90
|
|
90
|
0.66
|
0.73
|
0.81
|
0.90
|
0.91
|
0.92
|
|
95
|
0.68
|
0.75
|
0.83
|
0.92
|
0.93
|
0.94
|
|
100
|
0.70
|
0.77
|
0.85
|
0.94
|
0.95
|
0.95
|
|
Rainfall intensity of 1 inch per hour on 1 acre
|
= 1.008 cu. ft. per second on 1 acre
|
|---|---|
|
= 1 cu. ft. per second on 1 acre (approximately)
|
|
P x I = O
|
Runoff in cu. ft. per sec. per acre for given % imperviousness
of contributing area during a rainfall of given intensity corresponding
to the given duration and a selected frequency.
|
|
I =
|
Intensity of rainfall in inches per hour for given duration
and given frequency.
|
|
Runoff = P
Rainfall
|
Ratio of runoff contributed by an area of given % imperviousness
for a given duration period to the rainfall of a given intensity corresponding
to the same duration period and a selected frequency.
|
|
P (RUNOFF FACTORS) FOR VARIOUS IMPERVIOUS CONDITIONS
| |
