City of Warrenton, MO
Warren County
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Table of Contents
Table of Contents
[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:
DESIGN STORM EVENT
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).
DETENTION FACILITY
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.
DIFFERENTIAL RUNOFF
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.
EROSION CONTROL CLEANUP PLAN
A plan to clean up the property or any surrounding properties affected by erosion and stormwater runoff as a result of land disturbance activities.
EROSION CONTROL PLAN
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.
FREEBOARD
The difference in elevation between the top of the detention basin dam and the design surface water elevation.
LAND DISTURBANCE ACTIVITY
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.
MAJOR STORM EVENT
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).
RATIONAL METHOD
An empirical formula for calculating peak rates of runoff resulting from rainfall.
RETENTION FACILITY
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.
STORMWATER MANAGEMENT PLAN
The drawings, computations, data, proposed contours, reports, etc., that identify how stormwater runoff is to be handled.
STORMWATER MANAGEMENT SYSTEM
All means, natural or manmade, used for conducting stormwater runoff to, through or from a drainage area to the point of outlet.
STORMWATER RUNOFF
Water that results from precipitation which is not absorbed by soil, evaporated into the atmosphere, or entrapped by ground surface depressions and vegetation.
TIME OF CONCENTRATION
A calculation of the time of surface water flow from the hydraulically most remote part of the drainage area to the point in question.
TRIBUTARY AREA
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:
1. 
To prevent sediment-laden runoff from leaving disturbed areas.
2. 
To isolate disturbed areas from erosive surface runoff associated with significant undisturbed areas.
3. 
To protect stormwater drainage systems.
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.
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.
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:
1. 
Any emergency activity that is immediately necessary for the protection of life, property or natural resources.
2. 
Existing farming, nursery and agricultural operations conducted as a permitted or accessory use.
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.
e. 
Acreages and percentage of property proposed as:
(1) 
Impervious surface;
(2) 
Pervious surfaces (green areas);
(3) 
Lakes, canals, detention areas, etc.;
(4) 
Total acreage of project.
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
430a Figure A Rainfall Intensity and Duration Curves.tif
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