[CC 1988 §24-65; Ord. No. 3457 §1, 5-21-2001]
This Chapter seeks to provide those standards, criteria, procedures and controls necessary to minimize the harmful physical and economic effects of erosion and flooding from stormwater within or directed toward the City of De Soto. This is to be accomplished through the requirement of special measures to mitigate erosion both during and after development and the retention and controlled discharge of the differential runoff from any property whereon any grading, excavation, filling, or other disturbance of the natural vegetation or any construction, erection or alteration of a building or structure is to be undertaken.
[CC 1988 §24-66; Ord. No. 3457 §1, 5-21-2001]
As used in this Chapter, the following terms shall have these prescribed meanings:
DEVELOPED PROPERTY
Any tract of land in the City of De Soto whereon any grading, excavation, filling, or other disturbance of the natural vegetation or any construction, erection or alteration of a building or structure has been undertaken.
PROPERTY
Any tract of land in the City of De Soto.
UNDEVELOPED PROPERTY
Any tract of land in the City of De Soto whereon neither grading, excavation, filling, or other disturbance of the natural vegetation nor any construction, erection or alteration of a building or structure has been undertaken.
[CC 1988 §24-67; Ord. No. 3457 §1, 5-21-2001; Ord. No. 3551 §1, 1-22-2004]
A. 
General. An approved stormwater runoff control plan is required for all land development, subdivision and construction of buildings. Except as provided in Subsection (D) of this Section, it shall be unlawful for any person to develop or improve on any property within the City unless there is in force an approved stormwater runoff control plan issued as required under the provisions of this Chapter. The term "property", as used in this Section, shall be defined as any tract of land in the City of De Soto.
B. 
Construction Or Alteration Of Buildings. Except as provided below, it shall be unlawful for any person to construct any new building or structure or to enlarge or otherwise alter any existing building or structure on any property within the City in such manner as to change the land area covered by the building or structure unless there is in force an approved stormwater runoff control plan issued as required under the provisions herein.
C. 
Change Or Disturbance Of Terrain. Except as provided in Subsection (D) of this Section, it shall be unlawful for any person to clear, grade, excavate, fill, remove topsoil from or change the contour of any land in the City unless there is in force an approved stormwater runoff control plan issued under the provisions of this Chapter.
D. 
Exceptions. The provisions of this Section shall not apply to:
1. 
Any reconstruction, repair or alteration of any existing building or structure when no land, trees, shrubs, grass or other vegetation is to be disturbed, destroyed or removed.
2. 
Any undeveloped property of less than one (1) acre zoned in an "A-1", "R-1", "R-2" or single-family residential district.
3. 
Any already developed property zoned "A-1", "R-1", "R-2" or remaining in a single-family residential use.
4. 
The clearing, grading, excavation, filling, removing topsoil from or changing the contour of less than two thousand five hundred (2,500) square feet of land.
5. 
The planting, trimming, pruning or removal of trees, shrubs, grass, weeds, vegetation, ground cover or other plant material when such actions are incidental to and part of the normal maintenance of land and property in the City of De Soto.
6. 
In considering the applicability of these exceptions, the effective acreage for a project, development or subdivision not limited to a fractional part of the total concept. Rather, if a project is developed in phases or small plats, the total acreage of the project, development or subdivision will be considered. Furthermore, projects of less acreage than provided for in this Chapter shall also provide retention if, in the judgment of the City Engineer, conditions in the receiving system are inadequate, or harmful effects can be anticipated if retention is not implemented.
[CC 1988 §24-68; Ord. No. 3457 §1, 5-21-2001; Ord. No. 3551 §2, 1-22-2004]
A. 
General Standards.
1. 
Zoning classification and permitted land use determine the stormwater retention requirements for any given property. Minimum lot size and percent imperviousness are major factors in determining the future runoff from a property. An additional volume of stormwater will be caused to leave a property due to development thereon. The volume of stormwater which must be retained in accordance with the provisions of this Chapter is the difference between the volume of water expected to leave the property in an undeveloped condition (roughly five percent (5%) impervious) and the volume of water which will be caused to leave the property due to all development (existing and proposed) thereon.
2. 
Runoff rates for all categories of projects shall be evaluated by the rational formula. The runoff coefficients in the following table for a storm event with a twenty-five (25) year (frequency) and an assumed twenty (20) minute inlet time shall be used to calculate runoff volumes.
Average C.I. Factors in Cubic Feet Per Second Per Acre (CFS/Acre) 20 Minute Inlet Time
Zoning District
Use
% Imp.1
C
C.I. Factors2
25-Yr
50-Yr
100-Yr
A-1 Agricultural
All uses
5
0.37
2.00
2.18
2.37
R-1 Residential
One-family dwelling
All other uses
45
60
0.54
0.60
2.92
3.24
3.19
3.54
3.46
3.84
R-2 Residential
One-family dwelling
All other uses
47
75
0.548
0.665
2.96
3.59
3.23
3.92
3.51
4.26
R-3 Residential
Two-family dwelling
All other uses
60
75
0.600
0.665
3.24
3.59
3.54
3.92
3.84
4.26
R-4 Residential
Multiple-family dwelling
All other uses
70
75
0.645
0.665
3.48
3.59
3.81
3.92
4.13
4.26
C-1 Commercial
Office and professional
All other uses
Same as R-4
85
Same as R-4
0.705
Same as R-4
3.81
Same as R-4
4.16
Same as R-4
4.51
C-2 Commercial
Downtown
All other uses
Same as C-1
85
Same as C-1
0.705
Same as C-1
3.81
Same as C-1
4.16
Same as C-1
4.51
C-3 Commercial
General
Same as C-1 and C-2
Same as C-1 and C-2
Same as C-1 and C-2
Same as C-1 and C-2
Same as C-1 and C-2
M-1 Manufacturing
Light
90
0.73
3.94
4.31
4.67
M-2 Manufacturing
General
90
0.73
3.94
4.31
4.67
PUD — Planned Unit Development
As determined on a site-by-site basis.
NOTES:
1 The percent impervious (% Imp.) values were based upon the minimum lot size requirements for each use.
2 The C.I. factors were derived from the U.S. Weather Bureau Technical Paper No. 40: "Rainfall Frequency Atlas of the United States for durations from thirty (30) minutes to twenty-four (24) hours and return periods from one (1) to one hundred (100) years."
B. 
Retention Facilities. In general, retention facilities shall be provided with obvious and effective control strategies. The following shall be considered in determining the effectiveness and safety of these facilities in relation to the intent and purpose of this Section.
1. 
(Volume of runoff from the developed property) = C.I. factor x area of property (in acres) x 30 minutes x 60 seconds/minute.
2. 
(Volume of runoff from the property in undeveloped condition) = 2.00 cfs/acre x area of property (in acres) x 30 minutes x 60 seconds/minute.
3. 
Volume of retention for the developed property = (Volume of runoff from developed property) - (Volume of runoff from the property in an undeveloped condition).
4. 
Tributary (Q) peak runoff to basin.
5. 
Balanced maximum outflow rate from the low-flow structure.
6. 
Ratios of inflow to outflow rates.
7. 
Sizing of the overflow facilities.
8. 
Stability of retention dikes.
9. 
Safety features.
10. 
Maintenance features.
C. 
Open Dry Reservoirs.
1. 
Wet weather ponds or dry reservoirs shall be designed with proper safety, stability and ease of maintenance features and shall not retain stormwater to a depth greater than four (4) feet if specifically permitted by site plan review by the Planning and Zoning Commission in consideration of a special demonstrated need and special provisions to avoid safety hazards of such greater hazards of such greater depths.
2. 
Maximum side slopes for grass-edged reservoirs shall not exceed one (1) foot vertical for two (2) feet horizontal (2:1) unless adequate measures are included to provide for the stability of these slopes.
3. 
In no case shall the limits of maximum ponding elevation be closer than thirty (30) feet horizontally from any building and less than two (2) feet vertically below the lowest sill elevation.
4. 
The entire reservoir area shall be seeded, fertilized and mulched, sodded or paved prior to release of escrows.
D. 
Permanent Lakes Used For Retention.
1. 
Permanent lakes with fluctuating volume controls may be used as retention areas provided that the limits of maximum ponding elevations are no closer than thirty (30) feet horizontally from any building and less than two (2) feet below the lowest sill elevation of any building.
2. 
Maximum fluctuation from permanent pool elevation to maximum ponding elevation shall be three (3) feet.
3. 
Special consideration shall be given to measures to ensure the safety of small children in the design of permanent lakes especially when located in residential areas.
E. 
Parking Lots Used For Retention.
1. 
Retention is permitted in parking lots to maximum depth of twelve (12) inches.
2. 
In no case should the maximum limits of ponding be designed closer than ten (10) feet from a building unless proper provision is made for the waterproofing of the building and for pedestrian accessibility.
3. 
The minimum freeboard from the maximum ponding elevation to the lowest sill elevation shall be two (2) feet.
4. 
Closed retention tanks. Facilities which are fully enclosed to detain stormwater may be of any depth.
F. 
Discharge Systems.
1. 
The design discharge (Q) for the low-flow pipe shall not exceed the twenty-five (25) year (frequency) twenty (20) minute duration (inlet time), runoff from the tributary area for five percent (5%) imperviousness (2.0 c.f.s. per acre). The maximum discharge shall be designated to take place under total anticipated design-head conditions.
2. 
Low-flow pipes shall not be smaller than four (4) inches in diameter to minimize maintenance and operating problems, except in parking lot and roof retention where minimum size of opening shall be designed specifically for each condition. The low-flow pipe shall be provided with a bar-screen on a minimum 2:1 slope to reduce blockage by debris.
3. 
The overflow opening or spillway shall be designed to accept the total peak runoff of the improved tributary area with discharge velocity not to exceed five (5) feet per second unless special provisions are made.
4. 
Proper engineering judgment shall be exercised in analysis of secondary routing of discharge of greater intensity than the design twenty-five (25) year frequency in order to avoid economic losses or damage downstream. Review with twenty-five (25) and fifty (50) year frequency is recommended.
5. 
Sizing of the system below the control structure shall be for the total improved peak runoff tributary to the structure with no allowance for retention with discharge velocity not to exceed five (5) feet per second unless special provisions are made.
[CC 1988 §24-69; Ord. No. 3457 §1, 5-21-2001]
A. 
All stormwater discharge pipes shall be computed on a twenty-five (25) year rainfall frequency at a minimum.
B. 
Construction And Maintenance Of Stormwater And Erosion Control Facilities.
1. 
Retention facilities, when mandatory, are to be built in conjunction with the storm sewer installation and/or grading. Since these facilities are intended to control increased runoff, they must be partially or fully operational soon after the clearing of the vegetation.
2. 
Silt and debris connected both with early construction and with general erosion from the site and elsewhere in the watershed after construction shall be removed periodically from the retention area and control structure in order to maintain full storage capacity.
3. 
The responsibility of maintenance of the retention facilities in subdivision projects shall remain with the developer until such time as applicable escrows are released. Upon release of escrows the maintenance responsibility shall be vested in the trustees of the subdivision by virtue of the trust indenture. The indenture of the trust shall clearly indicate resident responsibility for maintenance in cases of projects without common ground.
4. 
The responsibility of maintenance of the retention facilities in single owner development projects shall remain with the general contractor until final inspection of the development is performed and approved. Upon approval of the project, the maintenance of retention facilities shall be vested with the owner of the property.
C. 
Submission, Review And Approval Of Required Stormwater Runoff Control Plans.
1. 
Requirements for building or grading permit. No permit shall be issued to construct, erect or alter any building or structure or to clear, grade, excavate, fill, remove topsoil from or change the contour of any property within the City until a stormwater runoff control plan has been submitted and approved by the City of De Soto in accordance with the provisions of this Chapter, except as provided in 425.030(D).
D. 
Procedure.
1. 
Application for an approved stormwater runoff control plan, as required, shall be submitted to the City Manager by the owner of the land prior to the time any work subject to this Chapter is begun on the land.
2. 
Upon receipt of any application and plan, the City Manager with the advice of the City Engineer shall consider the plan in light of the provisions of this Chapter and shall approve the plan, disapprove the plan or approve the plan with modifications, noting thereon any changes that will be required.
3. 
The City shall promptly notify the applicant of the City's decision on a plan. Failure of the City Manager to act on any plans submitted within forty-five (45) days after they have been properly filed should be deemed to constitute approval of the plans. Any approved plan shall be issued, dated, and bear the manual signature of the City Manager.
E. 
Submission Requirements.
1. 
All plans and specifications submitted for review and/or approval shall be prepared by or under the direct supervision of a registered professional engineer licensed in the State of Missouri and shall meet the minimum standards and requirements of the City and other applicable authorities. Each of the plan, profile and special drawing sheets for a project shall bear a legible stamp of the professional engineer in charge.
2. 
In order to facilitate review of plans, all projects shall be submitted with a letter of transmittal which shall include the name of project, name and address of owner or developer, name, address and telephone number of engineer, and clarification as to the purpose of submittal.
[CC 1988 §24-70; Ord. No. 3457 §1, 5-21-2001]
The stormwater runoff control plan shall be subject to all provisions of this Chapter relating to enforcement, violations and penalties. In addition, a corporate surety bond, conditioned upon carrying out all and every part of approved plans for at least the sum estimated to be the full costs of carrying out such plans, or a cash escrow, upon the same conditions and in the same amount, shall be furnished the City whenever such costs exceed five hundred dollars ($500.00). The bond or escrow shall be released upon proper completion of all of the requirements of such approved plans.
[CC 1988 §24-71; Ord. No. 3457 §1, 5-21-2001]
This Chapter shall be enforced by the City Manager with the assistance and cooperation of other officials including the City Engineer. If the City Manager finds that any of the provisions of this Chapter are being violated, he/she shall notify in writing the person responsible for such violation, indicating the nature of the violation and ordering the action necessary to correct it. He/she shall take any other action authorized by law to ensure compliance with or to prevent violation of the provisions of this Chapter.
[CC 1988 §24-72; Ord. No. 3457 §1, 5-21-2001]
A. 
Violations of this Chapter shall include, but are not limited to, the following:
1. 
Any activity of proceeding not in accordance with the procedures, requirements, standards or other provisions of this Chapter.
2. 
No owner, or agent of the owner, or any land located within a subdivision of the City of De Soto shall knowingly or with intent to defraud, transfer, sell, agree to sell, or negotiate to sell that land by reference to or by other use of a plat of any purported subdivision of the land before the final subdivision plat has been approved by the Planning and Zoning Commission and City Councilmen in accordance with this Chapter and recorded by the Recorder of Deeds of the County.
3. 
Failure to obtain the approvals and permits required by this Chapter and to comply with their terms and conditions.
B. 
Those chargeable, singly or jointly, with violations of this Chapter shall include, but are not limited to, the following:
1. 
Those who commit, assist in, or otherwise participate in a violation.
2. 
The owner or other persons who maintain the building, premises, property, or other place where the violation has been committed or exists.
3. 
The developer, agent, architect, contractor, or any other person who performs work or enters into a contract for work in violation of this Chapter.
C. 
Wherever in this Chapter any act is prohibited or is declared to be unlawful or an offense or misdemeanor, upon conviction of a violation of any such provision of this Chapter, the violator shall be punished by a fine not exceeding five hundred dollars ($500.00) or by imprisonment in the City or County Jail not to exceed ninety (90) days, or by both such fine and imprisonment. Each day any violation of this Chapter shall continue shall constitute, except where otherwise prohibited, a separate offense.