[Ord. No. 2994 §1, 3-15-2005]
A. 
Stormwater management plans shall be submitted to the City Engineer or his/her designated representative by the owner of any proposed residential, commercial or industrial development within the City unless the City Engineer waives such requirement in writing for one (1) of the following reasons:
1. 
Off-site facility, two (2) or more developments. If two (2) or more developments, including that of the applicant, have provided for a common system.
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 or if, as a result of the topographical conditions present at the development site, there exists in the opinion of the City Engineer a suitable natural retention area and the applicant has agreed to either contribute to a stormwater management fund or participate in the construction of an off-site system as part of a City project. The applicant must agree in writing to contribute to the City fund in accordance with Subsection (4) hereof.
3. 
Other management techniques. Management techniques other than detention facilities may be utilized by the development provided the techniques proposed meet the intent of this Chapter and provide a benefit to the watershed that equals or exceeds the benefit that a detention facility would provide.
4. 
Stormwater Management Fund. A Stormwater Management Fund is hereby created and established by City. Said fund shall be used exclusively by City for programs and projects designed to help control the effects of stormwater within the City limits. Any contribution made by an applicant in lieu of constructing an on-site facility shall be deposited into said fund with any interest income on such funds to remain a part of such fund. In order to participate in such find, the following shall apply:
a. 
Eligibility. It is determined that no adverse effects will result to adjacent property, and a contribution is made to the Stormwater Management Improvements Fund. Residential development of four (4) acres or less and commercial/industrial developments of two (2) acres or less will be considered as prime candidates for a contribution in lieu of on-site detention. It is the City's desire that regional detention storage be utilized to accommodate these smaller developments.
b. 
Contribution. The contribution shall be an amount equal to a cost estimate prepared by a professional engineer for site specific improvements necessary to provide detention as provided herein. All cost estimates for site specific detention facilities shall be subject to review and approval by the City Engineer. The cost estimate must include the value of the land which otherwise would have been used as part of the system with the value of the subject land determined by an independent appraiser paid for by the developer. Alternatively, the procedure detailed in Appendix "A", a copy of which is on file in the City offices, can be used to determine contribution.
[Ord. No. 2994 §1, 3-15-2005]
A. 
Sediment and erosion control on any new development in the City 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.
1. 
When controls are required. Standard vegetative and structural practices, as specified below, that filter, divert or promote the settlement of sediment particles from storm runoff shall be provided in the following situations:
a. 
To prevent sediment-laden runoff from leaving disturbed areas.
b. 
To isolate disturbed areas from erosive surface runoff associated with significant undisturbed areas.
c. 
To protect storm drainage conveyance systems at operable inlets.
2. 
Types of controls. Acceptable sediment and erosion controls shall be either vegetative or structural as described below.
a. 
Vegetative practices.
(1) 
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.
(2) 
Seeding. Of the rate and type to produce a dense vegetation.
(3) 
Sodding.
(4) 
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 4:1 (four (4) feet horizontal for every one (1) foot vertical) shall be stabilized with mulch.
b. 
Structural practices.
(1) 
Construction entrance. A rock stabilized pad located at points of vehicular ingress and egress on a construction site.
(2) 
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.
(3) 
Silt fence. Sediment shall be removed when it reaches one-third (€) to one-half (½) the height of the filter fence.
(4) 
Storm drain inlet protection. May consist of filter fabric, sand bags, excavated gravel, straw bale, block and gravel, and any combination of the above.
(5) 
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.
(6) 
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.
(7) 
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. They shall be sized to provide a minimum volume of three thousand six hundred (3,600) cubic feet per disturbed acre draining to the facility.
(8) 
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.
(9) 
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.
(10) 
Level spreader. An excavated depression to convert a concentrated flow to a sheet flow, allowing water to be released at less erosive levels.
(11) 
Erosion control fabrics.
3. 
Construction plans. A contoured development map must be submitted with all preliminary plans which clearly indicates 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 Engineer or his/her designated representative shall have authority to require proper controls as specified herein.
All required plans and maps are submitted by the owner or applicant to the City Engineer or other qualified professional in order to determine that all technical requirements of this Chapter have been met.
[Ord. No. 2994 §1, 3-15-2005]
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 storm drainage facility.
3. 
Provide protection from the design storm event and address the major storm so as to prevent major property damage and loss of life.
B. 
All systems shall conform to the Storm Water Master Plan. All structures and systems that are to be constructed that share common elements with the Storm Water Master Plan must be designed to accommodate the requirements stated or suggested by the Storm Water Master Plan.
C. 
Rainfall Frequency. All facilities shall be designed to carry a 25-year storm of a duration which produces the maximum peak flow rate of stormwater runoff, without inundation or surcharging for drainage basins of four hundred (400) acres of loss. For larger drainage basins, the design storm shall be the 100-year storm of a duration which produces the maximum peak flow rate. The City Engineer may require a different design storm if, in the opinion of the City Engineer, a public health or safety issue would exist otherwise. All systems shall be designed to allow for a 100-year storm to pass through the development without destroying or damaging property or inundating dwellings. Design information which substantiates both conditions shall be provided.
D. 
Calculation Of Runoff.
1. 
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 water shed development permitted by this Chapter.
2. 
The rational method for calculating stormwater runoff may be used for developments up to one hundred fifty (150) acres. Other common rainfall runoff calculation methods that may be utilized include graphical peak discharge, tabular, and the synthetic unit hydrograph. For development greater than one hundred fifty (150) acres, the method must be approved by the City Engineer.
3. 
Runoff coefficient. The runoff coefficient "C" is the variable in the Rational Formula least susceptible to precise determination and the one, which requires the greatest exercise of engineering judgment because of the many area characteristics, which affect the coefficient.
Among the factors to be considered in influencing the runoff coefficients are the following: present and future zoning; terrain; local ponding or depressions; the amount of pavement; roofs, turf, and other areas having different degrees of imperviousness.
The selection of coefficient should take into consideration the probable ultimate development of presently underdeveloped areas. Suggested values of runoff coefficients are included in the following table:
SUGGESTED RUNOFF COEFFICIENTS "C"
"C" Value
Surface Conditions
.10 — .15
Tall grass, brush
.15 — .20
Parks, golf courses, farms and on-acre, single-family residences
.35
Single-family residences on lots of not less than 15,000 square feet
.45
Single-family residences on lots of not less than 10,000 square feet
.47
Single-family residences on lots of not less than 7,500 square feet
.51
Single-family residences on lots of not less than 6,000 square feet
.90
Gravel surfaces
.95
Asphalt and concrete surfaces
1.00
Buildings and other structures.
4. 
Rainfall intensity. The average frequency of rainfall occurrence used for design determines the degree of protection afforded by a drainage system.
Maximum intensity of rainfall of a given expectancy is greater for a short period of time than for longer periods. Therefore, it is assumed that the maximum runoff will occur as soon as all parts of the drainage area under consideration are contributing. The length of time from the beginning of rainfall until runoff from the most remote point in the drainage area reaches the point under consideration is called the time of concentration. This may include overland flow time and channel or gutter flow time. Once the time of concentration is known, the design intensity rainfall may be determined from the rainfall intensity curves developed from the Weather Bureau data.
5. 
Special uses, such as schools, churches, etc., shall have the differential runoff computed and approved by the City Engineer.
6. 
Special circumstance may dictate that the developed impervious area may differ from that shown in the above table. An example may be single-family lots of larger than fifteen thousand (15,000) square feet. Calculations prepared by a licensed professional engineer may be submitted to the City Engineer or his/her designated representative for his/her evaluation to determine if a minimum impervious area which differs from that shown in the above table may be utilized. Likewise, the City Engineer or his/her designated representative may determine that the percent of impervious area for a particular development differs from that shown in the above table.
E. 
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 design storm. If velocities in channels exceed three and one-half (3.5) feet per second during the design storms, then erosion control other than vegetation shall be provided in channel construction. Channels shall have the hydraulic capacity to carry the design storm runoff within the channel bed and banks with one (1) foot of freeboard. Out of bank flow may be permitted on land slopes parallel to the channel where it can be shown that no erosion damage or property damage will result. Channels that function as part of the major drainage system 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.
F. 
Closed Conduit Storm Sewers.
1. 
Pipe sizes for closed conduit flow shall be based on the design storm runoff and minimum allowable velocities. The system shall provide for the clearing of sediment and other deposits by maintaining a minimum velocity of two (2) feet per second during the 2-year storm.
2. 
Manning's Equation is the most common method of estimating the capacity and flow resistance in closed conduits, although the Kutter, Hazen-Williams, and Darcy Weisbach formulas are also acceptable.
3. 
All drainage and storm sewer systems shall be designed and constructed in accordance with standards and specifications of the City. All facilities shall be designed to carry a 25-year storm while maintaining a minimum of one (1) foot of freeboard between the hydraulic grade line and the gutter. The developer's engineer shall verify that the 100-year storm may be contained in the road right-of-way and/or in a dedicated drainage easement. The engineer shall provide a storm water report to document meeting those requirements.
4. 
Generally, pressure 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.
G. 
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 25-year design storm. Inlets located on continuous grades may be designed to permit a portion of flow to bypass the structure; however, calculations for the downstream structure must consider the bypass. Street flow shall be limited by pavement encroachment and depth of flow as follows:
Street Classification
* Maximum Encroachment of a 2-year Storm
Local
No curb overtopping. Flow may spread to crown of street.
Collector
No curb overstopping. Flow may leave the equivalent of one (1) 10-foot driving lane clear of water.
Arterials
No curb overtopping. Flow spread must leave the equivalent of two (2) 10-foot driving lanes clear of water. One (1) lane in each direction.
* Where no curbing exists, encroachment shall not extend past property lanes.
The storm sewer system shall commence at the point where the volume of flow equals five (5) cfs.
Street Classification
Allowable Depth and Inundated Areas 100-year Storm
Local and Collector
Residential dwellings, public, commercial and industrial buildings shall not be inundated at the ground line. The depth of water over the gutter flowline shall not exceed eighteen (18) inches.
Arterials
Residential dwellings, public, commercial and industrial buildings shall not be inundated at the ground line. Depth of water at the street crown shall not exceed six (6) inches to allow operation of emergency vehicles. The depth of water over the gutter flowline shall not exceed eighteen (18) inches.
H. 
Plans And Calculations.
1. 
A drainage map shall be developed from a base reproduction of the site plan or grading plan. The existing and proposed contours shall be shown, of suitable scale and two (2) foot contour interval for the subject property, extending off-site one hundred (100) feet or less as determined by the City for proper design of the proposed improvements. Contour intervals other than the above shall be used as determined by the site topography.
2. 
The location of existing and proposed property lines, streets, sinkholes, railroads, areas within the tract subject to inundation by stormwater and other significant natural features, such as wooded areas and rock formations, etc., shall be included on the map. All existing and proposed stormwater facilities, such as inlets, manholes, pipes, culverts, bridges, channels, etc., and all existing and proposed improvements required for property design review, such as pavement, buildings, etc., shall be included on the map.
3. 
The location of streams and other floodwater runoff channels, calculations supporting the method and capacity needed for the safe and temporary storage of increased runoff resulting from the proposed development.
4. 
Basic information regarding the receiving watercourse into which the proposed stormwater system will discharge. This information should include a general cross section and existing downstream culverts, bridges, and other waterway openings.
5. 
The runoff details shall be required, showing individual flows for each existing and proposed structure and cumulative flows in pipes and gutters, including "Q" and area. The map shall show all bodies of water, such as ponds or lakes (including surface area and elevation), and all waterways (including their names or the names of creeks or rivers they flow into).
6. 
Lots shall be laid out so as to provide positive drainage away from all buildings. Individual lot drainage shall be shown and coordinated with the drainage pattern for the area and designed so that runoff from one (1) lot will not adversely affect an adjoining lot. All necessary grading to direct stormwater runoff shall be located within a drainage easement. A layout of the proposed stormwater management system including the location and size of all drainage structures, storm sewers, channels, channel sections, detention basins, and analysis regarding the effect said improvements will have upon the receiving channel and its high water elevation.
7. 
All computations, plans and specifications related to the implementation of this Chapter must be prepared and sealed by a professional engineer registered in the State.
[Ord. No. 2994 §1, 3-15-2005; Ord. No. 3362 §1, 9-15-2009]
A. 
The rates (pre-developed and post-developed) of runoff shall be determined for the 2-, 10-, 25- and 100-year rainfall frequencies. The minimum storm duration shall be twenty (20) minutes.
B. 
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.
C. 
In the event the natural downstream channel or storm sewer system is inadequate to accommodate the release rate provided above, then the allowable release rate shall be reduced to that rate permitted by the capacity of the downstream channel or storm sewer system.
D. 
Detention basin volume will be based on routing all post-developed runoff through the detention facility while satisfying the appropriate allowable release rate.
E. 
No credit will be given for existing impervious area, regardless of age or character or reuse of any existing improvements.
1. 
Exception for existing structures. Additions to existing structures that were constructed prior to detention requirements, that increase the gross area of the existing structure by fifty percent (50%) or less will only require detention for the addition and any additional impervious surface added for the addition such as parking. This exception shall also apply when redeveloping a parcel. If fifty percent (50%) or less of the existing building is razed and rebuilt, then only that portion and required impervious area such as parking, will require detention. If more than fifty percent (50%) of the building is razed or if more than a fifty percent (50%) addition is added, then detention will be required for the entire site calculated as if the site was undeveloped. This analysis shall be presented by the developer for acceptance by the City Engineer. This shall apply to detention, retention or payment in lieu of construction of detention.
[Ord. No. 2994 §1, 3-15-2005]
A. 
Dry Bottom Basins. 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:
1. 
Freeboard. Detention storage areas shall have adequate capacity to contain the storage volume of tributary stormwater runoff with at least one (1) foot of freeboard above the water surface for a 100-year storm event.
2. 
Outlet control works. Outlet works shall be designed to limit peak outflow rates from detention storage areas to below peak flow rates that would have occurred prior to the proposed development. Outlet works shall not include any mechanical components or devices and shall function without requiring attendance or control during operation, unless specifically approved by the City Engineer or his/her designated representative.
3. 
Emergency overflow/spillway. Emergency structures shall be provided to permit the safe passage of runoff generated in excess of the design storm event. Antivortex measures shall be provided along with the design plan.
4. 
Maximum depth. The maximum planned depth of stormwaters stored shall not normally exceed five (5) feet.
5. 
Side slopes. The maximum side slopes for grassed basins shall not normally exceed one (1) foot vertical for three (3) feet horizontal.
6. 
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.
7. 
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.
8. 
Multipurpose 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.
9. 
Aesthetics. Designs should result in aesthetically pleasing configurations which will enhance public acceptability.
B. 
Retention Basins. All such privately owned and maintained systems shall be subject to periodic inspection by the City Engineer or his/her designated representative. 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:
1. 
Normal pool depth. In order to manage weed growth, the normal pool depth should be four (4) feet minimum.
2. 
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.
3. 
Facilities for emptying. In order to ease cleaning of the pond or shoreline maintenance, the pond design should include provisions for emptying the pond.
4. 
Low flow bypass. The design of any pond may include a low flow bypass channel or pipeline to divert runoff that can be accommodated by downstream drainageways.
5. 
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.
6. 
Permanent pool volume. The permanent pool volume in a wet basin at normal depth should be equal to the runoff volume from its watershed for the 2-year event.
C. 
Detention In Flood Fringe Areas. The placement of a detention basin in a flood fringe area shall require compensatory storage for one and one-half (1.5) times the volume below the base flood elevation occupied by the detention basin including any berms. The release rate from the detention storage provided shall still be controlled consistent with the requirements of Section 410.080. The applicant shall demonstrate its operation for all streamflow and floodplain backwater conditions. Excavations for compensatory storage along streams and watercourses shall be opposite or adjacent to the area occupied by detention. All floodplain storage lost below the 25-year flood elevation shall be replaced below the 25-year flood elevation. All floodplain storage lost above the existing 25-year flood elevation shall be replaced above the proposed 25-year flood elevation. All compensatory storage excavations shall be constructed to drain freely and openly to the watercourse.
D. 
Rooftop Storage. Detention storage may be met in total or in part by detention on roofs. Details of such design, which shall be included in the building permit application, shall include the depth and volume of storage, details of outlet devices and downdrains and elevations of overflow provisions. Direct connection of roof drains to sanitary sewers is prohibited.
E. 
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.
F. 
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.
G. 
Detention Basins In Floodways. Detention basins shall not be placed in the floodway.
[Ord. No. 2994 §1, 3-15-2005]
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 engineer's calculations show the pipe material or soil condition to be adequate for the subjected load.
B. 
Pipes on twenty percent (20%) slopes or greater shall be anchored securely with concrete anchors or their 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 25-year design storm. The use of energy-dissipating devices may be necessary to reduce the velocity to acceptable levels for the receiving surface. The energy-dissipating device 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-tenth (0.1) 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 pre-cast or cast-in-place concrete with concrete 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 MHTD 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 per the manufacturer's requirements.
N. 
Grated inlets will not be allowed without special approval by the City Engineer.
O. 
All materials used in the construction of storm sewers shall be subject to inspection and approval of the City Engineer or his/her designated representative.
P. 
Acceptable pipe material shall be reinforced concrete pipe, corrugated metal pipe and corrugated polyethylene pipe. 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.
Q. 
Corrugated aluminized metal pipe shall conform to the appropriate requirements of AASHTO or Missouri Department of Transportation. 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. Use of corrugated metal pipe greater than forty-eight (48) inches in diameter shall only be allowed after approval by the City Engineer.
R. 
The City Engineer may consider for approval a written request to use other types of pipe. 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". Use of thermoplastic pipe in all locations shall be allowed only after approval by the City Engineer.
S. 
Reinforced concrete pipe shall be required under road pavement, unless other material is approved by the City Engineer.
T. 
All construction details pertaining to stormwater drainage shall be in accordance with the City and State requirements, unless otherwise noted herein.
[Ord. No. 2994 §1, 3-15-2005]
A. 
Whenever the stormwater analysis presented by the developer and accepted by the City Engineer shows that detention provides no significant benefit, the developer may apply for a buyout of the required detention volume. The cost is shown in the application in Appendix "A", a copy of which is on file in the City offices. Whenever the stormwater analysis shows that detention will increase downstream flooding, the developer shall be required to pay to the City the above rate for the equivalent volume of detention required due to the increase in impervious area.
B. 
Buyout funds shall be used by the City to construct and maintain regional detention and conveyance systems within the drainage basin where the stormwater facilities would have been constructed.
C. 
Detention buyouts are not automatic and must be considered on a case-by-case basis by submission of the completed application in Appendix "A", a copy of which is on file in the City offices. Initial determination of approval will be made by the City Engineer. That decision may be appealed in writing to the City Administrator for a final determination.
D. 
When a buyout is approved, it is the responsibility of the developer to convey the stormwater runoff from the development to the existing storm sewer system by making whatever modifications are necessary to the existing system.
E. 
When the detention volume is less than five thousand (5,000) cubic feet, the table shown in Appendix "A", a copy of which is on file in the City offices, may be used to determine the buyout amount.
[Ord. No. 2994 §1, 3-15-2005]
A. 
Easements shall be provided for stormwater detention facilities on forms approved by the City Engineer. These easements shall include an access easement.
B. 
All detention reservoirs, with the exception of parking lots and roof detentions, shall be enclosed by an easement. The limits of the easement shall extend a minimum of ten (10) feet beyond the total area required for maintenance. The limits of the ponding area and legal description with the designation of the detention facilities shall be shown on the improvement plans and the final plat. This easement shall also be continuous with or to a public access area to allow the City to maintain the easement if necessary. If it is required that the City maintain the easement, the City shall have the right to charge the party primarily responsible for maintenance as stated on the easement document.
C. 
A minimum twenty (20) foot wide easement shall be provided within the reservoir area connecting the tributary pipes and the discharge system for possible future elimination of the detention basin. The 100-year peak flow shall be contained within the limits of the drainage easement shown on the improvement plans and the final plat.
D. 
Easements not included as part of the final plat will have to be recorded on an easement form suitable for the type of development being proposed.
[Ord. No. 2994 §1, 3-15-2005]
It may be advantageous in some situations to delay the building of the permanent detention facilities until after the completion of the other improvements. In these situations, temporary detention facilities must be provided. The permanent or temporary detention facilities shall be constructed and be functional before proceeding with any other construction.
[Ord. No. 2994 §1, 3-15-2005]
A. 
Off-Site Detention. Stormwater detention facilities designed and constructed off-site or outside the limits of the proposed development will be considered for approval. This approval is contingent upon documentation being furnished to verify that drainage easements have been obtained from the proposed development to the detention facility in addition to easements for the detention area. The drainage easements must clearly set out provisions for maintenance.
B. 
Detention facilities designed and located to provide for detention on major drainage channels will be considered for a regional detention facility. The drainage area considered for a regional detention facility is generally several hundred acres. The regional basin must provide a detention volume for a 100-year storm for the entire drainage area. The regional detention facility must be designed with a low-flow, concrete channel through the limits of the basin. Upon conceptual approval of the location and final approval of the design and construction, the City may accept the responsibility for the maintenance of a regional facility. Drainage and access easements will be required giving the City the authority to gain vehicular access to the facility from a public street.
C. 
As additional development occurs upstream of the regional facility, on-site detention requirements may be bought out, provided the regional detention basin has been designed for full development of the basin, or if modifications are made to the regional facility by the developer to provide for the additional volume of detention required for the new development. Easements must be provided along the drainage channel from the new development to the regional facility, and the channel must be able to carry the peak rate of runoff from the 100-year storm from the entire basin upstream of the regional facility.
[Ord. No. 2994 §1, 3-15-2005]
Where detention, retention, or depressional storage areas are to be used as part of the drainage system for a property, they shall be completed before general property grading begins. This is to ensure that if soil erosion and sediment control practices are not adequately implemented, the eroded sediment will be captured in these areas and will have to be removed by the applicant before project completion.