(A) Any person, firm, corporation or other entity proposing to construct buildings or develop land within the jurisdiction of the city shall prepare, for approval by the City Engineer, a Storm Water Management Plan that described the manner in which erosion, sediment and run-off resulting from the development will be controlled and managed. No building or construction permits or plat approval shall be issued by the city until the Storm Water Management Plan has been approved by the City Engineer as meeting the requirements of this section, or the requirement for such Storm Water Management Plan has been waived by the City Engineer. Downstream property owners, watercourses, channels or conduits shall not receive storm water run-off from proposed upstream developments at a higher peak flow rate than would have resulted from the same storm event occurring over the site of the proposed development with the land in its natural, undeveloped conditions, nor shall storm water run-off exceed the capacity of the natural drainage system.
(B) Storm water run-off resulting from a proposed development shall be detained on-site:
(1) By wet or dry bottom reservoirs;
(2) By underground reservoirs;
(3) On flat roofs, parking lots or streets; or
(4) By other detention methods approved by the City Engineer.
(C) For purposes of designing adequate on-site detention facilities, the Illinois State Water Survey rainfall data for this region shall be used.
(D) (1) Detention basins. Basins may be constructed to temporarily detain the storm water run-off 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) Storage volume. The volume of storage provided shall be sufficient to store flows both during and immediately after the maximum storm event which can be expected to occur once every ten and 100 years.
(b) Outlet control works.
1. Outlet works shall be designed to limit peak outflow rates from detention storage areas to or below peak flow rates that would have occurred prior to the proposed development.
2. Outlet works shall not include any mechanical components or devices and shall function without requiring attendance or control during operation.
(c) Spillway. Emergency spillways shall be provided to permit the safe passage of run-off generated from a 100-year storm.
(d) Maximum depth. The maximum planned depth of storm waters stored shall not normally exceed four feet.
(e) Side slopes. The maximum side slopes for grassed basins shall not exceed one foot vertical for two feet horizontal (2:1 slope) for basins less than or equal to four feet deep; for basins greater than four feet deep the maximum side slope shall not exceed 3:1.
(f) Limits of ponding. In no case shall the limits of maximum ponding be closer than 30 feet horizontally from any building and less than two feet vertically below the lowest sill elevation.
(g) Interior drainage. The basin bottom should be designed to drain expeditiously. If the bottom is to be grass, it should have a minimum slope of 1%.
(h) Low flow channel. Small flows through the detention basin should be handled by paved ditches from inflow structure to outflow structure to minimize erosion.
(i) 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 run-off events.
(j) Aesthetics. Designs should result in aesthetically pleasing configurations which will enhance public acceptability.
(2) Detention ponds. Detention ponds may also be used to temporarily detain the differential run-off from the development. In addition to the general design features enumerated above for detention basins, the following features should also be incorporated into the design of any detention pond.
(a) Normal pool depth. In order to minimize weed growth, the normal pool depth should be four feet minimum.
(b) Depth for fish. If fish are to be kept in the pond, at least one-quarter of the area of the permanent pool should have a minimum depth of ten 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 run-off that can be accommodated by downstream drainageways.
(e) Bank stabilization. In order to minimize the effects of waves or ice, some type of bank stabilization such as rip-rap or concrete should be placed along the normal pool shoreline.
(f) Side slopes below normal pool. The side slopes below the normal pool elevation may exceed the maximum side slope permitted above normal pool. The design shall, however, include provisions for a safety ledge having a depth of water not greater than three feet immediately adjacent to the shoreline.
(3) Rooftop storage. Detention storage may be met in total or in part by detention on roofs. Details of such design, which shall be included in the building permit application, shall include the depth and volume of storage, details of outlet devices and downdrains, elevations of overflow scuppers, design loadings for the roof structure and emergency overflow provisions. Direct connection of roof drains to sanitary sewers is prohibited.
(4) Parking lot storage. Paved parking lots may be designed to provide temporary detention storage of storm water on all or a portion of their surfaces. Outlets will be designed so as to slowly empty the stored waters and depths of storage must be limited so as to prevent damage to parked vehicles.
(5) 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 and the like.
(E) Designs of detention facilities shall incorporate safety features, particularly at outlets, on steep slopes and at any attractive nuisances to include, as necessary, fencing, hand rails, lighting, steps, grills, signs and other protective or warning devices so as to restrict access during critical periods and to afford some measure of safety to both authorized and unauthorized persons.
(F) The provisions of this section shall be applicable in the following areas:
(1) Any residential development having a gross aggregate of five acres or more;
(2) Any residential development of less than five acres with a 50% impervious surface including roads, building, utility right-of-way and other improvements; or
(3) Any commercial, industrial, institutional or utility development having a gross aggregate area of one acre or more.
(G) The storm water detention facilities must be built in conjunction with the storm water installation and be fully operational after the clearing of vegetation.
(1) Silt and debris connected with early construction shall be removed periodically from the detention area to maintain full storage capacity.
(2) The maintenance responsibility of the detention area shall remain with the developer and/or contractor until final inspection and applicable escrows are released.
(3) Before a certificate of occupancy is issued, the developer shall submit his or her commitment for future maintenance responsibility of the detention area.
(H) When applicable, the provisions of this section shall be reviewed by the City Engineer to assure compliance.
(1960 Code, § 60-7-10) (Ord. 4632, passed 6-5-1989) Penalty, see § 162.999