Any person, firm, corporation or other entity proposing to construct buildings or develop land within the jurisdiction of the village shall prepare, for approval by the village staff, a Storm Water Management Plan that describes the manner in which erosion, sediment and runoff resulting from the development will be controlled and managed. No building or construction permits or plat approval shall be issued by the village until the Storm Water Management Plan has been approved by the village staff as meeting the requirements of this Code. Downstream property owners, watercourses, channels or conduits shall not receive storm water runoff 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 runoff exceed the capacity of the natural drainage system.
(A) Storm water runoff 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 village staff.
(B) For purposes of designing adequate on-site detention facilities, the state's water survey rainfall data for this region shall be used.
(C) (1) Detention basins. Basins may be constructed to temporarily detain the storm water 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) 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. After the appropriate volume has been determined a one-foot "freeboard" shall be added to the storage elevation to determine the final height of the detaining fill or structure.
(b) Outlet control works.
1. Outlet works shall be designated 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 runoff generated from a 100-year storm.
(d) Maximum depth. The maximum planned depth of storm waters stored shall not normally exceed four feet without properly designed safety features. (See division (D) below.)
(e) Side slopes. The maximum side slopes for grassed basins shall not exceed one foot vertical for three feet horizontal (3:1 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 four to one (4:1).
(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 structures to outflow structure to minimize erosion. Paved ditches to be constructed per I.D.O.T. Standards.
(i) Multi-purpose basins. If the detention basin is to have other uses, the design of the basin bottom should include under-drains to expedite drying of the bottom between runoff events.
(j) Aesthetics. Designs should result in aesthetically pleasing configurations which will enhance public acceptability.
(k) Basin edge. The basin edge must be located a minimum of ten feet, plus one and one-half times the basin depth from public rights-of-way.
(2) Detention ponds and lakes. Detention ponds and lakes may also be used to temporarily detain the differential runoff from the development. In addition to the general design features, the following should also be incorporated into the design of any detention ponds or lakes.
(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 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.
(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.
(g) For lakes. In addition to the requirements hereof, the final height of the dam and drainage easement calculations shall take into account the wave run up due to wind.
(3) Rooftop storage. Detention storage may be met in total or in part by detention on roofs. Details of the design, which shall be included in the building permit application, shall include the depth and volume of storage, details of outlet devices and down-drains, 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 depth of storage must be limited so as to prevent damage to parked vehicles. Depth of stored water shall not exceed six inches.
(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.
(D) Safety features. Design of detention facilities shall incorporate safety features, particularly at outlets, on steep slopes and at any attractive nuisances to include, as necessary, fencing, handrails, 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. (Design engineer to certify adequate safety features are included on the plans.)
(1) In addition to any other provisions herein, any structure built downstream of a dam shall have a lowest sill elevation of one foot above the maximum wave height associated with a dam breach at the structure location as per the state's Department of Natural Resources (IDNR) Division of Water Resources dam safety permit requirement.
(2) Any dam associated with a detention pond or lake shall be on a single parcel. Split ownership will not be permitted.
(3) Any subdivision which contains a dam or is downstream of a dam, the following statement shall be on the final plat:
"Owner of the parcel containing a dam and those downstream of a dam are hereby cautioned about the risks associated with parcels downstream of a dam and the responsibilities of dam ownership. For further information on the responsibilities and liabilities owners are advised to contact their own attorney, the State Dam Safety Office and the Illinois Department of Natural Resources, Office of Water Resources."
(E) Application to development and subdivisions. The provisions of this section shall be applicable to all development and subdivisions.
(F) Storm water detention facilities. The storm water detention facilities must be built in conjunction with the storm sewer 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 plat approval, the developer shall submit his or her plan for future maintenance responsibility of the detention area.
(G) Review by village staff. When applicable, the provisions of this section shall be reviewed by the village staff to assure compliance.
(H) Storm water detention facilities fully operational. No occupancy permit can be issued in any development phase, unless the storm water detention facilities to which the building area is tributary, are fully operational.