A.    Detention Basins. 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.    Storage Volume.

    a.    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 one hundred (100) years.

    b.    After the storage volume has been determined as required above, a one-foot freeboard shall be added to the dam height.

    2.    Outlet Control Works.

    a.    Outlet works shall be designed to limit peak outflow rates from detention storage areas to orbelow peak flow rates that would have occurred prior to the proposed development.

    b.    Outlet works shall not include any mechanical components or devices and shall function without requiring attendance or control during operation.

    3.    Spillway. Emergency spillways shall be provided to permit the safe passage of runoff generated from a one hundred (100) year storm.

    4.    Maximum Depth. The maximum planned depth of stormwaters stored shall not normally exceed four feet.

    5.    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 three to one (3:1).

    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 feet vertically below the lowest sill elevation.

    7.    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 one percent.

    8.    Low Flow Channel. Small flows through the detention basin should be handled by paved ditches from inflow structure to outflow structure to minimize erosion.

    9.    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.

    10.    Aesthetics. Designs should result in aesthetically pleasing configurations which will enhance public acceptability.

    B.    Detention Ponds. Detention ponds may also be used to temporarily detain the differential runoff 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:

    1.    Normal Pool Depth. In order to minimize weed growth, the normal pool depth should be four feet.

    2.    Depth for Fish. If fish are to be kept in thepond, at least one-quarter of the area of the permanent pool should have a minimum depth of ten 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 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.

    5.    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.

    6.    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.

    C.    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, the 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.

    D.    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.

    E.    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. (Ord. 1320 § 1 (part), 1995: prior code § 5-7-1(E))