(A)   General. Dams and berms for water impoundments shall be planned, designed, and constructed under the supervision of a structural or professional engineer and shall meet the requirements of §§ 151.145 through 151.154. The Director, after consultation with relevant county staff, shall be authorized to modify the standards of this section provided such modification is not in conflict with other provisions of this chapter.
   (B)   Stormwater detention basins.  In addition to the requirements of §§ 151.145 through 151.154, the following standards shall be met.
      (1)   Spillways.  An emergency spillway shall be constructed that is capable of passing the 100-year storm event, including any off-site flow that will be bypassed over the spillway. It shall be designed and constructed at the high water line for on-site detention requirements. Drainage calculations for the sizing of the spillway shall be required. The slope from the top of berm to the spillway shall not exceed 3:1. The emergency spillway shall be immediately stabilized with sod, rip-rap, or permanent turf reinforcement matting and native seeding as dictated by design velocities, based on the 100-year outflow.
      (2)   Freeboard.  A minimum of one foot of freeboard above the water surface in the reservoir with the emergency spillway flowing at design depth shall be provided to the top of berm elevation.
   (C)   Existing dams.  An engineering report shall be submitted to the Director on all existing dams within a proposed subdivision. Any dam found to be structurally unsafe shall be reconstructed or reinforced in accordance with the existing standards. The modification of an existing dam may require a dam safety permit from the Illinois Department of Natural Resources.
(Ord., § 10.14, passed 10-13-2009; Ord. passed - -)