(A) The applicant, through the Lake County Stormwater Management Commission, shall obtain approval from the Illinois Department of Natural Resources, Office of Water Resources for all development with a tributary drainage area of 640 acres or more located within the regulatory floodplain without a delineated regulatory floodway. The development shall not, singularly or cumulatively, result in an obstruction of flood flows or potential flood damages outside the development due to increased flood heights, velocities or loss of floodplain storage.
(B) The applicant shall meet the requirements of § 151.147 in accordance with following criteria and shall submit to the Lake County Stormwater Management Commission:
(1) An engineering study performed by a licensed professional engineer which will determine a floodway which meets the definition of the regulatory floodway and show the proposed development will meet all applicable requirements of § 151.147;
(2) An engineering study performed by a licensed professional engineer which will determine a base flood elevation and demonstrate that the proposed development will maintain the existing conditions conveyance, will not increase flood velocities, will not increase flood profiles and will compensate for all lost flood storage at a ratio of 1.2 to one in a manner that is hydraulically equivalent; or
(3) An engineering study performed by a licensed professional engineer which will demonstrate, for a range of flood elevations (which would exceed the expected 100-year flood elevation), the proposed development will maintain the existing condition’s conveyance, will not increase flood velocities, will not increase flood profiles, and will compensate for all lost flood storage at a ratio of 1.2 to one in a manner that is hydraulically equivalent.
(Ord., § 8.8, passed 10-13-2009; Ord. 23-1056, passed 8-8-2023)