(A) Requirements for detailed studies. Developments greater than fifty (50) lots or five (5) acres, or as requested by the Community Development Director, shall be subject to a detailed study to determine the regulatory flood protection elevation and the limits of the Floodway District. The determination of the floodway and flood fringe must be consistent with accepted hydrological and hydraulic engineering standards, and must include the following components, as applicable:
(1) Estimate the peak discharge of the regional one percent chance (1%) flood.
(2) Calculate the water surface profile of the regional flood based upon a hydraulic analysis of the stream channel and overbank areas.
(3) Compute the floodway necessary to convey or store the regional flood without increasing flood stages more than one-half (0.5) foot. A lesser stage increase than one-half (0.5) foot is required if, as a result of the stage increase, increased flood damages would result. An equal degree of encroachment on both sides of the stream within the reach must be assumed in computing floodway boundaries, unless development or geographic features warrant other analysis, as approved by the Department of Natural Resources.
(B) Alternative methods. For areas where a detailed study is not available or required, the regional flood elevation must be identified to determine the boundaries of the special flood hazard area. The Community Development Director must use the best available data to determine the regional flood elevation. The entire flood plain must be treated as floodway until there is a floodway determination.
(1) In those areas of the Special Flood Hazard Area where the floodway has not been determined, allowable uses are restricted to those identified in §§ 152.040 and 152.042. The proposed development must not increase flood stages more than one-half (0.5) foot, as determined by a professional engineer or by using accepted engineering practices approved by the Community Development Director. A stage increase less than one-half (0.5) foot must be used if increased flood damages would result.
(2) If buildings or other development prohibited in floodways are proposed, a floodway/flood fringe determination is required to verify the development is within the flood fringe. The floodway/flood fringe determination must be done by a professional engineer or by using other accepted engineering practices approved by the Community Development Director. Any such proposal must assume a one-half (0.5) foot stage increase for the purposes of determining the regulatory flood protection elevation to accommodate for future cumulative impacts.
(C) The Community Development Director will review the submitted information and assess the technical evaluation and the recommended Floodway and/or Flood Fringe District boundary. The assessment must include the cumulative effects of previous floodway encroachments. The Community Development Director may seek technical assistance from an engineer or other expert person or agency, including the Department of Natural Resources. Based on this assessment, the Community Development Director may approve or deny the application.
(Ord. 481, passed 2-16-2021)