§ 20-378. Procedures for determining floodway boundaries and regional flood elevations.

(a)

Detailed study. Developments greater than 50 lots or five acres, or as requested by the zoning administrator, 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) 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 foot. A lesser stage increase than 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. Provided no detailed study is available, an applicant must identify a base flood elevation, at minimum, to determine the boundaries of the special flood hazard area. The applicant shall obtain and utilize best available data to determine the regional flood elevation and floodway boundaries from a state, federal, or other source. If no such data exists, the applicant may determine the base flood elevation and floodway limits through other accepted engineering practices. Any such method shall assume a 0.5 foot stage increase to accommodate for future floodway determination.

(c)

The zoning administrator 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 zoning administrator may seek technical assistance from an engineer or other expert person or agency, including the department of natural resources. Based on this assessment, the zoning administrator may approve or deny the application.

(d)

Once the Floodway and Flood Fringe District boundaries have been determined, the zoning administrator must process the permit application consistent with the applicable provisions of division 2 and division 3 of this article.

(Ord. No. 636, § 2, 12-10-18)