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(1) All floodplain delineation studies, reports, maps, and water surface profiles used by the department and board to establish designated floodplains shall be based upon the base flood.

(2) Each floodplain delineation study arranged by the department will, insofar as time and funds permit, include a water surface profile showing the elevation of the base flood and a suggested designated floodway.

(3) The department and board will also utilize flood hazard maps and data provided by the U.S. department of housing and urban development or the federal emergency management agency for the national flood insurance program as a basis for establishing the designated floodplain. Such maps will delineate the boundaries of the base flood but will not generally include flood elevations or floodway data.

(4) Designated floodplains established for areas where flood elevations and/or floodway data are lacking shall be regulated in accordance with ARM 36.15.801.

(5) The designation of floodplains and floodways shall be based upon reasonable hydrological certainty. Flood hazard maps that do not include floodway data or base flood elevations constitute a rebuttable presumption of reasonable hydrological certainty.

(6) The designated floodplain boundary is based on base flood elevations. The mapped floodplain boundary may be used as a guide for determining whether property is within the designated floodplain, but the exact boundary shall be determined according to the base flood elevation. If the local administrator determines it is unclear whether property is in or out of the floodplain, the local administrator shall require the applicant to provide additional information which may include elevations obtained through a level survey performed by a professional engineer or register land surveyor.

History: Sec. 76-5-201, 76-5-202, and 76-5-208, MCA; IMP, Sec. 76-5-201 and 76-5-202, MCA; NEW, Eff. 9/4/74; AMD, 1989 MAR p. 1665, Eff. 10/27/89.

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