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
(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.