The standards contained in this part apply to the amendment or creation of local floodplain zoning ordinances.
To provide for comprehensive floodplain management, supplemental measures as contained in part 6120.5900 shall be enacted consistent with these standards.
These standards and criteria are considered to provide only a minimum degree of flood protection for floodplain developments. Local governmental units may enact local floodplain regulations which exceed these standards.
All mapping used to delineate floodplain zoning districts shall include the following properly identified regulatory districts: floodplains, floodways, and flood fringe areas. Where adequate information is available the limits of the area subject to inundation by floods larger than the regional flood, as provided in part 6120.5600, subpart 3, shall be designated for public information purposes.
Local ordinances may superimpose the floodplain zoning districts on the prior official zoning map or the ordinance may adopt, by reference, a supplemental official map providing the supplemental map is approved by the commissioner.
The floodplain limits on the zoning map shall correspond to the actual area subject to inundation, not street or property lines, unless use of the latter would include all areas subject to inundation.
The delineation of the floodplain shall be based on the flood protection elevation as set forth in subpart 5.
Procedures for floodplain determination shall conform to technical standards established in part 6120.5600, subparts 2 and 4. Each local floodplain zoning ordinance must include a floodplain map conforming to the standards established in subpart 2.
In special instances and upon approval of the commissioner, the use of other techniques such as maps indicating limits of past flooding, detailed soil maps, and/or aerial photographic interpretation may initially serve as a basis for the delineation of floodplains for regulatory purposes provided that:
the affected floodplains are generally undeveloped;
the associated text of the zoning ordinance provides for a special permit use procedure to determine the effects of proposed construction upon flood stages and flood flows and to establish the flood protection elevation; and
the local unit of government has initiated a program to ultimately obtain regional flood data.
Where a conflict exists between the floodplain limits illustrated on the official zoning map and actual field conditions, the flood elevations shall be the governing factor in locating the regulatory floodplain limits.
Local government floodplain zoning ordinances shall designate a floodway. Exceptions may be allowed by the commissioner for those conditions listed in subpart 3, item C. A portion of the floodplain, outside of the immediate channel of a watercourse, shall be selected and designated as the floodway by a local governmental unit upon approval of the commissioner. The selection must be based on an evaluation of the flood hazard for the area which may be involved or affected by such designation and must conform to the following standards:
The limits of the floodway shall be designated so that permissible encroachments on the floodplain will not cause an increase in stage of the regional flood of more than 0.5 feet in any one reach or for the cumulative effect of several reaches of a watercourse. If the increase in flood stage will materially increase the flood damage potential, the commissioner may require that such increases be less than 0.5 feet. The commissioner may authorize increases greater than 0.5 feet where studies show that further increases in flood stages will not materially increase the flood damage potential.
The limits of the floodway shall be based on a uniform degree of encroachment for a significant reach on both sides of a watercourse. Variances from this part may be authorized by the commissioner when topography, existing development patterns, and comprehensive land use plans justify a modified approach.
The flood protection elevations shall correspond to a point not less than one foot above the water surface profile associated with the regional flood plus any increases in flood stages attributable to encroachments on the floodplain established under subpart 4, item A. The flood protection elevations shall be clearly lettered at identifiable positions on the official zoning district map consistent with the water surface profile of the regional flood, or the profile shall be attached to and made part of the official zoning district map.
MS s 104.05
June 11, 2008