NR 116.10 NR 116.10 Conflicts between water surface profiles and floodplain zoning maps. Accepted engineering principles and techniques shall govern the transfer of profile elevation for use in delineation of the floodplain limits on the official floodplain zoning maps. If a conflict exists between the floodplain limits illustrated on the maps and the actual field conditions, the elevations from the water surface profile shall be the governing factor in locating the official floodplain limits.

NR 116.10 History History: Cr. Register, February, 1986, No. 362, eff. 3-1-86.

NR 116.11 NR 116.11 Criteria for establishing and rezoning floodplain districts.

NR 116.11(1) (1) Delineation of floodway, floodfringe and coastal floodplain districts. Except as provided in sub. (2), the following criteria shall apply to the delineation of floodway, floodfringe and coastal floodplain districts.

NR 116.11(1)(a) (a) Floodway district. The official floodway lines shown on floodplain zoning maps shall be the hydraulic floodway lines. These hydraulic floodway lines shall be determined by studies complying with the standards contained in s. NR 116.07.

NR 116.11(1)(b) (b) Floodfringe district. All areas within the floodplain landward of the official floodway lines shall be shown as a “floodfringe district.”

NR 116.11(1)(c) (c) Coastal floodplain district. All areas adjacent to Lake Superior or Lake Michigan within the regional floodplain shall be designated as a coastal floodplain district.

NR 116.11(2) (2) Redelineation or rezoning floodplain districts. In accordance with the criteria of sub. (3), the following redelineations or rezonings may occur:

NR 116.11(2)(a) (a) Redelineation or rezoning the floodway district to floodfringe district. Riverward delineations of the official floodway lines established in accordance with sub. (1) (a) are permissible provided the following criteria are satisfied:

NR 116.11(2)(a)1. 1. Any increase in regional flood height due to the delineation of the official floodway lines riverward from the hydraulic floodway lines shall be approved by the department prior to becoming effective. Increases may only be approved by the department if the provisions of sub. (3) are satisfied.

NR 116.11(2)(a)2. 2. The effects of delineating the official floodway lines riverward from the hydraulic floodway lines shall be calculated by comparing the regional flood profile determined from the hydraulic floodway lines to that profile determined by assuming that the area landward of the revised floodway lines is not available to convey flood flows. Calculations shall conform to the standards contained in s. NR 116.07.

NR 116.11(2)(b) (b) Redelineation or rezoning floodfringe district to floodway district. Landward modifications of hydraulic floodway lines to delineate official floodway lines may be permitted provided the following conditions are satisfied:

NR 116.11(2)(b)1. 1. The redelineation of the floodway lines is consistent with other municipal codes, ordinances, and ch. 30, Stats.; and

NR 116.11(2)(b)2. 2. The current hydraulic floodway lines, which reflect the water surface profile used for regulation, shall be kept on file by the municipality.

NR 116.11(2)(c) (c) Redelineation or rezoning floodway district to shallow depth flooding district. For areas subject to shallow depth flooding, the official floodway lines may be delineated riverward of the hydraulic floodway lines, provided all of the criteria in this paragraph are satisfied:

NR 116.11(2)(c)1. 1. The maximum depth of flooding during the regional flood in the shallow depth flooding district may not exceed one foot in depth nor 6 hours in duration. The duration shall be determined by a synthetic hydrograph developed for the watershed and routed through the area;

NR 116.11(2)(c)2. 2. The area is developed complete with existing streets and sewers and is subject to a land use plan, which includes provisions for drainage ways through the area with the capacity to convey that percentage of the regional flood which is flowing through the area under existing conditions;

NR 116.11(2)(c)3. 3. The municipality shall adopt standards outlined in s. NR 116.14 (1) pertaining to shallow depth flooding district;

NR 116.11(2)(c)4. 4. All areas within the hydraulic floodway landward of the official floodway lines shall be designated as “shallow depth flooding district”; and

NR 116.11(2)(c)5. 5. All areas within the floodplain landward of the hydraulic floodway lines shall be delineated as “floodfringe district”.

NR 116.11(2)(d) (d) Redelineation or rezoning floodfringe district to flood storage district. A “flood storage district” may be established for the area landward of the floodway in lieu of the floodfringe designation where floodplain storage will decrease the calculation of discharge and therefore the regional flood elevation, provided the following criteria are met:

NR 116.11(2)(d)1. 1. The department shall approve the methodology used to analyze floodplain storage to determine revised regional flood elevations.

NR 116.11(2)(d)2. 2. The municipality shall adopt standards outlined in s. NR 116.14 (2) pertaining to the flood storage district.

NR 116.11(2)(e) (e) Rezoning flood storage district to floodfringe district. Any proposal to rezone flood storage district to floodfringe district shall comply with the following conditions:

NR 116.11(2)(e)1. 1. Any increase in regional flood height shall be approved by the department prior to becoming effective. Increases in the regional flood elevation may only be approved by the department if the provisions in sub. (3) are satisfied; and

NR 116.11(2)(e)2. 2. The effect of rezoning the flood storage district to the floodfringe district shall be calculated by comparing the regional flood profile used as the basis for zoning to the regional flood profile determined by assuming that the area to be rezoned is not available to store floodwater.

NR 116.11(2)(f) (f) Rezoning the shallow depth flooding district to floodfringe district. Any proposal to rezone the shallow depth flooding district to floodfringe district shall comply with the following conditions:

NR 116.11(2)(f)1. 1. Any increase in regional flood height shall be approved by the department prior to the rezoning becoming effective. Increases in the regional flood elevation may only be approved by the department if the provisions in sub. (3) are satisfied;

NR 116.11(2)(f)2. 2. The entire shallow depth flooding district shall be rezoned to floodfringe district; and