Section 116.11. Criteria for establishing and rezoning floodplain districts.

 

(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.

(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 .

(b) Floodfringe district. All areas within the floodplain landward of the official floodway lines shall be shown as a "floodfringe district."

(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.

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

(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:

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.

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 .

(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:

1. The redelineation of the floodway lines is consistent with other municipal codes, ordinances, and ch. 30 , Stats. ; and

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

(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:

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;

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;

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

4. All areas within the hydraulic floodway landward of the official floodway lines shall be designated as "shallow depth flooding district"; and

5. All areas within the floodplain landward of the hydraulic floodway lines shall be delineated as "floodfringe district".

(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:

1. The department shall approve the methodology used to analyze floodplain storage to determine revised regional flood elevations.

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

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

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

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.

(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:

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;

2. The entire shallow depth flooding district shall be rezoned to floodfringe district; and

3. The effect of rezoning the shallow depth flooding district to the floodfringe district shall be calculated by comparing the regional flood profile determined by the hydraulic floodway lines to the regional flood profile determined by assuming that the entire shallow depth flooding district is not available to convey floodflows. Calculations shall conform to the standards contained in s. NR 116.07 .

(3)   Criteria for redelineation or rezoning floodplain districts.

(a) Initial determinations. Prior to redelineation or rezoning any floodplain district a municipality shall:

1. Assure that the applicable provisions of sub. (2) are met;

2. Require adequate technical data from the applicant or the municipality and submit such data to the department for review and concurrence in the effect of the proposed amendment on the height of the regional flood;

3. Assure that the proposed amendments meet the purpose of s. NR 116.01 ;

4. Assure that the appropriate legal arrangements have been made with all property owners affected by the increased flood elevations; and

5. Notify all affected municipalities of increased regional flood elevations.

(b) Amendment process. Upon completion of the steps in par. (a) , the municipality and any affected municipality shall meet all legal requirements for amending its water surface profiles, floodplain zoning maps and zoning ordinances as established in s. NR 116.21 (6) .

(c) Submission to the department for approval. If the municipality amends its official floodplain map, it shall also amend its water surface profiles and floodplain zoning ordinance and submit these amendments to the department for approval pursuant to s. NR 116.21 (6) . Prior to department approval, all municipalities affected by the increased regional flood elevation shall amend their water surface profiles, floodplain zoning maps and zoning ordinances to reflect the increased regional flood elevations.

(4)   Exception to criteria for redelineating or rezoning floodplain districts. If, as a result of improved data generated by a revised study approved by the department, and not as a result of changes due to encroachments in the floodplain, the hydraulic floodway line is revised landward of the official floodway lines, the municipality may continue to regulate on the basis of the official floodway lines provided the municipality meets all of the requirements of sub. (3) , except the requirement of sub. (3) (a) 4.

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