NR 116.06NR 116.06 Areas to be regulated. Municipalities shall develop floodplain zoning maps, reflecting the best available data, which show the areas to be regulated. They shall also develop floodplain zoning ordinances to define proper uses in those regulated areas. These floodplain maps and zoning ordinances shall regulate all floodplains where serious flood damage may occur. The minimum limits for regulatory purposes shall be all those areas covered by water during the regional flood.

NR 116.07(1)(1) General. The standards contained in this section shall be the basis for developing both hydrologic and hydraulic information to be used by municipalities for developing floodplain zoning maps and flood profiles, as defined in s. NR 116.09, and for administration of existing floodplain zoning ordinances as defined in s. NR 116.20 (2). The department shall review and approve all studies performed or completed under this section prior to use by any municipality.

NR 116.07(2)(2) Certification and responsibility of the study contractor. Studies shall be completed under the direct supervision of the study contractor who is a registered professional engineer in the state of Wisconsin. The study contractor shall be responsible for the technical adequacy of the study.

NR 116.07(3)(a)(a) Techniques. Studies to determine the regional flood flow discharge may use the following techniques, if done in accordance with the requirements of par. (b):

NR 116.07(3)(a)1.1. The log-Pearson Type III distribution method as described in Bulletin #17B of the Hydrology Committee, U.S. Water Resources Council, entitled “Guidelines For Determining Flood Flow Frequency”, September, 1981.

NR 116.07(3)(a)2.2. The current USGS empirical equations, developed from regression analysis of stream gaging data. (See USGS publication entitled “Technique for Estimating Magnitude and Frequency of Floods in Wisconsin”, by Conger, March, 1981.)

NR 116.07(3)(a)3.3. Synthetic hydrographs, which are combined and routed through the basin to the downstream end of the study area.

NR 116.07(3)(a)4.4. When using the synthetic hydrograph technique in subd. 3., the results shall be calibrated to past events where such information is available.

NR 116.07(3)(a)5.5. Technical Release No. 55 (TR55), entitled “Urban Hydrology For Small Watersheds”, Engineering Division, SCS, U.S.D.A., January, 1975.

NR 116.07(3)(a)6.6. Comparison of similar drainage basins at gaged sites.

NR 116.07(3)(a)7.7. Historic flood data.

NR 116.07(3)(a)8.8. Other methods with department approval.

NR 116.07(3)(b)(b) Required use of techniques. The following shall be the minimum standards for determining the regional flood flow discharge:

NR 116.07(3)(b)1.1. The techniques to determine skew under par. (a) 1. may not be used if data from a gaging station in the watershed is not available or is available for a period of less than 10 years. In other cases, the technique to determine skew in par. (a) 1. shall be modified as follows:

NR 116.07(3)(b)1.a.a. If data from a gaging station in the watershed is available for 10 or more years but less than 26 years, the station skew shall be weighted with zero skew in accordance with Bulletin #17B.

NR 116.07(3)(b)1.b.b. If data from a gaging station in the watershed is available for 26 or more years, the station skew shall be used.

NR 116.07(3)(b)1.c.c. Skew values differing from those obtained in subd. 1. a. or b. may be used if they are approved by the department.

NR 116.07(3)(b)2.2. If the difference in the drainage area at the study site and the drainage area at a gaging station on the same watershed is less than or equal to 50%, the regional flood discharge at the study site shall be determined by transferring the calculated regional flood discharge at the gage by using Bulletin #17B techniques to the study site using a drainage area ratio taken to the “n” power, from page 12 of “Techniques for Estimating Magnitude and Frequency of Floods for Wisconsin Streams”, U.S.G.S., Open File Report 80-1214, March 1981.

NR 116.07(3)(b)3.3. If the difference in the drainage area at the study site and the drainage area at a gaging station in the watershed is more than 50%, or if there is no gaging station in the watershed, at least 2 of the techniques described in par. (a) 2. to 7. shall be used to determine a weighted value of the regional flood discharge.

NR 116.07(3)(b)4.4. Comparison of similar drainage basins under par. (a) 5. shall be based on basin characteristics using Bulletin #17B 100-year discharges.

NR 116.07(3)(b)5.5. When using USGS empirical equations under par. (a) 2., the results shall be compared with Bulletin #17B 100-year discharges at gaged sites on similar drainage basins.

NR 116.07(3)(b)6.6. In all cases where dams or reservoirs, floodplain development or land use upstream have significantly altered the storage capacity or runoff characteristics of the watershed so as to affect the validity of any of the techniques listed in par. (a), the synthetic hydrograph technique in par. (a) 3. or the Technical Release No. 55 in par. (a) 4. shall be used for the determination of the regional flood flow discharge.