NR 116.07(3)
(3) Hydrologic analysis — determination of regional flood discharge. 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)(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.
NR 116.07(3)(b)7.
7. In rapidly urbanizing watersheds, the municipality shall require that computations for regional flood flow discharges reflect increased runoff from all projected future development. These computations shall be made using one of the following techniques:
NR 116.07(3)(b)7.a.
a. A synthetic hydrograph based upon projected watershed development shall be produced and routed to critical locations within the study limits.
NR 116.07(3)(b)7.b.
b. A mathematical model shall be developed to determine the effects of all projected future development in the watershed on the regional flood flow discharge. Local units of government shall project what percentage of watershed development may occur under existing land use or subdivision ordinances and regional flood discharges shall be based upon that data. Where there are no existing land use or subdivision ordinances which control or regulate future development, total projected development shall be assumed to occupy 70% of the watershed. Where watersheds contain more than one municipality, agreements between those municipalities may be necessary to restrict future watershed development. In order to insure that future regional flood flows do not exceed the regional flood flow discharges used in local regulations, changes in existing land use or subdivision ordinances which may allow an increase or decrease in the projected development in the watershed shall be reflected in regional flood flow discharge values.
NR 116.07(4)
(4) Hydraulic analysis — determination of the regional flood elevation. The following criteria shall be the basis for determining the regional flood profile:
NR 116.07(4)(a)
(a) Reconnaissance. The study contractor is responsible for the collection of all existing data with regard to flooding in the study area. This shall include a literature search of all published reports in the study area and adjacent communities and an information search to obtain all unpublished information on flooding in the immediate and adjacent areas from federal, state and local units of government. This information shall include specific information on past flooding in the area, drainage structures such as bridges and culverts that affect flooding in the area, available topographic maps, available community maps, photos of past flood events and general flooding problems within the community. The study contractor will coordinate the collection of all available data and published reports with the department. A field reconnaissance shall be made by the responsible engineer to determine hydraulic conditions of the study area including type and number of structures, locations of cross sections and other parameters including roughness values which are necessary for the hydraulic analysis.
NR 116.07(4)(b)
(b) Base data. Cross sections to be used for the hydraulic analysis may be obtained by one of several methods, including surveying or aerial photography. New or previously surveyed cross sections or topographic information obtained from aerial photographs may be used independently or in combination as the base data to be used in hydraulic analysis. The elevation datum of all of the information to be used in the hydraulic model shall be verified. All information used shall be referenced directly to NGVD unless the elevation datum is otherwise approved by the department.
NR 116.07(4)(c)
(c) Methodology. Flood profiles shall be calculated by the standard step method, using the Corps of Engineers HEC-2 computer model. Other methods may be used with prior department approval provided that any computer models submitted to the department for review are in a form acceptable for entry into the department's floodplain data repository.
NR 116.07(4)(d)
(d) Floodway determination. The hydraulic floodway lines shall be determined from the limits of effective flow based on the calculated regional flood water surface profile. Transitions shall take into account obstructions to flow such as road approach grades, bridges or natural restrictions. General guidelines for transitions may be found in “HEC-2, Water Surface Profiles-Users Manual, appendix IV, Application of HEC-2 Bridge Routine" published by the Hydrologic Engineering Center, Davis, California. All areas of the floodplain including overbank areas that can be assumed to convey flood waters shall be included in the hydraulic floodway.
NR 116.07(4)(e)
(e) Previous floodplain studies. If differences exist between a study previously approved by the department and the contractor's calculated hydraulic floodways or flood profiles, the study contractor shall document justification and obtain departmental approval for these differences. Where the contractor's study differs from existing flood profiles or hydraulic floodways for adjacent communities, verification of the differences will be necessary for department approval of the hydraulic analysis.
NR 116.07(4)(f)
(f) Calculation of the regional flood profile. The regional flood profile and changes to that profile caused by development in the floodplain, as determined by the hydraulic model, shall be calculated to the nearest 0.01 foot.
NR 116.07(4)(g)
(g) Adequacy of the hydraulic model. The following factors shall be considered by the department to determine the adequacy of the hydraulic model and the regional flood profile. Upon written request by the department the study contractor shall submit written justification for the following factors:
NR 116.07 Note
Note: Significant differences in the energy grade from cross section to cross section are an indication that cross sections should be more closely spaced or that other inaccuracies exist in the hydraulic model.
NR 116.07(4)(g)3.
3. Methods for analyzing the hydraulics of structures such as bridges and culverts.
NR 116.07 Note
Note: In certain circumstances, rapidly varied flow techniques shall be used in combination with a gradually varied flow model such as weir flow over a levee or dike, flow through the spillway of a dam or special applications of bridge flow.
NR 116.07(4)(h)
(h) Special applications. The methods defined in par.
(c) shall be used except in special cases, including circumstances where sediment transport, 2 dimensional flow or valley storage affects the accuracy of the hydraulic model. Where the standard step method is unwarranted, the department shall approve the method used for establishing the final water surface profile.
NR 116.07(4)(i)
(i) Base mapping. In the preparation of a floodplain zoning map to be used by the municipality, the study contractor shall use the best available mapping to delineate floodplain limits.
NR 116.07(4)(j)
(j) Final report. A narrative report shall accompany the maps and profiles and shall include the following:
NR 116.07(4)(j)5.
5. Engineering methods including a detailed description of the methodology used for hydrology, hydraulics and any special applications used in this study.
NR 116.07(4)(j)6.
6. A floodway data table showing cross sections, drainage area, distance between cross sections, floodway top width, discharge, cross sectional area, mean velocity and regional flood elevation.
NR 116.07(4)(j)8.e.
e. Sample calculations of the hydrologic analyses including all unit hydrographs.
NR 116.07(4)(k)
(k) Wave action on the Great Lakes. Standards used to determine the regional flood elevation for all municipalities adjacent to the Great Lakes shall be those specified in the publication, “Guidelines and Specifications for Study Contractors, Federal Emergency Management Agency, September 1982,
appendix 1B, Wave Runup Analysis".
NR 116.07(5)
(5) Document availability. The materials listed in this subsection are incorporated by reference in the corresponding subsections noted. The document referred to in sub.
(3) (a) 1. may be purchased from the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (mention title and stock number 052-045-00031-2). The document referred to in sub.
(3) (a) 2. is available for inspection at the Geological Survey — Water Resource Division, U.S. Department of the Interior, 1815 University Avenue, Madison, Wisconsin 53706. The document referred to in sub.
(3) (a) 5. is available for inspection at the Soil Conservation Service, U.S. Department of Agriculture, 4601 Hammersley Road, Madison, Wisconsin 53711; it may be purchased from the National Technical Information Service, U.S. Department of Commerce, 5285 Port Royal Road, Springfield, Virginia 22151 (mention title and appropriate accession number: TR55 = PB 244531/AS). The document described in sub.
(4) (c) and
(d) is available for inspection at the United States Army Corps' Hydrologic Engineering Center, 609 2nd Street, Davis, California 95616. The document referred to in sub.
(4) (k) is available for inspection at the Federal Emergency Management Agency Region V Office, 300 South Wacker Drive, Chicago, Illinois 60606 (mention title, date and appropriate appendix number).
NR 116.07(6)
(6) Inspection of documents. Copies of the documents referred to in sub.
(5) are also available for inspection in the following offices:
NR 116.07(6)(a)
(a) The department of natural resources, 101 South Webster Street, Madison, Wisconsin;
NR 116.07(6)(b)
(b) The office of the secretary of state, 30 W. Mifflin Street, Madison, Wisconsin;
NR 116.07(6)(c)
(c) The legislative reference bureau, One E. Main Street, Madison, Wisconsin.
NR 116.07 History
History: Cr.
Register, February, 1986, No. 362, eff. 3-1-86; corrections made under s. 13.93 (2m) (b) 6., Stats.,
Register, September, 1995, No. 477; correction in (6) (c) made under s. 13.92 (4) (b) 6., Stats.,
Register March 2011 No. 663.
NR 116.08(1)(1)
General. Adequately designed, constructed and maintained dams provide reduced damages and relief from flooding for developed areas. Areas downstream of dams shall be zoned and regulated by municipalities with floodplain zoning ordinances in compliance with the standards in this section, to reduce potential loss of life and property located downstream of the dams. Except as provided in sub.
(2), areas downstream of all dams shall be delineated on floodplain maps in accordance with s.
NR 116.09 (1) (b) 5. Flood studies and related mapping, completed and adopted prior to August 1, 2001, which calculated flood flow attenuation based on the existence of the dam structures within the contributing basin, may continue to use the dam in-place, no failure, profile.
NR 116.08(2)
(2) Exemptions. All dams having a structural height of 6 feet or less, or a storage capacity of 15 acre feet or less, and all dams having a structural height of more than 6 feet but less than 25 feet with a storage capacity of less than 50 acre feet are exempt from the requirements of this section unless the department determines pursuant to s.
31.19, Stats., that the dam is likely to endanger life, health or property.
NR 116.08(3)(a)
(a) A dam is considered compliant if all the following requirements are met:
NR 116.08(3)(a)3.
3. The dam has been certified by a professional engineer, registered in Wisconsin, to meet the requirements of subds.
1. and
2. NR 116.08(3)(a)4.
4. Written assurance of the dam owner's ability to operate and maintain the dam in good condition is obtained from the dam owner.
NR 116.08(3)(a)5.
5. An emergency action plan to minimize loss of human life has been developed for the area downstream of the dam based on the assumption that the dam fails during the regional flood.
NR 116.08(3)(b)
(b) Developed areas downstream of compliant dams shall be zoned and regulated as follows:
NR 116.08(3)(b)1.
1. For high hazard dams, assuming that the dam is nonexistent during the regional flood.
NR 116.08(3)(b)2.
2. For significant or low hazard dams, assuming the dam fails during the regional flood.
NR 116.08(3)(c)
(c) Undeveloped areas downstream of a compliant dam shall be zoned and regulated assuming that the dam fails during the regional flood.
NR 116.08(4)(a)
(a) If an existing dam does not meet the standards in sub.
(3) (a), the dam is considered noncompliant.
NR 116.08(4)(b)
(b) Both developed and undeveloped areas downstream of a noncompliant dam shall be zoned and regulated assuming that dam failure occurs during the regional flood.
NR 116.08(5)(a)
(a) Dams constructed after August 1, 2001, shall be considered compliant if the requirements in sub.
(3) (a) are met.
NR 116.08(5)(b)
(b) Developed areas downstream of the construction of a new dam shall be zoned and regulated as if the dam does not exist until construction is 100% complete and all the conditions of sub.
(3) (a) are met.
NR 116.08 History
History: Cr.
Register, February, 1986, No. 362, eff. 3-1-86;
CR 00-136: am. (1), (2), (3) (a) 1. to 5., (b), (c), (4) (a) and (b) and (5) (a),
Register July 2001, No. 547 eff. 8-1-01.
