Chapter NR 116

NR 116.03(31) (31) “Municipality” or “municipal” means a county, city or village.

NR 116.03(32) (32) “NGVD” or “National Geodetic Vertical Datum” means elevations referenced to mean sea level datum, 1929 adjustment.

NR 116.03(33) (33) “Nonconforming building” means an existing lawful building which is not in conformity with the dimensional or structural requirements of the floodplain zoning ordinance for the area of the floodplain which it occupies.

NR 116.03(34) (34) “Nonconforming use” means an existing lawful use or accessory use of a structure, building or development which is not in conformity with the provisions of the floodplain zoning ordinance for the area of the floodplain which it occupies.

NR 116.03(35) (35) “Obstruction to flow” means any development which physically blocks the conveyance of flood waters such that this development by itself or in conjunction with any future similar development will cause an increase in regional flood height.

NR 116.03(36) (36) “Official floodway lines” means those lines which have been approved by the department, adopted by the municipality, and which are shown on the official floodplain zoning maps and used for regulatory purposes. The official floodway lines are established assuming that the area landward of the floodway lines will not be available to convey flood flows.

NR 116.03(37) (37) “Open space use” means a use which has a relatively low flood damage potential, such as uses associated with agriculture, recreation, parking, storage yards, or certain sand and gravel operations.

NR 116.03(38) (38) “Private sewage system” means a sewage treatment and disposal system serving a single structure with a septic tank and soil absorption field located on the same parcel as the structure. This term also means an alternative sewage system approved by the department of industry, labor and human relations including a substitute for the septic tank or soil absorption field, a holding tank, a system serving more than one structure or a system located on a different parcel than the structure.

NR 116.03(39) (39) “Public utilities” means those utilities which employ underground or overhead transmission lines such as electric, telephone and telegraph, and distribution and collection systems such as water, sanitary sewer and storm sewer.

NR 116.03(40) (40) “Rapidly urbanizing watershed” means a watershed where more than 20% of the land area of the watershed has been developed for residential, commercial or industrial uses or where development of the watershed is projected to grow at a rate of 10% or more in the next 10-year period.

NR 116.03(41) (41) “Regional flood” means a flood determined to be representative of large floods known to have occurred in Wisconsin or which may be expected to occur on a particular lake, river or stream once in every 100 years.

NR 116.03 Note Note: The regional flood is based upon a statistical analysis of lake level or streamflow records available for the watershed or an analysis of rainfall and runoff characteristics in the watershed or both. The flood frequency of the regional flood is once in every 100 years. In any given year, there is a 1% chance that the regional flood may occur or be exceeded. During a typical 30-year mortgage period, the regional flood has a 26% chance of occurring.

NR 116.03(42) (42) “Shallow depth flooding areas” means those areas where the maximum depth of flooding does not exceed one foot in depth nor 6 hours in duration during the regional flood.

NR 116.03(43) (43) “Special exception” or “conditional use” has the meaning designated in sub. (5).

NR 116.03(44) (44) “Stormwater management” means public policy and action to control stormwater runoff associated with development within a rapidly urbanizing watershed in order to prevent the occurrence of, or an increase in, flood damage potential. It includes, but is not limited to, development of stormwater runoff data, flood profiles and enactment and administration of ordinances regulating land use in a watershed.

NR 116.03(45) (45) “Structure” means any man-made object with form, shape and utility, either permanently or temporarily attached to or placed upon the ground, river bed, stream bed or lakebed.

NR 116.03(46) (46) “Study” means any analysis that results in the calculation of discharge or elevation of the regional flood or the determination or delineation of boundary lines for any area within a floodplain.

NR 116.03(47) (47) “Undeveloped area” means an area which is not a developed area.

NR 116.03(48) (48) “Unnecessary hardship” means that circumstance where special conditions affecting a particular property, which were not self-created, have made strict conformity with restrictions governing areas, setbacks, frontage, height or density unnecessarily burdensome or unreasonable in light of the purposes of the ordinance.

NR 116.03(49) (49) “Variance” means an authorization by the board of adjustment or appeals under s. NR 116.21 (4), for the construction or maintenance of a building or structure in a manner which is inconsistent with dimensional standards contained in the floodplain zoning ordinance.

NR 116.03 Note Note: A variance can only be granted by the board of adjustment or appeals. A variance may not permit a use of property otherwise prohibited by the floodplain zoning ordinance or allow construction not protected to the flood protection elevation; it may, however, permit deviations from dimensional standards.

NR 116.03(50) (50) “Watershed” means the entire region or area contributing runoff or surface water to a particular watercourse or body of water.

NR 116.03(51) (51) “Water surface profile” means a graphical representation showing the elevation of the water surface of a watercourse for each position along a reach of river or stream at a certain flood flow. A water surface profile of the regional flood is used in regulating floodplain areas.

NR 116.03(52) (52) “Well” means an excavation or opening in the ground made by digging, boring, drilling, driving or other methods, for the purpose of obtaining groundwater regardless of its intended use.

NR 116.03(53) (53) “Zoning agency” means a commission, board, committee or agency created or designated by the governing body of a municipality which acts on matters pertaining to planning or zoning. Under the provisions of s. 62.23 (7) (d) 2., Stats., the term “zoning agency” also includes the governing body of a city or village.

NR 116.03 History History: Cr. Register, February, 1986, No. 362, eff. 3-1-86; cr. (1e), (1s), (30m), Register, June, 1996, No. 486, eff. 7-1-96; CR 03-091: cr. (6m) Register August 2004 No. 584, eff. 9-1-04.

NR 116.05 NR 116.05 Adoption and upgrading of floodplain zoning ordinances.

NR 116.05(1) (1) Adoption. Municipalities shall adopt, administer and enforce reasonable floodplain zoning ordinances for all floodplains where serious flood damage may occur within their respective jurisdictions. These ordinances shall meet or exceed the standards in this chapter.

NR 116.05(2) (2) Inclusion in local regulations, codes and programs. Where necessary, to insure the effectiveness of floodplain management and zoning objectives, the standards in this chapter shall be included in subdivision regulations, building and sanitary codes, flood insurance regulations, stormwater management regulations and other related programs.

NR 116.05(3) (3) Substitution. Where the department finds that one or more of the following regulations, codes or programs will accomplish the purpose of s. NR 116.01, these regulations, codes or programs may be substituted in lieu of all or portions of floodplain zoning ordinances:

NR 116.05(3)(a) (a) Zoning, acquisition of flooding easements or purchase of floodplain lands to permit only open space uses in floodplain areas.

NR 116.05(3)(b) (b) Flood warning systems.

NR 116.05(3)(c) (c) Building codes.

NR 116.05(3)(d) (d) Subdivision regulations.

NR 116.05(3)(e) (e) Private sewage system ordinances.

NR 116.05(3)(f) (f) Stormwater management regulations.

NR 116.05(4) (4) Upgrading ordinances. Within 6 months from the time any of the information listed below is made available to a municipality by the department, the municipality shall upgrade its floodplain zoning ordinance, using the amendment procedure in s. NR 116.21, to reflect current floodplain information, including, but not limited to, the following:

NR 116.05(4)(a) (a) Changes in floodplain management statutes.

NR 116.05(4)(b) (b) Changes in floodplain management rules.

NR 116.05(4)(c) (c) Changes in floodplain management case law.

NR 116.05(4)(d) (d) New study data.

NR 116.05(4)(e) (e) Improved technical information and methods.

NR 116.05 History History: Cr. Register, February, 1986, No. 362, eff. 3-1-86.

NR 116.06 NR 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 116.06 History History: Cr. Register, February, 1986, No. 362, eff. 3-1-86.

NR 116.07 NR 116.07 Standards for hydrologic and hydraulic studies.

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) (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)(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.

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(4)(g)1. 1. Cross section spacing.

NR 116.07(4)(g)2. 2. Differences in energy grade.

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(4)(g)4. 4. Lack of flow continuity.

NR 116.07(4)(g)5. 5. Use of gradually varied flow model.

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)(g)6. 6. Manning’s “n” values.

NR 116.07(4)(g)7. 7. Calibration of the hydraulic model with past flood events.

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.