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The basin characteristics (Appendix 4)which were used in the regression equation were obtained from the Wisconsin Department of Natural Resources(WDNR)Surface Water Data Viewer.The WDNR had developed a hydrography database for most stream and lake features in Wisconsin and boundary/contributing waters.The 25-year, 24-hour precipitation intensity was obtained from the NOAA's Atlas 14 Point Precipitation Frequency Estimate website, WI (Appendix 5) (http://hdsc.nws.noaa.gov/hdsc/pfds/pfds map cont.html?bkmrk=wi). The basin parameters and calculation of the 100-year flood are as follows: Drainage areal,A=7.85 km2=3.03 mil Main-channel slope,S=0.58%=30.624 ft/mi Forest cover, FOR= 19.30+0.1+ 1 =20.4 25-Year, 24-hour precipitation intensity, 125= 5.37-4.2= 1.17 in 25-Year flood, Q25=38.1A°.876 50.518 FOR-0.308 1257.16 Q1oo=44.2 X (3.03)0893 X(30.624)0571 X R0.4)41312 X(1.17)756= 1,073 cfs 3. Determination of Culvert Size The culvert size and hydraulic profile were determined using the HEC-RAS (Version 5.0 beta) computer software.The study reach extends from approximately 390 feet upstream of the bridge to approximately 280 feet downstream of the bridge, with a total length of about 670 feet. The geometric data for the HEC-RAS model was developed using 2009 2-foot DEM data (https://www.countyofdane.com/lio/metadata/dembareearth2foot2009.htm ), obtained from Dane County Land Information Office. A field survey was conducted by D'Onofrio Kottke&Associates on September 29, 2015. The elevations of the bridge crest and stream bed were determined based on the survey. Results of the survey are presented in Appendix 6. The Manning's roughness coefficient (Manning's "n")was assumed to be 0.055 for the channel and 0.08 for the overbank area. The existing and proposed conditions were simulated using the HEC-RAS program. The flow profiles under the 100-year flood conditions and the HEC-RAS summary table are presented in Appendix 7 and Appendix 8, respectively.The water surface elevation at the upstream end of the study reach for the proposed condition is 0.2 foot lower than that for the existing condition. The water surface elevation at the downstream end of the study reach remains the same for both existing and proposed conditions. The water surface elevation within the study reach for the proposed condition is lower than or equal to that for the existing condition except for a 30-foot-long distance immediately downstream from the existing bridge, where the water surface elevation would increase by up to 0.17 feet under the proposed 1 The drainage area at the Old JG Bridge is slightly less than the total drainage area of the stream; however,since the location of the bridge is very close to the confluence of the stream and West Branch Sugar Creek,the calculation was done using the total drainage area.As a result,the determined value of the 25-year flood is slightly conservative.