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YS1 International Consulting,LLC P.O.Box 46211 Madison,WI 53744 Mobile:608.438.7070 j(5:1 NTERNATIONAL Email:Yiying.xiong @ysjinternational.com November 20, 2015 Ruth Hansen, Clerk Town of Primrose 8468 County Road A Verona, Wisconsin 53593 Subject: Old JG Bridge Removal and Replacement—Culvert Sizing Dear Mrs. Hansen: In September 2015, YSJ International Consulting, LLC was retained by Town of Primrose, WI,to conduct a hydraulic analysis for the replacement of the Old JG Bridge.The objective of this analysis is to determine the appropriate size of a culvert which will be installed to replace the existing bridge.This letter report summarizes the data sources, methodology, analysis, and results of the hydraulic analysis. 1. Background The Old CTH JG Bridge is located at the southwestern intersection of the Old JG Road and County Highway JG in Mt. Horeb,WI. The Old JG Road is approximately 2,000 feet long with both ends intercepting with County Highway JG. There are three residential buildings and one school building along the Old JG Road. The bridge is primarily used for local traffic for these four buildings. The bridge was damaged during a heavy storm event.The owner of the bridge,the Town of Primrose, WI, has decided to remove the existing bridge and replace it with a culvert structure. The existing bridge is approximately 16 feet wide (in the direction of flow), 17 feet long, and 8.5 feet above the stream bed at the center of the bridge.The roadway surface is gravel.The stream underneath the bridge is an unnamed tributary of West Branch Sugar River. The immediate overbank area has heavy bushes and trees. The areas between the stream and the roads are primarily corn fields. The section of the gravel road between the bridge and County Highway JG is much lower than the elevation of the bridge deck. According to the 2009 Digital Elevation Model (DEM) data, a 130-foot-long section of the road is approximately 3 feet lower than the bridge deck. A vicinity map of the Old JG Bridge is presented in Appendix 1. Photos of the existing bridge are presented in Appendix 2. 2. Determination of Design Flow Based on the FHM 13-10-1, Design Criteria, Facilities Development Manual, Wisconsin Department of Transportation,the design flow for the proposed culvert was chosen to be the 100-year flood (i.e. 1% exceedance flood).The 100-year flood was determined using the regression equation published in Flood-Frequency Characteristics of Wisconsin Streams, Water-Resources Investigations Report 03-4250, US. Department of the Interior, U.S. Geological Survey, 2003. Table 2 of this publication which lists the regression equations for Wisconsin is included in Appendix 3. Page 1 of 12