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Approximately 0.5 miles upstream from the project site, Vinburn Road crosses the Maunesha River. The upstream structure is a single-span concrete flat slab bridge with concrete abutments. The structure is approximately 26.6 feet long between abutment faces. The clear roadway width is approximately 23.9 feet. The structure is not skewed. Approximately 0.5 miles downstream from the project site, USH 151 crosses the Maunesha River. The downstream structure is a single-span concrete T-beam bridge with concrete abutments. The structure is approxim ately 51.8 feet long between abutment faces. The clear roadway width is approximately 35.3 feet. The structure is skewed approximately 30 degrees. MAGNITUDE AND FREQUENCY OF FLOODS A flood frequency versus discharge analy sis of the Maunesha River drainage basin at the proposed site was performed. The design discharge for the 100-year frequency (regional) flood was determined by using Conger's Method (WRI-91-4128)for geographic region 5, as well as drainage basin corn parisons to similar watersheds. The drainage area at the site i s 24 square miles. The design regional flood discharge val ue adopted for the 100-year discharge is 1,200 cfs. The hydrology computations, dated February 13, 2014 were previously submitted on March 4, 2014 and were approved on June 27, 2014. T he relationship shown in Table 1 is based on the hydraulic analysis and is assumed for the project site. ANALYSIS OF HYDRAULIC CHARACTERISTICS The project site's hydraulic characteristics were modeled using the "Hydrologic Engineering Center-River Analysis System" (HEC-RAS) computer program. The hydraulic characteristics of the existing and various proposed conditions w ere modeled. Ayres Associates obtained cross section data and Manning's"n"values from the field survey and photographs. Six hydraulic cross sections were used to model this site. The cross sections are located approximately 70 feet, 30 feet, and 16 feet upstream and 16 feet, 30 feet, and 70 feet downstream from the existing Elder Lane centerline. Water surface shots were taken 940 feet upstream and 1,450 feet downstream of the existing bridge and at the existing bridge. The resulting 0.0004 ft/ft field survey hydraulic slope was not in close agreement with the 0.0015 ft/ft slope obtained from the quadrangle maps. A hydraulic slope of 0.0004 ft/ft was used as the starting stream slope for the analysis and the model agreed closely with flood history. The existing structure as well as various proposed structures were modeled. The results of the hydraulic analysis are shown in the attached Table 3. EXISTING STRUCTURE AND APPROACHES The existing structure is a single-span concrete T-Beam bridge with concrete abutments. The structure is approximately 34.9 feet long between abutment faces. The clear roadway width is approximately 26.8 feet. The structure is not skewed. The sufficiency rating was 40.1 on June 9, 2014. The existing structure is currently not posted. 2 u:\41-0668.00-dane county,town bristol,elder lane\reports\bsr\b-13-672_siz.doc 41-0668.00