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<br />I <br />I <br />I <br />I <br />I <br />I <br />II <br />I I <br />I, <br />I <br />I I <br />I I <br />, <br />I <br />I <br />II <br />II <br />I <br />I <br /> <br />Greiner also did the ns study for Westminster (FEMA, 1987); consequently, the same <br /> <br /> <br />sections were used to match water surfaces at Huron Street. <br /> <br />The water surface shows that water ponds about 0.5 feet on the southbound lane of 1- <br />25, but no water is on the northbound lane due to the concrete median barriers. <br /> <br />PROPOSED IMPROVEtvENTS TO 1-25 <br />Muller's (Aug. 1987) outfall study recommends improving the hydraulic conditions at 1- <br />25 by jacking three lO8-inch CMP's just to the north of the existing crossing. <br />However, improved hydraulic conditions can also occur by excavating the existing cobble <br />invert by about 3 feet and constructing a 3.1-foot drop structure just upstream of the <br />bridge. Considering the bridge foundation, it appears feasible to construct a lining and <br />drop structure. The proposed improvements are shown in Figures III-I and III-2. <br /> <br />HEC-2 analyses of the improvements show that the upstream water surface would be <br />162.2 feet for the 100-year flow of 11,480 ets. This is 1.2 feet above the low chord of <br />the bridge, but not above the highway elevation. The 100-year velocity is 9.6 feet per <br />second; consequently, the bridge invert and sides would probably be concrete. More <br />excavation could provide further improvement. <br /> <br />The proposed improvement lowers the lOO-year water surface from 168.1 to 162.2 feet <br />(5.9 feet) and reduces the velocity from 14 feet per second to 9.6 feet per second. The <br />invert excavation and drop structure proposed herein may be a more practical and cost <br />effective plan. <br /> <br />III-12 <br />