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<br />Tabl~-4 ~ontinu~d <br />DR1 CREEK NO. 1 PEAK DISCHARGES <br /> <br />CHAPTER VI <br />HYDRAULIC ANALYSIS <br /> <br />(a) See Flooded Area Plates (pages 42 through 51) <br /> <br />on two separate field investigations. Culvert and bridge geometry, channel <br />and overbank roughness coefficeints, flow obstructions, and the overall <br />Characteristics of the area were assessed during these investigations. <br />The Manning's roughness coefficients used in the hydraulic analysis were <br />documented in a separate report prepared as part of the technical addendum. <br />Photographs were in~luded in the repott to suppOtt the recommended values. <br />Recommended roughness coefficients ranged from 0.030 to 0.060 for the <br />channel and from 0.040 to 0.070 for the overbank areas. <br /> <br />I <br /> <br />ll. Procedures <br /> <br />The water surface eievations for the 5-, 10-, 50-, 100- and 500-year <br />floods were computed using the Corps of Engine~rs HEC-2 Step Backwater <br />Computer Program. This program utilizes a solution to the one_dimensional <br />energy equation to determine tbe shape of the profile betwcen eonttol <br />section where the water surface elevation is known or can be assumed. The <br />procedure for a steady flow profile calculation is called the "Sta ndard <br />StepM"thoJ..' Inthis.."thoJ,thedistanc"froruaJ"'WllstrcdUlorupstrea"L <br />point, where the conditions are known, to the point where the backwater effects <br />ate to be determined, is divided into reaches by cross sections at fixed <br />locations alo"lI the river. Startingfro",oncconlrolpoinl,calculations <br /> <br />33 <br /> <br />" <br />