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<br />lfe <br />I <br />, <br /> <br />I <br /> <br />fe <br /> <br /> <br /> <br />.. <br />[ <br /> <br />2.0 PURPOSE AND SCOPE OF WORK <br /> <br />The purpose of this study was to evaluate the flooding conditions <br />resulting from the IOO-year recurrence interval runoff in Ralston Creek. The <br /> <br />flood condit ions were to be evaluated at the proposed Water Treatment P1 ant <br /> <br />and emergency storage pond sites. Flood hazards from a small tributary water- <br /> <br />shed near the Water Treatment Plant Site were also to be investigated. The <br />location of these facilities is shown on Figure 3. <br /> <br />The following scope of work was followed during the study: <br /> <br />1. A site reconnaissance trip to evaluate field conditions relative to <br />flood potential was conducted. The friction values for channel and <br />overbank flows were estimated, the approximate sizes of channel bed <br />and bank materials estimated and the watershed characteristics of <br />the small tributary watershed were examined and photographed. <br /> <br />2. Previ ous reports by the Colorado Water Conservat i on Board, Urban <br />Drainage and Flood Control District, U.S. Army Corps of Engineers <br />and consultants were reviewed. <br /> <br />3. Supplemental cross sections were field located for surveying. <br /> <br />4. Using topographic mapping and supplemental cross sections supplied <br />by Cotter Corporation, a spatial representation of the hydraulics <br />of Ra 1 ston Creek was des i gned. Th is model was used to code the <br />U.S. Army Corps of Engineers HEC-2 Water Surface Profile computer <br />model. <br /> <br />5. Water surface profiles and channel and overbank velocities were <br />computed for existing conditions and several channel improvement <br />schemes. <br /> <br />6. Channel improvements were designed for Ralston Creek at the Water <br />Treatment Plant and the Emergency Storage Pond. <br /> <br />7. Peak flow rates and hydrau1 ic condit ions were computed for the <br />small tributary watershed. Drainage improvements were designed at <br />a feasibility level. <br /> <br />2-1 <br />