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<br />. <br /> <br />Glenwood Springs gages, downstream and upstream from the project <br />site, respectively. According to this calculation, an annual <br />average suspended sediment load of 1,289,900 tons/yr from the <br />6,9B3-sq-mi watershed passes the site. This appears reasonable <br />in comparison to the estimate calculated, for the 7,370-sq-mi Una <br />Reservoi r watershed. The Webster Hi 11 est imate is 80% of the <br />Una estimate. The somewhat different technique employed at the <br />Una site was based on a correlation made with sediment measure- <br />ments taken at Cisco, Utah. Another confirmation of the reason- <br />ableness of the estimate was provided by USBR personnel <br />(Robert Strand, USBR, personal communication). <br /> <br />. <br /> <br />A correlation was applied to the calculated suspended sediment <br />load to account for the unmeasured sediment plus bedload. This <br />15% increase results in a total sediment load of <br />1,4B3,000 tons/yr. Fifteen percent was chosen based upon <br />suggested 9ui de 1 ines from USBR gui de 1 ines from USBR 1 iterature <br />(USBR, 1982). The watershed annual average sediment yield of 212 <br />tons/sq mi appears reasonable when compared to reported va lues <br />of other river systems in the literature. <br /> <br />. <br /> <br />2. Reservoir Trap Efficiency and Sediment Deposition <br />Reservoir trapping efficiency, the ratio of the quantity of <br />deposited sediment to the total sediment inflow, is primarily <br />dependent on the sediment particle fall velocity and the rate of <br />f low through the reservoi r. Methods of est imat ing reservoir <br />trap efficiency are empirically based on measured sediment <br />deposits in a large number of reservoirs. For the purposes of <br />this study, the Brune (1953) method was selected. Brune <br />constructed curves from measured data that depict trappin9 <br />efficiency as a function of the ratio between reservoir capacity <br />to average annual inflow. In the case of a relatively low <br />storage capacity, as with Webster Hill, it is necessary to <br />compute the change in reservoir capacity and therefore the trap <br />efficiency over time due to the effects of sedimentation. <br /> <br />36B6-a/5 <br /> <br />1-13 <br />