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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />For most pl anni ng studi es, the 50-year sediment accumul ati on is subtracted <br />from the reservoir storage content for estimating project yields. In this <br />case, since the sediment yield is extremely small, the conservation storage <br />space has not been diminished. <br /> <br />The trap efficiency of a reservoir is defined as the ratio of the quantity of <br />deposited sediment to the total sediment inflow. Gunnar Brune has developed a <br />set of trap effi ciency curves for use wi th normal ponded reservoi rs usi ng <br />their capacity -inflow relationships. <br /> <br />The capacity -inflow ratio for Twin Lakes Reservoir is 0.35 for the <br />rehabilitated structure. Using the Brune curves gives a trap efficiency of 96 <br />percent. This information produces only 4 acre-feet of sediment in Twin lakes <br />over 50 years: Even this estimate is probably high, because the reservoir is <br />emptied or nearly emptied every year. Thi s type of operational scheme will <br />reduce trap efficiencies and encourage flushing sediment through the outlet <br />works. <br /> <br />6.0 WATER' QUALITY <br /> <br />Water released from any of the high mountai n reservoi rs is thoroughly mi xed <br />with river water prior to diversion into treatment facilities. For the water <br />quality analysis, the station on the Cache la Poudre River near Fort Collins <br />was selected for comparisons with municipal drinking water standards. It is <br />located 11 miles northwest of Fort Collins, just upstream of the North Fork of <br />the Cache 1 a Poudre Ri ver. Records are avail abl e from October; 1979 to the <br />present. Sampl es were coll ected monthly and SUbjected to a full range of <br />chemical tests: These data are sUi1l11arized on Table IV.ll. The table shows <br />the range of concentrations for each water quality parameter and its standard, <br />or 1 imit. <br /> <br />Generally speaki ng, water quali ty for the Cache 1 a Poudre Ri ver is excell ent <br />for domestic, municipal, industrial, and agricultural purposes. The water is <br />low in heavy metals and total dissolved solids. The concentrations of <br />nitrogen; sulfate, chloride, and fluoride are also very low. <br /> <br />-38- <br />