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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 /> <br /> <br />Beaver Creek, near Idyl wil de. These records were correlated with those for <br />the South Fork Cache 1 a Poudre Ri ver near Rustic gagi ng stati on, to fill <br />mi ssi ng records for the study peri od. Further adjustments were not necessary <br />because the contribu~ing drainage areas were nearly identical. <br /> <br />Discussions with the Water Commissioner for the Cache la Poudre River provided <br />i nsi ght for determi ni ng storabl e flows. Reservoi rs in the Cache 1 a Poudre <br />system normally fill in April and June from spring runoff. The remainder of <br />the year, senior ditches divert the entire supply for irrigation and municipal <br />purposes. For thi s i nvesti gati on, only the percentage of the annual flows <br />which occurred in April and June were considered storable in these reservoirs. <br /> <br />For Comanche, Peterson Lake, and Twi n Lakes Reservoi rs, the storabl e flows <br />were estimated as 46, 37, and 51 percent of the respective annual inflows. <br />The storable flows at Twin Lakes were adjusted to account for contributions <br />from the canal, which diverts from an adjacent drainage basin. The drainage <br />area above the canal diversion is about the same size as above the reservoir. <br />Since 51 percent of the annual flows occur in April and June, the entire <br />annual flow was assumed storable, to include canal diversions. <br /> <br />If Twin Lakes Dam is repaired and the outlet works replaced, the reservoir is <br />expected to fill every year; even if the storage capacity is enlarged to 460 <br />acre-feet, the reservoi r will fill 33 out of the 34 years in the study <br />period. The water supplies associated with enlarging either Peterson Lake or <br />Comanche Reservoi r, as an alternati ve to fixi n9 Twi n Lakes, are not nearly as <br />reliable. Peterson Lake and Comanche Dams are also operating under <br />restri cti ons imposed by the State Engi neer. Assumi ng repai rs are adequate to <br />operate at full capacity, Peterson Lake will fill 88 percent of the time at an <br />active capacity of 1,183 acre-feet, and Comanche will fill 76 percent of the <br />time at a 2,630 acre-feet capacity. <br /> <br />Enl argi ng each of these reservoi rs by 460 acre-feet requi res an increase in <br />the normal water surface of 8 feet for Peterson lake, and 4 feet for <br />Comanche. The reliability of the water supply for each of the enlarged <br />reservoirs decreases to a 68 percent chance of filling. <br /> <br />-29- <br />