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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 />I <br /> <br />4.0 WATER UTILIZATION <br /> <br />Reservoir simulations were conducted for evaluating the safe yield for the dam <br />rehabilitation project. The safe or firm yield is the maximum quantity of <br />water which can be guaranteed during a critical dry period. In this analysis, <br />the critical drought occurred from 1953 through 1956. <br /> <br />Operating the reservoir on a safe yield basis gives the City of Greeley a <br />dependab1 e water supply duri ng a drought. It al so provi des a year-round <br />supply. One of the City's problems during the winter is caused by the annual <br />shutdown of Co1 orado-Bi g Thompson (CBT) Project conveyance facil i ti es, from <br />November through March. This effectively el iminates use of CBT or Windy Gap <br />water in the winter. Currently, the City relies heavily upon their direct <br />fl ow ri ghts from the Cache 1 a Poudre Ri ver duri ng the wi nter. Reservoi r <br />releases are needed to augment the natural river flows, when Greeley's demands <br />exceed the flows or the water available under these direct flow decrees. A <br />si de benefi t from fi rm yi el d operati ons is that carry-over storage woul d <br />enhance the reservoir fishery. A larger minimum pool would be available at <br />all times. <br /> <br />The reservoi r operati ng pol icy coul d be enhanced by a water exchange between <br />the Water Supply and Storage Company and the City. Barnes Meadow Reservoi r <br />water coul d be released during the summer to meet City demands, and CBT or <br />Windy Gap water, owned by the City, could be used to meet the summer <br />irrigation needs of Water Supply and Storage. In exchange for the Windy Gap <br />or CBT water, the City wou1 d obtai n storage water in Chambers Lake. By <br />refi 11 i ng Barnes Meadow Reservoi r in the fall wi th water hel din Chambers <br />Lake, the City would obtain a reliable winter water supply. Theoretically, <br />after the exchange, CBT or Wi ndy Gap water wou1 d be stored in Barnes Meadow, <br />and a return flow credi t amounti ng to 87 percent of the exchange wou1 d be <br />allowed during the winter, because the water supply is derived from basin <br />imports. This operating scheme could nearly double the water yield from <br />reservoir storage. Obviously, the return flow credit now received during the <br />summer would be lost, but supplies are plentiful at that time of the year. <br /> <br />1231 H <br /> <br />-31- <br />