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<br /> <br />'. <br /> <br />" l. <br /> <br />. <br /> <br />. <br /> <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />Navajo Reservoir <br /> <br />As with all of the other Colorado River reservoirs, Navajo has experienced well below <br />normal runoff conditions in 1990. This has left the reservoir about 316,000 AF short <br />of filling. Releases to the San Juan River were reduced to 500 ff/s during much of <br />water year 1990 and will be increased only in order to satisfy downstream water rights. <br />This release pattern is expected to continue through water year 1991 and, with normal <br />runoff, the reservoir should refill in 1992. <br /> <br />Lake Powell <br /> <br />In order to achieve the objective of maintaining a minimum release of 8.23 MAF <br />annually from Lake Powell set forth in the Operating Criteria, the below average inflow <br />in 1988, 1989, and 1990 has reduced the storage in the reservoir by about 8 MAF. <br />Currently about 53 feet from full (or 74 percent of capacity at 17 MAF of storage), the <br />reservoir is projected to continue to drop through the fall and winter. reaching its <br />seasonal low point in March 1991, about 75 feet from full (or 14.7 MAF of storage). <br /> <br />During water year 1991. a release of 8.23 MAF will be made in an effort to preserve <br />the reservoir storage at Lake Powell. Under most probable conditions, the reservoir <br />will not reach a storage level in 1991 that exceeds that of 1990 due to the refilling of <br />upstream reservoirs. The 1990 AOP projected that Lake Powell would refill in the <br />spring of 1991 under most probable conditions. Due to the extended drought, this is no <br />longer expected. It will now take several years of average inflow in order to retill <br />Lake Powell. <br /> <br />Following the extreme flood runoff years of 1983 through 1986, the Glen Canyon <br />Environmental Studies and reports identified releases greater than powerplant capacity <br />as detrimental to the ecology of the Grand Canyon and recommended that steps be <br />taken to limit the frequency of these flood releases. Based on these recommendations <br />and similar concerns regarding powerplant bypasses voiced by the power customers, an <br />operation strategy was developed within the constraints of the existing Operating <br />Criteria for Glen Canyon Dam that reduced the probability of releases greater than <br />powerplant capacity. The frequency of these releases was reduced from approximately <br />once in four years to approximately once in 20 years. In addition to reducing <br />environmental damage, this also has the effect of decreasing spillway maintenance and <br />repair costs and increasing total power generation. <br /> <br />The two primary factors which produced these effects were (1) reducing by 500.000 AF <br />the July target storage content of Lake Powell, and (2) reacting more quickly to <br />changes in the forecasted runoff as the runoff season progresses. Each of these factors <br />contribute to late-spring tlexibiJity in accommodating large increases in the spring <br />runoff such as occurred in 1983, 1985. and 1986. <br /> <br />8 <br /> <br /> <br />- <br />