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<br />Water Operations <br />(Continued from page 2) <br /> <br />Easter to Labor Day. Most of the <br />currently ongoing research flows <br />for the Glen Canyon <br />Environmental Studies (GCES) <br />require higher minimum releases. <br /> <br />The minimum annual release from <br />the dam is 8.23 million-acre feet <br />(mat) as provided in the RCriteria <br />for Coordinated Long-Range <br />Operation of Colorado River <br />Reservoirs" (Operating Criteria). <br />Since closure of -the dam, this <br />minimum annual release has <br />occurred about one-half of the time. <br />The average of the annual releases <br />has been about 9.7 maf. The <br />maximum release was about 21.0 <br />maf, in water year 1984. The <br />computed "natural" annual <br />inflows to the reservoir have <br />ranged from about 5.0 mat in 1987 <br />to about 24.1 mat in 1984. During <br />1984, 3.1 maf of flood flows were <br />stored in Lake Powell. <br /> <br />Annual rJleasesfFO~en Canyon <br />Dam are primarily based on <br /> <br />meeting Lower Basin <br />commitments, avoiding <br />anticipated spills, maintaining <br />conservation storage, and <br />balancing storage between Lakes <br />Powell and Mead, in accordance <br />with the long range operating <br />criteria. Annual and monthly <br />release volumes are projected in <br />consultation with the seven states <br />in the Colorado River Basin. In <br />years when Lake Powell is not <br />expected to fill (due to a low <br />reservoir level and/ or a low inflow <br />forecast), the scheduled annual <br />release volume is the minimum <br />allowable of 8.23 maf and <br />considerable flexibility exists in <br />scheduling monthly release <br />volumes. <br /> <br />In years when Lake Powell is <br />expected to fill (due to a high <br />reservoir level and/or high inflow <br />forecast), the scheduled annual <br />release volume is substantially <br />greater than the 8.23 mat minimum <br />to avoid spills and maximize <br />conservation storage. Under such <br /> <br />conditions, operational flexibility is <br />necessmy to balance the need for <br />maintaining sufficient storage <br />space (to avoid spills) with the <br />objective of not releasing too much <br />water (which sacrifices <br />conservation storage). Such <br />operations require delicate <br />balancing in the face of the <br />uncertainty of streaI1lflow <br />forecasts. <br /> <br />Spills are undesirable for two <br />primary reasons: (1)flood flows are <br />damaging to resources <br />_ downstream from the dam, and <br />(2)some of the water may be <br />released at times or in amounts that <br />preclude its being effectively used <br />for power production or beneficial <br />consumptive uses. <br /> <br />Alternatives that affect the <br />necessary operational flexibility in <br />years when Lake Powell is expected <br />to fill could affect frequencies of <br />spills and the ability to maintain <br />conservation storage to meet Lower <br />Basin water delivery requirements. <br /> <br />River Level Changes <br /> <br />River morphology influences the amount of change in river levels resulting from changing volumes of water. In <br />narrow reaches of the canyon, river level changes are greater in response to fluctuating releases from the dam <br />than they are in the wider sections of the river. The Lees Ferry gage is in a wide section and the Grand Canyon <br />gage, near Phantom Ranch, is in a narrower section. At these two gages, the relationships between water release <br />changes (in cis) and river level changes (elevation in feet) are: <br /> <br />5,000 to 10,000 ds <br />10,000 to 20,000 ds <br />20,000 to 30,000 ds <br />5,000 to 30,000 ds <br /> <br />Lees Ferry <br />1.5 ft. <br />2.0ft. <br />1.5 ft. <br />5.0 ft. <br /> <br />Totals <br /> <br />Grand Canyon <br />3.2 ft. <br />4.5 ft. <br />3.1 ft. <br />10.8 ft. <br /> <br />17 <br />