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<br />probable maximum, most probable, and probable minimum <br />runoffs, respectively. Under most probable conditions, the <br />reservoir will not reach a storage level in 1991 that exceeds that <br />of 1990 due to the refilling of upstream reser",irs. The 1990 <br />Annual Operating plan projected that Lake Powell would refill <br />in the spring of 1991 under most probable conditions. Due to <br />the extended drought, this is no longer expected. Se",ral years <br />of average inflow will be required to refill Lake Powell. <br /> <br />Following the high runoff years of 1983 through 1986, research <br />by the Glen Canyon Environmental Studies office identified <br />releases greater than powerplant capacity as detrimental to the <br />ecology of the Grand Canyon and reconunended that steps be <br />taken to limit the frequency of these "flood"releases. Within the <br />constraints of the existing Operating Criteria, Glen Canyon <br />Dam is operated to reduce the probability of releases greater <br />than powerplant capacity. Because the le",l of Lake Powell has <br />dropped considerably since 1987, the risk of releases greater <br />than powcrplant capacity during water year 1991 is negligible. <br /> <br />Monthly releases in water year 1991 will be adjusted slightly to <br />meet the research flows for the Glen Canyon Environtnental <br />Studies that arc currently in progress. These research flows <br />wefe carefully selected in order to gi....-e researchers specific <br />release patterns and also meet the minimum release objective <br />of 8.23 million acre-feet. The research.effort at Glen Canyon is <br />aimed to improve understanding of the environmental <br />consequences of different release patterns from Glen Canyon <br />Dam. Reclamation, Western, and the Basin States are <br />committed to the cooperative effort required to complete the <br />Glen Canyon Environmental Studies. <br /> <br />ACTUAL STORAGE 1990 <br /> <br />MILLION ACRE-FEET <br />" <br /> <br />22 <br /> <br />'0 <br /> <br />18 <br /> <br />18 <br /> <br />i"---_ <br /> <br />" <br /> <br />" <br />ONDJFMAMJJAS <br /> <br />PROJECTED RELEASES 1991 <br /> <br />THOUSAND AeRE-FEET <br />1200 <br /> <br />... .RO' "'" +" ST p Oll .;.-,. . "' <br /> / ~ <br /> / ~ / <br />......... /' <br /> <br />1000 <br /> <br />.00 <br /> <br />000 <br /> <br />400 <br /> <br />200 <br /> <br />o <br /> <br />PROJECTED UNREGULATED INFLOW 1991 <br /> <br />THOUSAND ACRE-FEET <br />&000 <br /> <br />PROB WIN ....... ST P O. <br /> <br />PR . WA <br /> <br />4000 <br /> <br /> <br />3000 <br /> <br />2000 <br /> <br />1000 <br /> <br />o <br /> <br />PROJECTED STORAGE 1991 <br /> <br />MILLION ACRE-FEET <br />" <br /> <br />... "'RD' IN 1"'"" ". . ~ '00 "" <br /> ,/ <br /> 1/ <br /> / <br /> ./ V - <br /> ....... <br /> -- <br /> <br />22 <br /> <br />20 <br /> <br />18 <br /> <br />" <br /> <br />'4 <br /> <br />" <br />ONDJFMAMJJAS <br /> <br />14 <br />