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8 The State of the Colorado River Ecosystem in Grand Canyon Table 1. Glen Canyon Dam release prescriptions under the modified low fluctuating flow alternative (ets = cubic feet per second). Monthly release Minimum Maximum Allowable daily Uprampl volume (acre-feet) release (cfs)! release (cfs) fluctuation (cfs) downramp (cfs/hr) <600,000 8,000/5,000 25,000 5,000 4,000/1,500 600,000-800,000 8,000/5,000 25,000 6,000 4,000/ I ,500 >800,000 8,000/5,000 25,000 8,000 4,000/1,500 I 8,000 cfs between 7 a.m. and 7 p.m. and 5,000 cfs at night; releases each weekday during the recreation season (Easter to Labor Day) would average not less than 8,000 CEi lor the period from 8 a.m. to midnight. was concern for the effects on sensitive resources such as sediment or endangered species. On the basis of significant scientific research since 1995, some of the assumptions about how Colorado River resources would respond to ROD operations have been modified or rejected. As a result, several additional experimental flows that temporarily modified Glen Canyon Dam ROD operations have been implemented since 2000. Additional experimental flows discussed else- where in this report include the 2000 low summer steady flow (LSSF) test, the 2003-05 experimental fluctuating nonnative fish suppression flows, and the November 2004 experimental high flow. The LSSF test included 1966 National Historic Preservation Act passed 1968 Colorado River Basin Project Act passed i ! i two habitat maintenance flows (31,000 cfs for 4 d) in spring and late summer, with June through August flows held constant at 8,000 cfs. Fluctuating nonnative fish suppression releases allowed the flow of the river to fluc- tuate daily between 5,000 cfs and 20,000 cfs with relaxed hourly upramp and downramp rates of 5,000 and 2,500 cfslh, respectively, from January to l\ifarch. In summer and fall 2004, fine-sediment inputs from the Paria River (15 mi below the dam) reached the agreed-upon levels for triggering an experimental high flow of 41,000 cfs for 2.5 d (see chapter I, this report). Experimentation has largely focused on experimental flows of the type described above to achieve downstream 1970 Long-range Operating Criteria developed for Glen Canyon Dam operations ! i 1967 Humpback chub and Colorado pikeminnow (Ptychocheilus lucius) federally listed as endangered 1969 National Environmental Policy Act of 1969 passed requiring Federal agencies to consider the environmental impacts of their proposed actions and reasonable alternatives to those actions '. '