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Lake Powell (Colorado River) Water YGClr 1984 During water year 1984. lake Powell, which is impounded by Glen Canyon Dam, was operated os port of the CRSP in accordance with governing contracts and lows to provide river regulation, optimum power production, recreation, and fish and wildlife enhancement. Lake Powell was completely full 01 the beginning of water year 1984 at elevation 3.699 feet following Q near record-breaking 1983 runoH. Releases from Glen Canyon Dam, which impounds lake Powell, were at the moximum powerplant capacity of 28,000 cfs. The two spillway tunnels were pumped oul to facilitate on inspection to determine the extent oi ca'litoHon damage to the concrete lining. It WQS planned that both spillway tunnels would be restored to their original condition and modified with air 5\015 10 eliminate future cavitotion problems prior to the 1984 rurioff. As a contingency, in case this schedule of repair and modification become delayed, it was planned that Glen Canyon release be maintained at maximum powerplant capacity through the end of December 1983. This would build sufficient vacant reservoir space to reduce the risk of having to use the spillways during the 1984 runoff. By Januory 1, 198.4, lake Powell was at elevation 3,685 feet with an active content of 22,697,000 acre. feet . The January 6, 1984-forecast of-April through ;July runoff for lake Powell was 13,000,000 acre-feet which was 174 percent of normal. This necessitated that Glen Canyon releases be maintained at maximum powerplant capacity through the remainder of the water year and that plans be made to i~itiate discharges through the river outlet works 05 early os April 1984. Since it wa5 unknown whether Glen Canyon's spillways would be available for use during the 1984 runoff, it was planned 10 operate in expectation of incurring the reasonable maximum forecast error. Accordingly, releases from Glen Canyon were maintained 01 maximum powerplant capacity even though the runoff forecasts steadily declined over the next 3 months. 14 The April through July runoff forecast mode on April 5, 1984, hod dropped to 11,500,000 acre.feet or 154 percent of normal; however, by May 7, it hod incre-a5ed back up to 13,000,000 acre-feet. To contain this volume of runoff plus the forecast error, on May 4, 1984, the river outlet works at Glen Canyon were opened to bypass their maximum discharge of 17,000 cfs. This bypass release was maintained together with maximum powerplant releases for the entire month of May. The June 7, 1984, runoff forecast increased to 14,200,000 acre. feet or 190 percent of normal which required that the river outlet works remain open at 17,000 cfs for that month as well. The runoff forecast again increased on July 7, 1984, to 15,200,000 acre-feet which .....as 204 percent of normal. This incraase again required that the river outlet works remain open for at least port of the month of July. lake Powell itself peaked at elevation 3,702.46 on July 8, 1984, almost 2,5 feet into surcharge, and the river outlet works were gradually clos&d by July 23, 1984. The lotal releases from Glen Canyon Dam for the entire water year were 21,051,000 acre.feet, of which 2,&34,000 acre-feet were bypassed through the river outlet works. Glen Canyon's spillways were not used to pass any of the April through JulY' 1984 runoff. This was possible even while lake Powell was 2.5 'feet into surcharge because of the a-fool high steel extensions on the spillway gates which were added in 1983. The temporary use of the extensions wa~ to -reduce doyinslream flooding - and. damage to the spillways. These extensions will be on through the Hoover spillway modification construction period. Repair of Glen Canyon's spillways was completed by early August 1984. It was decided that one of the spillways should be tested at various discharges and also at a sustained rote to determine if the airs lot modification would prove successful in eliminating cavitation damage. During the week of August 6, 1984. the left spillway tunnel was tested 01 vorious flow rates of up to 50,000 cfs. Also, two separate 4.hour sustained tests of 30,000 cfs Were conducted. Examination of the spillway tunnel subsequent to these tests revealed no cavitation damage whatsoever. Water Vear 1985 Lake Powell began water year 1985 at eleva1ion 3,696 feet with an active content of 24,347,000 acre-feet (97.4 percent full). The operating plan through December of 1984 was to maintain Glen Canyon releases at a mal<.imum pOlNerplant capacity 0", 25,000 ds in order to develop sufficient vacant reservoir space to reduce the risk of spilling during the 1985 runoff season, Assuming overage runoff conditions, releases from lake Powell for water year 1985 will be 13,750,000 acre-feet. A reasonable minimum le'lel at \~How would produce on annual release of 10,700,000 acre.feet, and a reasonable maximum level of inflow would require that 18,100,000 acre.feel be released during the water year. Releases from lake Powell after January 1, 1985, will be based upon runoff forecasts reflecting current hydrologic conditions. It is expected that powerplanl bypasses will be avoided in all three operating plans. Lake Powell AC1ive Slorage" Chart 5 Reservoir Acre-Feet EI. (FI,) Maximum Storage Rated Heod Minimum Power Suna.ce Area (Full)- Reservoir length (Full) Powerplant Number of Units Total Capacity 25,002,000 3700 9,428,000 3570 4,126,000 3490 -'61,390 Acres 186 Miles B 1,021,000 Kilowatts 'D~'notincllldlo 1.998,0XI ocr..I_t of dllQd "orClso-b.lo.....3370 I_'.