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O. " c. .'50 U.::J . . The Lake Mead inflow forecasts are made by the Colorado River Forecasting Service located at the National Weather Service River Forecast Center in Salt Lake City, utah. A minimum August 1 empty storage space of 1,500,000 acre-feet is required at Lake Mead each year to control rain floods and to initiate the reservoir storage space building to achieve the January 1 space requirement. The forecasts on which the system operations are based are the maximum forecasts that have the probability of not being exceeded 95 percent of the time. The Bureau of Reclamation must meet the minimum flood control requirements, but beyond that it has some flexibility in the manner in which it operates the river. Specifically, for good cause it can release flows in excess of the minimum required by the regulations, develop flood control storage space greater than required by the regulations, and provide for the required flood control storage space by using available space in the different reservoirs, within constraints set by the regulations, the Operating Criteria promulgated in compliance with Section 602 of P.L. 90-537 and the remainder of the "Law of the River". 1983 Reservoir Releases and Flood Damages On January 1, 1983, there were 6,600,000 acre-feet of vacant reservoir storage space in the Colorado River system, about 25 percent more than the minimum required by the Flood Control Regulations. A very unusual combination of weather events in 1983 caused a rapid succession of increasing runoff forecasts from about 110 percent of normal (1961-1980) on May 1 to about 200 percent of normal in late June. The unusual weather cond i t ions r esul ted in a near record runoff of 14.7 million acre-feet for the April-July period and a peak daily inflow into Lake Powell of approximately 128,000 cfs on June 2, 1983. This occurred when the Lake was already full. Lake Powell began spilling on June 8, with a peak release of 91,000 cfs occurring on June 29. The storage in downstream Lake Mead reached the top of the Hoover Dam spillway gates on July 3, and the first spill occurred since 1941, when releases were made to test the dam's spillways. The nearly doubling of the forecasted runoff between the May 1 and late June forecasts, with the reservoirs full, could have required Hoover Dam flood control releases of up to 65,000 cfs pursuant to the regulations. However, the Bureau of Reclamation was able to manage the reservoir system so as to avoid these very damaging releases. The maximum average monthly release from Hoover Dam was limited to 42,000 cfs. with regard to the frequency of occurrence of such flows, a 1982 Corps of Engineers report shows a Hoover Dam release of 40,000 cfs for a one-month duration as a l-in-200 to a l-in-333 year .event. -5-