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50 HYDROLOGIC AND HUMAN ASPECTS OF THE 1976-77 DROUGHT average flow of the Humboldt River at Pali- sade in 1977 dropped to 130 ft3/s or 35 percent of normal. However, the average annual flow has been less in nine other years. The minimum annual flow was 34.8 ft3/s in 1934, and three consecutive years, 1959-61, were less than 1977 and averaged 100 ft 3/s. A new record low annual runoff occurred on the Logan River above State Dam, near Logan, Utah during the 1977 water year. The very low snowpack in the Wasatch Range was the primary cause. Though a new low in 81 years of record, the runoff was less than 10 percent below the runoff in 1931, 1934, 1941, and 1961. A low-flow frequency analysis for the Beaver River near Beaver, Utah which is about 48 mi northeast of Cedar City shows that flows in 1977 for all periods from 1 to 365 days were new minimums of record in 63 years of record, The flows have probabilities ranging from 0.01 to 0.0033 which are equivalent to recurrence intervals of 100 to 300 years. In 1976, low flows of the Beaver River were in the 5- to 13-year recurrence-interval bracket. The large reduction of storage in the Truckee RiVer basin is mentioned above; how- ever, there is other information of interest. The bulk of the releases from storage came from Lake Tahoe which dropped below the level of the lip at its outlet on September 22, 1977 and remained below until December 27, 1977, This was the first time that this has happened since 1962. Plans were made to pump water from Lake Tahoe into the Truckee River, but the legal implications and the cost could not be resolved; therefore the Truckee River flow below Lake Tahoe was only local inflow, The Truckee River flows into Pyramid Lake northeast of Reno, Nev" and the drought re- duced the inflow to the lake so that the water level of Pyramid Lake dropped 0,8 ft in 1976 and 2.9 ft more in 1977. The 2-year decrease in storage was 400,000 acre-ft, but this was less than half the 960,000 acre-ft decrease that occurred in 1930-31. Storage 'in Rye Patch Reservoir on the Humboldt River decreased 92,250 acre-ft dur- ing the 2-year drought. This is equivalent to the average inflow from the Humboldt River for about 8 months. Usable storage in Topaz Lake in the Walker River basin, Nevada was depleted to zero by August 1977, a reduction of 22,500 acre-ft, Thereafter, only the cur- rent runoff was available for irrigation. Reservoir storage in Utah was near 50 per- cent ,of average by October 1977 even though Bear Lake and Utah Lake, the two largest reservoirs, were at 76 percent of average. All usable storage was released from several small reservoirs. Ground-water Conditions The aquifers in many parts of the Great Basin are large with respect to the demand for ground water; therefore, with only a few ex- ceptions, increased pumping from existing wells and the added withdrawals from new wells had no major or long-lasting effect on ground-water levels. There were recharge areas around the margins of some closed valleys where moderate declines of a few feet occurred, but there was little or no change in water levels in the central parts of the valleys. Where ground-water development exists in closed basins, the declining trend in water levels caused by pumping greatly exceeds the changes that can be attributed to the drought, Ground water is the sole source of water other than small amounts of precipitation in many areas; therefore, the amount of water pumped during a drought is not much more than that pumped in a normal year. In Diamond Valley south of Elko, Nev" the water-level declines in 1977 were close to the rate of decline in previous years. Ground-water levels in valleys along the principal rivers in Nevada were directly af- fected by the drought. There was less re- charge from the streams and from deep perco- lation of irrigation water, and water levels were lowered by heavier pumping of ground water to supplement deficient surface sup- plies, For example: Reno and Sparks, Nev" normally obtain about 30,000 acre-ft per year from the Truckee River and pump 6,000 to 7,000 acre-ft per year of ground water for municipal uses, During 1976, releases from storage provided sufficient flow; but in 1977, streamflow was not sufficient, and nearly 20,000 acre-ft was pumped to offset the deficiency. However, the water level decline was not excessive anywhere in Truckee Mea- dows. In the Smith and Mason Valleys along the Walker River, ground-water pumpage in 1977 J