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,. He.Q. ...... .."..'~' {oV CHRONOLOGY OF THE 1976-77 DROUGHT 49 during the summer, and the waterfowl popula- tion was reduced. The Great Salt Lake is a good barometer of overall wet and dry conditions. During the wet period from 1861 to 1873 the lake rose 10,8 ft to a high level of 4,210.5 ft, Since then the lake has fallen to low levels in 1905, 1940 and 1963 with intervening high levels in 1923 and 1952. The development of irrigation and other consumptive uses in the Great Salt Lake basin is one of the reasons causing the general decline from the 1870's to the low of 4,191.4 ft in 1963. However, no major changes in irrigation use have occurred in about 15 years; therefore, the rise and fall of the Great Salt Lake is in direct response to wet and dry conditions. From 1963 to 1976 the trend was wet, and the lake rose 9 ft to 4,200.4 ft in 1976--a level 0,8 ft higher than that in 1952. But in the 1977 water year the lake dropped 1.5 ft which is comparable to the 2.0 ft drop during the drought of 1933-34 and the 1. 7 ft drop in 1961. The latter two values were at elevations 2,0 to 7,0 ft lower than in 1977; therefore, the volume of water lost was less. The water level continued to fall another 0.3 ft until Decem- ber 1, 1977 when one of the latest seasonal minimums occurred. The recession from the high level in 1976 to the lower level of,Decem- ber 1, 1977 represents an evaporation__ loss of about 3.41 million acre-ft which is a reduction of 20 percent in volume. Precipitation and Runoff Precipitation during 1975 in the Great Basin was generally near normal-within a range between about 10 percent below to 20 percent above normal, Deficiencies developed in 1976 as precipitation dropped to the 70 to 85 percent of normal range in many places, Though precipitation recorded at some valley floor locations was near normal, the snowpack in the mountains was below normal, See figure 24 for conditions in the Sierra Nevada which is the western boundary of the Great Basin. Many valley floor locations had near nor- mal precipitation again in 1977, though the heavy rains in May, at Salt Lake City, Utah and Ely, Nev., for example, accounted for about 30 percent of the total. At Alton in southern Utah, the total precipitation for the season from October through April was only 2,20 in, which is 20 percent of average and less than half the previous minimum. The snow- packs in the Sierras and in the Wasatch Range were much below normal, and their record low water content was the major cause of the drought. By May 1, 1977 most of the snow had melted. Another associated factor was the unseasonably warm temperatures in April, Large amounts of precipitation, 5 to 10 in., between May 1 and June 15, 1977 at high elevations in Nevada improved the seasonal runoff over that forecast for the Humboldt River. Runoff in the 1975 water year was above normal on the Truckee and Humboldt Rivers in Nevada and the Logan River in Utah. At Palisade on the Humboldt River about 25 mi southwest of Elko, Nev., 1975 was the seventh consecutive year of above normal runoff, but on the Truckee River east of Reno only five of those seven years were above normal, and just four of those seven years were above normal on the Logan River north of Salt Lake City. Overall, streamflow prior to the 1976-77 drought reflected good water supplies. During the 1976 water year, the runoff pic- ture was mixed. The adjusted flow of the Truckee River dropped to 24 percent of normal though the actual flow was 77 percent of average. This was accomplished by depleting the water in storage in Lake Tahoe and five reservoirs in the Truckee River basin by 365,000 acre-ft. This is the second largest reduction in storage since 1900 when records began and is only 5,000 acre-ft less than that in 1924, At Palisade, Nev. the Humboldt River runoff decreased to 76 percent of normal, but the Logan River runoff was 96 percent of normal. The runoff during the 1977 water year indi- cates the effect of the continuing drought and its spread. Once again, a large release, 355,000 acre-ft, of stored water in the Truckee River basin, maintained flow in the Truckee River. The actual flow at the mouth was only 14 percent of average. Without the releases from storage, the Truckee River would have had very little flow at its mouth, probably just some return flow from local irrigation. The Carson and Walker Rivers, draining the eastern slopes of the Sierras south of the Truckee River, had record low annual flows in 1977, about 23 percent of average, The