WSP08775 - Laserfiche WebLink

Home Browse Search

MHt.g 51 CHRONOLOGY OF THE 1976-77 DROUGHT was about three times normal. The annual net water-level decline was several feet, but a wet year or two will probably replenish the ground- water reservoir. Similar responses to the drought also occurred along parts of the Humboldt and Carson Rivers. The average number of new wells drilled each year in Nevada is about 600. During 1977, about 1,200 wells were drilled, most of them because of the drought. In Utah, the drought brought on a flurry of well drilling. About 1,100 new wells were drilled in 1977 and 180 of them were capable of large withdrawals. The number of new wells in the Great Basin was more than twice the average number of wells drilled per year statewide. The average annual withdrawal from wells is 570,000 acre-ft. In 1976 the pumpage rose to about 660,000 acre-ft, and in 1977 it increased to about 740,000 acre-ft, 30 percent above average. Close to 70 percent of the water pumped was used for irrigation, half the remainder was used for public supplies, and the other half was split between industrial use and domestic and stock use. Declines in ground-water levels in 1976 and 1977 were general, and maximum declines ranged up to 24 ft in localized areas, ln other localized areas, water levels rose as much as 6 ft. The irregular pattern is indicated by the changes in water levels in the Pavant Valley, about half way between Salt Lake City and ,Cedar City, where the 24 ft decline was ob- served, yet only 12 mi away a rise of 3,1 ft occurred, See figure 19. The month end water levels in 11 selected observation wells were new record lows for one or more months in 1976 or 1977. Some of the 1976 records lasted only to 1977 when new lows were reached. The low-level trend extended through March 1978 in four of the wells. Because the drought reduced the flow in the streams that provided most of the water to the Salt Lake County Conservancy District, the amount of water pumped from the Dis- trict's wells in 1977 was double the usual amount. On the other hand, the conservation program at Sandy, Utah about 8 miles south of Salt Lake City was so successful that water use from wells was reduced 19 percent. In southeastern Idaho, aquifers in the Bear River area had declines ranging from 1 to 11 ft that were caused by severely reduced recharge and increased withdrawals. Water Quality Water quality of streams, lakes, and aqui- fers was virtually unaffected by the drought. The majority of the streams in the Great Basin are ephemeral; therefore, when a drought occurs, some streams may not flow at all and others will go dry earlier than usual. Though the timing of the runoff pattern is changed, the pattern is similar to normal conditions; and any change in water quality is not necessarily related to the drought. Lakes and reservoirs are low in the fall in normal years because the water is released to meet the demands for irrigation, the fishery, compacts, etc. Reservoir levels were lower than usual in the fall of 1977, but no serious water quality problems developed. The additional stresses on the aquifers were small over the 1- or 2-year duration of the drought, and water quality did not deteri- orate significantly, Some of the water pumped for irrigation in Pavant Valley, Utah returns to the aquifers as recharge and is withdrawn again for irrigation, This recirculation does affect the chemical quality of the water, At the five sites shown in figure 19 where water quality is monitored, the general trend since 1957 has been an increase in the concentration of dissolved solids. The trend was not changed by the drought in four of the wells; but in the well in section 8 of township 23S, range 6W, the trend was reversed, the concentration decreased more between 1976 and 1977 than in any other year. A longer drought period might have brought some changes in a few areas. Forests The effect of the drought on forests in the Great Basin was not significant with respect to the number of fires or the acreage burned, The heavy precipitation in May and June in the forested areas and summer thunder storms apparently provided enough moisture to the tinder to inhibit the start of an abnormal num- ber of fires. The trees in an area south of Reno, Nev" and on the east slope of the Sierras near Washoe Lake had a high rate of die off. An inspection showed that the continued drought in this area was the prime cause and not insects or disease.