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1'\o~~~<M u '.... ~, '-.t'V l} ADAPTATION TO DROUGHT 19 (Corps of Engineers, oral commun., 1978). However, the combination of lower than usual flows in the Mississippi River between St. Louis, Mo., and Cairo, Ill. and the severe ice conditions halted navigation for several weeks in January and February 1977. Two ferries that cross the Missouri River north of Lewistown, Mont., were taken out of service in June 1977 because of low flow in the river. Usually, any cessation of ferry service does not occur until late fall. Minor naviga- tion difficulties occurred on the Sacramento River in California. ADAPTATION TO DROUGHT The adaptation to drought falls into two main categories, short-term planning and long- term planning, plus a parallel category, legal aspects, which relates to the first two. These are presented mainly in general terms with statements related to the 1976-77 drought to illustrate the general conditions. Short-term Planning The information base related to drought, both past and present, was an important factor in the adaptation to the drought by public and private entities and by individuals. Numerous Federal, State, and local agencies, and public utilities provided information on the weather, snow packs, streamflow, reservoir storage, ground-water levels, water quality, and water use. The field data collected had to be analyzed and forecasts or predictions made; otherwise the water managers and government officials would have no realistic basis for deci- sions on more efficient ways to allocate the limited water resources. Changes in Water Use The mandatory rationing of water in sev- eral areas was viewed with dismay and appre- hension. But residential use in one service area near San Francisco was reduced by 45 percent between April1 and December 31, 1977 rather than just the mandatory reduction of 25 percent. A contributing factor was the surcharge added to the water bills. The reader is cautioned to be aware of the bases for which percentages are given. In the preceding paragraph, 45 percent is an impres- sive figure, but domestic use in northern California is only about 6 percent of the total water use. Therefore, a 45 percent reduction is less than 3 percent of the total though it is an essential contribution to water conservation in time of drought. At the opposite end of the scale, flows in some streams in the Pacific Northwest dropped down to the 40 percent of normal range; but 40 percent of a relatively large flow was still enough water to supply domestic needs without rationing, though water for other uses had to be carefully managed. Several water-supply systems were ad- versely affected when their source of water was depleted or their storage was inadequate to equalize the supply. A number of utilities upgraded their systems when they developed ground-water sources to supplement surface- water supplies, installed storage tanks, or took other steps to meet current problems. Re- vamping distribution systems was usually either not feasible or took too long to meet the drought emergency. Where possible, an outright purchase was made of water from another user or another area to supplement dwindling supplies. A few municipalities were able to use the priority rights of agricultural ditch companies for their supply in exchange for effluent from the municipal sanitary system. Good quality water was pumped from mines in Colorado for municipal Use. However, where the water was allowed to flow over mine tailings once it reached the surface, the quality deteriorated. In many parts of the United States, more ground water was pumped than usual to sup- plement depleted surface-water supplies. But in Arizona where ground water is the major source of supply and the annual overdraft averages 2.2 million acre-ft or nearly half of the 5 million acre-ft pumped each year, the overdraft in 1977 was about the same order of magnitude. Ground-water levels dropped a maximum of 13 to 20 ft. Changes in Irrigation Practices The shortage of surface-water supplies or rainfall on nonirrigated land caused many problems for the farmers and ranchers and for the governmental units responsible for alloca- ting water. The latter groups distributed the