United States Department of Agriculture
Natural Resources Conservation Service
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National Water and Climate Center


Snow Surveys and Water Supply Forecasting

Water Management

The Western United States requires a dependable supply of reasonably priced, good-quality water if the economy is to prosper and the quality of life is to remain high. Vast areas that receive just a few inches of annual rainfall produce bountiful crops, but only with irrigation (fig. 3). Decisions on the types of crops to plant, the number of acres, and irrigation scheduling all depend on reliable forecasts of the year's water supply. Much of the power for cities as well as agriculture and industry is generated by hydroelectric energy. Water is truly the life blood of the West.

Picture of Crop Irrigation

Figure 3. Because of the very low annual rainfall in the West, many areas such as this field of
alfalfa depend on irrigation.

Wise management of existing water resources in the United States is essential. Water management, however, is complex even under the best of circumstances. Supply, demand, and cost are subject to the climate and to numerous economic and social influences, domestic and international. The decisions made early in the year, based on the best available information, often require significant revision as more data become available.

The Columbia and Colorado rivers are two examples of extremely complex snowmelt-fed river systems. The area draining into the Columbia River comprises about 258,000 square miles, which includes 40,000 square miles in Canada. Along the river, Federal agencies have built 30 major dams for power generation, flood control and irrigation storage. The Columbia and its tributaries support a wealth of fish and wildlife, including several species of fish such as salmon, which live in the sea but spawn in the river's fresh water (fig. 4). Barge traffic on the river is a major link in the area's transportation network for marketing agricultural and other products. Because many communities and industries and millions of acres of agriculture depend directly on this river system for survival, effective and timely management is critical.

Picture of an Elk

Figure 4. Snowmelt-fed rivers support wildlife
such as elk.

Like the Columbia, the Colorado River also begins in high mountain country. It drains about 247,000 square miles. Huge population centers in southern California and Arizona consume enormous quantities of water, as do the expanding agricultural developments, and demands for water of the Colorado are intense. As in the Columbia, numerous storage facilities have been constructed, impounding snowmelt water to produce electricity, irrigate farms, supply water to cities and towns, and prevent floods. Unlike the Columbia, however, the Colorado picks up dissolved salts as it flows through ancient deserts and areas shaped by prehistoric inland seas. Heavy withdrawal of water, evaporation, and irrigation return flows can increase salt concentration downstream and thereby lower the quality of the water. Because multistate agreements and compacts regulate the quality and quantity of streamflow on the Colorado River, accurate management of streamflow and water use is imperative.

Most smaller river basins throughout the West also have management requirements for limited water resources that are just as important for their users. Management decisions are vital every year for big rivers or small, but the years of vast surplus and extreme shortage intensity the demands for management excellence and the importance of snow surveys.