U.S. Bureau of Reclamation USGS: Science for a changing world WARSMP: Watershed and River Systems Management Program
Application to the Yakima River Basin, Washington. A cooperative effort between Department of the Interior Agencies

Application to the Yakima River Basin

The initial application of the WARSMP was in the 23,000 square mile San Juan River Basin, a major tributary to the Colorado River. Beginning in fiscal year 1997, the focus of the WARSMP has been the application of the DSS to the Yakima River Basin located in eastern Washington (fig. 2). The basin has a drainage area of about 6,200 square miles, and produces a mean annual unregulated runoff of about 5,600 cubic feet per second (4,055,000 acre-feet) and a regulated runoff of about 3,600 cubic feet per second (2,606,000 acre-feet). There are 8 major rivers and numerous smaller streams associated with the Yakima River.

The headwaters are on the humid east slope of the Cascade Range where mean annual precipitation is more than 90 inches. The basin ends at the confluence of the Yakima and Columbia Rivers in the low-lying, arid part of the basin that receives about 6 inches of precipitation per year. Most of the precipitation falls during the winter in the form of snow in the mountains. Mean annual precipitation over the entire basin is about 27 inches--equivalenty 12,000 cubic feet per second or 8.7 million acre-feet. The spatial pattern of mean annual precipitation resembles the pattern of the highly variable topography (fig. 2). Altitudes in the basin range from 400 to nearly 8,000 feet.

Figure 2.-- Location and topography of the Yakima River Basin.

Agriculture is the principal economic activity in the basin, followed by recreation and timber use. The average annual water-demand is about 2,500,000 acre-feet, or nearly 65 percent of the mean annual unregulated flow. Most of the demand is for irrigation of about 500,000 acres in the low-lying semi-arid to arid parts of the basin. The demand is met by storage of water in 5 major reservoirs that can store 1,065,000 acre-feet or about 26 percent of the mean annual natural flow of the river. The basin has more than 80 canals, 5 diversion dams, and 15 major return flows. Nearly 45 percent of the water diverted for irrigation is eventually returned as both surface and ground-water, at varying time-lags, to the river system. During the low-flow period, these return-flows account for about 75 percent of the water in the lower river system.

The headwater drainages are the sources of water, and the major water uses occur downstream in the drier parts of the basin. Thus, the variability in topography, climate, and water use creates long distances between the supply and demand areas, which in turn, results in spatial and temporal contrasts in the quantity and quality of streamflow.

Water Issues

Issues of many western states are common to the basin. These issues include Indian treaty rights, historical water rights, over-appropriation of water, reservoir and irrigation development, increasing demand for wildlife and anadromous and resident fish, water-quality of the streams and ground-water, and the interaction of ground-water and streamflow.  Mnay of these issues are compounded because all new demands are being met by ground-water sources. Judicial law also affects the water-management in the basin, and will continue to do so.

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