As explained in Chapter 2, there are many large dams (storage and run-of-the-river) and reservoirs along the river that compose the Federal Columbia River Power System (FCRPS). The Columbia River dams in Washington State are owned and operated by federal entities and by state public utility districts. Their daily operations are designed to meet the needs of many sectors, the most important being flood control, hydroelectric power generation, and instream flows. Like most regions of the western United States, irrigated agriculture is the largest consumptive water user in the region. Irrigated agriculture along the Columbia River in the State of Washington consists of one very large withdrawal—the Columbia Basin Project—and a large number of small (relative to the Columbia’s flows) withdrawals by individual irrigators. These structures and uses have affected stream flows, water quality, and water temperature. This chapter examines twentieth-century changes in Columbia basin hydrology and the annual hydrograph, the current and prospective future picture of water withdrawals (this study’s primary focus), water quality, and changes in water temperature and related prospective future changes in basin climate.1

This study focuses on the implications of water withdrawals from the mainstem Columbia River for salmon survival. An analysis of the relative impacts of mainstem surface and groundwater withdrawals in comparison to the hydrological impacts of Columbia River dam and reservoir construction and operations was beyond the scope of this study. This report focuses on mainstem water withdrawals because this topic was central to the committee’s Statement of Tasks, not because of the relative


This chapter includes several figures and tables containing hydrologic information. Some of those data are expressed in cubic feet per second (cfs) and some of the data are expressed in acre-feet per year (AF/yr.). This report does not present all hydrologic data in a single unit because both units (cfs and AF/yr) are traditionally and currently used by water managers, farmers, and scientists in different settings in Washington and across the western U.S. Furthermore, cfs represents a rate, while acre-feet represents a volumetric measure. For comparative purposes, however, 1 cubic foot/second of water equates to slightly less than 2 acre-feet/day—or roughly 724 acre-feet/year.

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