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Scientific Investigations Report 2007–5186

Scientific Investigations Report 2007–5186

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Description of Columbia River and Puget Sound Basins

Columbia River Basin

The Columbia River and its tributaries form the dominant water system in the Pacific Northwest (fig. 1). The main stem of the Columbia rises in Columbia Lake (not shown in fig. 1) on the west slope of the Rocky Mountains in Canada. After winding 1,942 km, of which 664 km are in Canada, the Columbia River flows into the Pacific Ocean near Astoria, Oregon. The river drains an area of about 567,000 km2 in Washington, Oregon, Idaho, Montana, Wyoming, Nevada, and Utah (fig. 1). An additional 99,700 km2 of the basin is in Canada.

Geographically, the Columbia River Basin borders the Rocky Mountains to the east and north, the Coast Range on the west and southwest, and the Great Basin to the southeast. The Columbia River flows through the basin from Canada’s Rocky Mountains and ultimately becomes the border between Oregon and Washington. Along the way, several major tributaries feed into the Columbia. The three largest basins are the Snake River (267,000 km2), the Clark Fork-Pend Oreille River (64,700 km2), and the Kootenai River (46,600 km2). Other contributing basins include the Willamette River (29,000 km2), the Yakima River (16,100 km2), the Payette River (8,390 km2), and the Cowlitz River (6,220 km2) (Foundation for Water and Energy Education, 2000).

The hydrologic cycle of the Columbia River reflects a unique relation between water flow and topography in the basin. In the United States, only the Missouri-Mississippi River system has annual runoff greater than that of the Columbia River. Precipitation, sunlight, and air temperature in the basin can vary from one year to the next and largely determine how much water the river will carry from year to year. West of the Cascade Mountains, precipitation falls largely as rain during the winter months, whereas in the Cascade Range and eastward, winter precipitation is mostly snow. Deep snow in the mountains eventually is released to the river during early to mid-spring. About 30 percent of the streamflow in the Columbia River occurs between January and March (primarily from rainfall) and about 30 percent occurs between April and June (from a combination of rainfall and melting snow). These values are based on the record of daily mean discharge for the Columbia River near the mouth at Beaver Army Terminal (fig. 2).

The population of the Columbia River Basin in the United States is about 4.6 million people (2000 census); this number is more than 20 percent greater than that recorded during the 1990 census, indicating that substantial growth is occurring in parts of the basin (U.S. Census Bureau, 2001). Land use of the basin in the United States is predominately forested (87 percent), with urban and agricultural land use comprising the remaining 2 and 11 percent of the basin, respectively. Land cover percentages are based on the enhanced National Land Cover Dataset (1992), further revised with 2000 population density by block group to indicate recent (2000) urban development (U.S. Geological Survey, 2006).

The two priorities for management of the Columbia River dam system historically have been hydroelectric power generation and flood control. Hydroelectric generation projects on the Columbia River provide upwards of 50 percent of the Pacific Northwest Region’s electrical power needs (Bonneville Power Administration, 2005). Other uses, such as irrigation, navigation, and recreation, are largely carried out in the context of meeting the two main priorities. Enforcement of Federal environmental laws related to endangered fish species also have resulted in the National Marine Fisheries Service’s indicating that anadromous fish recovery should receive priority over all river uses except flood control (Foundation for Water and Energy Education, 2000).

Puget Sound Basin

The Puget Sound Basin is a 13,500 km2 area located mostly in western Washington, but also encompasses parts of British Columbia (fig. 1). The area consists mostly of mountains and coastal lowlands. In all, 12 major and numerous minor tributaries drain to the Puget Sound and adjoining waters. The streams and rivers in the basin drain three physiographic providences (1) the Olympic Mountains in the west, (2) the Cascade Range in the east, and (3) centrally, the Puget Lowlands (Ebbert and others, 2000). About 70 percent of the population in Washington (4 million people) resides in the Puget Sound Basin, primarily in the metropolitan areas of Seattle, Tacoma, Everett, Bellingham, and Olympia. The population is expected to increase by 1.1 million by the year 2020 (Staubitz, 1994).

The Puget Sound has a Pacific Coast marine climate characterized by wet, cool winters and dry, warm summers. Annual precipitation can vary from 16 to 53 in/yr in the lowland areas to upwards of 60 to 200 in/yr in the mountains (Staubitz, 1994). Streams with headwaters in the mountains generally have the highest monthly flows in December and January, typically associated with winter rains, and in May and June as a result of spring snowmelt. Streams originating in the lowlands typically have the highest flows in January and February. The land use of the basin is predominately forested (75 percent), with urban and agricultural land use encompassing 11 and 6 percent, respectively. The remaining land is covered by lakes, reservoirs, glaciers, and shorelands. Historically, roughly 56 percent of the 810 Mgal/d of water used in the basin has been supplied by surface water and the rest from ground water (Staubitz, 1994). Excluding water used for hydroelectric power generation, 41 percent of the water was used for domestic purposes in 1995, with irrigation, industry, commerce, and livestock using the remaining 11, 30, 9, and 1 percent of the water, respectively (Ebbert and others, 2000).

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