TheColumbia River drainage basin is thedrainage basin of theColumbia River in thePacific Northwest region ofNorth America. It covers 668,000 km2 or 258,000 sq mi.[1] In common usage, the term often refers toa smaller area, generally the portion of the drainage basin that lies withineastern Washington.[1]
Usage of the term "Columbia Basin" inBritish Columbia generally refers only to the immediate basins of the Columbia andKootenay Rivers and excludes that of theOkanagan,Kettle andSimilkameen Rivers.
The Columbia Basin includes the southeastern portion of theCanadian province ofBritish Columbia, most of theU.S. states ofIdaho,Oregon, andWashington, the western part ofMontana, and very small portions ofNevada,Utah, andWyoming. The south and southeastern drainagedivide borders the interior drainage of the northernGreat Basin. To the northeast the region borders the basins of theSaskatchewan River (Hudson Bay) and theMackenzie River (Beaufort Sea), and to the northwest the basin of theFraser River. The Columbia Basin extends from theRocky Mountains in the east through theCascade Range to the Columbia River's outflow at thePacific Ocean in the west.
The Columbia River pours more water into the Pacific Ocean than any other river in North or South America. In its 1,270 miles (2,040 km) course to the Pacific Ocean, the Columbia flows through four mountain ranges—theRockies,Selkirks,Cascades, and coastal mountains—and drains 258,000 square miles (668,000 km2). The mainstem of the Columbia rises inColumbia Lake on the west slope of the Rocky Mountain Range in Canada. Its largest tributary, theSnake, travels 1,038 miles (1,670 km) from its source inYellowstone National Park in Wyoming before joining the Columbia.
Residents of the area surrounding the confluence of theColumbia andSnake rivers—a region centering on theTri-Cities, Washington metropolitan area—use the term "Columbia Basin" to refer to their own, much smaller region. This usage is roughly synonymous with theColumbia Plateau or roughly equivalent to the relatively unforested area bounded by theCascades,Blue,Wallowa, andRocky mountain ranges and theOkanagan Highland. This sense of the term Columbia Basin has expanded from its early focus on the land irrigated byGrand Coulee Dam and theColumbia Basin Project to include other irrigation districts such as theYakima andWalla Walla valleys.[2] The area includes valuable farmland that has excellent soil profile and underlying silty loess.[3] At its center is thePasco Basin, an area roughly double the size of, and fully containing, theHanford Site.[1]
Many major rivers that flow through Oregon are tributaries of the Columbia River, including the Umatilla River and John Day River in northeastern Oregon. The largest tributaries from the south are theDeschutes River inCentral Oregon, which provides much of the drainage on the eastern side of theCascade Range, and theWillamette River, which flows between theOregon Coast Range and theCascade Range. The Willamette accounts for 12 to 15 percent of the Columbia's flow, and the basin that contains two-thirds of Oregon's population, including the state capital,Salem, Oregon, and the state's largest city,Portland, Oregon which surrounds the Willamette's mouth at the Columbia.
WhenLewis and Clark explored the region in the early 19th century, huge numbers of fish (salmon) returned to spawn every year. "The multitudes of this fish are almost inconceivable," Clark wrote in the autumn of 1805. At that time, the Columbia and its tributaries provided 12,935 miles (20,817 km) of pristine river habitat.[4] In the early 20th century, the government and private interests began constructing dams on the tributaries of the Columbia River to provide water for irrigation or flood control.[5] The federaldams on the Columbia and Snake Rivers devastated salmon runs, inundated Columbia River Basin Tribes villages and burial grounds, and deprived tribal members of the ability to exercise traditional ways of life.[6]
