The Columbia-Snake River Basin

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The map of the Columbia River Basin and text description of the basin are taken from "Columbia River and Tributaries Review Study: Project Data and Operating Limits", US Army Corps of Engineers, North Pacific Division, CRT 69, July 1989. Both the map and text have been slightly modified from the original source.

Drainage Basin

The Columbia River and its tributaries form the dominant water system in the Pacific Northwest Region. The mainstem of the Columbia rises in Columbia Lake on the west slope of the Rocky Mountain Range in Canada. After flowing a circuitous path for about 1200 miles, 415 miles of which are in Canada, it joins the Pacific Ocean near Astoria, Oregon. The river drains an area of approximately 219,000 square miles in the States of Washington, Oregon, Idaho, Montana, Wyoming, Nevada, and Utah. An additional 39,500 square mile portion of the basin, or about 15%, is within Canada.

The Columbia River Basin is bounded principally by the Rocky Mountain system on the east and north, the Cascade Range on the west, and the Great Basin on the south. The basin area includes 3,000 square miles of waterways and lakes, of which 2,500 miles are within the United States.

To the west of the Cascade Range, the Columbia River is joined by the Willamette drainage and begins a transition to the ocean tidal reaches. Salt water intrusion into the Columbia River estuary reaches about 23 miles upstream from the mouth. The effects of tides upon the flow rate and level of the river are felt up to Bonneville Dam, river mile 146.1. Ocean influences also dominate weather patterns along the western slope of the Cascade Range as the majority of precipitation in the western portion is in the form of rainfall during the winter months.

Water Resources

Most of the annual precipitation of the Columbia River Basin is concentrated in the winter months with the bulk of the precipitation falling in mountainous areas as snow to be stored in deep snowpacks awaiting the warmth of spring for its release. As a result, winter streamflows are generally low with high sustained runoff flows occurring in the spring and early summer. This runoff pattern of the Columbia River exemplifies a major seasonal maldistribution of flow with about 60 percent of the natural runoff of the Columbia occurring during the months of May, June, and July. The Columbia has an average annual runoff at the mouth of about 198,000,000 acre-feet (275,000 cfs) making it second only to the Missouri-Mississippi River System in the United States (611,000 cfs) in average annual runoff. The Canadian portion of the basin generally contributes about 50,200,000 acre-feet annually, or about 25 percent of the basin total.

Columbia River System Uses

The Columbia River is a very complex and heavily utilized resource. No other single resource in the Pacific Northwest influences the character and way of life of people in the region as much as the Columbia River and its major tributaries. The Pacific Northwest is dependent to a large extent upon the Columbia River for its power, food and fiber through irrigation, transportation through navigation, recreation, fisheries, and to a lesser extent, municipal and industrial water supply.

Development of dams and storage reservoirs within the Columbia River Basin has taken place to meet the often competing needs and uses of the Columbia River and its major tributaries. How these various projects are operated determines the extent to which certain river uses can be met.

E-mail your comments and questions to: Nancy Yun (
File TMT/basin.html Last Modified 02/27/97