Willamette River - Watershed

Watershed

The Willamette River drains a region of 11,478 square miles (29,730 km2), which is 12 percent of the total area of Oregon. Bounded by the Coast Range to the west and the Cascade Range to the east, the river basin is about 180 miles (290 km) long and 100 miles (160 km) wide. Elevations within the watershed range from 10,495 feet (3,199 m) at Mount Jefferson in the Cascade Range to 10 feet (3.0 m) at the mouth on the Columbia River. Watersheds bordering the Willamette River basin are those of the Little Deschutes River to the southeast, the Deschutes River to the east, and the Sandy River to the northeast; the North Umpqua and Umpqua rivers to the south; coastal rivers including (from south to north) the Siuslaw, the Alsea, the Yaquina, the Siletz, the Nestucca, the Trask, and the Wilson to the west; the Nehalem and the Clatskanie to the northwest, and the Columbia River to the north.

About 2.5 million people lived in the Willamette River basin as of 2010, about 65 percent of the population of Oregon. As of 2009, the basin contained 20 of the 25 most populous cities in Oregon. These cities include Springfield, Eugene, Corvallis, Albany, Salem, Keizer, Newberg, Oregon City, West Linn, Milwaukie, Lake Oswego, and Portland. The largest is Portland, with more than 500,000 residents. Other cities in the watershed (but not on the main-stem river) with populations of 20,000 or more are Gresham, Hillsboro, Beaverton, Tigard, McMinnville, Tualatin, Woodburn, and Forest Grove.

Sixty-four percent of the watershed is privately owned, while 36 percent is publicly owned. The U.S. Forest Service manages 30 percent of the watershed, the U.S. Bureau of Land Management 5 percent, and the State of Oregon 1 percent. Sixty-eight percent of the watershed is forested; agriculture, concentrated in the Willamette Valley, makes up 19 percent, and urban areas cover 5 percent. More than 81,000 miles (130,000 km) of roads criss-cross the watershed.

In 1987, the U.S. Secretary of the Interior designated 713 acres (289 ha) of the watershed in Benton County as a National Natural Landmark. This area is the Willamette Floodplain, the largest remaining unplowed native grassland in the North Pacific geologic province, which encompasses most of the Pacific Northwest coast.