Willamette River
From Lane Co Oregon
The Willamette River is a tributary of the Columbia River, 187 miles (301 km) long,[4] in northwestern Oregon in the United States. Flowing northward between the Coastal Range and Cascade Range, the river and its tributaries form a basin called the Willamette Valley containing 68% of Oregon's population, including its largest city Portland, which sits along both sides of the river near its mouth on the Columbia. Its lush valley is fed by prolific rainfall on the western side of the Cascades, forming one of the most fertile agricultural regions of North America that was the destination for many if not most of the emigrants along the Oregon Trail. The river was an important transportation route throughout much of the early history of the state, furnishing a means of conveying the vast timber and agricultural resources of the state to the outside world.
Part of the river's floodplain (the Willamette Floodplain) was established as a National Natural Landmark in 1987; ten years later the river was named as one of ten national American Heritage Rivers.
The Willamette rises in three separate forks in the mountains south and southeast of Eugene, at the southern end of the Willamette Valley. The Middle Fork and North Fork rise on the western side of the Cascades between Three Sisters south to Diamond Peak, with the Middle Fork receiving the North Fork northwest of Oakridge and flowing northwest through the mountains to the southern end of the Willamette Valley. The Coast Fork rises in the lower mountains south of Cottage Grove, flowing north to join the Middle Fork 2 mi (3.2 km) southeast of Eugene.
From Eugene, the combined river flows NNW across the plain of the southern Willamette Valley to Corvallis, then follows a zigzag course past Albany and around the isolated hills in the central valley, passing west of downtown Salem. From Salem it flows north in a meandering course across the northwest plain of the valley, reaching the hills at Newberg, where it turns sharply ENE along the hills, passing through an opening in the hills at Oregon City, the location of the Willamette Falls and the head of navigation. From Oregon City it flows northwest, past Lake Oswego and Milwaukie on the south edge of Portland, then passing between east and west Portland, where it is spanned by a series of urban bridges. Downstream of downtown Portland it flows northwest through the industrial port area of Portland Harbor, then splitting into two channels around Sauvie Island, both of which hook around to enter the Columbia from the west, with the main channel entering on the north edge of Portland and the smaller Multnomah Channel entering approximately 15 mi (24 km) NNW at St. Helens.
The river's many tributaries drain the surrounding valley as well as portions of the Cascades and the Coastal Range. Downstream from the confluence of its forks, it is joined by McKenzie River on the north side of Eugene, and by the Long Tom River from the southwest approximately 10 mi (16 km) south of Corvallis. It is joined by the Marys from the west at Corvallis, and the Calapooia from the southeast 5 mi (8 km) northeast of Corvallis, and It is joined by the Santiam from the east and the Luckiamute from the west within 1 mi (1.6 km) of each other approximately 5 mi (8 km) north of Albany. It is joined by the Yamhill from the west at Dayton, by the Molalla from the southeast near Canby, by the Tualatin from the west at West Linn, and by the Clackamas from the southeast at Gladstone.
The river forms part of the boundary of the following counties: Benton, Linn, Polk, Marion, Yamhill and Clackamas. Tributaries of the Willamette River also drain some or all of Lane, Washington and Multnomah counties.
Although riverboats navigated the upstream part of the Willamette into the first decades of the 20th century, currently there is little commercial traffic on the river above the Willamette Falls. The Willamette Falls Locks allow boat traffic, primarily recreational vessels, around the falls. The river is crossed by three ferries along its route in the Willamette Valley. The three ferries are located (from south to north) at Buena Vista, Wheatland, and Canby. The only locks on the river are located at Oregon City. For information on canoeing and kayaking on the Willamette River, see "Canoe and Kayak Routes of Northwest Oregon," by Philip N. Jones.
The Willamette River is prone to periodic floods. Notable floods include events in 1861 (which destroyed Linn City, Oregon), 1899, 1964, and the Willamette Valley Flood of 1996.
The river below Willamette Falls is subject to semidiurnal tides caused by the Pacific Ocean, but also with the effects of dams on the Columbia River and Willamette river basin which are regulated for hydroelectric power generation. Reverse flow has been observed as far upstream as Ross Island (river mile 15).
The lower river flow rate varies considerably by season and due to weather. Warm winter rains, for example, cause extensive mountain snow melt which significantly raises the river level and flow rate. The Willamette Valley Flood of 1996 was an extreme combination of saturated ground, snow melt and heavy rain: The maximum flow rate is not known, however 283,000 cubic feet per second (8010 m³/s) was estimated on January 18, 1974 at river gage 23.84 feet (7.27 m). The peak river gage on February 9, 1996 was 27.74 feet (8.46 m). Flood stage is 18.0 feet (5.5 m). The other extreme occurred during a drought on July 10, 1978 at 4,200 ft³/s (120 m³/s).[3] The Willamette's mean discharge rate is approximately 32,000 cubic feet per second.
