page_title: Cowlitz River
section_title: Dams
hierarchical_section_title: Cowlitz River / Dams
caption_attribution_description: English: A dam on the North Fork of the Toutle River in Cowlitz County, Washington, USA. This dam was constructed 1986–1989 by the U.S. Army Corps of Engineers to retain some of the sediment in the Toutle River flowing down from the slopes of Mt. St. Helens. The Corps calls this dam a Sediment Retention Structure. The dam is approximately 22 miles upriver from the town of Castle Rock, Washington. Français&#160;: Barrage de rétention des sédiments sur l'embranchement nord la rivière Toutle (Cowlitz County, Washington, USA). Ce barrage a été construit de 1986 à 1989 par le corps des ingénieurs de l'armée (US Army Corps of Engineers) pour stocker la partie la plus lourde des sédiments dans la rivière Toutle dévalent des pentes du bassin versant du Mont St. Helens. Le barrage est d'environ 22 miles en amont de la ville de Castle Rock, Washington.
context_page_description: The Cowlitz River is a river in the state of Washington in the United States, a tributary of the Columbia River. Its tributaries drain a large region including the slopes of Mount Rainier, Mount Adams, and Mount St. Helens.
  The Cowlitz has a 2,586-square-mile drainage basin, located between the Cascade Range in eastern Lewis County, Washington and the cities of Kelso and Longview. The river is roughly 105 miles long, not counting tributaries.
  Major tributaries of the Cowlitz River include the Cispus River and the Toutle River, which was overtaken by volcanic mudflows during the May 1980 eruption of Mount St. Helens.
  When the smelt spawn in the Cowlitz River, the gulls go into a feeding frenzy that lasts for weeks. Kelso, Washington is known as the "Smelt Capital of the World".
context_section_description: The Cowlitz River has three major hydroelectric dams, with several small-scale hydropower and sediment retention structures within the Cowlitz Basin.
  The Cowlitz Falls Project is a 70 megawatt hydroelectric dam built in the early 1990s and completed in 1994. The dam is 140 feet (43 m) high and 700 feet (210 m) wide. The Cowlitz Falls Project produces on average 260 GWh annually for Lewis County PUD. Its reservoir, Lake Scanewa, is located at the confluence of the Cowlitz and Cispus Rivers downstream of Randle.
  Mossyrock Dam began generating power for Tacoma City Light in 1968. It rises 605 feet (184 m) from bedrock and created the 23-mile (37 km) long Riffe Lake (previously Davisson Reservoir). It is the highest dam in the Pacific Northwest. The dam is named for the nearby city of Mossyrock, and the lake for the town of Riffe, which, along with Kosmos, was destroyed by the flooding of the Cowlitz River valley above the dam.
  The Mayfield Dam is 850 feet (260 m) long and 185 feet (56 m) high. An 860-foot (260 m) tunnel connects the reservoir to the powerhouse. The dam began producing electricity in 1963. Mayfield Lake offers many recreational opportunities: there are several county and state parks and the lake is below the Mossyrock Dam. The modulated inflow from the Mossyrock Dam allows Mayfield Lake to maintain a water level that rarely fluctuates more than a few feet. It is located several miles downstream of Mossyrock.
  Packwood Lake was dammed in 1964 by the Washington Public Power Supply System (now called Energy Northwest). The dam holds back the lake (previously held back by an ancient landslide), redirecting streamflow to a 27 megawatt hydroelectric generator in the Cowlitz River valley floor 2,000 feet (600 m) below just outside the town of Packwood. When designing and building the dam, care was taken so as not to affect the abundant wildlife of the lake and surrounding area: the dam raised the water level by only a few feet.
  A serious side effect of the Mount St. Helens 1980 eruption has been the downstream movement of enormous amounts of sediment through the North Fork Toutle River. After the eruption, river-borne sediment increased over five thousand-fold, making the Toutle River one of the most sediment-laden rivers in the world. The Toutle River Sediment Retention Structure was constructed to trap this sediment before it was carried farther downstream, where it could clog the river channel, exacerbate floods along the lower Toutle and Cowlitz Rivers, and fill the Columbia River shipping channel, which still requires periodic dredging. An overflow channel has been added to divert lahars around the dam.
caption: The sediment retention structure on the North Fork of the Toutle River. The dam is approximately 22 miles (35 km) upriver from the confluence of the Toutle and the Cowlitz.
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