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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 drainage basin,〔(Lower Columbia Tributaries ), Northwest Power and Conservation Council〕〔( Toutle Management Plan ), Northwest Power and Conservation Council〕 located between the Cascade Range in eastern Lewis County, Washington and the cities of Kelso and Longview. The river is roughly long, not counting tributaries. Major tributaries of the Cowlitz River include the Cispus River and the Toutle River, which was overtaken by volcanic mudflows (lahars) during the May 1980 eruption of Mount St. Helens. ==Dams== The Cowlitz River currently has 3 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 that was constructed in the early 1990s and completed in 1994. The dam is high and wide. The Cowlitz Falls Project produces on average 260 gigawatthours 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 from bedrock and created long Riffe Lake (previously Davisson Reservoir). It is the highest dam in the Pacific Northwest.〔(Cowlitz River Project ), Tacoma Power〕 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 long and high. An tunnel connects the reservoir to the powerhouse. The dam began producing electricity in 1963. Mayfield Lake offers many recreational opportunities due to the presence of several county and state parks and its location 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). As an ancient landslide used to, the dam supplanted the job of holding back the lake, redirecting streamflow to a 27 megawatt hydroelectric generator in the Cowlitz River valley floor 2,000 feet (300 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 that calls the lake and surrounding area home; the dam raising 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「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 drainage basin,(Lower Columbia Tributaries ), Northwest Power and Conservation Council( Toutle Management Plan ), Northwest Power and Conservation Council located between the Cascade Range in eastern Lewis County, Washington and the cities of Kelso and Longview. The river is roughly long, not counting tributaries. Major tributaries of the Cowlitz River include the Cispus River and the Toutle River, which was overtaken by volcanic mudflows (lahars) during the May 1980 eruption of Mount St. Helens.==Dams==The Cowlitz River currently has 3 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 that was constructed in the early 1990s and completed in 1994. The dam is high and wide. The Cowlitz Falls Project produces on average 260 gigawatthours 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 from bedrock and created long Riffe Lake (previously Davisson Reservoir). It is the highest dam in the Pacific Northwest.(Cowlitz River Project ), Tacoma Power 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 long and high. An tunnel connects the reservoir to the powerhouse. The dam began producing electricity in 1963. Mayfield Lake offers many recreational opportunities due to the presence of several county and state parks and its location 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). As an ancient landslide used to, the dam supplanted the job of holding back the lake, redirecting streamflow to a 27 megawatt hydroelectric generator in the Cowlitz River valley floor 2,000 feet (300 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 that calls the lake and surrounding area home; the dam raising 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.」の詳細全文を読む スポンサード リンク
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