| Cowlitz River |
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The Cowlitz has a 2,480 sq mi (4,017.6 km²) 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 (170 km) in total length, not counting tributaries. Major tributaries of the Cowlitz River include the Toutle River , which was overtaken by volcanic mudflows ( Lahar s) during the May 1980 eruption of Mount St. Helens (see 1980 Mount St. Helens Eruption ). 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 1990’s and completed in 1994. The dam is 140 feet high and 700 feet 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 605 feet from bedrock and created 23-mile 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, 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 long and 185 feet high. An 860-foot 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). The dam has taken over the job of holding back the lake from an ancient landslide and redirects streamflow to a 27 Megawatt hydroelectric generator in the Cowlitz River valley floor 2000 feet (300 meters) below just outside the town of Packwood . Great care was used when designing and building the dam 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 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 destroy the Columbia River shipping channel, which still requires period dredging. An overflow channel has been added to divert Lahar s around the dam. OTHER RIVER STRUCTURES When the Cowlitz Salmon Hatchery began operation in 1968, it was the largest salmon hatchery in the world. Currently, it produces nearly 13 million fish each year. Adjacent to the salmon hatchery is the barrier dam, which diverts spawning and upriver migrating fish to a separating station where fish are sorted by species. Some of the fish are used by the hatchery while others are transported upstream to continue migration. The Bonneville Power Administration , in cooperation with the Lewis County PUD, state and federal agencies and Tacoma Power, constructed a downstream anadromous fish collection facility as part of the Cowlitz Falls Project. The fish facility, along with the Cowlitz River Salmon Hatchery's diversion dam below Mayfield Lake, has permitted the reintroduction of salmon and steelhead in the upper Cowlitz River basin for the first time since the construction of the Mossyrock and Mayfield Dams in the 1960’s. With an arch span of 520 feet, the Cowlitz River Bridge on Highway 12 just east of Mossyrock was the largest concrete arch bridge in North America until 1971. EXTERNAL LINKS
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