Mount St. Helens Ecosystem Restoration General Reevaluation Study Reconnaissance Report
ARMY ENGINEER DISTRICT PORTLAND OR
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The purpose of the General Reevaluation Study Reconnaissance study is to determine if there is a federal interest in pursuing ecosystem restoration actions in the Toutle River watershed, while maintaining Congressionally authorized levels of flood protection for communities along the Lower Cowlitz River. The Toutle River watershed encompasses about 512 square miles primarily in Cowlitz County, Washington. The Toutle River drains the north and west sides of Mount St. Helens and flows generally westward towards the Cowlitz River. The three primary drainages in the watershed include the North Fork Toutle River, South Fork Toutle River, and Green River. Most of the North and South Forks were impacted severely by the 1980 eruption of Mount St. Helens and the resulting massive debris torrents and mudflows. A sediment retention structure SRS was constructed on the North Fork Toutle River 5 years following the 1980 Mount St. Helens eruption in an attempt to prevent the continuation of severe downstream sedimentation of stream channels, which created flood conveyance, transportation, and habitat degradation concerns. The SRS totally blocked volitional upstream access to as many as 50 miles of habitat for anadromous fish. To mitigate for this effect to these fish, the U.S. Army Corps of Engineers funded habitat enhancements development of off channel rearing areas, hatchery supplementation at Green River Hatchery, and construction of a fish collection facility FCF below the SRS to trap and haul salmonids to tributaries above the SRS. The Toutle River system historically supported populations of several salmonid species that are currently listed as threatened under the Endangered Species Act including winter steelhead Oncorhynchus mykiss, coho salmon Oncorhynchus kisutch, spring and fall Chinook salmon Oncorhynchus tshawytscha, and chum salmon Oncorhynchus keta. The North Fork Toutle historically provided productive habitat for these species.
- Hydrology, Limnology and Potamology
- Civil Engineering
- Environmental Health and Safety