The Corps of Engineers is developing a long-term sediment management plan designed to manage the amount of sediment depositing in the lower Cowlitz River. The purpose of the Mount St. Helens Sediment Retention Structure and associated features is to maintain flood risk protection at specified levels for the cities of Castle Rock, Lexington, Kelso and Longview, Wash.
The national Environmental Policy Act of 1970 established procedures for federal agencies to document their environmental impact analysis for proposed activities, such as long-term management planning for existing structures (40 Code of Federal Regulations 1500-1508). The existing NEPA document for the Mount St. Helens SRS was published in December 1984 (Final Mount St. Helens, Washington Feasibility Report & Environmental Impact Statement, Toutle, Cowlitz and Columbia Rivers).
The Corps has started drafting a Supplemental Environmental Impact Statement to address environmental changes that have occurred since the original EIS was published. In order to update the original EIS, the SEIS will incorporate changes to the affected environment that have occurred over the past 30 years. The SEIS will also analyze potential impacts from four proposed long-term management alternatives not previously discussed.