The 1985 Long-Term Plan recognized that additional actions would be needed in the future to maintain the authorized levels of flood risk reduction. The Corps is currently evaluating how to best manage sediment to provide authorized levels of flood risk reduction through the year 2035, in a manner that does not jeopardize the continued existence of any endangered or threatened species or result in the destruction or adverse modification of designated critical habitat.
USACE has conducted a limited re-evaluation of sediment management in the North Fork Toutle River and is proposing to implement updated sediment management measures to manage flood risk to established levels for the Washington cities of Castle Rock, Lexington, Kelso, and Longview through the year 2035. In addition to a No Action alternative, three sediment management alternatives were identified and evaluated that would address the flood risks associated with sediment build up through 2035. They are:
• Cowlitz River dredging only
• SRS spillway and embankment raise
• A phased construction plan (preferred alternative) consisting of:
o SRS spillway crest raises
o Grade-building structures
o Dredging, as needed
The FSEIS also includes an evaluation of the fish conservation measures that were developed to ensure the proposed sediment management plan will not jeopardize the continued existence of any endangered or threatened species or adversely modify or destroy the species’ designated critical habitat. Fish conservation measures evaluated include:
• Replace the fish collection facility on the North Fork Toutle River operated and maintained by the Washington Department of Fish Wildlife (WDFW) and establish a fish release site on Deer Creek
• Modify the fish collection facility on the North Fork Toutle River and establish a fish release site on Deer Creek
Environmental impacts of the no action, sediment management alternatives and fish conservation measures are evaluated in the FSEIS.
The Corps’ preferred alternative for managing sediment and flood risk includes phased construction of spillway crest raises at the SRS; grade building structures on the sediment plain upstream from the SRS; and, dredging as needed to maintain the authorized levels of protection. The Corps’ preferred alternative for improving fish passage includes modify the existing FCF and constructing one additional fish release site.