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~ US Army Corps Mount St. Helens of Engineers• Long-Term Sediment Portland District Management Plan Record of Decision September 2018 Sediment retention structure and upstream sediment plain on the North Fork Toutle River U.S. Army Corps of Engineers photo RECORD OF DECISION MOUNT ST. HELENS, WASHINGTON LONG-TERM SEDIMENT MANAGEMENT PLAN The Mount St. Helens Limited Re-Evaluation Report (LRR) and Supplemental Environmental Impact Statement (SEIS), both dated 2018, address long-term sediment management actions necessary to maintain flood risk reduction for the cities of Castle Rock, Lexington, Kelso, and Longview, Washington. The purpose of the proposed action is to manage flood risk to established levels of protection (LOP) for the cities of Castle Rock, Lexington, Kelso and Longview, Washington through the year 2035, as authorized by Public Law No. 99‐88 (1985) and Section 339 of the Water Resources Development Act of 2000 (Public Law No. 106- 541), and to do so in a manner that does not jeopardize the continued existence of any endangered species or threatened species or result in the destruction or adverse modification of designated critical habitat. The recommended plan and preferred alternative described in the LRR and SEIS represent a complete and complementary effort that maintains the congressionally-authorized LOP. The recommend plan is contained in the LRR and is the preferred alternative identified in the SEIS. The 2018 LRR and SEIS are incorporated herein by reference. Based on these reports, the reviews of other Federal, State, and local agencies, Tribes, input from the public, and review by my staff, I find the plan recommended by the Commander, Portland District, to be technically feasible, economically justified, in accordance with environmental statutes, and in the public interest. The recommended plan includes: Phased Construction of sediment management measures o Up to two incremental raises of the sediment retention structure (SRS) spillway crest elevation (totaling up to 23 feet to a total elevation of 970 feet (NGVD29) without raising the top of dam elevation; o Constructing grade-building structures (GBS) in the sediment plain upstream of the SRS; and, o Conducting as-needed dredging in the lower Cowlitz River. Modify Fish Collection Facility o Modifying the Fish Collection Facility (FCF) in partnership with the State of Washington; o Establishing a new fish release site at a location to be determined on Deer Creek. Each phase of sediment management measures would be implemented as needed, based on the results of annual monitoring. The recommended plan includes adaptive management to ensure sediment deposition upstream from the SRS does not eliminate hydrologic connectivity between Alder Creek and the NF Toutle River; and, as recommended by the U. S. Fish and Wildlife Service (USFWS) conservation measures to avoid impacts to ESA-listed streaked horned lark and Nelson’s checker-mallow. The Mount St. Helens, Washington Feasibility Report and Environmental Impact Statement (FR/EIS), dated 1984, evaluated sediment management alternatives and environmental impacts to provide authorized levels of flood risk reduction through the year 2035 for the cities of Castle 1 Rock, Lexington, Kelso, and Longview, Washington. The FR/EIS resulted in the Mount St. Helens, Washington, Decision Document, Toutle, Cowlitz, and Columbia Rivers, dated October 1985. The 1985 Decision Document identified the final sediment management strategies and a recommended plan to maintain LOP. A major component of the 1985 Decision Document was the construction of the SRS at river mile 13 on the North Fork (NF) Toutle River. The purpose of the SRS is to retain sediment upstream of the SRS, thereby reducing downstream transport and deposition of sediment. Other features of the 1985 Decision Document included levee improvements on the lower 20 miles of the Cowlitz River, as-needed dredging within the lower Cowlitz River to further mitigate flood risk for communities on the lower Cowlitz River, and construction of an adult FCF to be operated and maintained by the State of Washington. Initial construction of project features, including construction of the SRS, was completed in 1989, and implementation of the selected plan has been ongoing since that time. Interim management actions include improvements to the Castle Rock levee, a 7-foot raise of the SRS spillway crest, and as-needed dredging of the Cowlitz River. U.S. Army Corps of Engineers (USACE) documented further reviews of LOP in subsequent reports, including the Mount St. Helens Project, Cowlitz River Levee Projects—Level of Protection and Sedimentation Update, dated 2006; the Mount St. Helens Ecosystem Restoration, General Reevaluation Study Reconnaissance Report, dated 2007; the Mount St. Helens Project, Cowlitz River Levees Safe Water Level Study, dated 2010; and the Mount St. Helens Project Cowlitz River Levee Systems, 2009 Level of Flood Protection Update Summary, dated 2010. The 1985 Decision Document adopted by USACE recognized the likely need for a future reevaluation of sediment management based on changes in future conditions. In 2010, USACE initiated a reevaluation of sediment conditions and potential sediment management alternatives through the year 2035, as envisioned in the 1985 Decision Document. The sediment management plan reassessment resulted in the development of plans and studies, including: MSH Long-Term Sediment Management Plan for Flood Risk Reduction Progress Report, dated 2010, Mount St. Helens Future Expected Deposition Scenario, dated 2011, and SRS Raise Final Environmental Assessment, dated 2012. The LRR and the SEIS builds on information from these baseline and planning documents. The SEIS provides an update to the 1984 EIS and 1985 Decision Document by comparing the current conditions and projected on-going effects of the USACE’s sediment management activities to what was documented in the 1984 EIS. The SEIS also evaluates the potential environmental impacts from a range of long-term sediment management alternatives as a supplement to 1984 EIS and 1985 Decision Document. The draft SEIS dated 2014, documented a proposed sediment management strategy; the draft SEIS was revised in 2017 to include measures to avoid causing jeopardy to endangered species or threatened species or result in the destruction or adverse modification of designated critical habitat, in accordance with a Biological Opinion provided by the National Marine Fisheries Service (NMFS) in 2017. Alternatives evaluated in the SEIS include a no action alternative and three sediment management alternatives—Dredging Only, SRS Raise, and Phased Construction (preferred alternative). The sediment management alternatives evaluated in the SEIS would maintain the authorized LOP and are consistent with the range of out-year management options described in the 1985 Decision Document. The differences among the sediment management alternatives 2 are related to the scope and timing of modifications to the SRS and/or the extent to which dredging is relied upon. The Dredging Only Alternative essentially reflects continued implementation of the existing management direction. Additionally, fish conservation measures are evaluated in the SEIS, including replace the FCF, modify the FCF, and establishment of a new fish release site in a tributary of the upper NF Toutle River, upstream of the SRS. These measures were included to address the NMFS 2017 Biological Opinion. The selected sediment management alternative is the Phased Construction Alternative, which is the identified preferred alternative in the SEIS and is the recommended plan. As compared to the other sediment management alternatives—the Dredging Only and SRS Raise Alternatives—the Phased Construction Alternative would have the lowest overall cost, both in terms of present value and average annual cost. Additionally, the recommended plan is the most adaptable to changing conditions. The recommended plan is the environmentally preferred alternative. Modifying the FCF and establishing a new fish release site in a tributary of the upper NF Toutle River are the fish conservation measures that have been selected for implementation in concert with the recommended plan. USACE has selected the Modify FCF measure because it is cost effective and has a high probability of successfully ensuring the sediment management action does not jeopardize the continued existence of any endangered or threatened species or result in the destruction or adverse modification of the species' designated critical habitat. In comparison to the replacement of the FCF, modification of the existing FCF is least costly and is would have fewer environmental impacts, as it would result in less disturbance to upland areas and would involve less in-water work. Environmental effects were analyzed in the 1984 FR/EIS and mitigation was identified in the 1985 Decision Document. The 1985 Decision Document explained USACE’s approach to providing mitigation for fish and wildlife resources anticipated to be affected by the SRS preferred alternative. This approach primarily focused on maintaining upstream fish passage. The 1985 Congressional authorization of the SRS authorized USACE to construct the FCF, subject to the provision that non-Federal interests (e.g., the State of Washington) operate and maintain any federally undertaken mitigation project, including the FCF. To mitigate the loss of upstream fish passage, USACE constructed the FCF. This mitigation commitment was identified in the

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