Public Notices

Record of Decision: Mount St. Helens long-term sediment management plan

Published April 19, 2019


Cowlitz County, Washington

Issue Date: April 17, 2019

The U.S. Army Corps of Engineers (USACE), Portland District, is providing notice that the Record of Decision for the Mount St. Helens Long-Term Sediment Management Plan was signed on September 26, 2018. USACE is the lead agency under the National Environmental Policy Act of 1969 (NEPA), 42 U.S.C. §§ 4321–4347.  

A Draft Supplemental Environmental Impact Statement (DSEIS) was issued in October 2014. Following the completion of the public comment period for the DSEIS, USACE engaged in consultation with the National Marine Fisheries Service (NMFS) as required by the Endangered Species Act (ESA). This consultation resulted in the need to develop measures to ensure the sediment management plan would not jeopardize listed species or adversely modify or destroy the species’ critical habitat.  In September 2017, USACE published for public comment a revised DSEIS to give the public and interested stakeholders an opportunity to comment on changes to the SEIS and on the fish conservation measures. The public comment period was from September 15, 2017 to November 6, 2017. A final SEIS was published for a 30-day public review period that concluded on September 10, 2018.  

Background: The eruption of Mount St. Helens in the spring of 1980 caused approximately three billion cubic yards of sediment and debris to deposit in surrounding watersheds, creating an ongoing threat of flooding to a population of 50,000 people in downstream communities. In 1984, USACE issued an EIS which evaluated alternatives in managing sediment flowing downstream from the debris avalanche to avoid flooding in the Cowlitz River and disruption of navigation on the Columbia River caused by sediment buildup. The 1985 Mount St. Helens Sediment Management Decision Document included construction of a sediment retention structure (SRS), levee improvements and dredging, as well as construction of a Fish Collection Facility (FCF) and associated fish release sites. The 1985 Decision Document recognized the likely need for a future re-evaluation of the long-term sediment management measures based on changes in future conditions. The SRS was completed in 1989. Since the SRS began operating as a run-of-the-river structure in 1998, increased sediment from the North Fork Toutle River basin is being transported downstream and accumulating in the lower Cowlitz River.  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 (continued management direction from 1985 Decision Document)
  • SRS spillway and embankment raise
  • A phased construction plan (preferred alternative) consisting of:
    • SRS spillway crest raises
    • Grade-building structures
    • 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 were evaluated in the FSEIS.

The FSEIS includes information on the discharge of dredged or fill material that may occur during construction of the preferred alternative, as well as information on waters of the United States present within the project area and the impacts on those waters under Section 404 of the Clean Water Act (CWA). If dredging is necessary in the lower Cowlitz River, it would include dredging, dredged material placement and storage, and monitoring.  Mechanisms for potential effects include the movement of sediment from the river channel, up through the water column, and onto upland storage stockpile locations.  Dredging activities would be conducted by two to three hydraulic dredges operating at various reaches of the lower Cowlitz River. Dredging would occur during the in water work window, as determined in coordination with WDFW.  Prior to dredge material placement, a field wetland determination would be conducted to confirm the absence or presence and acreage of wetlands.  A sample of past dredged material placement sites, that could potentially serve as future placement sites, were surveyed in 2013 for wetland and habitat conditions.  Of nine sites surveyed, only one site had wetlands.  Discharge of dredged or fill material will be evaluated using the guidelines under Section 404(b)(1) of the CWA. A Section 404(b)(1) analysis is found in Appendix G of the FSEIS. 

Endangered Species:  USACE has completed formal consultation with the National Marine Fisheries Service (NMFS) as required by Section 7 of the ESA. NMFS issued a Biological Opinion (BiOp) in August 2017. The BiOp concluded that the preferred alternative was likely to jeopardize the continued existence of threatened Lower Columbia River (LCR) coho salmon and LCR steelhead and likely to result in the adverse modification of both species’ designated critical habitat.  The BiOp includes a Reasonable and Prudent Alternative (RPA) to ensure the preferred phased construction alternative 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.  USACE developed fish conservation measures to meet the requirements of the RPA.  Fish conservation measures were evaluated in the revised DSEIS. 

Informal consultation with U.S. Fish and Wildlife Service (USFWS) resumed in October 2017 and was completed on January 17, 2018. USFWS concurred with USACE that the effects of the preferred fish conservation measure would be not likely to adversely affect (NLAA) on bull trout.  USACE and USFWS agreed upon conservation measures that would be implemented for placement of dredged material, with the inclusion of these conservation measures, USFWS concurred with USACE’s NLAA determination for streaked horned lark and Nelson’s checkermallow. 

Historic Properties/Cultural Resources: Section 106 of the National Historic Preservation Act of 1966, as amended (54 USC 306108), requires Federal agencies to consult with the appropriate State and Tribes to take into account the effects of actions they undertake on historic properties listed in or eligible for listing in the National Register of Historic Places.  Due to the phased approach of this alternative, USACE, in consultation with State of Washington, Department of Archaeology and Historic Preservation (DAHP), the Cowlitz Indian Tribe and the Washington Department of Fish and Wildlife (WDFW) developed a programmatic agreement that lays out a mutually agreed upon approach to the management of those NRHP-eligible resources potentially adversely affected by this action, continued consultation, and mitigation. The Cowlitz Tribe did not respond to the Corps letter inviting them to be a signatory to the programmatic agreement.  The WDFW agreed to be an invited signatory on January 18, 2019. The USACE will need to determine eligibility for inclusion in the National Register of Historic Places (NRHP) for each of the five recorded resources and three unrecorded but noted resources that will be adversely affected within the sediment plain due to the SRS spillway crest raise. The SRS, NRHP eligible historic property, will not be adversely affected as the structure was designed to be raised as needed. However, the Fish Collection Facility will be evaluated for eligibility for inclusion in the NRHP, as a contributing element to the SRS.  A programmatic agreement between the USACE and DAHP was signed on January 15, 2019.

Decision:  As documented in the record of decision (ROD), the selected alternative is the Phased Construction Alternative in conjunction with the modify FCF measure. This alternative was identified as the 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.  USACE considered comments received on the FSEIS in the preparation of the record of decision (ROD). The ROD documents the USACE’s decision and includes an attachment that provides a summary of comments received and USACE’s responses.

An electronic copy of the ROD is available for download at:

Additional information may be found at the project’s web page: