Experts, elected officials and agencies call for coordinated action on Mount St. Helens sediment: ELJs, spillway rises and dredging under discussion

Colin Thorne, a river scientist and University of Nottingham researcher who now lives in Vancouver, Washington, told a Cowlitz County workshop that engineered log jams and flood‑plain roughening have increased sediment capture on the North Fork Toutle River and can be cost‑effective additions to Corps of Engineers measures.

Thorne summarized four decades of work on the Sediment Retention Structure (SRS) and the river system that drains Mount St. Helens. He said the SRS initially trapped a large share of sediment but trap efficiency dropped over time. Pilot grade‑building projects using engineered log jams (ELJs) installed in 2010 produced vegetation and sand islands that, Thorne said, increase trapping and help the river rebuild grade. He described the ELJ pilot as successful and said further ELJs and related actions could store substantially more sediment than further small raises of the SRS crest.

Thorne and other presenters gave these key technical points (figures reported during the workshop are approximate and were presented on the record): the original phase‑one SRS dead storage was about 88 million cubic yards; the corps’ long‑term design capacity is about 258 million cubic yards; ELJ pilot work and a 2012 spillway raise temporarily restored trap efficiency above 60 percent; trap efficiency later declined and corps analyses showed values as low as about 15 percent before countermeasures were added; a proposed 10‑foot spillway raise has been estimated in public materials at roughly $56 million; and pilot ELJ work was described as costing “less than $1 million” in the meeting but exact figures were not provided on the record.

Speakers from state and local agencies said downstream effects on the Cowlitz River are an immediate concern. Dave Howe of the Washington Department of Fish and Wildlife said his agency is participating in a multisector Toutle–Spirit Lake collaborative that brings tribes, federal and state resource agencies and local governments together to assess tradeoffs and jointly recommend actions. County officials and stakeholders emphasized repeated downstream impacts: rising sandbars and channel changes that have lowered the level of protection for Castle Rock and Lexington, sediment covering intake and wastewater infrastructure, and eroding private banks and public trails.

Multiple attendees called for a coordinated, high‑priority push to Congress for authorization and funding. Workshop participants noted that the Corps’ current congressional authority for some program elements runs through 2035 but that the Corps also has a long‑term duty to manage sediment; several speakers urged that the county and congressional delegation seek a feasibility review or expanded authorization. One speaker in the meeting said a feasibility review could cost on the order of $175,000 and take four to six months; other meeting participants emphasized the need to secure disposal sites before large‑scale dredging because local disposal capacity has been reduced by development of former spoil areas.

Panelists and public speakers raised additional considerations: seismic risk constrains how many times the SRS crest can be raised, spillway rises can temporarily improve trap efficiency but may drown vegetation near the structure, and increased shallow water behind a raised crest could change fish passage, water temperature and habitat. Thorne said ELJs encourage vegetation and beaver recolonization, which generate longer‑term, self‑sustaining sediment storage benefits.

State Senator Jeff Wilson and local elected officials called for a unified, documented set of requests for federal action so the county, port and regional stakeholders can speak with one voice to the federal delegation. Several attendees asked that the county schedule follow‑up briefings with the Army Corps of Engineers and with the collaborative to address specific questions about authority, funding and engineering tradeoffs.

The discussion closed with agreement among county leaders and stakeholders that the problem is multi‑jurisdictional and requires coordinated advocacy and technical study. No binding county action or appropriation was taken at the meeting; commissioners and several state and federal staffers said they would pursue follow‑up engagements with the Corps, the congressional delegation and state agencies.