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…