Validation of a Live Bed Physical Model of the North Fork Toutle River, Mount St. Helens Fish Collection Facility

The Fish Collection Facility (FCF), located downstream of Mount St. Helens and the Sediment Retention Structure (SRS) on the North Fork Toutle River, serves as a critical site for the collection and relocation of migratory fish to their native spawning streams upstream of the SRS. The SRS functions as a sediment trap, designed to capture sediment remnants resulting from the 1980 eruption of Mount St. Helens. However, a portion of the sediment load bypasses the SRS, with some finer sediment, such as sand, being deposited at the FCF. This sediment accumulation limits the effective operation of the facility. To address this issue, a Froude-scaled 1:12 physical model of the FCF was developed to evaluate potential mitigation strategies for sediment deposition. Limited availability and uncertainty of key data, including only a single channel survey of the FCF reach and minimal sediment data greatly complicated the validation process. Ultimately, the team was able to successfully validate the model based on the formation of key features found in the prototype and observations from facility operators.