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Army Corps briefs Juneau on glacier‑outburst modeling and short/medium/long‑term flood measures
Summary
USACE Alaska District engineers told the Juneau assembly that limited observational records and constrained bathymetry make GLOF peak discharge estimates uncertain; they outlined short‑term construction, medium‑term concepts and a draft technical study due to Corps HQ in early August.
Engineers from the U.S. Army Corps of Engineers told the Juneau Assembly that model estimates for glacier lake outburst floods (GLOFs) carry wide confidence intervals because of limited period‑of‑record flood data and incomplete bathymetric surveys.
Mike Records, the Corps’ Alaska District hydraulic engineer and technical lead, said annual exceedance probability (AEP) events for the Mendenhall system were derived from physics‑based modeling of the basin and limited observations. “There is a lot of uncertainty in the system,” he said, noting confidence intervals for peak discharge estimates can be large and that the Corps will update tables as new data become available.
The Corps described a three‑tiered response approach: short‑term measures (riprap, HESCO and barrier placement), medium‑term measures (improved barriers, in‑river channel adjustments, sheet‑pile or composite walls) and long‑term enduring solutions (dams or major infrastructure changes). Daryl Downey, the Corps’ phase‑2 project manager, said the Corps issued a construction contract in February and mobilized crews in March to work across six reaches, aiming to have riprap and temporary barriers in place by mid‑July.
Army Corps officials emphasized outreach steps: property owners were notified in advance, the Corps has quality assurance representatives on site to address concerns, and a public sandbagging training is planned for July. John Rajik, the Corps’ geotechnical branch chief, said medium‑term technical reports are in review and that a draft technical study will be submitted to Corps headquarters in early August for further review.
On the limits of modeling and overtopping: the Corps cautioned that HESCO barriers are not designed to be overtopped and that modeling an overtopping failure mode is inherently uncertain. Records and improved ground‑penetrating radar would materially reduce uncertainty, Records said.
What’s next: the Corps will continue construction work this season, refine AEP tables after additional data points, and coordinate with CBJ on medium‑term study deliverables and potential requests for expanded Corps assistance in 2027.
