Army Corps says Juneau's temporary Mendenhall flood defenses are complete

Temporary flood defenses along Juneau's Mendenhall River are finished ahead of the 2026 glacial lake outburst flood season. The U.S. Army Corps of Engineers says Phase 2 of the temporary flood-mitigation work in the Mendenhall River Valley is complete.

The Corps' headquarters account posted Friday that its Alaska District had completed Phase 2 of flood mitigation measures in the valley. The work is meant to reduce flood risk from Suicide Basin, the ice-dammed basin above Mendenhall Glacier that has produced repeated summer floods in Juneau.

The completion does not end the flood risk. Juneau officials have continued to warn residents along the river to prepare for a major flood.

For weeks, the immediate public-safety question was whether temporary barriers and armoring would be in place before the basin released. Juneau emergency programs manager Ryan O'Shaughnessy said at a July 9 media availability that officials have "a tremendous amount of confidence in the HESCO system," but added: "We saw it perform relatively well last year and we're very confident for this year, but the entire system is fragile. And that's really why we want everyone in the evacuation area to heed that advisory and to evacuate. These are resilient structures. We do have a little bit of testing with them, but they are essentially sandbags, right?"

An earlier Sealaska project update said the emergency work was being done under contract with the Corps. It included about 14,000 linear feet of HESCO barriers, more than 90,000 tons of rock armoring and earthen berm construction along about four miles of river corridor. Sealaska said the work was designed as an immediate defense before peak August flood risk while the Corps worked on longer-term answers.

Valley residents have been preparing alongside the construction. The Alaska District posted that residents picked up sandbags at a July 11 public flood preparedness event at Dimond Park, and that community volunteers helped fill and load sandbags for Mendenhall Valley neighbors the next day.

Juneau has already been through two damaging summers. A 2023 outburst flood undercut homes along the river. A 2024 flood damaged hundreds of homes and forced a broader emergency response. This year, Alaska News previously reported that nearly 1,900 homes were under an evacuation advisory as officials prepared for another Suicide Basin release.

Federal legislation is also moving on a separate track. Alaska News previously reported that a U.S. Senate water-resources bill would direct the Army Corps to study and accelerate engineering work for Juneau's glacial flooding problem. That bill would not replace this summer's temporary defenses. It would shape whether the Corps has a clearer permanent role after the emergency work.