Juneau Bolsters Flood Wall for Double-Sized Glacial Outbursts

JUNEAU, Alaska—Contractors with the City and Borough of Juneau and the U.S. Army Corps of Engineers are rebuilding the flood wall along the Mendenhall River to withstand a 50-year flood event measuring 90,000 cubic feet per second—nearly double last summer's peak that threatened hundreds of homes in the Mendenhall Valley. The wall, which protected residences from Marion Drive to Postal Way during the 2025 outburst, sustained damage and is now being armored with additional boulders, raised higher and wider, and extended further along the riverbanks. City officials have redirected $5 million from the proposed Capital Civic Center project to fund Phase 1 repairs, with completion targeted for July 15.

Last summer's glacial lake outburst flood from Suicide Basin sent billions of gallons roaring through the valley, testing the temporary barrier of over 10,000 reinforced sand-filled units that held firm despite seepage. At a flood response training in Dimond Park this month, project leaders expressed optimism the upgraded wall will again shield homes this season, though they are designing for the worst-case scenario. State, local and federal agencies coordinated closely last year, with the Corps supplying materials while local crews monitored the structure through the peak.

Long-term, the Army Corps is advancing a 'lake tap' solution—a tunnel bored through Bullard Mountain to slowly drain Suicide Basin into Mendenhall Lake, preventing catastrophic bursts of up to 16 billion gallons. Endorsed by the City and Borough of Juneau, the U.S. Forest Service and the Central Council of Tlingit and Haida Indian Tribes of Alaska, the project could take six years and cost $613 million to $1 billion. A technical report with preliminary designs, cost details and environmental review is due for public comment in May 2026.