City and federal leaders have settled on a long-term solution to mitigate glacial lake outburst floods: a lake tap.
The lake tap would be a tunnel drilled through Bullard Mountain, allowing water to drain from Suicide Basin into Mendenhall Lake, so that the basin would not have the chance to catastrophically burst.
The tap would drain water at a rate of about 800 cubic feet per second, explained Denise Koch, City and Borough of Juneau director of engineering & public works, far below the extimated 52,000 cubic feet per second peak flow during the 2025 outburst.
The U.S. Army Corps of Engineers hosted the three-day, closed-doors ‘charrette’ last week alongside the CBJ and the Central Council of Tlingit & Haida and the U.S. Forest Service to discuss possibilities for a long-term solution to the floods. Each of the government bodies agreed on the solution.
“This is kind of an important step on that pathway — an exciting step,” said Koch. “It’s also different from authority and ability to construct the solution.”
The Army Corps of Engineers estimates the project would take about six years to complete, including permitting, and could cost between $613 million and $1 billion, according to Koch.
Koch said that risk analysis was one of the primary factors for considering solutions, and that the lake tap ranked highest. She added that it was also the quickest and least expensive of the long-term solutions considered.
Tlingit & Haida Public Safety Manager Sabrina Grubritz said that the tribe went into last week’s meetings with the goal of identifying the approach that would “best safeguards citizens, protects cultural resources, and supports the wellbeing of the broader Juneau community.”
“The lake tap option appears to best meet those goals with the data currently available,” Grubritz said.
The lake tap was one of four other options on the table: one or more flood-control dams, levees or floodwalls, relocation of communities affected by the floods or a hybrid option.
Because the lake tap would be gravity-fed, it would pose fewer operational challenges than some of the other options, Koch said. The broad cost estimate is expected to narrow as the Army Corps completes more detailed planning and design work.
CBJ plans to apply for full federal funding for the project, though the city could ultimately be responsible for covering between 10% and 35% of the cost, Koch said.
The push for a long-term solution follows CBJ’s contract with the Army Corps to study flood mitigation options. CBJ formally accepted assistance from USACE during a committee meeting on Thursday, Oct. 30. Under that agreement, the Corps will fund materials and installation for another round of HESCO barriers ahead of the anticipated 2026 flood season.
USACE will move forward with a technical report for the lake tap, which Koch said she estimates will be finished by late spring. At that point, the Corps will solicit another round of public comments.
Correction: This story has been updated to correct that the peak glacial outburst flood in 2025 was 52,000 cubic feet per second, and that CBJ could be responsible for up to 35% of the lake tap project cost, not 30%.
