By: Grace Dumas, News of the North
Juneau officials said they were “deeply frustrated” after learning that the U.S. Army Corps of Engineers has abruptly backed away from pursuing a preferred long-term fix for the catastrophic glacial outburst floods threatening the Mendenhall Valley.
At a Committee of the Whole meeting Monday night, City and Borough of Juneau leaders detailed new modeling that shows a worst-case glacial lake outburst flood could send an estimated 118,000 cubic feet per second of water down the Mendenhall River, far beyond anything the city has experienced.
“So in August of 2023 when we had our first majorly destructive GLOF, that impacted about 30 homes. Then the next year, in the August of 2024 we wound up with a very different type of event. It wasn’t as much of a riverbank erosion event, it was more of an inundation event. It impacted about 300 homes. So just get a sense of that.” Said Director of engineering Denise Koch, “Then in August of 2025 we had an even more severe GLOF. The HESCO barriers were largely successful in protecting the areas that they were designed to protect. We think without HESCO barriers in 2025, we would have had anywhere from 750 to 1000 homes that would have been impacted. So just to give you a sense of how much more severe each one of these GLOFs is getting.”
Maps presented at the meeting showed that a maximum event could push water beyond the Central valley, crossing Riverside Drive and Mendenhall Loop Road, affecting neighborhoods on both sides of the river.
“We’re talking about a GLOF of this magnitude, if you did not have sufficient mitigation, going beyond what people experienced in 2024 which was terrible in and of itself.” Said Koch, “We’re talking about water also having impacts on the western side of the river, having impacts all the way down, impacting the Mendenhall wastewater treatment plant, having impacts to the airport, a GLOF of this magnitude really gets beyond the Central Valley.”
Scientists from the University of Alaska Southeast, the National Weather Service, the U.S. Forest Service, and Tribal representatives from Tlingit and Haida identified a “lake tap” of Suicide Basin as the preferred enduring solution.
“The lake tap was the most attractive option. It has a very high likelihood of reducing the GLOF risk. It is designed to drain out Suicide Basin at approximately the Basin’s inflow rate.” Said Koch, “There are a lot of assumptions that went into this. A lake tap is essentially a tunnel, there’s a lot of tunnel building capacity in Alaska, It is definitely a technology that is out there and exists.”
The Lake Tap option, the least costly of the long term mitigation efforts discussed, would include construction of a roughly 2.3‑mile tunnel from Suicide Basin to an outfall between Nugget Falls and the face of the Mendenhall Glacier, according to officials.
City Manager Katie Koester said that until recently, CBJ had been told the lake tap was the selected alternative, and that the Army Corps would move quickly toward a technical report on a timeline strongly backed by Sen. Dan Sullivan.
Koester said the city had been in “multiple times a week” coordination with the Corps, but that a couple weeks ago those check ins ceased.
“We were under the impression that it was all going smoothly.” Koester said, “We began inquiring, why haven’t we had a check in a while? Then on Thursday of last week, we had a meeting with Army Corps headquarters where they rescinded all of the direction that they had previously given to pursue a lake tap as the selected alternative. They directed staff to wrap up all efforts on the lake tap as the selected alternative, which included environmental work and feasibility and preliminary engineering.”
Koester described the change as “a really disheartening pivot that left us a little bit speechless,” adding, “I imagine also leaves you speechless.”
“I’m deeply frustrated with this change of course from Army Corps of Engineers. They certainly have been a great partner, really we need them.” Koester said, “We need them to fight the flood fight, to keep this community safe and whole until we can get to an enduring solution.”
According to Koester, Alaska’s delegation, Sen. Murkowski and Sullivan are both committed to an enduring solution, with Sen. Sullivan meeting with the Assistant Secretary of the Army for Civil Works on Wednesday.
Koester urged residents to advocate specifically for the lake tap, and to speak as a unified community.
“I think that it certainly doesn’t help our position to have a divided community on what the best option is, because we are asking for so much so quickly.” Koester said, “I’m confident that we are all advocating for a solution. We need to be aligned, and it doesn’t help when we’re unaligned. But we’re not that unaligned. We all, everyone in this room, everyone who has written their delegation and talked to their delegation, wants an enduring solution and wants it quickly, and I have never heard anyone advocate for anything other than that.”
Officials did emphasize however, that HESCO barrier flood protection work is proceeding.
Koester confirmed the Corps has a signed agreement and continues to cover 100% of Phase Two HESCO costs.
