Juneau expands flood evacuation zone to just over 1,900 homes as glacier basin fills

Just over 1,900 Juneau residences in the Mendenhall Valley are now under an evacuation advisory as Suicide Basin fills toward capacity and officials say a major glacial outburst flood is expected within weeks. That's almost double the roughly 1,000 homes advised to leave last year. The expanded zone reflects a new approach to mapping: planners modeled not only where floodwaters would go, but where roads could become impassable for residents trying to leave or first responders trying to get in.

The expansion pushed the zone deeper into the southern Mendenhall Valley and wider along the river corridor. CBJ Emergency Programs Manager Ryan O'Shaughnessy explained that areas were included where "access or travel, including by first responders, may be compromised" — meaning some residents may not be able to get to safety if barriers fail.

CBJ is already operating under an emergency declaration and is working with the State Emergency Operations Center toward a pre-event state disaster declaration. State officials have said a declaration should wait until monitoring confirms an imminent threat. O'Shaughnessy said Thursday that "all indications" are that the state will seriously consider a pre-event declaration again this year.

The HESCO barriers for both the CBJ-led Phase 1 project and the U.S. Army Corps of Engineers Phase 2 project are complete. Access gaps will be sealed starting July 20, and large pumps will begin deploying the week of July 14 to manage water that percolates under the barriers.

But officials are clear that the barriers are not a reason to stay put. O'Shaughnessy said the system performed relatively well last year and that confidence remains high, but added that "the entire system is fragile" and that barriers "are essentially sandbags." He urged everyone in the evacuation area to heed the advisory.

CBJ Chief Engineer John Bohan pointed to last year as a reminder of how fast things can go wrong. "a tree completely blew up the barriers behind the Field House very quickly, very easily," he said. "And that's also why we're requesting evacuation because they are temporary and we don't know what force might crack one open."

Officials described a Ready, Set, Go framework for the event. The basin is currently in the Ready stage: residents should monitor conditions, make a plan, and sign up for emergency alerts. When the basin reaches capacity, most likely between Aug. 1 and Aug. 9, CBJ will send a wireless emergency alert moving the community into the Set phase, at which point residents should have go bags ready. A second alert will signal Go, when residents should activate their evacuation plans. CBJ will test the wireless emergency alert system Thursday, July 16, at 3:30 p.m. Only phones with test alerts enabled will receive it.