Glacial Outburst Flooding

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Juneau’s next annual glacial outburst flood will test a temporary levee the city installed this spring for the first time. Although city officials said they expect it will protect residents, they want everyone in the flood zone to evacuate anyway.

Suicide Basin is almost full. Once the glacial dam releases, the basin could unleash a torrent down Mendenhall River. As the flood approaches, the community is preparing for the worst-case scenario. 

The levee that was installed to protect most neighborhoods in the Valley is made up of HESCO barriers — large metal baskets lined with fabric and filled with sand, which are stacked in backyards along the river.

Ryan O’Shaughnessy is Juneau’s emergency manager. He said an analysis the city commissioned from engineering firm Michael Baker International shows that the levee should hold back floodwaters properly. 

But he said people shouldn’t bet their lives on that. 

“We’re extremely confident in the HESCO barriers,” O’Shaughnessy said. “We’re still recommending that people evacuate. You just cannot be too careful with life and, you know, the potential for death or injury.”

If the levee fails, O’Shaughnessy said it would trigger a flash flood and people wouldn’t have much time to escape. 

“It will be difficult to extract anyone in a search and rescue operation with water moving that swiftly,” he said.

So he recommends that Valley residents pack go-bags in advance and arrange to stay with friends or family in areas outside the flood zone. 

The city and U.S. Geological Survey plan to watch how the levee performs during the flood using drones and other cameras. O’Shaughnessy said the city will bolster the levee with large sandbags called supersacks if they see extreme bank erosion. 

“Where there are those bends in the river, where we’ve historically seen that kind of activity, are the places that we’re prepared to respond to it,” he said. 

Those bends include the corner of Riverside Drive and Killewich Drive, along Meander Way and near Dimond Park. 

Evacuation Timeline 

The city plans to issue an evacuation warning as soon as the remote camera in Suicide Basin shows the water is draining out — that’s the same time that the National Weather Service will issue a flood warning. 

The evacuation notice will buzz on cell phones located in the Juneau area through a federal alert system. But to ensure you receive a warning — even if you’re not in the area at the time — O’Shaughnessy said residents should sign up for the city’s alert system.

From the moment the evacuation warning is issued, Valley residents will have an estimated 36 hours to get out of the flood zone before floodwaters reach the river.

City officials will publish a map of the flood zone when the National Weather Service issues a forecasted flood height. Forecast updates are likely to come about a day later. Residents can also see if their home is in the flood zone by plugging the forecasted height into the interactive map at juneauflood.com and toggling “HESCO Barriers OFF.”  

Floyd Dryden will serve as an emergency shelter during the flood. Its gymnasium can hold around 50 cots. Folks with RVs will be able to park in the lot and there will also be an area where people can pitch tents outside.

Britt Tonnessen is the community disaster program manager for the Red Cross of Alaska in Southeast. She said the shelter will be available for as long as Valley residents need it. 

“If it happens during the day and the flood clears out, maybe it’s just an evacuation point,” Tonnessen said. “If it happens in the night, it could be a sheltering situation.”

People who stay at the shelter can expect a cot, food and access to information and services. Tonnessen said that the Red Cross is prepared to assist elders and those with disabilities and medical needs.

“If people are separated from medication, durable medical equipment — we have disaster health services volunteers, and they try to more immediately reconnect those people with those services,” she said.

Ahead of the flood, Tonnessen is still accepting volunteers and said that those interested can sign up on the Red Cross website. 

In a Facebook survey, Valley residents affected by the floods said they need help filling sandbags and setting them up on their properties. 

The city, the Central Council of the Tlingit & Haida Indian Tribes of Alaska and volunteers with United Way will be handing out free sandbags at the Dimond Park field house this Saturday and July 26 from 11 a.m. to 3 p.m. 

Correction: A previous version of this story stated that the annual glacial outburst flood was forecast to begin Aug. 8. That’s when the National Weather Service projects Suicide Basin will be full. Also, NWS can only forecast when the basin will be full, not when it will release.

Dozens of Juneau residents in the glacial outburst flood zone filed into the Mendenhall Valley library on Saturday afternoon to learn how to prepare for flooding expected later this summer. 

Members of the Juneau Lions Club walked residents through the new flood map website made by UAS researchers and handed out weather alert radios. Local insurance providers talked about how FEMA’s National Flood Insurance Program (NFIP) works. The program is still operating, but that might change given the Trump administration’s past statements about weakening the agency. 

Reuben Willis, a State Farm insurance agent in Juneau, explained that the price for NFIP is based on FEMA’s risk zone maps, last updated in 2020. He recommended that homeowners lock in lower pricing before FEMA updates the city’s maps again. 

“If they change your zone and put you in a higher-risk zone, which would allow them to require us to charge a higher premium, if you purchased the policy you’re grandfathered in,” Willis said. 

He added that if homeowners with NFIP policies sell their place in the future, that grandfathered price transfers to the new owners. A new policy takes 30 days to go into effect, so Willis said Mendenhall Valley homeowners should consider applying now to protect their assets from potential flooding this year. Catastrophic floods hit neighborhoods during the first week of August the past two years.

Elizabeth Figus, a Valley resident whose home on View Drive flooded in 2023 and 2024, said that NFIP made a huge difference for her financially and shared tips for how to document losses after a flood. 

“If you are feeling stressed out after a flood, you might be urged to just throw stuff away,” Figus said.

But instead of tossing damaged property, she recommends taking photos of everything before moving it and cataloging each item — even small things like cleaning supplies. 

Laird Jones has lived in the Valley since 1982. His place is on Skywood Lane, near the library. He said his home was spared during last year’s record-breaking 16-foot flood, but that could change if a future flood breaches 17 feet. Last year, he watched the water level rise too close for comfort.

“The ditch was full of water, and we had a salmon swimming by in the ditch,” he said.

He said FEMA maps put his home in one of the lower-risk zones, so when he got a quote for flood insurance, it was just under $360 per year. 

Insurance providers said that’s the base price for the program, but it can be around $2,000 for those in higher-risk zones. The standard policy covers $250,000 for residential structures and $100,000 for belongings inside.

In the parking lot behind Thunder Mountain Middle School, staff from the city and Tlingit and Haida, along with a handful of volunteers, filled free sandbags for residents to stack against their homes. The U.S. Army Corps of Engineers donated the bags, and the city and tribe evenly split the cost of the sand — about $18,000. Another sandbag event will take place on June 14. Tlingit and Haida will also host Community Emergency Response Team trainings on June 14, 21 and 28.

Anton Rieselbach, a program associate at the Juneau Economic Development Council, attended the event to talk with people about a survey to capture how the 2024 flood affected the community. 

“We want to figure out the gap between the amount of help that’s been given to flood victims and the amount of impact that they actually incurred,” Rieselbach said. “We also want to try to figure out some of the social impacts of the flooding — for example, is this flooding causing people to try to leave Juneau in higher numbers than usual? Is it causing people to have negative mental health experiences or any other health issues?”

He said getting a comprehensive picture of the issue will help inform future flood responses. So far, roughly 60 people have responded to the mail-in survey, and Rieselbach said the council is aiming to get 150 responses by the end of the month.

Researchers launched an interactive glacial outburst flood website today to help Juneau’s Mendenhall Valley residents plan for annual floods. It’s a project of the University of Alaska Southeast and the Alaska Climate Adaptation Science Center. 

The website features flood inundation maps the city published earlier this month. Instead of being sliced into multiple 2D image files, the maps are stacked in layers on an interactive viewer. Residents can now scroll over their property to see the projected water depth for different flood heights.

That detail is new to the public. Eran Hood, an environmental science professor at UAS who led the project, said it will ideally help people understand the risk to their home when the National Weather Service puts out a flood forecast. 

“Well the main outcome is just to allow people to have more information to plan ahead,” Hood said.

The website includes historical data and other information, like how Suicide Basin formed to create the floods and how scientists make flood forecasts. That information was already public, but Hood says it wasn’t accessible before.

“All of that stuff was somewhere, but it wasn’t in places where people probably ever would have found it,” he said. 

Now it’s all in one place.

Hood came up with the idea for the website. With a $30,000 grant from the Alaska Climate Adaptation Science Center, he hired a programmer named Sean Fagan to bring it to life. They hosted forums with residents to receive feedback on the website before launching it and incorporated suggestions to make things easier to understand. 

Hood says the new site compliments the National Weather Service’s Suicide Basin monitoring webpage, which is still the go-to spot for emergency flood information.