Juneau’s annual glacial outburst flood event is underway, and record high water is expected this year.
That record-high peak for the Mendenhall River is forecast to hit 16.6 feet Wednesday afternoon. That’s after summer meltwater filled up Suicide Basin, to the point it was spilling over the natural glacial dam on Sunday.
In the past, a sudden release of the dammed-up water undercut parts of the riverbank downstream, even destroying homes. Disaster preparedness planners have been working to mitigate the risks, and residents are waiting and watching to see how bad the flooding will get.
KTOO’s Alix Soliman is part of the team reporting on this year’s glacial outburst flood. She spoke to Alaska Public Media's Casey Grove about it on Tuesday.
Below is the transcript of an interview with Soliman on Alaska News Nightly. It has been lightly edited for length and clarity.
Casey Grove: What's the situation there now, as of Tuesday afternoon? And what are emergency managers telling residents?
Alix Soliman: So flood waters are rising at this point. We have not reached the peak yet, but emergency managers want people in the flood zone to evacuate. That includes roughly 1,000 homes along the river, and that includes those who are protected by a flood barrier. So they really don't want folks to test their lives with these new barriers. They want folks to evacuate, and there's a shelter down the street at a former middle school.
CG: Gotcha. So how worried are residents closest to the river in those most vulnerable areas?
AS: Some are really worried, especially those who aren't protected by that barrier. Like I said, there's a street called View Drive. It's kind of like a dead end street that goes just right into the river. A lot of people there are preparing to evacuate, but I walked that street today, and there are some residents who did their own sort of preparedness, built their own berms, and they're planning to stay. So I think it really depends on who you talk to.
I mean, just walking around the Valley, there's still kids riding their bikes and people walking their dogs, and it's a sunny day. It's been raining the past few days, so lots of folks are just getting out and about today.
CG: Yeah. Tell me more about those barriers. How are they actually supposed to work? And do officials think that they're going to hold?
AS: Yeah, so the temporary levee is what they're kind of calling it. It's made of what are called HESCO barriers. So it's sand filled in steel baskets and then stacked along the river in people's backyards. It's supposed to harden the riverbanks and block water from flowing into people's homes, and they're supposed to sort of push the water to the west side of the river, which is mostly uninhabited forest land.
Officials say an engineering analysis makes them confident the barriers will hold at a 17-foot flood and below, which is what we're expecting now, but anything higher, like an 18-foot flood, there could be some water that flows around the barriers, and they actually don't know how it would perform in, say, a 20-foot flood. So at this point, officials are pretty confident that they will hold, but again, they don't want folks to test the barriers with their lives, since this is the first test run.
CG: Well, I think a lot of people will remember seeing video of, you know, there was a particular house that was undercut and just kind of fell into the river one year. Remind us, how did we get to this point? Why has the flooding been such a big problem in recent years?
AS: Yeah, so climate change has really sharpened the risk of glacial outburst flooding in Juneau. That's because warming causes the glacier to melt faster. So Suicide Basin is the glacial lake responsible for unleashing the flood, and when the ice melts back, it actually makes that basin grow. There's more room for the water to to fill it up. So as it can hold more water, it can release bigger floods.
This year, they're expecting another record breaker. As you mentioned, last year was a record breaker at 16 feet, and the year before, that was 15 feet, which was the record at the time, and that's when you saw that house crash into the river. At this point, they have hardened the riverbanks with large boulders. It's called riprap, so they're not expecting as much erosion along the riverbanks, but the water level in the river could still be quite high.
CG: And I guess one thing I've been trying to understand is, is it a situation where the the glacial dam there just breaks and there's this huge torrent of water, or just that there's sort of a peak, in that the water has overtopped and it's just reaches its peak flow?
AS: That's a great question. So it's actually a really complicated process, like the mechanics behind how the flood releases. You saw on Sunday that it started over-topping. It's not actually putting that much volume of water out into the river when it starts to over top. It's basically like if you just started to pour a little bit of water in a full cup, just that tiny bit of overflow, is what you're seeing on Sunday.
Now we have what's called a subglacial release. So Suicide Basin, the water, billions and billions of gallons of water in Suicide Basin, are boring a hole under the glacier, and then it finally breaks through to the bottom, through the glacier, to the lake, and that is when the release happens. So you start to see this rapid rise in the lake.
It's uncertain at this point whether the water level always floats the glacier, but the researchers think that the water under, like flowing under, the glacier gets to a point where there's so much pressure that it can actually float all of that ice. And that's when you get this big release.
CG: So where can people find the most up to date information?
AS: So people can find up-to-date information at KTOO.org, we have live coverage as well as pre recorded videos with experts and emergency managers, and we have a new podcast. It's called "Outburst." Episodes 1 and 2 are live now. The podcast dissects how the floods have evolved over time, the science behind the phenomenon and how people are preparing.
CG: And then last question, Alix, do you anticipate being able to keep your feet dry?
AS: That's a really good question. Will my feet stay dry? You know, that remains to be seen. I don't plan to get into the flood waters, because I've been explicitly told not to. So we're going to say, yes, my feet should stay dry.
