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Initial assessment of 2026 glacial lake outburst flood confirms less damage than last year
- Jasz Garrett
- 6 hours ago
- 5 min read
Tree strikes remain the biggest threat to HESCO barriers; extent of their reinforcement and repairs still under review, CBJ says
By Jasz Garrett
Juneau Independent
Although this year’s glacial lake outburst flood caused the Mendenhall River to crest at 14.7 feet on Thursday afternoon, there was still risk, said the city’s emergency manager in an update to the Juneau Assembly on Monday.
“Frankly, we’re very lucky that there was a slow release and that the crest of the lake and the river was not much higher,” Ryan O’Shaughnessy said. “When we have these slower releases, generally that can mean a lower crest in the lake and the river. But I’d like to highlight that tree strikes are the most probable failure mode of the HESCO barriers.”
He said a slower release means more time water is pushing against the semipermanent levee, which stretches approximately five miles along the Mendenhall River.
“There’s more vulnerability from a timing perspective for tree strikes against the HESCO barriers,” he said.
The addition of Phase 2 barriers installed by the U.S. Army Corps of Engineers this summer added more homes to the Mendenhall Valley evacuation zone in the case of a breach. O’Shaughnessy said some residents in the new evacuation zone of 1,900 homes took the advisory seriously, but others did not.
“We continually see people standing on top of the HESCO barriers in extremely dangerous situations. Even during active tree strikes in that moment at that spot,” he said, asking the public to heed the advisory in future years.
An American Red Cross emergency shelter at the Floyd Dryden gymnasium was open for two nights. Six people stayed the first night and 18 people the second night, along with cats and dogs, according to O’Shaughnessy.
The 14.7-foot crest at about 2:15 p.m. Thursday was the lowest for a full release of Suicide Basin in the past four years, and was significantly later and lower than initially forecasted by the National Weather Service Juneau.
Suicide Basin was announced to be full last Tuesday and began releasing that same day. The river was initially forecast to crest between 16.1 and 16.6 feet early Thursday morning, but was shifted multiple times due to the basin releasing more slowly than anticipated into Mendenhall Lake.
The exact cause of the later timing and slower release is currently unknown, but the University of Alaska Southeast, U.S. Geological Survey and the weather service are working closely to better understand the event and improve forecasting for future years.
Flood damage was significantly less than in years past, according to the city’s preliminary assessment.
O’Shaughnessy said of 186 homes along the river, 10 were listed as “affected damage” and two sustained minor damage.
The city uses a Federal Emergency Management Agency damage assessment matrix for flooding in conventional homes.
“What affected would mean…there’s some amount of water in a crawl space, but generally doesn’t affect the living area of a home. When we say minor damage, we mean that there was some amount of water in the living area of a home, but generally not enough to exceed the height of a standard electrical outlet,” O’Shaughnessy explained.
The preliminary assessment shows damage was concentrated in two primary locations: the bend of Meander Way and on View Drive. Last year, damage was concentrated in similar areas.
More than three dozen homes sustained damage during a 2023 flood that peaked at a then-record 14.97 feet and severely eroded the banks of the Mendenhall River. Nearly 300 homes were damaged during a 2024 flood that crested at an unexpectedly high 15.99 feet. Both disasters caught officials and many residents off-guard.
2025 also broke a record at 16.65 feet, but O’Shaughnessy said in the past two years damage has been significantly reduced due to the installation of HESCO barriers. This year’s addition of 41 pumps provided by the Army Corps made a difference, along with the construction of Phase 2.
The two homes with minor damage were on View Drive, where HESCO barriers are not installed.
“View Drive fared far better than it has in years past, but absolutely not without risk and not scot-free,” O’Shaughnessy said.
He said many residents living in the flood zone who know to expect a disaster feel anxiety ahead of the flood every August. O’Shaughnessy said homeowners expressed that cycle had already started again.
He encouraged members of the public who felt damage at their home was missed to self-report.
“People can fill out a form with photos, any description of damage that they may have, and we'll follow up with that and make sure that their property is included in our initial damage assessment,” he said.
O’Shaughnessy added the damage assessment is not tied to state individual assistance — a disaster declaration by Gov. Mike Dunleavy on Wednesday only authorizes public assistance.
But the damage assessment will be forwarded to the state, O’Shaughnessy said. Individual assistance was not available after the 2025 outburst, which also caused minimal widespread damage, according to the city.
“At this point, we believe that impacts to public infrastructure are very low. We’re aware of some scour around the abutment of the pedestrian bridge at Dimond Park, but as far as impacts to our utility — our wastewater, water supply, stormwater — we believe those to be relatively minor,” he said, adding the footbridge near Dimond Park is currently closed with plans to reopen in coming days. The Kaxdigoowu Héen Dei trailhead from River Road is also closed.
“Just for our awareness as we document this event and forward that information to the state, it's really important for folks, if they have damage in their home, we'd love to hear about it,” O’Shaughnessy said. “And that really helps us get a full picture of the impacts of this event.”
Another incomplete “full picture” is the full extent of damage to HESCO barriers and how they were impacted. An initial assessment is ongoing by the city’s Engineering and Public Works department and the Army Corps.
O’Shaughnessy said the system performed well, with Phase 2 experiencing minor issues. Assembly member Christine Woll asked how much damage would need to be fixed before next year’s outburst.
“That’s the many-million-dollar question,” O’Shaughnessy replied.
He said the ongoing assessment involves opening up the HESCO barriers.
City Manager Katie Koester said Monday the city’s ongoing annual maintenance of barriers may be higher than previously thought, according to feedback from the Army Corps.
The city anticipated $6 million to $10 million in annual costs earlier this summer. Koester told the Juneau Independent it’s unclear at this time how much higher that number could be.
“That really adds to the sense of urgency,” she said.
Koester said she looks forward to the Army Corps’ promise to fast-track a permanent solution and an “industry day” is planned Friday at Tlingit and Haida’s council chambers. The goal of the event is to receive ideas from potential partners and bidders.
• Contact Jasz Garrett at jasz@juneauindependent.com or (907) 723-9356.
