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Assembly told risks and costs of glacial floods are rising, decides worst-case protection too costly for now
- Mark Sabbatini
- May 5
- 7 min read
Updated: May 6
USACE says 26% chance of 20-foot flood affecting 2,000 homes during next 15 years; Assembly opts for higher barriers than last year, with more protection later possible
By Mark Sabbatini and Jasz Garrett
Juneau Independent
This article has been updated to correct specifics about options being considered by Assembly members to pay for maintenance of HESCO barriers. It has also been clarified that the risk of future basins is unknown, instead of "seen as a strong likelihood."
Preventing potentially catastrophic glacial flooding in the Mendenhall Valley during the next 10 to 15 years may be more costly and difficult than previously thought, Juneau Assembly members were told Monday night.
There’s a 2% chance each year — and 26% chance during the next 15 years — of a flood with a crest of 20 feet that could affect more than 2,200 homes, schools and other buildings, U.S. Army Corps of Engineers officials said during an Assembly Committee of the Whole meeting.
Record crests of 14.97, 15.99 and 16.65 feet occurred the past three years.
“There is a low chance of that happening, but over time those chances compound,” Mike Records, USACE’s lead technical engineer for the Mendenhall flooding project, told Assembly members. He also noted the estimates are subject to wide variability and uncertainties.
The figures presented focused on the rate of water discharge in cubic feet per second (cfs) rather than a projected flood level from that flow. The discharge from Suicide Basin the past three years was 34,000, 42,000 and about 50,000 cfs, respectively.
The 20-foot flood projection is based on a discharge of 90,000 cfs. Last month, city leaders were working toward a decade-long solution for that level of flooding primarily by raising the height of a HESCO barrier levee installed last year.
However, City Manager Katie Koester said Monday that level of protection is likely to cost about $20 million — far more than first anticipated — and the city’s currently available flood funding is more than $8 million short of that amount.
“As staff got into this project and started really digging they realized they had to undo large chunks of the HESCO barriers,” she said. ”So instead of just going in and fortifying them or adding a couple barriers they’ve actually been rebuilding entire sections of the wall. It meant twice as many barriers as in phase one and those things they didn't know until they had crews out there working.”
“So that's when engineering came to me and said, ‘We actually think this, this project that we originally thought was going to be $5 million is actually a $20 million project.’ And I'm like, ‘Well, let's find another solution then.’”
Assembly members, as a result, advanced a plan Monday to spend an additional $3 million to protect against a 63,500 cfs flow rather than $8 million for a 90,000 cfs incident in time for the coming flood season this summer.
The plan still needs approval from the Assembly during a regular meeting that accepts public testimony. The next regular Assembly meeting is scheduled May 18.
Like last year, the Committee of the Whole decision was urged due to the tight construction timeframe to complete barrier installations and repairs before the 2026 glacial lake outburst flood. Construction began nearly a month late compared to last year as a result of Juneau’s extreme winter, according to CBJ.
“Similar to last year, we’re always having to make decisions quickly with incomplete information,” said Denise Koch, CBJ director of engineering and public works. “It always feels uncomfortable, and to some extent, I think that this is a risk tolerance and financial question.”
City and USACE officials said adding more protection is possible in future years.
“I think we're going to have a really hard time coming to agreement on that and where that funding is coming from if we get to that place,” said Christine Woll, chair of the Assembly’s Finance Committee, referring to the higher level of protection. “The community is not with us yet. I just figured out what's going on about 45 minutes ago in terms of how serious this is…So that makes me want to take a more measured approach here.”
The Assembly, approaching the later stages of drafting a budget for the fiscal year starting July 1, is pondering significant spending cuts due to tax cuts passed by voters last year.
Furthermore, city leaders expect to drain most of the city’s fund balance repaying Goldbelt’s $10 million investment in an Eaglecrest gondola project that’s in the process of being cancelled, thus limiting options for providing millions of dollars in additional flood protection.
But the immense cost and destruction of recent floods — and potential future risks — also mean the issue has been at the forefront of the Assembly’s agenda the past couple of years.
A 63,500 cfs flood, without HESCO barriers, is projected to affect $840 million of property including 1,371 homes, and 50 commercial and 35 government structures, according to a presentation by leaders with the city’s Engineering and Public Works department. A 90,000 cfs flood would affect $1.5 billion of property including 2,067 homes, and 145 commercial and 53 government structures.
Glacial lake outburst floods from Suicide Basin have been an annual occurrence since 2011, but scientists say the record flooding the past three years is likely to continue and possibly worsen due to climate change. That risk may exist for a couple more decades until the Mendenhall Glacier retreats enough that its ice dam is no longer a factor for Suicide Basin. But other basins could pose threats in the future and are being assessed.
USACE officials say it may take 10 to 15 years to implement a long-term solution, such as a subterranean drainage tunnel under Suicide Basin that keeps water levels low enough to prevent major floods, a memo by City Manager Katie Koester to Assembly members on Monday notes.
The next major milestone for a Mendenhall glacial lake outburst flood technical study is the submission of a draft technical study to USACE headquarters for review, scheduled for early August.
“Our report is not going to make a recommendation or select an alternative,” said John Rajek, chief of the geotechnical and engineering services branch for the USACE Alaska District. “It’s gonna provide an array of measures at different peak flows that decision makers at the headquarters level can then evaluate and make a recommendation to move forward with.”
To prepare for this year’s flood, city leaders approved a short-term solution that relies primarily on HESCO barriers provided by the Army Corps of Engineers. The first phase of barriers installed last year along about 2.4 miles of one side of the Mendenhall River, designed for a 49,000 cfs flood, was deemed highly effective in protecting 90% of homes in the potential flood zone from damage. The city is responsible for phase one.
City officials acknowledged the solution was not perfect during Monday’s meeting. Seepage and damage meant the barriers needed repairs, leading to the plan this year to raise the barriers to a 90,000 cfs protection level. Flood-impacted residents were notified of this in April, but the plan was downgraded to withstand a discharge of 63,500 cfs by the Assembly on Monday due to the cost.
However, some work had already been done for the 90,000 cfs protections, according to CBJ Engineering and Public Works.
“We are currently about just over $5 million in expenses right now and we have been working on access and fortifying to 90,000 cfs as we’ve been working,” said John Bohan, city project engineer. “As Director Koch had said, we were working at Dimond Park, as well as at Killewich and Melvin Park and Riverside.”
The work on the barriers already raised will not be undone, even if the shift to a 63,500 cfs discharge protection is finalized.
A second phase adding 3.6 miles of barriers to the riverbank, placed on both sides in many locations, is now being installed by USACE contractors. They are intended to protect against a 63,500 cfs flood this year, but “further protection will be considered as part of the mid-term solution, likely in the 2027 timeframe,” according to Koester. The second phase is expected to be completed by July 15, according to USACE.
While the USACE is paying for phase two’s barriers and installation costs, the city is responsible for the ongoing maintenance costs and likely will need to contribute a share toward the development of a long-term solution. Efforts by city and local tribal leaders are being made to seek funds from multiple sources including state loans, federal grants and help from Alaska’s congressional delegation.
A total of 466 property owners were each required to pay $6,300 to cover part of the installation cost of the first HESCO barriers via a Local Improvement District (LID) approved last year by the Assembly.
The possibility of dissolving the LID and considering other funding options — such as a special tax district or areawide tax — to pay for future maintenance of HESCO barriers was discussed by Assembly members Monday. Mayor Beth Weldon said she believes a funding method beyond just collecting from affected homeowners should be considered at future meetings.
“Initially we did the LID because at that time we thought it was smaller,” she said. “Now, looking at the chart and how many houses we’re protecting I think we need to share the burden a little more broadly.”
• Contact Mark Sabbatini at editor@juneauindependent.com or (907) 957-2306. Contact Jasz Garrett at jasz@juneauindependent.com or (907) 723-9356.
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