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Five ‘mid-term’ flood solutions, including $1.5B steel wall along Mendenhall River, detailed in Army Corps report to CBJ
- Jasz Garrett
- 1 day ago
- 7 min read
Updated: 1 day ago
Residents worry high-cost wall could deter long-term solution; city manager says options won’t get further scrutiny until after this year's outburst
By Jasz Garrett
Juneau Independent
A “mid-term” glacial flooding solution with a cost estimate of $1.5 billion — more than the price tag for a preferred long-term “lake tap” alternative — is included in a May draft report to the city from the U.S. Army Corps of Engineers.
The mid-term alternative of sheet piling would form a continuous cantilever steel wall along the Mendenhall River for approximately five miles. The sheet pile walls would be between four and 19 feet high, extend 13 to 73 feet underground, and be 54 to 66 inches in diameter, according to the Army Corps.
The draft report details three other mid-term solutions: further reinforcement and raising of HESCO barriers, improving the Mendenhall River’s channel, and a combination of flood risk management measures.
There is also an “additional concept” of a Suicide Basin pumping system. A cost estimate for this option is not included since it was not developed beyond a conceptual level.
City Manager Katie Koester said the City and Borough of Juneau is holding off on making any decisions until after the 2026 flood. As of Monday, the National Weather Service Juneau’s Suicide Basin monitoring website is projecting the flood will occur in early to mid-August.
“Right now all the focus is on preparing for that,” Koester said. “And like every year, we will have more information after the event.”
The report was drafted by AECOM, a consulting firm contracted by the Army Corps. Its report notes the concepts rely on preliminary data and final designs require extensive subsurface investigations, particularly for sheet pile walls.
“Existing geotechnical data along the Mendenhall River corridor are insufficient to fully support design or evaluation of a continuous wall system,” the report states. “While this does not preclude the concept, additional subsurface characterization is necessary to reduce uncertainty and advance the design.”
All draft concepts were evaluated against a design peak flow of 90,000 cubic feet per second. This year’s recently completed HESCO barriers were constructed to protect against a peak flow of 63,500 cubic feet per second.
The baseline project costs are based on a 20% design level, with the estimates subject to change as the
design process progresses, according to the report.
The proposed option of about $130 million improves barriers, stacking HESCOs up to four units high. The estimate assumes that labor, fill material, and the required equipment are locally available, with units shipped to Juneau for construction.
The nearly $288 million option titled “flood risk management measures within Mendenhall River” constructs cutoff channels at oxbows to reduce peak water surface elevations. It does not eliminate the need for HESCO barriers. The primary cost risk for this option is the disposal of the excavated material, according to the report.
Another alternative of approximately $407 million would combine flood risk management measures, utilizing both HESCO improvements and channel modifications to reduce flood risk. It would reduce the number of barriers needed due to protection provided by channel cuts.
Sheet piling along the most flood-vulnerable portion of the Mendenhall River was tentatively identified as the mid-term option offering the highest flood protection, according to the Army Corps.
“Unlike the other alternatives, this alternative will require testing and long-lead material/equipment acquisition which cannot be directly sourced in the Juneau area,” the report states, recognizing it is significantly more costly.
The steel wall system would replace HESCO barriers installed and reinforced this year.
Reinforcing and elevating Phase 1 of the levees required an approximate $14.8 million investment from the city this season, and the construction for Phase 2 cost the Army Corps about $35 million.
The city anticipates $6 million to $12 million in annual maintenance costs for HESCO barriers, which could be reduced with sheet piling, according to Koester.
However, in response to inquiries sent by the city about municipal responsibility, the Army Corps stated upon completion of construction and formal project turnover, the infrastructure is handed over to CBJ.
“At that point, all Operations, Maintenance, Repair, Rehabilitation, and Replacement (OMRR&R) responsibilities, including rebuilding any failed sections, become the sole responsibility of CBJ as the non-federal sponsor,” the reply states. “CBJ can always make a formal request for assistance with this effort, if desired.”
The Army Corps asked if CBJ would support continued evaluation of the sheet pile alternative.
“We responded with a long list of questions about what the project would look like, the potential impact of sheet piling, and concurred with the USACE's request to further evaluate the option alongside their evaluation of other alternatives, including an emergency tunnel or lake tap,” wrote Deputy City Manager Robert Barr in an email Friday. “No formal recommendation from the USACE has been made, nor, for that matter, has one been accepted by CBJ.”
He added CBJ cannot speak to the decision-making process regarding the Army Corps’ final recommendation for a mid- or long-term solution.
John Budnik, a spokesperson for the Corps’ Alaska District, wrote in an email Monday that inquiries from the Juneau Independent would be sent to federal headquarters, giving no timeline for a response.
Koester shared information about updated USACE mid-term flood solutions to the Juneau Assembly in a staff report on June 8.
“We don’t have any information on where those would go, what they would look like,” she said regarding sheet piles. “It is reasonable to assume that they would be concentrated in the Phase 1 area because again, Army Corps has looked at the whole river and said it’s too expensive to do the whole river.”
The city has given authority for the design to be further developed while it conducts outreach.
Koester said there are many steps left in the process, including community engagement in the future as more questions are answered.
“I know community members are going to be like, ‘Wait, I live on the river. Will I get sheet piling? What will that be like? When would that happen?’” she told the Assembly. “And those are just answers that we don’t know.”
A July 20 Committee of the Whole meeting intended to discuss mid-term solution design and flood mitigation updates as a whole was canceled, with promises to reschedule after this year’s flood.
About 40 residents gathered at the Mendenhall Valley Public Library on Thursday for a Juneau Flood Solution Advocates meeting. The mid-term solutions are intended as temporary measures to reduce risk until a permanent project is developed. But attendees had their doubts a lake tap would be pursued if a medium-term alternative is chosen.
The sheet piling would take five years, while all other mid-term solutions are estimated to take about a year, according to the report. As of June, the Army Corps and AECOM said corrosion protection would be incorporated into the final sheet pile design.
While untreated steel piles can last 30 to 50 years, the exact rate of degradation depends heavily on environmental conditions, according to the Army Corps.
“Where in the world do you begin?” Debbie Penrose-Fischer, leader of the advocacy group, asked the room. “Does anyone think this is a good idea?”
Not one person raised their hand. The majority of homeowners shook their heads, citing the cost, time and disturbances from pile driving and drilling as reasons.
“I can't even imagine it being physically possible. And the mental health implications would be nuts — boom, boom, boom, for five years,” said Tim Geib, who lives on Northland Street.
The report states much of the sheet piling work would occur on privately owned property, possibly requiring residents to leave their homes temporarily due to the construction.
It says Valley residents would be placed in local hotels paid by the city and does not specify how long individual households might be displaced. Large crawler cranes could be positioned in front yards, the report states. Access would occur through residential driveways and yards.
The draft report states continuous inspection would be necessary to monitor potential structural impacts as a result of the drilling.
It also states flood risk reduction for the View Drive peninsula is not feasible under any of the mid-term concepts due to its low elevation, and that buyout or relocation may be the neighborhood’s only option.
Members of Juneau Flood Solution Advocates started collecting signatures to expedite an enduring solution with the assistance of local mining expertise last month. One of their slogans is “fund the solution, not the band-aid.”
“It didn’t feel very temporary,” Penrose-Fischer said while presenting the mid-term solution report. “So I asked myself, is this all that we would get? And then the long-term would just be not attainable?”
She said she was shocked when she saw the $1.5 billion cost estimate. Early Army Corps’ cost estimates range from $613 million to $1 billion for a long-term lake tap solution, but a local mining expert claims the cost could be reduced significantly using a drill-and-blast method.
“We don’t want to spend any more money on anything that’s not a solution,” Penrose-Fischer said.
The lake tap alternative, recommended by the city, U.S. Forest Service and Central Council of Tlingit and Haida Indian Tribes of Alaska, would bore a tunnel through Bullard Mountain to continuously drain Suicide Basin.
Ashley Heimbigner, CBJ communications director, reiterated the city is still seeking a permanent solution.
“The city continues to focus on the fastest, most cost-effective, safest way to mitigate and eliminate this issue, which again we’re hoping is an emergency tunnel,” she said.
At Thursday’s meeting, she said the mid-term solutions are part of Army Corps Sec. Adam Telle’s vow that all options — short, medium and long — are on the table.
• Contact Jasz Garrett at jasz@juneauindependent.com or (907) 723-9356.
