The U.S. Army Corps of Engineers is prioritizing short and medium-term solutions to glacial outburst flooding in the Mendenhall Valley, but that doesn’t mean the agency has lost sight of the lake tap they chose as their preferred long-term solution late last year.
That’s according to Assistant Secretary of the Army for Civil Works Adam Telle, who spoke at a press briefing in the Juneau International Airport conference room on Tuesday, along with several other Army Corps staff. Telle said the agency never backed out of its commitment to provide the Mendenhall Valley with a long-term solution to glacial outburst flooding. He said the agency is working on short, medium, and long-term solutions at the same time.
“In my view, we can’t wait a decade to deliver — or six years or 15 years — we can’t wait that long to deliver results for the citizens of this community,” Telle said. “So we’re tackling short-medium with the same aggression that we’re tackling long.”
The Army Corps had landed on a lake tap as the long-term solution after a 3-day meeting in Juneau in December. The lake tap would involve digging a tunnel through Bullard Mountain to continuously drain the glacial basin that fills with rain and meltwater, so the water can’t rush out and flood the Valley each year. The local city and tribal governments favored the idea.
But last month, City Manager Katie Koester announced in a Juneau Assembly committee of the whole meeting that the Army Corps had reversed on the long-term solution.
Telle said that’s not what happened. He said the Army Corps has been consistent on getting a long-term solution since the beginning, and the only thing that’s changed is his immediate focus.
“I’ve turned my focus to ensuring we’re doing everything we can right now to protect the citizens of Juneau through short and medium-term strategies,” he said. “We’re expanding the HESCO barriers. We’re raising the HESCO barriers. We’re looking at the channel. We’ve got a significant portion of our national inventory of pumps headed this way today to get ready for the summer.”
Short-term protection
The temporary levee the city built last year remains the short-term solution meant to protect hundreds of homes in the Mendenhall Valley from the flood expected this summer. It’s made of HESCO barriers, which are steel cages lined with fabric and filled with sand that are lined up along the Mendenhall River through suburban neighborhoods.
The temporary levee just barely protected Valley neighborhoods from catastrophic flooding last summer, when floodwaters rose within inches of the top, leaked through in some areas and caused the barriers to slump in others.
Col. Jeff Palazziniis the Alaska district commander for the Army Corps. He said at the press briefing that the Army Corps is working with the city to help raise the levee somewhere between one and two feet. The agency will also build Phase 2 of the levee at no cost to the city, which will extend the barrier to unprotected areas from Back Loop Bridge to just before the Juneau International Airport.
“That adds about four to four and a half miles to the system — we’re talking both sides of the river,” Palazzini said.
He said the agency will also haul more boulders in, called rip rap, to create a continuous armored riverbank and guard against erosion.
Telle said that raising the barriers even a small amount could result in much more protection for the community.
“A small investment in the height can make the chances of overtopping five times smaller,” Telle said.
The city issued a press release earlier this month saying the temporary levee should be completed in July. For the last three years, the flood has occurred in August.
But the HESCO barriers were never meant to last forever, and engineers have said there’s a limit to what they can withstand.
Medium-term abatement
Telle said that the Army Corps is looking at intermediate options that could protect the Valley when the temporary levee expires, and a long-term solution is still on the way.
He said everything is on the table, but named two ideas: sturdier barriers that would go in along the river, or modifying the river channel in some way.
That could potentially look like dredging out a side channel through the floodplain or straightening out the river to move floodwater out to sea more quickly.
“I think there’s been conversation within the community for years about straightening the channel,” Telle said. “This could be done relatively quickly and for low cost. The question is, does that straightening actually just move the risk to a different part of the community?”
He said extensive modeling of the river channel is underway, and at this point, the agency has a pretty good understanding of the upper half of the river and will understand the lower half in the coming weeks.
Long-term solution
Short and medium-term solutions handle the torrent once billions of gallons of water are already coursing through the river, close to neighborhoods, businesses and community infrastructure like bridges and the wastewater treatment plant.
Telle said the lake tap is still the Army Corp’s preferred option to put an end to Juneau’s glacial outburst floods at the source. A tunnel through Bullard Mountain would work like a bathtub drain and continuously empty water from Suicide Basin so it can’t rise to a level that would create a catastrophic flood.
“If you’re looking to solve this problem over the course of 10 or more years, it’s — at this moment — appears to be the most viable technically, but that doesn’t mean that the other ones — other options — are off the table,” Telle said.
He said the agency is working to build infrastructure more quickly, with less paperwork nationwide.
“As we talk about timelines, we have to be clear-eyed about where we are as an organization and our ability to deliver quickly — and I’m committed to fixing that nationwide,” Telle said. “But in terms of timeline, we’re — nothing has changed about our timeline.”
Although he said nothing has changed in the Army Corps’ timeline for a long-term solution, Telle did not specify what that timeline is.
In past estimates, Army Corps staff have said a long-term solution could take from six years to around a decade.
Major General Jason Kelly, deputy commanding general for civil and emergency operations at the Army Corps, said that going through the proper process is important. He said there is still some technical work and modeling that need to be done to make sure that the chosen solution is designed properly.
“There’s absolutely no daylight in our commitment to get the engineering right, get the project management right, and get the business right, of making sure that we’re able to offer a viable solution,” Kelly said.
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