Another major flood due to a full release of water from Suicide Basin is possible in October, although a partial release could occur earlier or the ice dam could freeze more solidly as winter weather sets in, city leaders said during a Juneau Assembly Committee of the Whole meeting Monday night.
The possibility was presented by experts to city leaders on Friday, during a meeting to discuss issues related to record flooding in early August that damaged about 300 homes, although it was also noted releases of water from the basin have occurred in previous years following a large summer-season release.
City leaders told Assembly members they don’t want to overstate or understate the situation — simply to make sure the public is aware of it and make what preparations are possible. City Manager Katie Koester, in response to a question from an Assembly member, said that having just been told Friday there’s a reasonable possibility of another large flood next month there aren’t plans in place yet.
“The answer to your question is, no, I do not have a clue what we would do if we had a full release in October,” she said.
However, it is something city leaders and other officials are immediately starting to work on, Deputy City Manager Robert Barr added.
“It would certainly be extraordinarily challenging,” he said. “Thinking through that question is a task that we and our agencies have in front of us in the next week or so.”
A regular meeting of the Local Emergency Planning Committee is scheduled at noon Wednesday at the University of Alaska Southeast’s Rec Center Room 116, and will also be available via Zoom.
The water level in the basin is at 11,156 feet as of Tuesday morning, which is about where it was in mid-June, said Eran Hood, a hydrologist at the University of Alaska Southeast who is among the experts studying the basin. He said it’s not possible to say how probable a large flood from the basin is this fall, but as of now “we need a lot more water in the basin” for such a scenario.
“We’ve never seen a double release that was a large-magnitude release similar to the last two years,” he said. “It doesn’t mean that it can’t happen.”
Primary factors that could lead to higher water accumulation and thus a larger release include warmer or wetter weather, Hood said. However, unlike the flood in August that occurred after record rainfall in July, conditions are generally cooler.
“We’re getting near the time when the higher elevations we should start to see snowfall within the next month, and that would be important because that’ll really shut down melt into the basin,” he said.
An official monitoring website for Suicide Basin established by the National Weather Service states while “another release may occur again this year,” that isn’t necessarily an extraordinary event.
In 2023, there were multiple releases after the very large one from Suicide Basin,” the website notes.
The recording flooding that peaked on Aug. 6 saw the Mendenhall River crest at 15.99 feet, more than a foot higher than what was record flooding the previous year that damaged or destroyed about 40 homes. While the 2023 flood did some of its worst damage by severely eroding the riverbanks along which homes stood, this year’s flood caught many people by surprise as homes in previously unaffected areas were rapidly swamped in the early morning hours of Aug. 6.
Repairs to damaged homes are still ongoing, with people affected telling Assembly members at a meeting last month there aren’t enough workers and supplies available to complete work before cold weather sets in. Furthermore, widespread concern is being voiced about making repairs if homes will again be threatened by another similar flood next summer.
Glacial outburst floods from Suicide Basin have been an annual occurrence since 2011, but experts have stated the recent severity of them is likely to continue in future years.
Barr, presenting information from last week’s meeting with representatives from a multitude of state and federal agencies, said ideally the water building up in the basin will release “as soon as possible,” but “the likely scenario is if the basin releases again this season it will probably release down to its base.”
Friday’s meeting included representatives from the National Weather Service, Alaska Department of Transportation, Natural Resource Conservation Service, Army Corps of Engineers, U.S. Geological Survey, U.S. Forest Service, Central Council of the Tlingit and Haida Indian Tribes of Alaska, and the offices of U.S. Sens. Lisa Murkowski and Dan Sullivan, according to a memo presented by Koester to Assembly members on Monday.
Among the key topics of discussion were short- and long-term mitigation measures. Among the long-term possibilities being evaluated are a drainage tunnel through a mountain into Mendenhall Lake, trench channels in the Mendenhall River to divert water flow and allow it to reach the ocean quicker, and massive blasting around the basin to partially fill it with rock.
But because the basin and much of the area involved is either federal or state land, any long-term solution is years away and will have a high price tag that includes some city funding, Koester said.
“It became pretty obvious that there’s really no short-term construction, trenching (or) building that could be done successfully before next summer,” she said. “So that really pivoted the group’s attention to flood planning.”
One short-term option is six-foot sandbags that could be strategically placed to redirect water flow, Koester said. She said a large section of undeveloped land on one side of the river is one area where water could be diverted.
• Contact Mark Sabbatini at mark.sabbatini@juneauempire.com or (907) 957-2306.
