As expected, Suicide Basin is filling back up with water after emptying into Mendenhall Lake early last month, Juneau’s emergency programs manager said Wednesday, but the rate of buildup is slow enough that another drainage event might not occur before the winter freeze.
Tom Mattice told the Juneau Local Emergency Planning Committee at its Wednesday meeting that monitoring equipment placed in the basin, which is dammed by the Mendenhall Glacier, by University of Alaska Southeast researchers is showing water levels rising again after last month’s release.
“It is building again, slowly,” Mattice said of the water in Suicide Basin. “It’s very, very low right now.”
A team from UAS installed equipment to track water levels in the basin after last month’s jökulhlaup, or glacier dammed outburst flood, brought high water to parts of the Mendenhall Valley.
Last summer, a jökulhlaup caused minor to moderate flooding in low-lying areas near Mendenhall Lake and the Mendenhall River. It was followed by another smaller event about a month later.
While last month’s event saw water levels on the lake and river crest well below their flood stages, an especially large buildup of water inside Suicide Basin could potentially cause more flooding.
“As we see this thing release over and over and over again, it may get to where there’s a pattern and it releases at about the same level,” said Mattice. “But … you could theoretically always have a bigger one later.”
Mattice said after the meeting that his job is to prepare Juneau for the worst-case scenario, however remote the possibility of it occurring.
“My job is emergency management, right?” Mattice asked rhetorically. “I’m supposed to dream up worst-case scenarios and find a way to solve them. So we’re not saying the Valley’s going to flood tomorrow, but we’re saying, ‘Oh my God, what if it ever did happen?’”
The relative paucity of data from Suicide Basin outburst events adds to the complexity of the situation. The National Weather Service and other researchers only have data from this year and last year.
“I think it’s hard to say when it’s going to flood and how often it’s going to flood,” Mattice told the committee. “Last year, we had two outbursts, so this year, we’ve had one, and we’re moving toward another one, slowly, slowly, slowly.”
Mattice also observed afterward that more frequent releases of less water would be easier to deal with, remarking, “I hope it releases early and often, because then I don’t have to worry about it.”
• Contact reporter Mark D. Miller at 523-2279 or at firstname.lastname@example.org.