A possible worst-case scenario — the Snow Glacier Lake flooding its contents into the Kenai River this week on the heels of the Skilak Glacier Lake also releasing — actually worked out to be the best-possible scenario for residents living in flood-prone areas downstream.
According to the National Weather Service Alaska-Pacific River Forecast Center in Anchorage, Skilak Glacier Lake released the week of Oct. 10, and forecasters announced Monday that the Snow Glacier Lake is draining into Kenai Lake this week. It’s unusual for the jokulhlaups — an Icelandic term meaning the release of a glacier-dammed lake — of the Skilak and Snow glaciers to happen so close together, and such an event could cause significant flooding concerns. But in this case, current conditions made for as uneventful a release of both lakes as possible.
“You couldn’t have planned it any better,” said Eric Mohrmann, director of the Kenai Peninsula Borough Office of Emergency Management.
The lakes — formed by meltwater and rain runoff accumulating behind the glaciers — release on a two-year cycle. The ice can only hold back so much water before the pressure becomes too much for the glacier to withstand.
“They need to fill to a certain level to form enough hydraulic head to actually sort of lift up the glacier that’s blocking it, and it starts to erode pipelines, basically, through the glacier for the water to start to slowly leak out,” said Ben Balk, a hydrologist with the river forecast center. “It finally just completely flushes and then the lake is empty so (the glacier resettles and the water release) just stops.”
Both glacier lakes last released in 2009, with Skilak Glacier Lake draining in August 2009 and Snow Glacier Lake releasing in October 2009. So both were due to release again this year, and just happened to release around the same time. And the lakes have been tending to release a little earlier, Balk said, possibly due to thinning of the glaciers.
Depending on conditions, one glacier lake release could be enough to cause flooding downstream, especially in low-lying areas in Cooper Landing, Kenai Keys near Sterling and Big Eddy in Soldotna, and both releasing extra water into the Kenai River could double the odds of flooding.
“The biggest concern for residents down there is that they both go out together, because there’s two big lakes all draining at once, but this year they were staggered just enough to avoid any problems,” Balk said.
It usually takes several days to a week for extra water from a jokulhlaups to filter through the river
system. In a high-water event from heavy precipitation, the river sees a sharp rise in water level and a slow recession. It’s the opposite with a jokulhlaup, where the glacier lake release starts slow and builds to a quick surge, which then abates quickly.
The influx of water from the Skilak outburst had already filtered through the river system by the time the Snow outburst began. When Skilak released, the river forecast center predicted a 1- to 2-foot rise in river levels, and the water fell quickly due to dry weather at the time. The Snow release is expected to cause water levels to rise 2.5 to 3 feet at Cooper Landing by Friday and 1 to 1.5 feet on the lower Kenai River following that. The flood crest is expected to reach no more than 12 feet in Cooper Landing, where the minor flood stage level is 13 feet.
The releases are coinciding with lower water levels typical of late fall. Even though fall and early winter can see increased storm activity dumping precipitation over the Kenai Mountains, temperatures are typically cool enough this time of year that most precipitation over the headwaters of the Kenai River falls as snow, not adding much to runoff and water levels in the river.
The water level of the Kenai River already was low, making it easy to accommodate the outbursts that were staggered luckily enough to not contribute to each other.
“If one of those lakes release when the river is high it can be enough water to lift it further to flood levels or maintain it at high flood stage levels for a while,” Balk said. “But the water level has been dropping.”
Another concern is that the lakes will release in the middle of the winter when the Kenai River is iced over. Even though water levels are lower in winter than spring, an increase of water when the river is iced over can break up the ice cover and send it jumbling downstream, scraping along the banks and causing damage to any structures in the way. Ice chucks can get caught in a succession of tangles downstream and cause water to dam up behind the blockages, creating flooding. That happened when the Skilak Glacier Lake released in January 2007 and caused significant damage to river structures downstream, such as boat launches and fishing platforms, as well as substantial flooding to low-lying areas, including Big Eddy in Soldotna.
“It causes a big mess. Historically the worse flooding in the Soldotna area is due to winter releases of Skilak,” Balk said.
“But these actually are releasing at the best time — late fall before winter freeze-up and after a period
when we haven’t had significant heavy rainfall,” he said.
Snow Glacier Lake is actually bigger than Skilak, but it feeds into Kenai Lake, upstream of the Skilak Glacier Lake. The large lakes mitigate the effects of the extra water, so even though the Snow Glacier Lake releases more water, its impact on river levels downstream is less because the water flushes through Kenai and Skilak lakes, rather than just Skilak, Balk said.
Even though flooding is not anticipated from the Snow Glacier Lake release, Balk said it would be wise for river residents to keep an eye on water levels. Now would be a good time to remove boats, docks, stairways, fishing platforms or other river structures for the winter, if they haven’t already been removed.
Mohrmann took the opportunity to remind residents that, even though the lake releases aren’t causing an emergency at this time, it’s a good reminder to be ready in case a disaster does strike. Families should make an emergency plan and each household should prepare an emergency kit with supplies to last at least three days in case they have to fend for themselves.
Monday was a good reminder to be prepared for scary occurrences, Mohrmann said.
“Here it is Halloween, there will be all kinds of monsters and zombies out there. People ought to make sure they’ve got their emergency preparedness kits ready in case the zombie apocalypse comes,” he said. “Have supplies for 72 hours so if you have to fend for yourself for a few days you can make it.”
Residents can check flood warnings at River Forecast Center’s website, http://aprfc.arh.noaa.gov.