Water rose several feet above its normal level at Mendenhall Lake and Mendenhall River Thursday due to subglacial drainage, but experts said water levels were not expected to peak until Friday morning.
Outside the Mendenhall Glacier Visitor Center, grassy fields and beaver dams were underwater by Thursday afternoon, courtesy of drainage from the glacier’s Suicide Basin. The United States Forest Service closed three hiking trails due to high water.
“We left Nugget Falls (Trail) open as long as we possibly could,” said Visitor Center ranger Laurie Craig. The trail was closed at about 4 p.m. Thursday after returning hikers reported ankle-high water in places, she said.
Tongass National Forest public affairs specialist Wendy Zirngibl said West Glacier Trail was closed earlier in the day, as were low-lying parts of the Mendenhall Lake Campground. Dredge Lake Trail was also closed Thursday afternoon, Craig said.
While a few houses’ yards may get soaked and a few garages could be flooded with about a foot of water, National Weather Service forecaster Rick Fritsch said, the flooding is not expected to be as severe as it was last year.
The NWS issued a Flood Advisory Thursday after previously issuing a Flood Watch. As of Thursday evening, that advisory was expected to remain in effect until 6 p.m. Friday, with water levels reaching minor flood stages by 4 a.m. Friday.
The NWS advisory said water levels were expected to peak at 9.54 feet at Mendenhall Lake and 12.08 feet at Mendenhall River between 9 a.m. to 10 a.m. Friday. Those levels would put six inches of water over parts of Mendenhall Lake Spur Road between Skater’s Cabin and the West Glacier Trailhead, according to the report.
“At this point in time, we’re going to see a little bit of water on the road out to West Glacier … and (on) View Drive,” said Tom Mattice, city emergency programs manager.
The predicted peaks are well off those seen when Suicide Basin emptied last July, raising water levels at Mendenhall Lake to 10.92 feet and levels at Mendenhall River to 13.07 feet, Fritsch said.
“One foot makes a difference between people on View Drive being fully inundated, and a little water in the yard … (and) up to a foot of water in some people’s garages,” Fritsch said.
Mattice said the city does not anticipate needing to evacuate anyone from the area. He said he has been in contact with residents whose property could be affected by the flooding.
“We know which two homes get affected first, and … have spoken with those homeowners,” Mattice said. “This is not a big event, unless it exceeds expectations.”
Eran Hood, associate professor of environmental science at the University of Alaska Southeast, said a lot of uncertainty remains in the flood forecast.
“The hard thing is knowing how much water is up in the basin there,” said Hood. “That’s kind of the guess we have to make.”
Hood said that even if there is a similar amount of water in Suicide Basin as there was last year — when the basin dumped 9.8 billion gallons into the lake, according to the NWS’ Aaron Jacobs — the peaks were expected to be lower because Mendenhall River’s water levels before the drainage began were lower than they were before the basin emptied last July, and the rate of increase appears to be slower this time as well.
Jacobs said the rate of rise in water levels Thursday closely tracked the NWS forecast, but it was difficult to know for certain how much water would drain from the basin.
“We’ll know once it’s all done,” Jacobs said.
Craig said the Forest Service, United States Geological Survey, City and Borough of Juneau, University of Alaska Southeast and National Weather Service are all working together closely as the situation develops.
• Contact reporter Mark D. Miller at 523-2279 or at firstname.lastname@example.org.