Update: 12:40 p.m.
The city and borough of Juneau has closed View Drive and all roads leading into Meander Way, from Rivercourt Drive to Killewich Avenue along Riverside Drive.
The city is asking that all non-essential persons stay out of the area, as roads may become impassible due to flooding from the Mendenhall Lake and River.
Power may be shut off to isolated areas affected by flood waters.
The city also has closed the Brotherhood Bridge Trail, including the pedestrian bridge.
“Anywhere between 4 p.m. and 10 p.m. is our best guess for the peak,” says National Weather Service Meterologist Bob Tschantz.
He says people should stay away from the saturated banks of the Mendenhall River.
They get under cut by the water that’s running, and eventually the ground over the top just kind of sloughs off,” he says. “River bank erosion is a very big concern and you don’t want to be caught standing on the edge of the riverbank when it collapses into the river.”
Wednesday evening’s jökulhlaup, or glacial outburst from Suicide Basin above Mendenhall Glacier, has prompted flood warnings for Mendenhall Lake and Mendenhall River.
As of 9:15 a.m. Friday, Mendenhall Lake was measured at 10.18 feet and Mendenhall River registered 12.1 feet, or over flood stage for both those water bodies.
The National Weather Service expects new records will be set before the Mendenhall Lake and Mendenhall River crest late Friday afternoon or early evening. Their forecast calls for the lake to peak at 11.99 feet, beating the previous record of 11.2 feet. The river is forecast to top out at 14.95 feet, breaking the old record of 13.8 feet.
Prior to Wednesday evening’s jökulhlaup, the Mendenhall Lake was measured at a level of between 5 and 6 feet and Mendenhall River was measured as between 8 and 9 feet.
“So, the campground is beginning to flood,” said meteorologist Rick Fritsch said during KTOO’s Morning Edition program on Friday. “If we don’t have water over the West Glacier Spur Road (at 5:30 a.m.) that goes past Skater’s Cabin, (then) it will soon be over that road as well.”
Fritsch said water volumes at peak flood will be about 20,000 cubic feet each second, or over three times the river’s usual flow for this time of year. The total amount of water discharged from Suicide Basin may be as high as 11 billion gallons.
The National Weather Service advises against tying up traffic by rubber-necking at the bridges, and warns people not to walk or drive through flood waters.
“You really don’t have a full appreciation for how strong the power of a swiftly moving river is,” Fritsch said. “It only takes a few inches to actually start dragging cars sideways and a lot less than that for people.”
Also, stay away from the river bank which can erode quickly with flood waters and swiftly flowing current.
The U.S. Forest Service has already closed the Mendenhall Lake campground to new visitors and planned on evacuating current tenants of the campground on Friday. Other facilities within the Mendenhall Glacier Recreation Area — such as Skaters Cabin, East and West Glacier Trails, and the Nugget Falls Trail — are closed on Friday.
Forest Service managers also warn that rising water levels could prompt rock falls and collapse the ice caves.
The City and Borough of Juneau is warning residents and drivers that streets in the Mendenhall River area could flood through the storm drain system.
The Airport Dike Trail, formally called the Emergency Vehicle Access Road, has been closed to all vehicle and pedestrian traffic.