This is a developing story.
An uncharacteristic late-October glacial outburst flood from Suicide Basin caused the Mendenhall River to crest at 10.77 feet at 11:30 p.m. Sunday — both earlier and lower than had been forecast — with a flood warning for the area canceled at 3 a.m., according to the National Weather Service Juneau.
A drop in Suicide Basin’s water level observed Thursday night had forecasters on Saturday morning predicting a river level of up to 11.5 feet between 1 and 4 a.m. Monday.
But Grant Smith, a NWS Juneau meteorologist, said in an interview at about 12:45 a.m. Monday the water level has been declining steadily since the reported crest and was at about 10.3 feet as of 12:30 a.m.
“The laser sensor was showing that we were at the bottom of what has been measured as the base of the bottom of the basin,” he said. “So at this point we’re thinking it’s done.”
The water level in the basin fell to 927 feet during the release, compared to 945 feet during the record flood that occurred on Aug, 6, thus “indicating a full release,” according to NWS Juneau’s Suicide Basin monitoring website. The most recent release was triggered with the basin at about 1,244 feet.
An update issued by the City and Borough of Juneau shortly after 9 a.m. Monday states “minimal impacts were observed to residential neighborhoods.”
Areas that were closed — View Drive, Skater’s Cabin Road, Kaxdigoowu Héen Dei (Brotherhood Bridge Trail) and the Dimond Park pedestrian bridge — were scheduled to be reopened shortly, according to the announcement.
“Please continue to avoid the Mendenhall River during this time,” the announcement adds. “The banks are unstable and the river is full of trees and debris following the flood.”
While the water is retreating, temperatures in the Mendenhall Valley at about 12:45 a.m. were 23 degrees, Smith said. That means streets and other surfaces covered with water will become icy. Juneau set a low-temperature record on Sunday night at 22 degrees, breaking the previous record of 23 degres set in 1961.
A flood warning for vulnerable areas, including View Drive and Meander Way, was canceled by NWS Juneau at about 3 a.m. Monday when the river level dropped to 8.67 feet, below the nine-foot minor flooding stage. However, the agency warned at its monitoring website, “mariners should be advised during the outburst event, numerous trees and debris have been reported in the river and may have washed downstream.”
The lower-than-expected crest of this weekend’s flood reverses the situation that occurred Aug. 6 when the Mendenhall River crested at a record 15.99 feet — a foot higher than the worst-case forecast — causing damage to nearly 300 homes, many in neighborhoods not expecting impacts.
Flood-related issues, including ongoing recovery efforts from the August flood and preventative measures for future years, are scheduled to be discussed by the Juneau Assembly at its meeting at 7 p.m. Monday. The city also announced Sunday it has already distributed virtually all of the 75,000 free sandbags it started offering residents in flood areas on Saturday, so distributions scheduled Monday and Tuesday have been canceled.
• Contact Mark Sabbatini at mark.sabbatini@juneauempire.com or (907) 957-2306.
