This is a developing story.
A flood warning due to a break in Suicide Basin, which could result in the Mendenhall River cresting at 11.5 feet by early Monday morning, was issued Saturday morning by the National Weather Service Juneau.
However, the alert notes “there is greater uncertainty in crest timing due to cold temperatures and this being an unusually late season event.” Also, the NWS Juneau noted at its Suicide Basin monitoring website, snow is interfering with equipment used to provide readings of the basin’s water level.
“We really don’t know if it’s going to be a full release,” Nicole Ferrin, warning coordination meteorologist for NWS Juneau, said in an interview at about 9:30 a.m. Saturday. “We don’t have the laser in the basin right now to tell us if it’s completely emptied or not. So we have to assume that it would be a full release, which is what the forecast is for.”
The crest is expected to be between 11 and 11.5 feet between 1-7 a.m. Monday. That is far below the record 15.99 feet on Aug. 6 that damaged nearly 300 homes.
“As of Saturday morning at 9:30 am, Mendenhall Lake was at 4.47 feet and is continuing to rise with its rate of rise increasing over time,” an update posted at the monitoring website at 10:15 a.m. Saturday notes. “We noted a drop of 2.6 feet in the basin into Friday afternoon from the laser pool elevation gauge before snowy weather impacted the reporting of data.”
The water level is expected to reach nine feet by Sunday afternoon and 10 feet by Sunday evening, according to the NWS Juneau alert. At nine feet water will start to affect Skaters Cabin Road and Mendenhall Lake Campground, while at 10 feet the campground will be flooded and “portions of West Glacier Trail will be impassable
“At 11ft View Drive will be flooded and impassable with significant flooding to homes in the area,” the alert notes. “Locations below back loop bridge will see bank erosion along unreinforced river banks Homes along Meander way will begin to see flooding of backyards. Portions of the Dredge Lake trail system will be impassable.”
“At 11.5ft houses along the south side and east end of View Drive will start to flood.”
A hydrograph shows the water levels of Suicide Basin and the Mendenhall River as 10 a.m. Saturday. (National Weather Service Juneau)
NWS Juneau also issued a separate warning on its Facebook page for people to avoid flooded areas due the wintry conditions following the city’s first snowfall Friday and Saturday.
“Stay away from flood waters,” the post notes. “Snow and water on river banks can cause slick conditions which could lead to falling into the flood waters. And with the cold air temperatures and cold water temperatures, there would be a risk of hypothermia.”
Annual glacial outburst floods have been occurring from Suicide Basin since 2011, although record-level floods in early August during the past two years have elevated concerns such flooding may become common. City leaders were warned in early September a second full release from Suicide Basin this year was possible in October, but earlier this month were told a flood level similar to the one in August was unlikely since the water level in the basin was well below full.
The water level in the basin Friday morning was about 1,244 feet, while in early August the basin reached 1,381 feet before the record flood occurred, according to NWS Juneau.
Multiple releases during a year have occurred in the past, although there has not been two large-magnitude releases within a year, Eran Hood, a hydrologist at the University of Alaska Southeast, said in September.
Saturday’s warning was issued while the city is distributing 75,000 sandbags to residents in the area affected by this year’s flood. The distribution is occurring at the Mendenhall Valley Public Library through Tuesday from 9 a.m. to 4 p.m., with sand to fill the bags available at the Thunder Mountain Middle School parking lot and Melvin Park.
The sandbags provided to the city by the U.S. Army Corps of Engineers are part of a multi-tiered effort toward short- and long-term protective measures.
A four-mile semi-permanent levee along the Mendenhall River using Hesco barriers provided by the Corps is currently being evaluated by city leaders as a safeguard that could be in place by next summer. The Juneau Assembly is scheduled to get an update about the proposed project and other flood-related measures at its meeting Monday evening at City Hall.
• Contact Mark Sabbatini at mark.sabbatini@juneauempire.com or (907) 957-2306.
