Water levels in Mendenhall Lake and River began rising Sunday morning, indicating that Suicide Basin has started to drain and glacial outburst flooding has begun. The National Weather Service has issued a flood warning that is in effect until Tuesday afternoon.
“The forecast is a worst case scenario forecast, where we’re assuming all of the water in the basin is going to release,” said Nicole Ferrin, a meteorologist with the National Weather Service.
If the basin does indeed drain completely, it will send billions of gallons of water downstream and push flooding to a crest near 15 feet, around the same height as last year’s record-breaking flood, which caused extensive damage to riverside homes.
The Mendenhall Lake and River are expected to reach minor flood stage around 10 a.m. on Monday, and will continue to rise to moderate levels around 10 feet by Monday afternoon. At that stage, Mendenhall Campground will be inundated with up to 3 feet of water covering low areas and 1.5 feet of water blocking Skaters Cabin Road.
Sometime Monday evening flood waters could reach 12 feet, which is when water starts to back up between Riverside Drive at Tournure Street and Mendenhall River School. This is when significant erosion could begin, especially along unarmoured riverbanks.
Flooding is expected to peak at 4 a.m. on Tuesday.
“So hitting those maximum levels in the middle of the night when most people are sleeping,” Ferrin said. “They would want to make action plans ahead of time, so over the next 24 hours.”
Near peak flooding, several feet of water will threaten yards and houses along Meander Way, Killewich Drive, View Drive and low-lying areas of Riverside Drive near Melvin Park.
The south side of Marion Drive, Rivercourt Way, Lakeview Court, Center Court, Parkview Court, Turn Street and Northland Street could also see more than a foot of water starting later Monday night. Some roads may be covered.