What makes potential flooding in Utah this weekend different from normal runoff?

Mar 10, 2023, 9:14 PM

SALT LAKE COUNTY —  The flooding potential Friday evening is different than the flooding that Utah prepares for when the snow starts to melt in April and May.

The high-elevation snowpack will not start to run off this weekend.  But a lot of properties on the east bench, the Wasatch Back, and in the Ogden Valley have several feet of snow.  If a lot of rain falls on this snow, that can be a problem.

“We’re expecting some very localized kind of nuisance flooding in some areas,” said National Weather Service Hydrologist Glen Merrill.

Anywhere there are feet of snow on the ground below 8,000 feet in elevation could present a problem on any property without good drainage.

The outside sandbag set up is for residents to pick up in Salt Lake County. (KSL TV) The orange sandbags are those ready to use by Unified Fire Authority in the event of neighborhood flooding. (KSL TV) FILE: The outside sandbag set up is for residents to pick up in Salt Lake County. (KSL TV)

Merrill said some properties could be vulnerable on the Wasatch Back.

“They just have so much snow right now, and whenever we get a rain-on-snow event, it’s something to definitely pay close attention to,” the hydrologist said.

It’s called sheet flooding because the rain hits the snow and runs off like a sheet.

“You melt the water through the snowpack, you saturate the soils. It’s got nowhere to go other than where it wants to,” Merrill said.

That’s different than the snowmelt runoff later in the season that can overflow creeks.

Sheet flooding soaked Mendon in Cache County in February 2017.  Flood water was running in the streets, and into basements.

“We had that rain on snow where three feet of snow was lost, and you also had two to five inches of rain on top of it, and that’s where the sheet flooding happened,” Merrill said.

Salt Lake County Emergency Management raised its level of readiness Friday morning.

“It’s a big enough deal for us that we are trying to lean forward into this so that we’re not caught flat-footed,” said Clint Mecham, Salt Lake County Emergency Management Director.

“All of these piles of snow that have been built up in parking lots and places like that are going to melt and runoff and they have a potential to overwhelm those storm drain systems and create flooding problems that are different from the spring runoff,” Mecham said.

If you’ve had flooding before, you might have problems again, he said.  Create a buffer around the foundation of your home.

Most communities offer sandbag supplies, and fire departments are ready for neighborhood flooding.  The Unified Fire Authority always keeps 14 pallets of sandbags in its warehouse and pumps ready to go.

“So we can help pump that water away from property,” the emergency manager said.

The hydrologist is not expecting the volume of rain that caused the problems they saw in Mendon six years ago, but localized storms could still cause problems.


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What makes potential flooding in Utah this weekend different from normal runoff?