With the snowpack reaching record proportions, and more storms on the horizon, both residents and officials are starting to worry about flooding. No one can predict the future, but history is helpful to understand if flooding will occur.
Matt Lindon is a long-time Park City resident and hydrologist with Loughlin Water Associates. He said 1983 and 2011 had huge snowpacks, but the difference between the two seasons was how fast it melted. 1983 saw historic flooding while 2011 did not.
“‘'83 was a pervasive snowpack at all elevations, at all aspects. The south facing Snow was there, the low snow was there,” Lindon said. “And it hung on until till about Memorial Day, and then it all came off all at once. And that's when we experienced flooding from a fairly healthy snowpack. Whereas in 2011, we had had a good snowpack, but it came off slowly, it came off the South faces first it came off the low elevations first. And, and that's pretty typical.”
Lindon said the key to snowpacks this large and unprecedented is the weather in April and May.
“So Thaynes Canyon we have maybe 35 inches of water up there and in Alta and Snowbird say we have 60 inches worth of water up there waiting to come down,” Lindon said. “You know, if that comes down an inch a day, we don't even notice it. But if it stacks up until late April into May and comes down to three or four inches a day, that's like getting a three or four inch rainstorm every day. That's when we start seeing the flooding.”
Lindon said there are three factors to look for in a snowpack to determine when it’s going to begin the runoff.
“The snowpack has to reach isothermal, which means the snowpack has all the same temperature through the whole snowpack. And we're not we're not warming up our snowpack yet,” he said. “Number two, the snowpack should reach a density of about 50%. And when those two things are realized, if we get three days in a row without a freeze, then the snowpack then the runoff starts, you can almost set your clock to it when you get those three things.”
Lindon explained that groundwater will benefit from the snowpack if it doesn’t run off too quickly. The soil typically can absorb an inch or two a day, but three to four inches will become a problem.
“And, you know, the deep groundwater has kind of a deficit from, you know, we're in a 20 year drought. And we've been over pumping things for a long, long time. And so this snowpack can go a long way towards recharging that deeper groundwater.”
As far as flood preparation goes, Lindon said make sure that sump pumps are working and check under drains in low lying communities and make sure they are flowing and viable. He also had this to say.
“And the last thing that you know, that we always say is with the higher water, higher flows, take care of yourselves, take care of your children around running water. There's always accidents, and we need to be aware that this water is cold. It's fast. It's very dangerous.”
For more information on flood preparation visit the web version of this report at KPCW.org https://summitcounty.org/2342/14629/Flooding-Information
