Heavy snow may result in more spring flooding

This winter has brought plenty of snow, setting a monthly record in December for Duluth. Most of the Northland has gotten more snow than normal, and a lot of it has been the wet, heavy type. 

“So in December, January, and February, we had over six inches of liquid equivalent precipitation, which is double the amount of liquid equivalent precipitation we normally see in a winter season,” said National Weather Service Warning Coordination Meteorologist Joe Moore. “Those December snowstorms that we’ve had and the snow since have all kind of added up and that’s all going to contribute to possible flooding this spring.”

Another factor for flood risk is frost depth, which has benefited from our warmer weather.

“If we look at how much frost we have in the ground, we have about 2 to 4 inches of frost right now. That is really good,” said Moore. “Last year this time we had something like 18 inches of frost. It was a really deep and really solid frost core. and this year we don’t have a lot of frost. That means that when the snow melts in the spring, it should get absorbed into the ground and the soil.” 

The Rainy River Basin is still recovering from last year’s historic flood, but this year’s outlook is looking better. 

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“They actually have near to actually slightly below normal snowfall amounts up there on the International border for the Rainy Basin. And while that doesn’t mean they won’t see flooding, it does mean that the chances are a lot less,” explained Moore.

As for the rest of the Northland, the risk is elevated. 

“We have anywhere from like 5 to 10 inches of water sitting in that snowpack right now, and that is causing us to have an above-normal chance for flooding this spring,” said Moore. “The areas where we have the most snow water, where we’re kind of most concerned right now are on the North shore and on the South shore and also in the Mississippi River Basin. We do expect rivers to be running high in the spring.”

Some rivers handle the extra water better than others. 

Across the Western Lake Superior Basin which is on the North Shore and the South Shore, these are pretty what we call fast basins. These aren’t really big rivers that we have on the North Shore. In the South Shore, they’re usually pretty quick to drain out, and so we aren’t going to see significant flooding that’s going to impact a lot of infrastructure here or homes,” Moore explained. “However, the Upper Mississippi Basin, which is going to affect communities like Aitkin, Fort Ripley, and Brainerd, we do expect to rise. And that is a slower rise, and that’s also a much wider river than we see on the North Shore. 

Portions of the Mississippi River had minor flooding for weeks in 2022, a pattern likely to repeat.

“There probably will be a time late mid-to-late April into maybe even early May where we could see flood levels on the Mississippi River again and maybe further downstream,” said Moore.

Whether we see flooding or not is dependent on the weather pattern over the next six to eight weeks. Rain on melting snow or too much snow melting at once could result in flooding. 

“We would love to have a slow and steady increase in temperatures that resulted in a measured and equal runoff of the snow into the reservoir, into the tributaries, and into the ground,v so that if we did get, you know, some rain events, that there would be capacity in the system to absorb that water,” said IRLWWB Water Levels Committee Co-Chair Eric Swenson. 

With the flood risk beginning in late spring, there is time to prepare. 

“Storm resilience needs to be my watchword. I need to think about all of the actions I take of my property and my family and think about what can I do to strengthen the position that I’m currently in? If I have docks, can I make them adjustable?” said Swenson. “You know, if I’m rebuilding parts of my home, can I engineer my improvements such that they’ll provide more structural flood protection to fend off of these storms?”