MPR’s Tom Weber interviews Sean Christenson, Willmar's city engineer, about how the city is dealing with historic deluge on August 10, 2016…one he considers a 1,000-year rainfall event.
This extreme rainfall event pounded parts of central and southeastern Minnesota. The highest total of 9.74 inches was recorded just east of Willmar. The storms created two 6-inch rainfall areas combined to cover just over 1,000 square miles, making 2016 a rare year with two "mega" rain events in Minnesota (a larger event hit northern and central Minnesota on July 11-12, 2016).
Transcripts
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SPEAKER: After last night's heavy rain, some towns received nearly two months' worth of rain in the last 24 hours. Olivia in Central Minnesota's Renville County was the unofficial rainfall leader, getting more than 8.5 inches of rain. And in Wilmar, just North of there, they received close to the same.
This morning on MPR News with Tom Weber, Wilmer's city engineer, Sean Christensen, laid out what the historic deluge had people in the area dealing with.
SEAN CHRISTENSEN: We've got a number of intersections that are still underwater-- some of the lower ones-- and coned off or barricaded off. And we're, of course, still urging people to not go through those intersections. We've got a number of stalled cars in the middle of them, of people that want to try it anyway. So we've got that going on.
We've got a lot of water in basements. Unfortunately, some is stormwater, some is sanitary sewer. That's really overwhelmed our new wastewater treatment plant.
TOM WEBER: So what does that mean? The wastewater system is overwhelmed, meaning what? Stuff's draining improperly? What's going on there?
SEAN CHRISTENSEN: No, so what happens is any large storm event-- of which, by the way, the last numbers I heard, I've heard anywhere from 8 and 1/2 to 12 inches of rain in about 18 hours.
And which, doing the math and doing a quick check on the NOAA charts, that pushes the 1,000-year rain event, for those that are counting years. So it's something that, you can't talk to anybody that's ever seen this much rain before.
So what happens is we've got you get an amount of water that you've got to deal with, that's going in pipes and low areas. Ends up in a sanitary sewer and ends up out at the wastewater treatment plant, which can't handle the amount of flow. Even our design-- on a wet design, is what they call it on that wastewater treatment plant.
So rain events, considered there, is designed for about 7.5 million gallons per day. And we touched about 23 million gallons here the last 12 hours.
SPEAKER: That was Wilmar city engineer Sean Christensen speaking earlier this morning with MPR News' Tom Weber.