WILLMAR -- Pressure from rain water backing up in the storm sewer caused the road surface to buckle early Wednesday morning in the intersection of 10th Street and Kandiyohi Avenue Southwest in Willmar.
Public Works Director Mel Odens explained that pressure from backed up storm water forced water to escape around the manhole casting below the street surface and caused a portion of the road surface to break apart.
Odens said the surface was made passable Wednesday and the casting will be repaired as soon as possible. He also said the solid manhole cover over the storm sewer will be replaced with an open grate to allow water to come up out of the grate.
The current cover is welded in the manhole to prevent back pressure from blowing the cover off and creating a dangerous situation for pedestrians and vehicles. In the past, said Odens, the cover has blown off. Odens said water will try to move its way out through any crack or crevice if enough pressure is built up.
"There's a lot of back pressure that I'm sure lifted the casting a little bit and allowed water to come around the bottom of it and into the road surface,'' he said.
The situation occurred during a heavy thunderstorm between 2:55 a.m. and 4:55 a.m. Wednesday. The official weather station at the Willmar Municipal Airport reported receiving 3.95 inches of rain.
The storm caused the third major street and property flooding event of the year at that intersection and other areas around Willmar.