MANKATO — The increase in field drainage systems across southern Minnesota has caused a dramatic increase in the flow of water in the Minnesota River and other tributaries, leading to bank erosion and a widening of the channel that pollutes water and is causing a rapid fill-in of Lake Pepin on the Mississippi River.
That’s the conclusion of a three-year study published last week by a team of researchers at the Science Museum of Minnesota and several major universities.
“Any type of drainage that reduces the time water is on the landscape will increase river flow,” said Shawn Schottler, senior scientist at the St. Croix Watershed Research Station of the Science Museum of Minnesota.
Schottler said they were surprised to find it wasn’t simply the fact that drainage moves more rain water to rivers quickly, but that the advanced drainage systems have significantly reduced the amount of evaporation.
Historically, 70 to 80 percent of all rain that falls on southern Minnesota evaporates into the atmosphere, either through plants or from sitting water.
“Drainage takes water that would have evaporated and sends it to the river,” Schottler said.
There are critics of the study.
Leon Schoenrock, a farmer in Waseca County and former president of the Waseca County Soybean Association, read the study and said he isn’t convinced.
“I think even in their own study they say they don’t necessarily know all the answers yet,” he said.
“There’s a perception out there that farm drainage is causing this problem. But all the low wetlands were drained in the ’40s and ’50s and that may have caused a problem in the rivers then. But studies show that when you drain high ground, it acts like a sponge and reduces water coming off.”
Schoenrock said he believes the increased rainfall and more big rain events are more of a problem. “Those big events cause flooding.”