MANKATO — ■ The more powerful flows are altering the river.
The Minnesota River from Mankato to St. Paul has widened by 50 percent since 1938. The scene along Seven Mile Creek County Park is playing out all along the lower half of the Minnesota River.
Farm groups have begun a more aggressive campaign to counter the image of drainage as the primary foe, pointing to research that high bluff erosion and bank erosion are coming from more precipitation.
But researchers increasingly say otherwise.
“ We don’t know absolutely everything,” said Norman Senjem, who recently retired from the Minnesota Pollution Control Agency after many years of overseeing river research. “But post-World War II to about 1980 is when we see the biggest uptick in sediment, the biggest uptick in Lake Pepin filling in. It’s the time of increased mechanization in agriculture.
“Precipitation plays a role, but primarily it’s landscape changes.”
Shannon Fisher, who heads the Water Resources Center based at Minnesota State University and is director of the multi- county Minnesota River Board, said he’s seen enough credible research to believe farm drainage is a major factor.
“In my opinion, the drainage we’re doing is having an impact on the hydrology and we’re going to have to address it. Water storage (on the landscape) is going to be very important, and it’s hard to sell to people as we put more tile in the ground.”
The latest study to peg farm drainage as the culprit was recently released by scientists at the St. Croix Watershed Research Station and the University of Minnesota. The research included examination of 70 years’ worth of records on rainfall, flow and land use changes along the 21 tributaries to the Minnesota River.
Shawn Schottler, one of the scientists who worked on the research, said everyone agrees streambank and bluff erosion are putting a majority of sediment in the river. Their latest study looked at how much of that could be tied to increased precipitation.