There’s been no shortage of footage on this year’s flooding of the Upper Mississippi River in Minnesota and Wisconsin. For those concerned about the ongoing sedimentation of Lake Pepin, this flood brings more bad news. MPR News reported on the partial failure of the Rapidan Dam, which had an estimated 11.6 million cubic yards of sediment behind it. “More than a century’s worth of sediment was unleashed downstream into the Blue Earth River after the partial failure of the Rapidan Dam last week.” Rapidan Dam partial failure sent more than a century’s worth of sediment pollution downstream | MPR News
The Blue Earth Dam outlets directly into the Minnesota River, which sends close to 1 million metric tons of sediment to Lake Pepin every year. The Blue Earth and Le Sueur Rivers collectively can account for up to 50% of the Minnesota River’s annual sediment load.
Meanwhile, workers at the top of the Lake Byllesby Dam, west of Cannon Falls, are close to completing a $48 million renovation to replace the hydroelectric turbines originally installed in 1910, reported the Pioneer Press. “Last month, heavy rainfalls drenched Minnesota, causing significant water flows throughout the state, notably along the Blue Earth River near Mankato. The Rapidan Dam was overwhelmed by the rushing water, as 34,800 cubic feet per second blasted down the river…Both dams have a similar hollow concrete construction and are of the same age, but the geography between the two sites varies greatly and the Rapidan Dam experienced water flow rates at a much higher clip. To put the historic water flow figures from the Blue Earth River in perspective, the Cannon River at the Lake Byllesby Dam crested at about 15,000 CFS on June 22, less than half of what Rapidan experienced.” Dakota County dam upgrade expected to double hydro power output (twincities.com)
Both the Cannon River and the Minnesota River need to cut their sediment loads in half by 2030 to meet Minnesota’s water quality standards for the impaired portion of the South-Metro Mississippi River to Lake Pepin.
The Waterways Journal reported on the closure of Lower St. Anthony Falls Lock and Dam to all traffic on June 17 and Minneapolis area locks and dams to recreational vessels on June 21st from the resulting high water in Minnesota.
The pressure put on our waterways by peak flow events like we just experienced create the most destructive impacts to our waterways, our ecosystems, and our infrastructure. We need everyone on board to keep the river healthy and viable for all. Increasing opportunities for groundwater recharge, wetland restoration, water storage for irrigation, water and sediment control basins, and continuous living cover (perennial and winter-annual crops) in vulnerable areas can help!