By Rich Larson
As the City of Northfield begins conversations about acquiring the Ames Mill Dam in order to tear it down, Jennifer Tonko said this week that replacing the dam with a rock arch rapids would make the Cannon River safer, healthier and better connected.
Tonko is the Executive Director of Clean River Partners. The non-profit organization works to help people and organizations value, protect and improve the land and water of the Cannon River watershed, which covers nearly 1 million acres across parts of six counties. The group helps residents take practical conservation steps and pursues long-term projects, including permanent land protection.
Clean River Partners is reconstructing a low-head dam at Gorman Lake in Le Sueur County into a rock arch rapids to improve fish passage. Tonko said the group hopes the project will help the pugnose minnow, which she said is endangered and, in Minnesota, is believed to survive only in the Cannon River watershed.
She also pointed to the yellow sandshell mussel, which she said became endangered after its shells were harvested to make buttons. The mussel depends on the longnose gar to carry its young upstream to spawning areas. Because mussels filter water, Tonko said, more of them would improve the river’s clarity.
Tonko said the benefits would grow if other projects move forward. Faribault is considering reconstructing its two dams. If those and the Ames Mill Dam were converted, the Cannon would be reconnected from Morristown to Lake Byllesby. Owatonna has already partially reconstructed a dam on the Straight River, part of the Cannon system.
Tonko said much of what has built up behind the dam is likely ordinary sediment. An environmental assessment would determine whether any contaminants require special handling. In many projects, she said, sediment moves through the system during a short flushing period saying that the Minnesota Department of Natural Resources and the U.S. Army Corps of Engineers would ensure upstream and downstream water levels do not change.
Finally, also pointed out that low-head dams like the one in downtown Northfield have been called “drowning machines” because of a dangerous current, called a hydraulic roller, that forms below them, and she compared dams to blocked arteries, saying they stop the natural flow of water and sediment through the river system.
The Northfield City Council will discuss the dam at a work session Nov. 10. Tomorrow we will have a story focusing on the reasons the City of Northfield is exploring the dam’s demolition
Rich Larson is the owner and General manager of KYMN Radio. Contact him at rich@kymnradio.net
