Minnesota Falls dam may be demolished before the start of the new year
MINNESOTA FALLS — One of the state’s largest dam removal projects in recent years is about to unfold: The Minnesota Falls dam could come tumbling down before the start of the new year.
Rachel Construction of St. Michael, Minn., hopes to start work on the project this coming week, pending final approval from the U.S. Army Corps of Engineers and the Minnesota Department of Natural Resources.
The U.S. Army Corps of Engineers recently approved the permit needed for demolishing the 107-year-old structure on the Minnesota River, according to Jim Bodensteiner, a senior environmental analyst and scientist with Xcel Energy. Final approval is still needed on aspects of the contractor’s plan.
The 600-foot long, 14.5-foot tall structure will be removed as well as sediment in the upstream reservoir. The company is estimating that up to 15,000 cubic yards of silt may need to be moved, and between 2,500 to 3,000 cubic yards of material from the dam.
The dam is built mainly of concrete and granite block, and most of it is free of rebar.
The company plans to use most of the material and sediment as the base for restoring the north riverbank, where a channel for a hydro-electric system exists. Excess sediment will be transported to the Minnesota Valley coal plant owned by Xcel Energy (and slated for demolition in the future).
Records show that 21 dams have been removed in the last 28 years in the state, according to Jason Boyle, state dam safety engineer with the Minnesota Department of Natural Resources. This is one of the larger and more significant, he noted.
Two other, similar sized dams — the Shady Lake dam near Oronoco on the Zumbro River and the Mud River dam near Redby on the Red Lake Reservation — are also eyed for removal this year, according to Luther Aadland, river ecologist with the Minnesota DNR in Fergus Falls.
The Minnesota Falls dam no longer serves a purpose for Xcel Energy. The company chose to remove the dam as a less costly option than repairing it. Estimates for its removal were in the range of $2 million, as compared to $6 million for repairing it and meeting state safety requirements.
The dam held a hydro-generation system until 1961 and its reservoir had provided cooling water for the Minnesota Valley coal plant, which no longer operates.
As a result of the drought conditions, river flows at the Minnesota Falls site are ideal for the removal, noted Bodensteiner. The Minnesota River is running at 200 cubic yards per second upstream at Montevideo, below the low flows normal for this time of year.
“Other than the cold, there are a lot of benefits to doing the work this time of year,’’ said Bodensteiner.
If the schedule goes as hoped, the removal project will start with the removal of the final stop logs on the dam this coming week. The contractor will also install a silt curtain downstream.
The contractor will build a coffer dam upstream of the dam and divert the river channel to isolate the area.
The main channel will be restored to what is approximately the middle of the existing spillway on the dam.
Granite Falls Energy has a water intake structure at the dam, and has its permits and contractor lined up to modify it once the removal project is underway.
Steve Christensen, company CEO and general manager, said the company will need to either make the intake deeper or move it to a deeper portion of the river. The company cannot know the best site for the intake until the dam is down and the new channel shows itself.
The company is hopeful the site it chose for the original intake will work. It continues to operate despite the river having been drawn-down for the dam removal.
The ethanol producer will not need to interrupt production for the project. It can use groundwater if it needs to temporarily replace the river water now used.
Demolition work on the dam will begin on the south shore and proceed northward. Bodensteiner is hopeful that the bulk of the work could be completed in January, although some work will likely continue into February.