Dakota County officials are nearing completion of a $48 million renovation of the Lake Byllesby Dam that replaces hydroelectric turbines first installed more than a century ago.

The new hydropower plant will double the dam’s electric production capacity to 4 megawatts. Previously, the dam produced capacity in the neighborhood of 1.8 megawatts to 2.2 megawatts, according to county officials.

The goal is to turn on the new hydropower turbines this fall, with a final connection to the power grid in early 2025, as the county coordinates the final stages with Xcel Energy. Building installation work has been completed, and workers onsite are making the finishing touches.

The dam, which collects flows from the Cannon River, is just west of Cannon Falls on the boundary of Dakota and Goodhue counties. It was built in 1910 as a power source that also created a recreational reservoir, with the original hydroelectric turbines going online in 1912.

Other than some light refurbishing during the 1980s, that equipment remained operational at the dam site ever since.

After more than 100 years, the equipment clearly outlived its intended lifespan. County officials had reached the point of either securing funding for a large-scale renovation, or allowing the turbines to run to the point of failure.

“The bigger picture was, ‘When do you rip off the Band-Aid,’ or when do you make the decision to invest and improve your facility?” Dakota County Senior Water Resources Engineer Mark Ryan said.

The project was paid for with a mix of county, state and federal dollars. The federal government’s American Rescue plan provided $28 million, state bonding dollars covered $12 million and the county kicked in the remaining $8 million.

Of the dam’s three aging turbines, one had a troublesome amount of water leakage, while suffering a number of mechanical issues that created a lot of downtime, county officials said.

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“It wasn’t super efficient, and it would break down pretty often. The fixes became somewhat predictable, but it’s large and heavy equipment,” Dakota County Environmental Resources Supervisor Brad Becker said.

Similar to an aging furnace that no longer operates at peak efficiency, it was estimated that the Lake Byllesby turbines were operating at about 70 percent efficiency. The two new turbines should operate at about 93 percent efficiency, Ryan said.

“We hope this provides the next 50-year window and really ensures the long-term life of the facility,” Ryan said.

Dakota County is projecting about $1.8 million in annual revenue from the dam’s electric output once the Xcel interconnection is completed.

Rapidan Dam comparison

The Lake Byllesby Dam near Cannon Falls. Dakota County Environmental Resources Supervisor Brad Becker compares the upgrade from the old dam turbines to the new system as a change from a Model T car to a Tesla. (Devanie Andre / Pioneer Press)

Outside of the electric generation, the dam portion of Lake Byllesby has undergone several different phases of safety and remediation projects.

Whereas some cities across the state have chosen to remove dams and return rivers to their natural waterflow, the Lake Byllesby reservoir has proven a popular recreation spot for nearby landowners, who enjoy fishing the lake’s mix of walleye, bass and crappie.

Many of Minnesota’s more than 1,000 dams are aging, said Jason Boyle, a dam safety engineer with the Minnesota Department of Natural Resources, as communities find themselves deciding between committing to repairing the dams, or letting them return to nature.

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.

Dakota County officials declined to speak about specifics related to the Rapidan Dam.

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.

An outdoor staircase leads from the powerhouse to the top of the Lake Byllesby Dam. (Devanie Andre / Pioneer Press)

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.

The dam sites themselves are in different states of condition, too.

After a 2019 flood, Blue Earth County officials said the Rapidan Dam was in a state of disrepair. The National Inventory of Dams ruled likewise, as an April 2023 study said the Rapidan Dam was in poor condition, according to reporting from the Associated Press.

Blue Earth County officials have been in the midst of defining the future of the Rapidan Dam, as either renovating the dam or removing the dam would both prove costly.

Meanwhile at Lake Byllesby, Dakota County stakeholders over the past decade decided to keep the dam in their future plans.

In 2014, a $5.8 million water capacity upgrade to the dam site was completed. Those repairs included addition of two concrete crest gates to address dam and spillway safety during massive rain events.

Those gates were put to work in early June and later last month.

The water level at Lake Byllesby was high, but crews were able to safely manage it, Becker said.

The Lake Byllesby Dam typically manages between 500 and 1,500 CFS. During last year’s particular dry months, the flows trickled down to 250 CFS. To put the cubic feet per second figure in context, one engineer compared 1,000 CFS to a flow of 1,000 basketballs per second.

New life after 100 years

Two new generators in the powerhouse at the Lake Byllesby Dam. Dakota County Environmental Resources Supervisor Brad Becker explains that the old system looked very different with the turbines and moving gears out in the open but the new system looks much more modern with only the generators exposed on the level of the powerhouse and the turbines hidden approximately two stories lower. (Devanie Andre / Pioneer Press)

The Lake Byllesby Dam was built in 1910, in turn creating the Lake Byllesby Reservoir, a 3.5-mile long, 1,432-acre lake. The original owner of the hydro dam was Northern States Power, now known as Xcel Energy. In 1969, as the site started to reach the end of its originally expected lifespan, Dakota and Goodhue counties purchased it from the energy company.

By 2009 though, the dam portion of Lake Byllesby needed safety renovations, and rather than foot part of the bill, Goodhue County officials at that time decided to relinquish control to Dakota County.

Since then, the focus has been on ensuring the dam’s viability in the long term, with a hope that the hydroelectric updates can deliver new life to the site, Ryan said.

“All of this work is really ensuring the long-term life of the facility,” Ryan said.

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