Update, Saturday July 18: In today's Mankato Free Press, Tim Krohn reports Rapidan dam hydro company plans to end lease; dam repair costs mount. Good interviews with company, local leaders. [end update]
Back in February, Mankato's KEYC-TV News' Ryan Sjoberg reported in Rising waters cause damage at Rapidan Dam:
The Rapidan Dam has more damage, and this time it’s ice-related.
On Jan. 15, officials noticed water below the dam beginning to rise because of numerous ice jams near the structure.
The rising water resulted in the powerhouse being flooded with about 10 feet of water.
“That’s all the controls for the electrical, the two large electrical generation turbines, all the controls, all the equipment that meters the electricity and then transforms it and then sends it into the distribution lines,” explained Blue Earth County Engineer Ryan Thilges.
This is in addition to damage officials noticed in summer 2019 to the downstream apron. The apron isn’t a pressing repair right now, but the powerhouse will need to be repaired rather quickly to resume normal controls of the dam.
“Then they’ll have to go through all the electrical generation components and see what the extent of the damages are, but we assuming it’s going to be significant,” added Thilges.
While Blue Earth County is in charge of the dam structure itself, Eagle Creek Renewable Energy is in charge of operations. The company has reviewed the structure of the dam and determined the flooding has not resulted in structural damage.
Recent agenda items for the Blue Earth County Board of Commissioners show that Eagle Creek Renewable Energy plans to terminate its lease to operate the hydropower generation at the county-owned 110-year-old dam on the Blue Earth River.
As far as we are able to determine, the damage in January has caused the power generation to end--and repairs to return the dam to service are estimated at $2,335,000, and that's in addition to repairs needed on the dam's apron
That estimate is from a memo to the Blue Earth County Board of Commissioners presented at the board's July 7, 2020 Work Session:
Blue Earth County Rapidan Dam Memo uploaded by Sally Jo Sorensen on Scribd
There's been discussion of the future of the dam for years. The most comprehensive discussion in the local media was Mark Fischenich's article in the Mankato Free Press, Ask Us: Rapidan Dam could be removed — but at a very high cost. Fischenich hits the major points:
Since 2008, $3.82 million has been spent on the 109-year-old Rapidan Dam on the Blue Earth River southwest of Mankato, according to Blue Earth County Public Works Director Ryan Thilges. In that same period, revenues have totaled $4.67 million, although the majority of that revenue was repair grants from the state and federal government — not simply earnings from the power generated at the hydroelectric dam.
In the past decade, hydroelectric revenues have totaled $1.25 million, Thilges said.
Going back further, he had only general figures. From 1999 to now, $5.96 million was spent on the dam with revenues during that same period at $6.19 million. Again, most of the revenue came from sources other than energy production.
"The bulk of the revenue side is FEMA reimbursements or state and federal grants. So there's certainly tax dollars at work," Thilges said, noting that the dam has largely avoided being a drain on local property tax dollars. " ... I can't say local money hasn't been used on the dam. But it seems historically, it's staying afloat financially."
As for the reader's suspicion that the dam, if privately owned, "would be long gone by now," the structure was privately owned for most of its existence. Built for $500,000 in 1910 by Consumer Power, the company ultimately became Northern States Power (now Xcel Energy), according to a study of the dam completed in 2004 by a team of Minnesota State University graduate students.
The dam suffered extensive damage in the infamous floods of 1965, which was a time when NSP officials were pessimistic about the future of hydro power.
"... Therefore NSP decided against repairing the dam, and eventually presented ownership of the dam to Blue Earth County in 1975," the MSU study reported. "The dam remained abandoned for 18 years until the rehabilitation project began in 1993."
Ask Us Guy, who once covered the Blue Earth County Board, recalls a couple of times when commissioners suggested they wished their predecessors had refused to accept NSP's "gift."
Still, the dam does have some historical, cultural and recreational attributes. An 80-foot high hydroelectric dam is a rarity in the Midwest, making it a tourist attraction, a fishing destination and the focal point of a large county park and campground.
It also has some ecological benefits. The dam blocks invasive species such as Asian carp from moving upstream on the Blue Earth River. And the reservoir serves as a trap for a variety of pollutants that would otherwise end up in the Minnesota and Mississippi rivers.
More than a century of performing that second task has left the reservoir filled — within a few feet of the surface — with silt that drops from the water when the river current is slowed by the dam. And the sediment is contaminated with a variety of agricultural chemicals. That's another reason that county officials aren't keen on the idea of removing the dam.
The 11 million cubic yards of sediment behind the dam, if removed by a standard dump truck, would require more than 785,000 round trips to remove it all. Which, Ask Us Guy figures, means the county would need to hire at least two or three dump trucks.
In reality, according to a 2000 study by Barr Engineering, only 1.9 million cubic yards of sediment could be mechanically removed from behind the dam — and probably landfilled because of the contaminants. Crews would need to simultaneously recreate a river valley with gradual slopes from some of the remaining silt.
And an estimated 1.4 million cubic yards would be lost downstream — something that would undoubtedly be very unpopular with the Department of Natural Resources, the Environmental Protection Agency, downstream communities along the Minnesota River, fans of Lake Pepin and Gulf of Mexico shrimpers, among others.
"That's a pretty massive number," Thilges said. "With the increased environmental regulations, I think that would be even more challenging than in the year 2000. ... There's just tremendous water-quality implications."
Beyond environmental issues, the cost of the project would be daunting. Engineers typically say that anything — from putting a man on the moon to removing the Rapidan Dam — can be done with enough money. In 2000, Barr Engineering put the cost of removing the dam at $25 million. Thilges applied a standard construction-cost inflation factor to that number and came up with $45 million for removing the dam in 2019.
There's another thing, too. The County Road 9 bridge, which crosses the Blue Earth River about 200 feet upstream of the dam, was constructed after the reservoir filled with sediment and its piers were built on top of the sediment. If the Blue Earth River was returned to its pre-dam elevation, the bridge would need some new 80-foot-high piers or the bridge would have to be replaced.
"So, there are several reasons why we worked so hard to keep the dam up and in a good state of repair," Thilges said. "It's in pretty decent shape with all the work that's taken place in the last 20 years. ... It's far from new, but it's holding up pretty well."
Since this article was filed back in April 2019, Free Press staffer Trey Mewes reported in December 3, 2019 Blue Earth County seeks up to $3M to fix, improve Rapidan Dam:
Blue Earth County officials say it could cost $1.5 million to $2 million to repair the Rapidan Dam after this spring’s flooding, with another $1 million needed to improve the structure.
Public Works Director Ryan Thilges told the Blue Earth County Board Tuesday the county expected to finalize its cost estimates this week to secure Federal Emergency Management Agency funding to repair the dam.
“(It’s) extremely frustrating, I agree,” Thilges said. “But with the condition of the apron and the availability of the money, I want to right now try to go after it to make those repairs and do whatever measures we can do to prolong the longevity of the dam.”
Thilges said the dam’s concrete apron — slabs at the bottom of the dam meant to absorb energy from the flowing water — was significantly damaged once more after it was repaired a few years ago. About 1,300 square yards of the apron were damaged with about 250 square yards gouged out at least 10 feet deep.
“Once the apron peeled out, there’s large big red boulders underneath that are used to fill in, and they were pulled out and washed downstream,” Thilges said.
One of the dam’s five gates experienced a pulley system being damaged in the spring, while an electronic drive system on another gate was dislodged.
Workers recently finished other dam repairs, while damage upstream of the dam was covered by nearby hydroelectric station operator Eagle Creek Renewable Energy’s insurance.
A nearby flow separator wall was also washed away; Thilges said the wall will be included in the projected repairs.
The damage was caused by weeks of flooding in late February through April as the winter thaw caused near-record water flow through the Blue Earth River.
Thilges said the damage isn’t an immediate safety threat, but the dam’s structure could worsen if left as is.
Blue Earth County will have to wait for funding from FEMA before scheduling a fix, but Thilges hopes an additional $1 million in federal money can be used to grout rock anchors about 40 feet deep to keep the apron in place and mitigate future damage.
Board Chair Will Purvis said this is the third time the dam needed repairs in that area since he was first elected in 2006.
“It’s wonderful having a dam,” Commissioner Mark Piepho said.
Thilges said in April the county had spent $3.82 million on the dam since 2008. In that same period, the dam earned $1.25 million in hydroelectric revenue with another estimated $3.4 million coming from state and federal grant programs for repair costs.
It's an interesting mix of revenue for the county from power generation and government grants. Will another company step up to operate the dam once the interior power equipment is repaired? The memo lays out a number of alternatives--including removal of the dam.
Stay tuned.
Photo: Flooding and erosion have caused damage to the Rapidan Dam. Mankato Free Press file photo by Jason Forderer.
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