Monday, September 23, 2019

Granite Falls, MN: Dams and Powerhouse on Minnesota River

Granite Falls Dam: (Satellite)
Minnesota Falls Dam: (Satellite, Google Earth Images are below from when it still existed)

John A. Weeks III, during 2008 Spring flows
"The Granite Falls Dam was built in the late 1800s to supply mechanical power to a mill. It was abandoned in 1896. The City of Granite Falls bought the dam in 1911 and installed hydro power generators. The hydro plant was recently upgraded with more efficient equipment, resulting in a total electrical output of 1.2-Megawatts. The city hydro plant manager suggests that this is enough energy to supply the needs of 70% of the city."

John A. Weeks III, during 2010 Spring flood
"The river is higher than the water levels in the 2008 photos above, but it has not significantly overflowed its banks."

John Harker posted six photos.






While trying to find the MW capacity of this dam, I discovered that the Minnesota Dam that was three miles downstream was removed in 2013 to restore the three mile long rapids of the Minnesota Falls. John Weeks indicated in 2008 that Granite Falls wanted to convert it to another hydropower plant. But the need of the fish in the Mississippi River to use this rapids as a spawning ground prevailed. Remember, a couple million watts of generating capacity is a drop in the bucket compared to one 600MW water boiler (coal or gas) unit. And power plants generally have more than one unit.

Fortunately, John got photos of the Minnesota Falls Dam before it was removed in 2013.
John A. Weeks III
"This 1905 era dam is owned by Northern States Power, which is now known as Xcel Energy. The hydro power generator was dismantled in 1961. The dam was used to store cooling water for the nearby Minnesota Valley Generating Plant. That plant closed in 2004, leaving the dam obsolete. Xcel Energy considered rebuilding the dam, but the hydro power potential was too small to be worth rebuilding by a major utility."
The demolition photo below confirms that the upstream side of the dam is just a flat wall. The dam is built on exposed granite bedrock. So they did not have to worry about a "gentle" spillway curve to minimize scouring at the base of the spillway.

I excerpted two "before" images to capture a high Spring flow (April) and a low late-Summer (Sept.) flow.
Google Earth, Apr 2011

Google Earth, Sep 2012
Google Earth, Apr 2015
(new window) They not only removed the dam, they dredged quite a bit of the sediment that had accumulated behind the dam. And it looks like they spent more time doing bank restoration work than it took to remove the dam itself. Since all of the work was done in just two months, I don't understand why they built a rock bank and then removed the rocks to build a dirt bank.

DNR dam inspectors had ordered Excel to repair or remove the 14' tall, 107 year old dam. The estimate for repair was $15m whereas demolition was estimated as $2m. "Between the two dams [Granite Falls and Minnesota Falls] are five areas where the granite is pushed up, which will create a long area of rapids that will be useful for fish and sought out by paddlers." The deep pools in the fragmented granite riverbed creates spawning beds for fish, particularly for sturgeon. The removal of the dam was easy because the mortar was so soft from age. [MankatoFreePress] (I reached my article limit.)

After they removed the 1905 Minnesota Falls dam in 2013, the base of an 1871 dam in Granite Falls was exposed. The remnants of that dam was removed in 2015. "Dr. Luther Aadland with the Minnesota DNR, who has built an international reputation for restoring fish habitat when dams are removed from riverine systems, oversaw the restoration. Its goals are to restore the spawning habitat needed by the river's rock stars: Lake sturgeon, paddlefish, walleye, and sauger among them....Aadland has been part of research that is showing that fish naturally migrate long distances in river systems. Radio tags have tracked sturgeon that migrated in the Mississippi River from near the Iowa border to locations in the Minnesota and St. Croix Rivers to find the spawning habitat they need. They returned to the waters near Iowa within two weeks, indicative of how important the right spawning habitat is for this species. There are walleye in the Missouri River system that annually make 200 mile migrations. Aadland said he has little doubt that once discovered, this newly-restored site will attract many fish species for spawning....Since its removal, 12 of the 39 native species that had been blocked have now returned upstream, according to a study published in 2015." [wctrib]

Xcel Energy selected Rachel Contracting to remove the existing dam and all remaining features that were originally part of their Hydroelectric facility.  The work included installing and maintaining erosion control features, clearing and grubbing, designing, installing and maintaining water control measures, demolishing the dam and related structures, removing sediment upstream from the dam, hauling and placing sediment at the MN Valley Power Plant, and performing final grading, seeding, tree planting and restoration of the site.  All work was performed in the MN River Basin, consequently the project team had to be aware that significant changes in flow and water level could occur at any given time.  Over 2,000 The Rachel Team efficiently executed the work plan and completed the project safely and on schedule.

  • Design & Install--Water Control & Management Plan to Re-Route Flow of River
  • Design & Install--Steel Box Bridges for Equipment Crossing
  • 7,000 CY--Sediment Removal
  • 5.5 Acres--Site Restoration
  • 105 Each--New Trees Planted
Dams don't allow the native (desirable) fish upstream. And mussels need fish to help them reproduce. In fact, specific mussels need a specific fish. "When Lock and Dam 19 was built on the Mississippi in Iowa in 1913, migratory skipjack herring disappeared from the watershed upstream of the dam. Previously found upstream to Big Stone Lake on the Minnesota River, skipjack herring are the sole hosts of ebonyshell and elephant ear mussels. The disappearance of these two mussel species followed suit. Ebonyshell had been the dominant mussel of the upper Mississippi and lower Minnesota rivers. Half of the roughly 40 species of native mussels that once existed in the Minnesota River can no longer be found." But carp love the feted waters of dam reservoirs. Ironically, two dams built as carp barriers didn't stop nonnative carp but did stop "desirable native species unable to tolerate low oxygen levels and pollution." I wonder if these carp-barrier dams were built to stop the Asian Carp. Or if they were fighting an earlier carp invasion. "Projects that reconnect river systems are bringing back native fish and mussel communities across the state. Approximately two-thirds of the fish species that were absent upstream have returned after dams were removed or converted into rapids. Lake sturgeon have been reintroduced to several watersheds, and 5-foot-long fish are being caught where the species hadn't existed for generations. To bring back some species, we will also need to work on restoration of degraded rivers, riparian buffers, downstream barrier removal, wetland restoration, water quality improvements, or reintroduction." []

Our “stop the beast″ strategy of relying on dams and other barriers to block Asian carp has two very big drawbacks. It doesn’t work, and it causes more harm than good, according to a river ecologist and researcher....Dams are one of the factors responsible for what some are calling the sixth mass extinction in the earth’s history. The extinction rate for freshwater species is five times that of the extinction rate for creatures on land....As for stopping Asian carp, there are 22 other ways that Asian carp can reach new waters besides upstream migration. On the Minnesota River, they will readily get by the dams now in place, he pointed out....The Granite Falls dam on the Minnesota River is 21-feet high, but during flood conditions there is only a five-foot elevation difference. Asian carp easily jump 10-feet high to reach new waters....
The Minnesota River now runs free for 257 miles from Granite Falls to the Mississippi River, leading some to argue for at least a fish passage at the Granite Falls dam. Del Wehrspann, a founder of CURE and river advocate, noted that the City of Granite Falls is in the process of replacing two small hydro-electric turbines in the municipal dam without so much as discussing the need for a fish passage. “With all we know...,″ he said, “Why isn’t this even considered.″ [GraniteFallsNews]

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