The city of Spearfish, S.D., will replace deteriorating 107-year-old redwood pipes that carry water to its hydroelectric plant with a modern product: high density polyethylene pipes.
The plant originally was built in 1910 to power the Homestake Mine in nearby Lead, which once was owned by business magnate George Hearst. He and some partners bought the claim for $70,000 during the Black Hills Gold Rush in 1877.
Located a few miles from the shanties, saloons and brothels of Deadwood, the mine became the second-largest gold producer in the U.S., yielding 39.8 million ounces of ore before it ceased operations in 2002.
For power, water was — and still is — diverted from the fast-moving Spearfish Creek and conveyed underground through a 5.5-mile tunnel system to a confinement area called a forebay.
From there, the water is carried by a pair of redwood pipes, which will be updated to HDPE, to a series of stand pipes that act as an elevation buffer. At that point, the water drops down a steel pipe to the hydro facility, where it spins twin turbines that activate a generator, which produces electricity.
The water exits the plant back into Spearfish Creek, which cuts through the city of Spearfish on the way to its confluence with the Redwater River just north of town.
Spearfish officials bought the hydroelectric plant in 2004, obtained a federal permit to operate it and have enjoyed a stable source of electricity, which is sold to the local utility, and revenue, which totaled $788,400 in 2016.
"The driving goal for our city to acquire this 100-plus-year-old facility wasn't to create electricity. It was for the purpose of keeping water in the tunnel and through the community," Public Works Administrator Cheryl Johnson said in a phone interview.
The tunnel system moves the creek water around an area of the stream bed with such unpredictable hydrology it has been dubbed a "loss zone."
"In drought years and other low-flow situations, the flow of the creek literally drops underground and travels in the aquifer," Johnson said. "We knew if the plant didn't continue to operate, there would have been times of the year when we had no flow of our creek through our community. We wanted to maintain the volume of water that flows through Spearfish. It's very much a feature of our community."
From the plant, the creek flows through a city park and fish hatchery to truck farmers with irrigation rights. Unusual in that it freezes from the bottom up, the creek also allows for year-round fishing for locals and tourists.