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FORT PECK — Looming above the plain like a great grassy green berm, Fort Peck Dam has impounded more Missouri River water this spring than ever before — enough to cover all of Yellowstone National Park with 6 feet of water.

Nearly a mile wide at the base and four miles long, the compacted dirt behemoth is the second-largest dam in the United States. This year, the dam has made headlines as record amounts of rainwater and snowmelt are released downstream, flooding towns in North and South Dakota and Nebraska.

Located in northeastern Montana more than 1,700 miles from the Missouri River's mouth, Fort Peck Dam and its powerhouses stand as a testament to engineering prowess. Construction was authorized by President Roosevelt on Oct. 24, 1933, as part of the Public Works Administration's efforts to employ workers during the Great Depression. Work began in 1934 and was completed in 1940.

Everything about Fort Peck Dam and reservoir is massive. Backed up behind the earthen structure, when the water level is at 2,250 feet elevation, is 18.6 million acre-feet of water.

And that's still 30 feet below the top of the dam.

And when the lake elevation is at just 2,234 feet above sea level, the reservoir has 1,520 miles of shoreline, more than the state of Florida.

"It's probably the most iconic manmade structure in Montana," said John Daggett, dam operations manager for the U.S. Army Corps of Engineers. "I can't think of any other manmade structure in Montana that would compare. It's just a unique area."

Generating power

There's nothing small about Fort Peck Dam's two power plants, either: bolts as big around as a man's wrist, 10-story surge towers that were at one time the tallest buildings in Montana, mile-long steel tunnels you could drive a truck through.

"This is the biggest power plant on the Missouri River in Montana and pretty important for its capability," Daggett said.

Daggett gave a tour of one of the powerhouses recently, going from the cool concrete works of the basement, past the humming, almost antiseptically clean midsection where the generators are housed and up to the top of one of the two surge towers. The structures are awe-inspiring in their proportions.

The first of the two powerhouses was finished in 1943, the second in 1961. Together, the power plants' five generators provide an average of 1.1 billion kilowatt hours of electricity each year.

The plants are easily identified by their gray surge towers, two concrete columns looking like something out of the fictional Gotham City in Batman cartoons — a bit eerie, ominous and imposing. They stand at the downstream toe of the dam.

Big stuff

Penstocks, metal pipes 24 feet in diameter, supply water taken from above the dam. There are four of them, each made of inch-thick steel and carrying water pressurized to 90 pounds per square inch. Each pipe carries about 7,500 cubic feet per second of water. The penstocks branch off into smaller, 14-foot diameter pipes that drive the generators.

The giant generators require 1,200 gallons of oil to lubricate the moving parts. When the power plant is operating at capacity, running about 15,000 cfs of water through the generators, they produce about 215 megawatts.

The power is transmitted by the Western Area Power Administration over lines that travel east and west.

In a normal year, the power plants would have flows from 10,000 to 12,000 cfs in the summer, dropping down to as low as 4,000 cfs in the winter. During recent drought years, when the lake level was at an all-time low, summer flows were reduced to 6,000 cfs.

The surge towers act like shock absorbers for the system. When a generator is shut down, water surges into the tanks to relieve pressure. At the top of the towers, windows on louvers flap open to release air as the water rises. An orange life buoy attached to a rope hangs from the hand railing around the top of the towers, although as far as anyone knows it's never been needed.

Keeping it running

The power plant is operated and maintained by a crew of 20 full-time personnel. Another 18 people round out the rest of the Corps' personnel in Fort Peck, including reservoir recreation workers and office staff.

At the power plants, George Schuster is at the helm. As the power plant shift operator, he oversees the many computerized displays in the control room that tell him how much water is pouring through the system, the energy that's being generated and how much water is being released over the spillway in what has been a record wet year. Before this year, the spillway had been used only four times and never at flows this high.

Last week, Schuster's monitor showed 49,650 cfs of water being released down the 16 spillway gates, an amount Daggett calculated would generate more than 1 million horsepower.

In Schuster's four years at the plant, this was the first time the spillway had been used. Water is money in the hydropower business, and Schuster said it was difficult to see the gates open, especially on the heels of severe low-water years.

"After 10 years of drought, it's hard to do," he said.

Contact Brett French, Gazette Outdoors editor, at french@billingsgazette.com or at 657-1387.

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Montana Untamed Editor

Montana Untamed editor for the Billings Gazette.