A Hundred Years of Hydro - NorthWestern Energy · and more importantly to its developers,...
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A Hundred Years of Hydro Located in a remote, narrow canyon between Ennis and West Yellowstone, Hebgen Dam and its 15-mile-long reservoir didn’t attract much fanfare in its early years. The water stored behind the dam was intended for irrigation and more importantly to its developers, increasing electric production at Madison Dam north of Ennis and even Rainbow Dam, far down the Madison and Missouri rivers near Great Falls. An early report showed the stored water could increase the output of the two dams by 40 percent during low-water periods. The Butte Electric and Power Company began investigating the Hebgen site in 1909 and the Great Falls Water Power and Townsite Co. lent financial support. A geological examination by the chief geologist of Anaconda Copper Mining Co. bolstered belief in the solidity of the project. Construction began in earnest in 1910 but the progress was slowed by the short construction season at 6,500 feet, and the fact that some construction materials had to be transported nearly 80 miles to the site. The winter of 1910- 11 saw snowslides damage coffer dams and a flume. A nearby quarry provided fill rock for the downstream side of the dam, while earth fill was placed over the concrete core wall on both sides. The dam is 87.5 feet high and 715 feet long. It forms a reservoir with a volume of 386,000 acre- feet, which was the seventh-largest reservoir in the world at completion in 1915. The dam is named for Max Hebgen, who was general manager of the Montana Power Co. and a key figure in the developmental of several Montana hydroelectric dams. Hebgen never got to see the completed dam that carries his name; he died of pneumonia and heart trouble in August 1915 at age 45. While Hebgen Dam functioned without major incident for decades, a catastrophic 7.5-magnitude earthquake late on Aug. 17, 1959 ruptured a fault near the right abutment of the dam. Downstream, the quake was measured in human lives. A massive landslide killed 28 people, many of them camped below the dam, and largely blocked the Madison River, forming Quake Lake. While the dam held, the concrete core was cracked in several spots and water going over the dam caused significant damage to the downstream fill. Along with repairing the core, adding new fill and repairing the road across the dam, Montana Power also replaced the spillway. The repair work was completed in 1960 at a cost of about $315,000. The Hebgen-Yellowstone area continues to experience quakes. The intake structure, main dam and spillway are currently being upgraded to meet current structural requirements for another 100 years of operation. The project which has cost more than $30 million is scheduled to be complete within the next two years. Hebgen Dam The dam in the early days (Date unknown) Hebgen Dam survived a powerful 1959 earthquake. (Date unknown)
Transcript of A Hundred Years of Hydro - NorthWestern Energy · and more importantly to its developers,...
A Hundred Years of Hydro
Located in a remote, narrow canyon between Ennis and West Yellowstone, Hebgen Dam and its 15-mile-long reservoir didn’t attract much fanfare in its early years. The water stored behind the dam was intended for irrigation and more importantly to its developers, increasing electric production at Madison Dam north of Ennis and even Rainbow Dam, far down the Madison and Missouri rivers near Great Falls. An early report showed the stored water could increase the output of the two dams by 40 percent during low-water periods.
The Butte Electric and Power Company began investigating the Hebgen site in 1909 and the Great Falls Water Power and Townsite Co. lent financial support. A geological examination by the chief geologist of Anaconda Copper Mining Co. bolstered belief in the solidity of the project.
Construction began in earnest in 1910 but the progress was slowed by the short construction season at 6,500 feet, and the fact that some construction materials had to be transported nearly 80 miles to the site. The winter of 1910-11 saw snowslides damage coffer dams and a flume. A nearby quarry provided fill rock for the downstream side of the dam, while earth fill was placed over the concrete core wall on both sides. The dam is 87.5 feet high and 715 feet long. It forms a reservoir with a volume of 386,000 acre-feet, which was the seventh-largest reservoir in the world at completion in 1915.
The dam is named for Max Hebgen, who was general manager of the Montana Power Co. and a key figure in the developmental of several Montana hydroelectric dams. Hebgen never got to see the completed dam that carries his name; he died of pneumonia and heart trouble in August 1915 at age 45.
While Hebgen Dam functioned without major incident for decades, a catastrophic 7.5-magnitude earthquake late on Aug. 17, 1959 ruptured a fault near the right abutment of the dam. Downstream, the quake was measured in human lives. A massive landslide killed 28 people, many of them camped below the dam, and largely blocked the Madison River, forming Quake Lake.
While the dam held, the concrete core was cracked in several spots and water going over the dam caused significant damage to the downstream fill. Along with repairing the core, adding new fill and repairing the road across the dam, Montana Power also replaced the spillway. The repair work was completed in 1960 at a cost of about $315,000.
The Hebgen-Yellowstone area continues to experience quakes. The intake structure, main dam and spillway are currently being upgraded to meet current structural requirements for another 100 years of operation. The project which has cost more than $30 million is scheduled to be complete within the next two years.
Hebgen Dam
The dam in the early days (Date unknown) Hebgen Dam survived a powerful 1959 earthquake. (Date unknown)
Workers repair the spillway (1960)
MPC hired a plane to check the dam’s condition the day
after the quake. (1959)
Aerial view of the landslide that formed Quake Lake. (1959)
Dam attendant George Hungerford demonstrates
the height of waves that came over the dam. (1959)
The top of the dam was also rebuilt. (1959)
Water that topped the dam damaged the downstream wall. (1959)
Source: A History of Montana Power, C.H. Kirk; newspaper accounts and NorthWestern Energy engineering employees.
August 2015
The dam spillway was heavily damaged by the quake. (1959)
