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Madison Dam damaged by loose boulder

Posted: Aug 30, 2010 3:29 PM by KBZK News Staff - Montana's News Station

BOZEMAN - A boulder broke loose and fell on Madison Dam near Ennis Monday, causing a small oil spill and impacting river levels.

PPL Montana reports in a news release that no one was injured and the facility is in stable condition.

"We've taken immediate action to start an emergency drawdown of Ennis Lake so we can identify where repairs need to be made and reduce pressure on the dam. There is leakage around the boulder in the spill gate section on the west side of the dam," said David Hoffman, director of External Affairs for PPL Montana.

The damage is causing river flows downstream of the Madison Dam to run about 2,000 cubic feet per second, which is about 500 cubic feet per second more than before the event.

"The lake will be lowered by about 9 feet, which will affect boat docks and public launch sites along the lake," he said. "We apologize for this inconvenience to our neighbors at Madison Dam, but the drawdown is required to make repairs to the dam."

PPL Montana engineers have inspected the dam and will develop plans to remove the boulder and make repairs, Hoffman said. Spill gates damaged by the falling boulder cannot be opened, but three undamaged spill gates are functioning. The hydroelectric plant continues to generate electricity.

Booms have been deployed in the Madison River to capture a small amount of oil - about 15 to 20 gallons - that spilled into the Madison River when the boulder severed a hydraulic line. No additional oil is leaking into the river. Flashboards were also damaged as a result of the falling boulder.

Madison Dam is a four-unit hydroelectric plant on the Madison River at the head of Bear Trap Canyon, about 10 miles north of Ennis.