Equipment at PPL Montana’s Madison Dam near Ennis was damaged early Monday (8/30) after a boulder broke loose and fell on the top of the dam. There are no injuries, the facility is in a stable condition and there is no need for public action.
“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.
Because of the damage caused by the falling boulder, river flows downstream of the Madison Dam are about 2,000 cubic feet per second, which is about 500 cubic feet per second more than before the event.
Flow rates on the lower Madison River will be increased while the drawdown occurs, which should take several weeks.
“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.
PPL Montana has notified local, state and federal officials, local law enforcement and its agency partners about the incident.
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. The units have a total generating capacity of 9 megawatts. Madison Dam is 257 feet long and 35 feet high.
PPL Montana provides safe, reliable energy from coal-fired power plants at Colstrip and Billings, as well as 11 hydroelectric plants along West Rosebud Creek and the Missouri, Madison, Clark Fork and Flathead rivers. It has a combined generating capacity of nearly 1,200 megawatts and has offices in Billings, Butte and Helena. PPL Montana and its 500 employees are dedicated to Montana and its communities, supporting educational, environmental and economic development programs across the state. PPL EnergyPlus operates a trading floor in Butte that markets and sells power for PPL Montana in wholesale and retail energy markets throughout the western United States. PPL Montana and PPL EnergyPlus are subsidiaries of PPL Corporation (NYSE: PPL).