Chronicle Outdoors

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Massive boulder collapse causes damage to Madison Dam north of Ennis

A boulder the size of a semi truck broke loose and fell on the top of PPL Montana’s Madison Dam in the early hours on Monday. There were no injuries and the dam is reportedly secure, but river flows downstream jumped 500 cubic feet per second following the event.

“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,” David Hoffman, director of External Affairs for PPL Montana, said. “There is leakage around the boulder in the spill gate section on the west side of the dam.”

Ennis Lake, which was created as a result of the dam, will be drawn down nine feet over the next several weeks to make repairs to the dam. The drawdown will affect recreationists on the lake including boaters.

“We apologize for this inconvenience to our neighbors at Madison Dam, but the drawdown is required to make repairs to the dam,” Hoffman said.

Hoffman said PPL engineers have inspected the dam and are working on plans to remove the boulder. The accident damaged several of the dam’s gates. Only three undamaged gates remain and will be opened to release water from the lake.

PPL Montana said booms have been deployed on the Madison River to collect between 15 and 20 gallons of oil that spilled when the boulder ruptured a hydraulic line. The release said there is no more oil leaking into the river.

Madison Dam, also known as Ennis Dam, is a located on the Madison River at the southern end of Bear Trap Canyon just north of Ennis. The area is popular with boaters, whitewater rafters and anglers.

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This entry was posted by on Monday, August 30th, 2010 at 5:36 pm and is filed under Bear Trap Canyon, Boating, Fishing, Madison River. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

About The Author

Ben Pierce lives, works and plays in Bozeman, Montana. He blogs about the outdoors for Chronicle Outdoors. Catch him on the river, in the mountains or at bpierce@dailychronicle.com.

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