Engineers hope to peek inside Hebgen Dam intake tower today

By JESSICA MAYRER Chronicle staff writer

More than a week after an intake tower at Hebgen Damn malfunctioned, sending water rushing downstream and spooking area residents, engineers are hoping to peek inside the tower today and identify what went wrong.

To do that, PPL, the utility that owns the dam, must slow the water flow into the 75-foot-high tower, PPL’s David Hoffman said Sunday.

And in order to do that, crews spent Sunday installing a 14-inch round casing in the tower, which will guide a bulkhead to slow the water. The casing will then be filled with cement to keep the whole apparatus steady, he said.

If all goes as planned, the crews should have visual clearance by tomorrow, Hoffman said.

The 93-year-old damn itself remains structurally sound, but after last Sunday’s afternoon tower breach, water flow increased from 800 cubic feet per second to 3,400 cfs, mimicking normal spring run-off conditions.

As it stands, said Carrie Harris from PPL, even if the tower completely failed, the Madison River would rise between one and one and a half feet above where it is now. So, she said, there is little danger to people downstream.

“We don’t believe there’s any danger potential to human safety,” Hoffman said.

But even so, it’s a tricky feat they’re trying to pull off. So far, the toughest part has been making the tower platform stable and level so a drill rig may be used to insert the casing.

“A lot of what’s been going on the last couple of days is prepping that platform,” Hoffman said. “It’s a very complicated and difficult process.”

And once inside, there is an entirely different set of difficult challenges.

“It’s just a nightmare of churning water,” said Madison County Undersheriff Roger Thompson.

And high water in the Madison expected to last until repairs are completed. If the tower completely malfunctions, PPL calculated the closest population center, Ennis, would have time to asses the situation before impacted, said Mark Lambrecht from PPL.

PPL is in contact with the Madison and Gallatin County Sheriff’s offices, which will have people on hand as the bulkhead is placed inside the tower, Thompson said.

Everyone is keeping their fingers crossed.

“The No. 1 issue is to protect public safety, contractor safety and employee safety,” Hoffman said.

Jessica Mayrer can be reached at jmayrer@dailychronicle.com or 582-2635.

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