'Strange sucking sound' raises tensions

PPL continues efforts to repair dam

by Carol Hoffmann

The water thundering down the spillway at Hebgen Dam Sunday afternoon was noticed first by a fisherman, who reported to the sheriff's office that he heard a loud pop and "a strange sucking sound' and saw a lot of water frothing at the headgates of the intake tower.

Madison County Undersheriff Roger Thompson and Steve Covas, PPL supervisor of the Madison Dam at Ennis, drove to the dam and inspected the water intake tower. They found a manhole cover weighing about 175 pounds had popped off and was lying 6 feet away.

The intake tower is about 75 feet deep, most of it underwater. It has four gates that allow water to flow into four chambers, through the dam structure to a tunnel and out to the Madison River. Normally, only two of the four gates would be letting in water.

Thompson said they could see water churning in both chambers that should have been empty. That indicated the timber and concrete structure must have a breach somewhere underwater.

"We started evacuating from Hebgen Dam to Quake Lake, and all the way down to Ennis Dam." Thompson said. Only campers or people who might be affected if the water rose 3 feet were evacuated.

"Ennis was never in any danger," he said, but people who live along the river, when they heard about the situation, became alarmed. "People started hearing rumors the dam was breaking," Thompson said.

It wasn't, and volunteers were sent door-to-door in Ennis to quash the rumors.

On Monday, the river between Quake Lake and Ennis Lake was reopened to fishing and other day uses, but not to overnight camping. Signs were posted warning of unusually high water, and the river between Hebgen Lake and Quake Lake remained closed.

Ironically, Hebgen Dam underwent its annual federal inspection last Thursday, said Carrie Harris, manager of hydro-engineering for PPL Montana LLC, which owns and operates the 93-year old earth-and-concrete dam, "and everything seemed fine."

After the Sunday tower breach, water flow increased from 800 cubic feet per second to 3,400, which mimics peak run-off levels. High water is expected to last several days, until repairs are complete.

If the tower completely malfunctions, PPL calculated the closest population center, Ennis, would have time to asses the situation before impacted. Mark Lambrecht, PPL Montana manager of regulatory affairs, said Ennis would have eight hours notice before the water would reach the town.

Lambrecht said Wednesday that engineers are determining a course of action that will solve the problem.

"Two hydrolic headgates at the intake structure malfunctioned," he said,

and crews are cutting through 2-foot concrete on top of the intake structure to determine the cause.

"A steel bulkhead is being fabricated with the intention of installing that to stop the flow to the headgates," Lambrecht explained, "and the flow will be redirected to the other spillway. It will give us the opportunity to fix the problem. We should know by Friday."

The lake level behind the dam has gone down maybe six inches since Sunday, reported a cabin owner on Hebgen's south shore.

The dam itself remains structurally sound, Harris said, and even if the tower completely failed, the Madison River would raise between one and one and a half feet above where it is now. "So," she said, "there is little danger to folks downstream."

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