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Rising Waters: Officials take measures last week to ensure safety of dam at Lake Como

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The scenario was what nightmares are made of for John Crowley.

The reservoir at Lake Como was full to the brim and water was already spilling over the concrete spillway. There was rain coming down on heavy snowpack and the water gushing out of the mountain was roaring down the tributaries.

And if that wasn’t enough to make the man charged with the operation of the earthen dam shake in his shoes, Bureau of Reclamation officials tossed in an earthquake for good measure.

Suddenly, there was seepage coming through the dam and the county’s emergency management team was being tested to see how quickly it could respond.

“We like to go a little Hollywood during these tests,” said Suzanne Marinelli, the Bureau of Reclamation’s emergency management program coordinator for the Pacific Northwest Region. “I felt a little guilty packing all of this into one exercise…they all performed wonderfully.”

After the recent near failure of the earthen dam at Oroville, California, some folks in the Bitterroot Valley had questioned the community’s ability to respond to a sudden break in one the two larger earthen dams in Ravalli County.

This past week, Bureau of Reclamation officials put those responsible for addressing a potential breach at Lake Como though their paces in a fast-paced exercise that offered opportunities to review disaster procedures associated with the dam.

“I was pretty much mentally exhausted when it was over,” Crowley said. “Any time we have this type of emergency planning exercise, it helps us to prepare. We always learn from it.”

The original earthen dam that creates Lake Como between Hamilton and Darby was built between 1906 and 1909. The water stored in the reservoir irrigates farms and ranches along a 72-mile ditch that winds its way along the east side of the valley.

The dam is owned and operated by the Bitterroot Irrigation District. The Bureau of Reclamation serves as the agency overseeing safety measures at the dam.

Last Friday, Crowley led a small group of interested federal, state and local officials on a tour of the monitoring sites the irrigation district uses to ensure the stability of the structure.

Dallas and Ginny Erickson of Stevensville accompanied the group. The Ericksons have expressed concerns about the lack of an early warning system at the dam. A breach would have devastating consequences for downstream communities, especially Hamilton.

In the early 1990s, safety modifications costing $1.8 million were added to the structure. They included building a new concrete spillway and adding thousands of yards of fill material to shore up the toe of the dam.

The funding also paid for adding five large monitoring wells that are big enough for dam operators to climb down about 50 feet to measure and visually observe the ground water that runs below the dam.

Irrigation users will eventually be responsible for paying for the improvements and measuring devices.

Crowley said the monitoring wells are important because they would provide the first clues that something irregular was happening within the earthen structure.

That warning would show up as turbidity in the water, which Crowley said would result in immediate action in isolate the problem.

“As a dam operator, any time you start seeing muddy water, the hairs stand up on the back of your neck,” Crowley said.

Fortunately, so far, turbid water has not been an issue in any of the monitoring wells.

The modifications also included the installation of 19 small tubes placed along the toe of the dam that are used to track the depth of ground water levels.

And finally, just downstream of the dam, two weirs were installed that offer another opportunity to check the amount of groundwater and turbidity levels.

“It’s all about checks and balances,” Crowley said.

Managing the water levels in the reservoir is an annual dance between gathering the water necessary to supply downstream irrigators throughout the summer and keeping the water level low enough early in order to provide some flood control.

“Once the water starts going over the spillway, those are uncontrolled releases,” he said. “We do whatever we can to control floodwaters.”

As an example, the past week, Crowley made the decision to bring the reservoir down several feet because the annual snowpack is about 104 percent of normal for this time of year.

“We figure that we have about 70,000 acre feet of water sitting up there in the snowpack right now,” he said. “My lake holds 38,495 acre feet of water. I think we have an ample snowpack this year.”

Irrigators can expect to see water showing up at their head gates sometime between April 17th and 24th.

Of course, Crowley’s challenge is knowing when and how fast the snowpack will melt.

“We try to stay one step ahead of Mother Nature,’' Crowley said. “She’s a hard one to predict. She can turn on you in a minute.”

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