Big dam will need a big fix

Depending on the weather, you might have walked across the Waterbury Dam, swum near it, or even skied down it.

Towering over the 850-acre reservoir is the dam that holds back the water waiting to get to the Winooski River.

Metal railings and wide paths keep onlookers above the water. Chain-link fences keep trespassers away from the mechanics of the dam.

The dam was built in the 1930s by the Civilian Conservation Corps. It provides flood control; the reservoir has become a hugely popular recreation spot in central Vermont; and hydropower turbines in the dam produce electricity.

The dam, one of the five largest in Vermont, is classified as a high hazard dam — if it were to fail, people would die.

The dam has been through three major rehabilitation projects, in the 1950s, the 1980s and the early 2000s. Local people have still-fresh memories of the years that the reservoir was drained for work on the dam; without swimming and boating and beach-lounging, those summers seemed a lot longer than normal.

Each set of improvements was designed to make sure the dam holds up.

Next up, within the next decade, is a $45 million project to replace the main spillway and dam gates. That project is still in the preliminary planning stages.

This winter, however, Green Mountain Power plans major repairs to the dam’s powerhouse. To get new permits for its hydropower operation, it needs to exert better control over the river flow downstream from the dam. Now, the flow can vary from very low to very high; tougher rules under the federal Clean Water Act require that the river flow be far more consistent to protect aquatic life.

What’s in the dam?

Last week, the Friends of the Waterbury Reservoir partnered with the state Department of Environmental Conservation to usher people past the “Do Not Enter” signs outside the gatehouse and out onto the spillway bridge to celebrate Vermont’s Clean Water Week.

“We decided to do a tour because lots of people had never been to the dam,” said Laurie Smith, president emeritus and board member for Friends of the Waterbury Reservoir. “They didn’t know how it worked, or how the water worked.”

“We have lived here a long time and are interested in what happens with the reservoir. We use it for recreation all the time,” said Bob Kirch, a Stowe resident. The tour gave him and other residents look at the technical side of the dam.

First they went inside the gatehouse, down steep stairs. Ben Green, facilities engineering division dam safety engineer section chief, explained how the gates and pulleys all worked.

Then, outside, Green took visitors onto the spillway bridge, explaining that the principal spillway gates remain open unless the downstream water levels in the Winooski get too high, and water has to be held back for flood control.

Green and his small department monitor the river’s water levels and can usually tell a few days in advance if they will have to close the floodgates. For the Waterbury Dam, the action level — where if the water in the Winooski hits the floodgates must be closed — is 417 feet above sea level and the flood level is 419 feet.

Things have become increasingly automated since the dam was built in the 1930s. Green and his department can track water levels from their computers and phones.

However, if things take a serious turn, Green and his crew will wind up out on the spillway bridge, turning knobs and pushing buttons to manually close the spillway gates.

More information: friendsofwaterburyres.org.