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Nature delays flooding repairs

Beaver, dragonflies complicate project

By James O’Brien
Globe Correspondent / December 11, 2011
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Dam-building beavers, coupled with the offspring of an endangered species of dragonfly, have frustrated Upton’s attempts to lower water levels around Southborough Road this fall. It is an effort that town officials say is key to keeping the roadway open this winter.

“We need the water level at least 2 feet below the surface of the road,’’ said Town Manager Blythe Robinson, who explained that water cresting over the road’s surface when temperatures drop below freezing would make the thoroughfare dangerous to travel.

“It was a huge public safety hazard,’’ Robinson said, “and it would have meant a several-mile detour through Hopkinton for the people that live in that area.’’

With the help of state and local conservation officials, the ice issue may now be solved, Robinson said. What remains is the problem of a large beaver dam and resulting water levels that could still lead to frost heaves if the roadbed is soaked through.

Southborough Road cuts through what used to be cranberry bogs. Some 14 culverts that run under the road carry water between the north and south sides of the wetlands, and also under adjoining Westborough Road.

With a budget of about $75,000, contractors went to work this fall to replace the aging culverts, some of them nearly 50 years old. They made 11 replacements along Westborough Road, and then turned to three that needed work under Southborough Road.

That’s where the beavers came in.

The animals had built dams near the culverts, as well as a larger dam about 100 feet into the bog. The dams added to water levels that late-summer storm debris and fall rains had already boosted, making it impossible to pull out the old pipes and put in the new.

The solution, it seemed, was to remove the beavers and pull down the dams. Not so fast, as it turned out. That’s where the dragonflies entered the story.

The bogs were not only holding a lot of water, they are a hatchery for the ringed boghaunter, a small, delicate, orange-and-black-striped dragonfly that is very rare throughout North America. It is a protected species in Massachusetts.

There are only a few locations in the state that harbor the insect, according to Tom French, an assistant director in the state Division of Fisheries and Wildlife.

“At one time it was being thought of for federal listing as endangered,’’ French said of the ringed boghaunter. “They’re limited, in the northeastern part of the country, to a small range, a few sites mostly in the southeastern part of the state.’’

In Upton, the boghaunter larvae live in shallow pools of wet sphagnum moss found around Southborough Road. If, however, in cooler weather the water level of the bog drops quickly, and the larvae don’t have time to crawl deeper into the moss and muck, they’ll die.

When contractors breached the first beaver dam on Nov. 16, starting with one on the north side of the road, water flowed into the cleared culvert and the level in the surrounding area of bog began to drop. However, a town conservation official monitoring the work decided the change was too abrupt, and stopped the process.

“We should not be lowering the water more than 6 inches per week’’ to ensure the larvae can stay safe, said Chris Scott, who chairs the town’s Conservation Commission.

“If the water is lowered at a slow pace, they can migrate down and not be exposed to cold temperatures,’’ she said. “But certain times of the year are more critical. I think November and December is a very critical time.’’

And so, the work came to a halt. “And we ended up putting material back in the trench to slow the water down,’’ said Robinson.

State and town officials then came together to find a way to protect the ringed boghaunters while also getting the culverts replaced before ice forms this winter.

On Nov. 23, a group went out to the site, looked at the problem, and took new measurements.

According to Matthew Selby, the conservation agent for Upton, a compromise was reached. State officials said the town could lower the bog level by 1-foot increments. That would bring the water to a point at which the road was no longer threatened, allow the culvert work to continue, and also protect both the boghaunters and beavers.

The trick now, according to Robinson, is to make sure that the lowered water level stays 2 or more feet under the roadbed, so that the town can avoid late-winter and early-spring frost heaves in the pavement.

This would involve dealing with the large dam. Rather than destroy it outright, the Conservation Commission wants to install a device known as a pond leveler - a pipe that limits the water level in the bog without destroying the beaver habitat, or alerting the creatures to the human modification to their home.

“Beavers respond to the sound of running water and their instinct is to just stop it when they detect it,’’ Selby said. “You start tampering with the dam, they just come back and fix it. The pipe is under water, and we cage it off so the beaver won’t come over and block it up.’’

Robinson said the cost of implementing the plan would be close to $3,000. A funding decision is pending, with a meeting scheduled for Wednesday.

Going forward, Robinson said, she wants to see a more comprehensive beaver-management plan in Upton.

Elsewhere in town, trappers have taken eight beavers from dams near Fowler Street, and Department of Public Works crews recently cleared dams near Hartford Avenue South and Old Grafton Road, where rising water levels also threatened to ice over the pavement. Trappers are now focusing on those areas.

“We need to regularly trap beavers in the future,’’ said Robinson. “They’re a problem throughout the state, and we have to be more mindful about moving them so they don’t cause the problem to get this bad again.’’

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