A beaver dam holding back a pond collapsed Tuesday afternoon, sending a deluge of water over a portion of Elm Street in Penacook and closing the road for a day.

The dam had created a large pond on Dagoty Hill. When it broke, it sent water rushing downhill, overloading culverts that carry a small creek underneath Elm Street near the intersection with Peaceful Lane. At times, more than a foot of water flowed over the pavement.

City crews shut down the road until the flood could subside and they could determine whether it was safe for traffic to cross. The road was closed between Peaceful Lane and Weir Road.

“We wanted to be sure the road wasn’t undermined,” said Kevin Rowell, foreman of the General Service crew working on the site Wednesday morning.

Fortunately, he said, the side-by-side culverts – one roughly 18-inch-diameter galvanized steel and one 24-inch concrete – held. The headwall, the stones and concrete facing upstream that took the brunt of the force, had to be repaired, but the road is expected to reopen sometime Wednesday.

The pond in question is not far from the Weare Road Trail hiking trail.

It’s not uncommon for beaver dams to give way, especially in the spring when high water increases the pressure on them.  

“They keep trying to raise that water level as much as they can. If there’s a weak spot and if they don’t arm that weak spot, the water pressure from the height of the dam builds up,” said N.H. Fish and Game wildlife biologist Patrick Tate. 

 

Tate said that if there if the beavers stick around, the dam may well return. 

“My experience is that they do rebuild the dam in the same spot … The shape of the dam may end up being a little bit different, depending on how the ground eroded, but they will rebuild,” he said.

Trapping nearly eliminated beaver from New Hampshire by the late 1800s. Six beaver were released in the state between 1926 and 1930 as part of a restocking program and by 1955, the entire state was repopulated. 

Tate said the number of beavers “ebbs and flows” from year to year but that “we certainly have an abundant population.”

The state has an active wildlife control program that is often called to trap or remove beavers whose dams are causing flooding that threatens buildings or, more often, roads.