Work on the Beaver Meadow Dam has been significantly impacted by the rain during the month of June.
Derry Public Works Director Mike Fowler said trying to effect the repairs in the face of the 12 to 15 inches of rain that has fallen has been a challenge, but one he thinks they have overcome.
After crews poured concrete for the face of the dam, rain caused the water to overtop the cofferdam that had been constructed to allow for dam repair. A cofferdam is a watertight structure from which water is pumped to expose the bottom of a body of water and permit construction. The town was later able to construct a siphoning pipe to speed up dewatering by increasing discharge from the meadow above the dam to the brook beyond the dam. Once water levels dropped enough, they removed the water from within the cofferdam and went back to the repairs.
Fowler said fortunately the work held that was done before the rains came, and the dam remains stable. He said the state has been inspecting it periodically and his department does so daily. The repair to the hole under the dam is now fixed, Fowler added, and the firm doing the pressure grouting to the fissures in the dam was to be finished by Monday, July 8. He said while doing the pressure grouting, a 4-foot hole was discovered inside the dam and was filled as well.
“I am told by the company that this pressure grouting will work just fine even with that size hole,” he said. Once the pressure grouting is completed, it will be necessary to back fill around the dam and remove the cofferdam that has been keeping the water away from the repair work. “The clean-up in the area will be done over the next couple of weeks,” he said.
Fowler said no change was made to the height of the dam and when everything is complete, the dam will function just as it has in the past. The levels in Beaver Lake are determined by weather events, the springs and the watershed. “This project has taken much longer than we anticipated when we started but we didn’t expect to have to deal with all the rain,” he said. “The good news is we are almost at the end and the repairs are successful.”
This spring, a vigilant resident noticed the flow of water under the dam down the stream and reported it to Fowler’s office, initiating his inspection and action to address the situation. The spill was slowly emptying the meadow and keeping the level of water low in Beaver Lake.
The dam protects Beaver Lake and controls its level. It dates back to the early 1900s, when Benjamin Chase, owner of the Chase Mill – now condominiums – erected it to create water power, and later electric power, for his mill.
A second dam stood at the end of Beaver Lake as well, between the lake and the meadow, but it had ceased to function and the town, rather than repair it, removed it last year.