SOUTHWICK — The federal Natural Resources Conservation Service will hire a consultant to survey Congamond Lake in person to settle on a flooding plan.
“They are in the final throes of hiring a boots-on-the-ground consultant,” said Richard Grannells of the town’s Lake Management Committee during a recent meeting of the committee. “They got the funding for it,” he said of the consulting work that would probably start in the late spring or early summer.
In January 2023, the lake committee asked the NRCS to develop a plan to maintain the water levels of Congamond Lake in the event of a 100-year flood, an event that raises the level of a body of water between 1 and 3 feet, and has a 1% chance of occurring annually.
The lake committee, a local volunteer group that monitors Congamond’s water level and its overall condition, has been trying for several years to maintain consistent water levels after heavy rain, and prevent the flooding of homes and other property along the lake.
When the NRCS issued its preliminary report in June 2023, it offered four options to mitigate a flooding in the ponds, including one of “take no action.”
Two options are characterized by the NRCS as “structural solutions.” One is to build an outlet pipe in North Pond, replace the culverts between the ponds, and install a larger weir at the entrance of Canal Brook. The other is to do all of those things, and also build a new weir on the Great Brook Canal.
The fourth option, called a “non-structural solution,” was to purchase and demolish 79 homes along the shore at risk for flooding in a 100-year storm.
The cost of the solutions in the NRCS report ranged from zero, for the “take no action” option, to $43 million for the “non-structural” option, to $54 million for the structural option that addresses Canal Brook only, and $72 million for the option that includes Great Brook.
Deron Davis, the state conservation engineer and watershed operations program manager for the NRCS, said when the preliminary report was released, if the flood mitigation project were approved, it would probably be a combination of the elements of each option.
Grannells said after the meeting that what the committee hopes is decided is a project that would clear the natural buildup of sediment, falling trees and thickening plant growth that have narrowed and clogged Canal Brook and Great Brook over decades, and restore them to their original dimensions of 9 feet wide and 9 feet deep.
The committee currently keeps the lake level at 224.4 feet above sea level by raising or lowering a concrete weir — a small dam — on Canal Brook at the south end of South Pond.
When there are particularly heavy rains, the brooks, which are supposed to allow the water to drain out of the lake, run the opposite way, and water from the surrounding marshy and wetland areas is flushed into the lake, carrying nutrients from the land that contribute to algae blooms.
As the algae decays, it consumes the water’s oxygen, which can lead, in extreme situations, to the suffocation death of fish. Annual alum treatments of the lake have helped minimize algae blooms, but that only treats the problem. It doesn’t address the root cause, the lake’s inability to naturally flush itself.
The NRCS, which is part of the U.S. Department of Agriculture, contracted with a consultant to draft the preliminary report using only readily available geological and watershed data. The consultant didn’t visit the area, but was provided photographs of the lake by the town.
Grannells said the next step is for the committee’s members to develop a list of “action items” that will be shared with the consultant before arriving in town to collect the data and complete the next report.
