Lake Boon Dam will undergo $3 million renovation in effort to combat climate change

STOW — A 175-year-old dam is in need of immediate repair, and Stow officials are seeking action to ensure that any enhancements can manage future climate change.

"The fact is the engineering numbers have changed — the expectations for what would be considered a once-in-a-500-year rainstorm have been raised," said Bruce Fletcher, a project manager working for the town. "And currently the prediction would say that the lake water level would rise so high, it would top over the dam, and spill onto the other side, which would cause erosion on the downstream side, and could lead to a rapid failure of the dam.

"Suggested improvements to the dam would remediate those concerns."

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The Lake Boon Dam is an earthen dam — that which is constructed primarily using compacted layers of soil, rock, clay or other natural materials — that runs along Barton Road in Stow. It sits at the crest of Lake Boon and controls the water level around the lake coming from the Assabet River, which lies on the other side of Barton Road and the dam.

Originally constructed in 1849, the dam was built to help power the former Assabet Woolen Mill, downstream in Maynard.

Lake Boon covers about 160 acres across Stow and Hudson, and is a major recreation site for residents. There are also dozens of residential homes along the lake's shores in both communities.

Water was seeping through soil, trees growing on dam

Modern concerns regarding the dam date back to the 1990s, when Fletcher was working for Stow's highway division.

"During that time it was noticed that water was seeping through the soil, and if that is getting through downstream, that is concerning," Fletcher said. "There were also trees that were growing on the dam, which is not good. If a tree gets knocked over in a storm, it can destabilize the dam, and also the roots going into the dam can cause interior issues. So we removed the trees and tried some remediation on the site."

The Massachusetts Office of Dam Safety has frequently inspected the dam, and has noted a need for repairs and improvements in recent years. In 2017, the agency issued a notice of non-compliance to the Town of Stow for issues with the dam.

The problems with the dam were accelerated in 2021 when a sinkhole formed near a guardrail on Barton Road, which had to be addressed immediately by the town.

"When the sinkhole appeared on the road, we realized that the spillway and culvert underneath the road were allowing water to get into the soil, and we needed to take careful action," Fletcher said.

The town is producing a three-year, $3.2 million plan to reinforce the dam and make improvements needed to avoid potentially damaging failures and issues caused by wear and tear, and extreme events brought on by climate change.

"The plan is to drive down steel sheet piles all along the lakeside of the dam, and install a new concrete spillway and culvert, and realigning the crest of the dam near the lake, creating a flatter side for the downstream side," Fletcher said. "That would create a stronger dam, as well as make sure that is no longer at risk during any seismic activity (earthquakes), which were not considered a concern when the dam was first constructed."

Town hopes state grants can foot the bill

In 2022, Stow received a $1 million grant from the state to help with the first phase of the project. Also that year, Town Meeting voted to approve $300,000 in funding for the project. The town has also hired Weston & Sampson, a Wilmington-based engineering firm, to oversee improvements.

Fletcher expects final improvements to be made by 2025 or 2026.

Stow Town Administrator Denise Dembkoski told the Daily News that additional funding options are being investigated, and that the town may have to fund the remainder of the project itself.

"We are still looking into grant opportunities; otherwise, I will put forth a borrowing (within the levy) to fund the remainder of the project," she said.

This article originally appeared on MetroWest Daily News: Lake Boon Dam to undergo renovations to handle climate change impact