Seymour Dam Removal Plan Set to Restore River Ecosystem

Plans to remove a deteriorating Connecticut dam are nearing completion, and include an innovative design that will repurpose silt and sediment dredged from the river.

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First constructed in the 1850s, Seymour Dam is located across the Bladens River, immediately upstream of its confluence with the Naugatuck River in Seymour, Connecticut. Its original purpose was to provide hydraulic power and cooling water for the Kerite Company, a manufacturer of high-voltage electrical cable founded in 1854 by Austin Goodyear Day, nephew of Charles Goodyear.

“Kerite was an important company, which installed the power cable under New York Harbor in the late 1800s, and supplied cable for the Panama Canal in the early 1900s,” said Hans Hasnay, of WSP, who is a member of the project team.

The dam was rebuilt around 1918, but wear and tear over time gradually overwhelmed the stone structure, deteriorating to the point where it was causing significant water issues—particularly in an adjacent building where water was continually filling up the basement through floor cracks and elevator shafts. During the most recent inspection—which the Connecticut Department of Energy and Environmental Protection requires every seven years for dams—numerous deficiencies were discovered.

At that point, the facility owner, Marmon Utility, determined that the most practical solution was to remove the dam entirely.

“Since the dam does not serve a purpose for the company any longer, Marmon Utility desired to remove the dam to relieve their financial liabilities and regulatory burdens, eliminate repair and maintenance costs, and reduce high water table issues.” Hasnay said.

Marmon Utility selected WSP, in partnership with Princeton Hydro, to provide engineering design, permitting, contractor procurement, construction administration and inspection for the removal project. Allan Estivalet serves as project manager for WSP, and Jim Sobieraj is the principal-in-charge.

©WSP USA

An aerial view of the Seymour Dam shows the current flow of the Bladens River and the pond that currently forms behind the dam structure.

Silt Savings

In March 2018, WSP measured the water depth to sediment in two transects across the pond behind the dam to determine the vertical extent of the sediment, and collected samples of the sediment for characterization. After analyzing the sediment to determine if removal was viable, WSP provided a proposal to safely remove the dam, reclaim land to provide more space for business operations, and minimize project costs.

After the dam is dismantled in sections, the plan calls for an innovative use of the remaining silt to create additional parking and a plant work area.

“We envision a fill access road will be installed on the upstream side and will be lower along with the dam in phases,” Hasnay said. “Most of the thousands of yards of silt that has built up behind the dam will be used to construct a new laydown area and parking lot next to the manufacturing facility.”

The concept for the restoration of the Bladens River will work with the natural occurring bedrock in the downstream channel areas, but transition to a higher channel bed with the riffle pool complex through the old pond area.

“This design approach will allow us to better balance the cut-fill ratios of the legacy sediments, thus avoiding costly haul away and disposal fees to the extent possible,” Hasnay said. “This approach will also result in a decrease in groundwater levels and flood levels along the stream margins, thus helping mitigate water intrusion and flood issues currently impacting the adjacent manufacturing structures.”

WSP is committed to creating a world today that is Future Ready™—and while that often involves a new way of approaching the construction or design of a project, Seymour Dam demonstrate how sometimes this is accomplished through the removal of an outdated structure in order to the overall health of a natural area for the benefit of the community, as well as sustainable practices that turn waste material into an asset, as demonstrated by the use of silt for the parking area.

©WSP USA

Once removed, the river will flow through the area more naturally, and create an area where a new parking lot can be created using silt removed from the former pond.

Environmental Benefits

Despite the age and former importance of the dam, there were no plans to preserve the structure.

“Typically, dams are not subject to historic preservation restrictions due to concerns regarding life safety issues,” Hasnay said. “Though the structure won’t be restored, the project will result in the restoration of 650 feet of streambed, providing additional fish access from the Housatonic and Naugatuck Rivers located upstream of the existing dam.”

The design process started last September and will wrap up in April, with construction set to begin in August. Construction work to remove the dam should be completed by the end of the year.

Though his engineering efforts usually center around construction of a dam, Hasnay views this demolition project as being important to the benefit of the community.

“I believe that dams have an important place in society,” Hasnay said. “They have been providing navigation lanes, power generation, drinking water and recreational opportunities for centuries. However, legacy dams that no longer provide sufficient benefits to justify the environmental impacts they cause should be removed, so I am glad to be part of this effort.”

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