Restoration on the Cocheco River: Gonic Dams Removal Project underway

No one knows exactly when the first dam was built by Euro-Americans on the Cocheco River in Rochester, New Hampshire. However, historical documents indicate that in 1743, the Squamanagonic Falls Garrison along the Cocheco River was accompanied by a mill, and presumably a dam. Squamanagonic, an Abenaki word for either “waters that run by the clay place hill,” or “salmon spearing place” was ultimately shortened to Gonic, which became the namesake for the village in the southern part of the City of Rochester. The historical record also shows that a series of mills at the Squamanagonic Falls were built and subsequently destroyed by flood or fire in 1785, 1805 and 1848. By 1849, the Gonic Manufacturing Co. was created, setting course for the expansion of the Gonic Mill infrastructure and further development of the Gonic Village that at that time was lauded as a “pleasant and thriving New England village.”  

Today, after more than 25 years of planning, the Gonic Dam and Gonic Sawmill Dam are in the process of being removed. Gosport Properties, LLC, the former owner of Gonic Mill, is working to remove the dams and restore the river in collaboration with the New Hampshire Department of Environmental Services (NHDES) and the City of Rochester. NHDES is providing technical and financial support, while the City of Rochester has a dual role on the project, serving both as fiscal agent for the American Rescue Plan Act (ARPA) grant and owner of municipal sewer infrastructure buried beneath the Cocheco River that will be affected by the dam removal project.  

The existing Gonic Dam was built in the 1910s and is 15.5 feet tall and 155 feet long. The Gonic Sawmill Dam, located 1,700 feet downstream of the Gonic Dam, was built sometime around 1925 and is 25 feet tall and 80 feet long.  

There is a long history of dam safety issues at the Gonic Dam. In 1980, the New Hampshire Water Resources Board (a predecessor to NHDES) required the dam owner at the time to repair it. Four years later, no action had been taken and the owner declared bankruptcy, so the General Court reached a settlement with the dam’s new owner to remove stop logs and maintain the dam in a dewatered condition, which is how it has remained for the past 40 years. In 2004, the NHDES Dam Bureau issued letters of deficiency (LOD) for the Gonic Dam and Gonic Sawmill Dam, requiring that the dams be repaired or removed. Gosport Properties accepted responsibility for the Gonic Dam, but the company did not agree that it owned the Gonic Sawmill Dam.  

Questions of landownership and dam ownership are a common occurrence in dam management. This ownership question of the Gonic Sawmill Dam is the result of a 1987 subdivision of the Gonic Mill property into three lots. Ultimately, ownership issues delayed resolution of the dam safety issues at both dams. To this day, ownership of an 8.3-acre parcel on the eastern side of the river, known as Lot 3, remains unresolved.

Given the land and dam ownership issues, as well as the technical questions that needed to be answered to satisfy environmental and safety concerns, the NHDES Coastal Program (NHCP), with grants from the National Oceanic and Atmospheric Administration (NOAA), funded a dam removal feasibility study in 2003 to evaluate the potential impacts on the nearby environmental, historic and socioeconomic resources, as well as upon any private or public infrastructure. Published by Gomez and Sullivan Engineers in 2005, the study found that dam removal was technically possible but that more due diligence investigations were needed. From 2009 through 2019, NHCP advanced several phases of investigation in partnership with Gosport Properties and the City of Rochester, including additional sediment contaminant testing, preliminary dam removal engineering, scour analysis of the sewer line, deed and title research, environmental site assessment of Lot 3, and pre-permitting meetings with regulatory authorities. Between 2000 and 2020, NHDES provided $292,000 of grant funding to help advance planning for the Gonic Dams Removal Project.  

Ultimately, enforcement of NHDES Dam Bureau Administrative Rules by the New Hampshire Attorney General’s Office brought the case to the New Hampshire Water Council, and then to Strafford County Superior Court. In 2022, Gosport Properties reached a settlement agreement with the State of New Hampshire to remove both dams with grant funding provided by NHDES.

Funding and planning

NHDES is providing an additional $2,699,225 to support the comprehensive implementation of the dam removal project, including site restoration, five years of post-project monitoring, re-mapping of the FEMA floodway, and potential adaptive management interventions. The following grant programs are part of this funding:  

In 2023, the NHDES ARM Fund received a grant application from Gosport Properties for funds to support the removal of both dams as well as channel and riparian buffer restoration, and approved it in 2024. The ARM Fund grant ensures that the project will provide state and federal compensatory mitigation to offset losses to aquatic resources that occurred in the Salmon Falls-Piscataqua Watershed from state and federal permits. As an in-lieu fee mitigation project, it will undergo performance monitoring, and adaptive management if necessary, to ensure that the ecological objectives of the project are achieved and sustainable. Additionally, the restored river and riparian buffer will be permanently protected through a conservation instrument to prevent future artificial impoundments, destruction or degradation of the restored areas.

With grant funding for the implementation phase secured in 2025, Gosport’s project team, comprised of BCM Environmental and Land Law, as well as Gomez and Sullivan Engineers, began working to complete final engineering plans and securing all necessary permits and approvals. In spring 2025, Gomez and Sullivan Engineers gave presentations to the Rochester Conservation Commission and the Cocheco River Local Advisory Committee, and in August of that year it had secured the necessary wetlands permit from the NHDES Wetlands Bureau.  

The Gonic Dams Removal Project is a public/private partnership that was designed to address public interests and liabilities to public resources that occur on private property. In addition to the removal of both the Gonic Dam and Gonic Sawmill Dam, the project includes the following elements:

• A new river channel, called a constructed riffle, will be built between the Gonic Sawmill Dam site and a buried city sewer line.
• Workers will remove about 2,000 cubic yards of contaminated sediment from the river and send it to a permitted landfill. Any remaining sediment will be stabilized and covered with plants.
• To protect two sewer pipes from being exposed or damaged once the dams are gone, engineers will place large rocks around them to prevent erosion. Smaller rocks will go on top to create a more natural riverbed.
• The new riffle will include pools, rounded river stones and boulder clusters to create better fish habitat. The riverbanks and floodplain will be strengthened and replanted. Also, 3.4 acres along the river will be permanently protected from development.
• When the Gonic Dam is removed, a natural bedrock waterfall will likely appear. Because nobody knows exactly what it will look like, it’s unclear if fish, turtles and other animals will be able to move upstream. The contractor, project engineer and New Hampshire Fish and Game will work together to make adjustments to the channel if needed to help wildlife pass through the area.

Project underway

In June 2026, Sargent Corp. mobilized to the site of the Gonic Sawmill Dam to build the constructed riffle, remove the dam and restore the adjacent floodplains. After that dam is removed, Sargent Corp. is expected to start removing the Gonic Dam with substantial completion of the overall project expected by December 31, 2026.