Dam History and Current Use
A dam/impoundment structure has been present in this area of the Charles River since the 1700s. Historical documents indicate a timber dam that once served local mills was destroyed by a flood in the early 1930s and replaced in 1934 with the current configuration: an earthfill embankment, stone masonry, and concrete structure. Today, the impoundment formed by the dam creates a pond area that is used for aesthetic and recreational purposes. The dam does not provide flood control.
The current dam spanning the Charles River in South Natick was constructed in 1934. It is owned and maintained by the Town of Natick. The dam is regulated by a permit issued by the Department of Conservation and Recreation’s Office of Dam Safety (DCR-ODS) and is considered a High Hazard dam due to the potential for loss of life and significant property damage in the event of dam failure.
Residents who are interested in learning more about the dam’s history are encouraged to review research published by Charlotte Diamant, a student at Wellesley College, available here. The Charles River Dam Advisory Committee's Indigenous representatives also shared a history of the river and dams during the Committee's November 9, 2021 meeting, available here.
Dam Project Timeline
2007 - 2014: Dam Deficiencies Identified
Bi-annual inspections starting in 2008 identified deficiencies in the dam, including:
- Mature tree growth on the earthen berm
- Erosion on the upstream face and top of the earthen berm
- Deteriorated stone and masonry associated with entraining walls on both sides of the spillway
In 2009, the Town completed a Phase II study of the Charles River Dam, which is an in-depth analysis that includes a hydraulic study. The study determined the dam is able to pass the river flow from a 500 year storm (i.e., the worst storm in any given 500-year period, based on historical data) without failure; however, the level of the river would be less than a foot below the crest of the earthen dam. More recent rainfall events in various locations across New England have raised the possibility of experiencing a storm that would be in excess of the rainfall previously estimated from a “500-year storm,” which could overflow the dam and increase the probability of dam failure.
Addressing these deficiencies was identified as a priority in the Town of Natick’s 2010 Hazard Mitigation Plan, and was subsequently added to the Capital Plan. It is listed in Natick’s 2018 Hazard Mitigation Plan Update and Community Resilience Building Report.
2019: Design and Early Permitting of Dam Repair
Following Town Meeting appropriations, Natick hired GZA, who developed a dam repair design and submitted a Notice of Intent application to the Natick Conservation Commission. In accordance with the Office of Dam Safety’s “No Trees on Dams” policy, the design required the permanent removal of 60 trees on the earthen berm.
Fall 2019: Community Requests Feasibility Study of Dam Removal
The Conservation Commission notified riverfront and neighborhood abutters and hosted a public meeting to discuss the proposed dam repair design. Community members asked the Town to explore options that do not require permanent tree loss, including dam removal.
2020: Initial Sediment Testing and Feasibility Study Confirm Viability of Dam Removal
As part of the initial feasibility study, GZA performed soil sampling to determine if there were any levels of contamination in the sediment that would prevent dam removal from being a viable option. The results showed low levels of contamination upstream and downstream of the dam. All contamination levels fall well below the threshold for significant impact on groundwater and human health. This means that, while there is some low-level contamination in the river, there are no concerns about contamination from a dam removal, as these levels were consistent upstream and downstream of the dam. These results were confirmed through additional testing by Stantec during the Advisory Committee process, and further testing by GZA in 2022 (see Relevant Documents).
Based on the river sediment results, the Town directed GZA to perform a preliminary Dam Breach Analysis, estimating the impact to the river of breaching the concrete spillway. It was determined that even a partial (50%) breach of the spillway would lower the river water elevation to less than jurisdictional levels during larger rainfall events. This would remove the structure’s classification of a dam, reduce upstream inundation during extreme rainfall events, and eliminate the Town’s liability for dam ownership. These findings encouraged the Town to consider a dam breach alternative in further detail.
May 2021 - September 2022: Charles River Dam Advisory Committee Process
Natick’s Interim Town Administrator created the Charles River Dam Advisory Committee and appointed members representing different municipal boards and perspectives to conduct research on the two options, dam repair or dam removal, and recommend a path forward.
Key documents from the Committee’s work include:
- Summer 2021 - Findings From Public Awareness and Community Engagement Campaign
- December 2021 - Findings From Community Use and Recreation Survey
- January 2022 - Analysis of Dam Repair Alternative Methodologies to Reduce Tree Loss
- June 2022 - Stantec Report: Preliminary Analysis of Dam Removal
- September 2022 - Final Report and Recommendation
Additional information about the Advisory Committee is available here.
Ultimately, the Advisory Committee advised the Town to remove the dam, restore the river and improve the riverfront parks.
November 2022: Select Board Votes to Pursue Dam Removal and River Restoration
The Advisory Committee presented their recommendation to the Select Board. The Board received public comment over four public meetings, and voted to pursue dam removal on November 9, 2022.