Eagle Dam Removal Feasibility

Eagle Dam Removal
Feasibility Assessment

Project Overview

CRWA is working with the Town of Wrentham to assess the feasibility of removing Eagle Dam, an outdated structure in poor condition that presents a hazard to downstream residents and infrastructure, and is detrimental to local wildlife. This project is funded by a Municipal Vulnerability Preparedness (MVP) grant awarded to the Town in 2019.

History of Eagle Dam
The small dam on the uppermost section of Eagle Brook dates back to the early 1800s when a corn mill was constructed on the site. A few decades later Red Dam was constructed a few hundred yards upstream to create Lake Pearl, which residents and visitors enjoy for its many recreational opportunities. Note: removing Eagle Dam would not impact recreation on Lake Pearl. Since the construction of Eagle Dam, there have been multiple dam breaches at the site: one in 1876, which was reported to cause significant downstream damage; a second in 1968, and potentially a third, more recent, breach as the dam is presently in disrepair. Historical records indicate that Atlantic salmon once made their way up Eagle Brook. However, due to this dam and many others along the Charles, there are no longer Atlantic salmon, but the dam still presents a barrier to native fish that reside in the brook.

Eagle Dam Today
Eagle Brook connects Wrentham’s Lake Pearl to the Mill River, which flows into the Charles River. The dam is owned and maintained by the Town of Wrentham. The Town engages a firm to conduct regular safety inspections of the dam as required by the state. A recent dam safety inspection found the dam to be in “poor condition”: failure of the spillway, which was damaged but never professionally repaired; severe erosion of the embankment; and overgrowth of vegetation, including large trees, which can impact the structural integrity of a dam. The report recommended the Town either remove the dam to eliminate the risk of failure, which would also provide an opportunity to restore natural stream conditions, or repair the dam -- but due to the dam’s condition and location the status quo is not an option. The dam’s close proximity to State Route 140, it’s poor condition, and the increased frequency of extreme rain events, mean something needs to be done. The dam was identified as a vulnerability during the Town’s municipal vulnerability climate planning session in 2018.

In 2019, the Town partnered with CRWA to take advantage of state funding through the Municipal Vulnerability Preparedness Action Grant program to explore dam removal. There is presently no state funding available for dam repair; if the Town elects to repair the dam it will need to be funded by the Town or private interests. The small impoundment behind the dam does not have any public access for canoeing or other recreation at this time.

Feasibility Study Complete

The Town of Wrentham engaged ESS Group to conduct an initial feasibility assessment of barriers to dam removal. ESS Group completed this study in April 2021, results are presented in a summary technical report: Eagle Pond Dam Removal Feasibility Study (coming soon). The study has concluded that Eagle Dam is likely a candidate for dam removal although additional study, and extensive community engagement would be needed before taking that step. The study found that the sediments in the impoundment are not significantly contaminated and can be released downstream, this is a common barrier to dam removal in areas with industrial histories. Initial modeling also demonstrates that dam removal would not have much of an impact on downstream flows, however, it did find that this area may face impacts from flooding regardless of the presence of the dam due to climate change and therefore this requires further study, ideally in coordination with MassDOT who owns the culvert directly downstream of the dam. Additional study is also needed to confirm that removal will not impact the Town’s nearby drinking water wells. While the dam has an interesting history, it is not protected with any historical status that could make dam removal a challenge. Finally, the study estimates that dam removal may be less costly than dam repair.

The project team engaged with residents that abut the impoundment and they expressed considerable concern over removing the dam. Additional community-wide conversations are necessary before any decision about the future of the dam is made.

CRWA is hopeful about future opportunities to restore Eagle Brook for native fish species and reduce flooding hazards to downstream communities in the face of climate change and interested in continuing to engage with continued community conversations. While not specifically a part of this project phase, removing the dam may also provide public access along Eagle Brook to Lake Pearl.
To learn more you can watch the presentation to the Wrentham Board of Selectmen. If you are interested in following more on this project get in touch with Julie Wood.

Water Quality Sampling
Though conditions vary seasonally and annually, benthic macroinvertebrate sampling results provide a long-term snapshot of stream water quality conditions. Because benthic macroinvertebrates spend their entire lifecycle within one stream reach, the assemblage of bugs living there from year to year stays relatively consistent.

Biological monitoring of Eagle Dam’s benthic macroinvertebrates was conducted on four dates in 2019 and 2020: August 16, 2019, September 3, 2019, November 19, 2020, and December 4, 2020. Sampling was conducted by CRWA staff and trained volunteers. Upstream of the dam was sampled twice (in 2019), and the downstream was sampled on all four dates. Additionally, habitat assessments were conducted on three dates (all but September 3, 2019) downstream of the dam. The data collected on December 4, 2020 was collected by four pairs of volunteers, and their results were averaged to produce one score for the day.

Upstream water quality was observed to be very poor, which is not uncommon for areas behind a dam as it becomes stagnant and inhospitably warm for many native creatures.

Next Steps

Conduct more robust hydrologic and hydraulic modelling
Engage with abutters, community members, and MassDOT (who manages state Route 140)
Confirm dam removal would not impact town water supply wells

additional materials