Water Quality

When water velocity is slowed, as it is behind a dam, the temperature increases as it’s warmed by the sun. This temperature shift, and associated water quality changes, can make the water uninhabitable for some species during the warmer months. The Concord, Sudbury, and Assabet Rivers have many dams, resulting in a compounding effect on temperature increase as the water moves downstream and spends time in the impoundments behind each dam. As temperature increases and water slows, dissolved oxygen decreases. Most aquatic organisms rely on oxygen dissolved in water to breathe, and limited dissolved oxygen can be deadly for aquatic life. Improving water quality does not only benefit aquatic life, however. Thousands of people currently get their drinking water from the Concord River and improved water quality will benefit them as well.

Improved riverine functions

The upstream areas of watersheds supply the downstream estuaries and marshes with sediment, nutrients, and all of the other components necessary for a healthy ecosystem. Dams block natural sediment and nutrient transport, disrupting their conveyance downstream, and often resulting in a buildup behind the dams. Excess nutrients, especially when compounded with warm water, can result in algae blooms, some of which may be toxic for people and animals, and other nuisance aquatic plants.

Flood mitigation 

The dam creates an artificially higher water level upstream. Because it is a run-of-river dam, it does not control flooding downstream as some larger dams do. Removal of the dam would both reduce flooding upstream, and remove the risk of a catastrophic failure of the dam; which would release a significant amount of water at once, potentially flooding downstream properties.

Climate resilience and floodplain access

The Talbot Mills Dam is surrounded by development, which means the river channel upstream is currently constricted on either side. With the removal of the dam, the river width above the dam site will decrease as the natural channel returns, and some   of its historical floodplain will be restored. When large storms occur, the river can then fill the floodplains with water, rather than the surrounding streets and properties. Larger floodplains also slow the speed of the water, which makes it less destructive as it moves downstream. As we expect more intense rainstorms with climate change, allowing the river to utilize these floodplains to manage flood water naturally will be particularly beneficial to the surrounding communities.

Invasive species reduction

Water chestnut is an invasive plant that grows on the surface of shallow, stagnant water. It currently covers the Mill Pond behind the Talbot Mills Dam. The dense mats of non-native vegetation crowd out native aquatic plants that provide food and shelter to native fishes, birds, and insects. Water chestnut also blocks sunlight from reaching the water and creates wild swings in dissolved oxygen in the water. When the plants decompose, they reduce the available dissolved oxygen. With the dam removed, the conditions that encourage water chestnut growth will be largely gone.

Healthier ecosystems 

All of the above benefits together restore a river’s natural  functions, resulting in a healthier ecosystem. When the river benefits, all of the systems that rely on it benefit as well. For example, a migratory bird that passes through the Concord River watershed and is able to feed on fish and insects, then has the nourishment to travel to another completely different ecosystem where the bird contributes to the food web and ecosystem functions. Fish that migrate up through the Concord River to spawn also feed bass, bald eagles, seals, whales, tuna, cod, and other fish and birds out in the ocean.  These examples demonstrate how interconnected the SuAsCo watershed is with the greater ecosystem.

Recreation

The SuAsCo watershed is already a great place for people to enjoy canoeing, kayaking, rafting,fishing, picnicking and bird-watching along the rivers. Removal of the Talbot Mills Dam would provide an opportunity to engage in each of these activities in a new and different way. It is currently very difficult for boaters to get around the Talbot Mills dam.

Decommission Aging infrastructure

There are over 150 dams in the SuAsCo watershed. Many of these, including the Talbot Mills Dam, are privately owned. The Talbot Mills Dam is an intermediate-sized, significant hazard dam, meaning that due to its size and the amount of water stored behind it, failure of the dam could result in economic loss, environmental damage, disruption of lifeline facilities, or other impacts. As the dam ages and its condition deteriorates, this risk to the community downstream and the liability to the dam owner become more imminent.

2016 Concord River Diadromous Fish Restoration Feasibility Study: In 2014, the Massachusetts Division of Marine Fisheries (DMF) contracted Gomez and Sullivan Engineers to study if and how fish passage to the Concord River watershed could be restored. In 2016 the study concluded that fish passage restoration is possible, with some modifications to the existing infrastructure in the river. Most notably, it was found that the Talbot Mills Dam is the primary blockage for fish accessing the SuAsCo watershed.

2020 Review of Talbot Mills Dam Removal Feasibility Study: In 2020, the Town of Billerica contracted Streamworks, PLLC to conduct a review of the 2016 Feasibility Study. Streamworks generally agreed with the findings of the study, and made suggestions for follow-up analyses.This review mentioned that removal of the Talbot Mills dam had the potential to improve water quality in Concord River.  

2021 Merrimack River Comprehensive Plan for Diadromous Fishes: In 2021 the Technical Committee for Anadromous Fishery Management of the Merrimack River Basin, made up of representatives from federal and state agencies in New Hampshire and Massachusetts, completed a comprehensive plan for restoring diadromous fish populations to the Merrimack River Watershed. Removal of Talbot Mills dam was identified as a top priority project resulting in significant potential to restore fish populations to the Merrimack River watershed.

2021 Talbot Mills Dam Removal Targeted Impact Analysis: In 2021, DMF contracted Gomez and Sullivan Engineers to study the impacts that dam removal would have on the Town of Billerica’s drinking water intake, located 1.25 miles upstream of the dam. The study concluded that no significant impacts to the intake or water supply in general are expected from dam removal.

2022 Review of Targeted Impact Analysis: In 2022, the Town of Billerica contracted Streamworks, PLLC to conduct a review of the 2021 Targeted Impact Analysis. Streamworks found the conclusions of the analysis to be accurate and reasonable but suggested further studies. They supported Gomez and Sullivan’s recommendation to move forward with design and permitting of the dam removal.

2022 Talbot Mills Dam Removal–Intake Pump Performance Analysis: In 2022, the Town of Billerica contracted Woodard and Curran New England to also study the potential impacts that dam removal would have on the Town’s drinking water intake. The study concluded that dam removal would not likely cause issues at the intake structure. They recommended that the Town consider developing a second intake at another location on the river or an alternative water supply source due to the existing water quality concerns, and the Town having only one drinking water intake.

2022 Talbot Mills Dam Removal Conceptual Design: In 2022, DER contracted Gomez and Sullivan Engineers to develop a conceptual design for the removal of the Talbot Mills dam. This included an assessment of upstream and downstream impacts and an analysis of scour of existing infrastructure that could occur as a result of dam removal, and a plan for managing sediment behind the dam once the dam is removed.

2023 Talbot Mills Dam Removal Preliminary Design: In 2023, OARS contracted Gomez and Sullivan Engineers to advance the dam removal design to the preliminary (permit-ready) stage. 60% complete drawings were included with the MEPA EENF filing, and 75% complete drawings were included with the MEPA SEIR filing (see links to these documents below under Regulatory Review).