The Carlisle Mosquito Online

Friday, February 3, 2006


ConsCom hears River Restore expert on benefits of dam removal

A presentation on the possible benefits of dam removal brought a sizable delegation from the environmental community to the January 26 Conservation Commission (ConsCom) meeting. The speaker, Rachel Calabro, is from the Massachusetts River Restore program, a state agency dedicated to promotion and facilitation of river and stream quality through removal of obsolete dams. These dams may constitute a threat to safety or are detrimental to the overall health of a river, steam or ecosystem. It was not her role to emphasize counter arguments or discuss specific local structures.

Carlisle's dams

Why should Carlisleans be particularly concerned? Residents may be surprised to learn that Carlisle is home to at least nine dams. More importantly, the Greenough Dam, in the Carlisle conservation parcel of the same name, was declared to be "in fair to poor condition" by the state's Department of Environmental Management in the year 2000.

Because the 75-year-old structure checks the flow of Pages Brook to form the scenic Greenough Pond and extensive upstream wetlands, the 2001 Town Meeting authorized expenditure of $13,050 to study the hydrology and hydraulics of the dam and its environs and prepare engineering specifications. These were completed in 2004, just as lean budgets at both the state and local levels made funding scarce.

Why remove dams?

The Restore program's arguments in favor of dismantling an old dam are based in part on recognition that wildlife needs to move — fish for spawning and good water quality and many aquatic animals for transfer of the young from nursery to adult habitat. Dams present a barrier to these critical activities. They also trap sediment and increase water temperature. This may lead to intense plant growth, choking a pond and eventually lowering water quality.

To buttress the argument for removal, Calabro showed before-and-after slides to prove that "where dams fall, rivers thrive." The photographs depicted derelict dams with rock-choked streambeds next to two-years-later scenes of water-filled channels winding through verdant meadows in Connecticut and Massachusetts.

Without proper attention to replanting, non-native species may invade an emptied pond. Calabro noted, "You have to look out for loosestrife as you re-vegetate your riverbanks."

From an economic standpoint, Cabral stressed that removal carries a one-time cost, whereas maintenance is ongoing and may become mandatory. She cited River Restore's figures showing that repair of small dams usually costs three to five times more than removal. Furthermore, she said grants to owners for removal are easier to get than funds for repairs. Certainly, many owners are happy to avoid potential liability problems.


Having established the benefits that can accrue to the River Restore program, Calabro warned that there are often strongly competing views, starting with stakeholders' preferences for either pond or river landscapes. There can be serious neighborhood issues when changing established wetland patterns or eliminating popular recreational activities such as skating, canoeing etc. Therefore she advised that when considering the options, a community should focus first on a vision of what the results might look like and what could replace familiar features, perhaps a park, hiking trails or agriculture. Asked what the program had to say about beaver problems, Calabro said only, " We don't really have an opinion on beaver dams."

To a double query from chairman Tom Schultz, "What does it typically cost?" and "What do you do for remediation of contaminated sediments?" Calabro found the first question impossible to answer, but linking the two, conceded that contamination problems can be very expensive. Expanding on that and other risk factors, she noted that the state helps with an initial reconnaissance and will soon have a risk assessment package available. She said other factors that require careful consideration are water quality and water supply. However, once the assessments are found to favor dam removal, the state taps an array of "partners" both technical and financial. Specifically mentioned were American Rivers, Conservation Law Foundation, Fish America Foundation and the U.S. Army Corps of Engineers.

Commissioner Kelly Stringham sought more concrete assurances, asking, "Can you perhaps end up with a swamp rather than a stream or clear channel?" Calabro considered that to be an unlikely scenario, but conceded that it could occur.

Former Commissioner Tom Brownrigg asked if the risk analysis included a wildlife study, informing her that the area around Carlisle's Greenough Pond is currently recognized as an endangered species habitat for both flora and fauna. Calabro termed that "a very valid consideration" and assured him that habitat assessment would be an important part of the recommended capability study, which carries a $30,000 to $60,000 price tag.

The mention of price tags led Commissioner Peter Burn to think in political terms and ask, "How active a role would River Restore play in a community debate on these issues?" Calabro again indicated that they and the aforementioned "partners" would help inform the public and assist them in evaluating their options, but at present the Commonwealth itself does not offer funding.

To a final question from Conservation Administrator Sylvia Willard about the likelihood of legal problems if stakeholders such as abutters and upstream or downstream landowners foresaw different versions of the result, Calabro responded, "it's very hard for us to answer a question like that," but added that the state's database on projects to date is available to the public, though not online.

The Commissioners thanked Calabro for her presentation, while making it clear to the audience that the session was purely informational and did not represent their personal or official leanings on the matter.

2006 The Carlisle Mosquito