A new decade-long study of the Connecticut River watershed has provided scientists some valuable tools for understanding how dams affect a river’s ecological health, but also suggests that little can be done to alter dam operations for environmental gain.
“Our question was, can we modify the operations of these dams to both benefit the ecosystem and maintain the human services they provide?” said Katie Kennedy, a river scientist with the Nature Conservancy involved in the study.
Researchers from the Nature Conservancy, Army Corps of Engineers and University of Massachusetts Amherst found the corps’ dams could not be managed in a more environmentally friendly way without increasing risk of flooding.
“The Army Corps dams are already doing their job at optimizing the flows,” Kennedy said. “There are definitely impacts, but they pretty much maxed the system out meaning they do all that they can to protect their resources to the point of managing risk.”
The 60-page Connecticut River Flow Restoration Study, titled “A watershed-scale assessment of the potential for flow restoration through dam re-operation” was released on June 11.
“Essentially the report looks at how can all these owners and operators take a look at managing (the dams) in a way that is more environmentally sensitive to the area,” said Timothy Dugan, a media relations officer for the corps.
Congress approved the joint study with the Nature Conservancy and the corps and then signed the Water Resources Development Act in 2007, which authorized the corps’ partnership with the Nature Conservancy. A total of $2.6 million was spent on the endeavor, according to Dugan, with costs shared equally by both agencies.
Work began in 2008 with teams of scientists, consultants, stakeholders and dam operators. In all, Kennedy said well over 150 people participated in the study. Together they created computer models of the river’s past, present and future using using satellite data and hydrologic models
They chose to focus on the 73 largest dams along the Connecticut River, 14 of which are owned by the corps.
“We chose these because, in general, the larger the dam the bigger the impact to the ecosystem,” Kennedy said.
While the study did not find the efficiencies they had hoped for, these models are the first of their kind and invaluable to the scientific community. Kennedy especially liked working with the Connecticut River Unimpacted Streamflow Estimation tool, a snapshot of daily, historical streamflow created by the U.S. Geological Survey.
“One of the biggest challenges with experts, people who are the best in their field, they still only have a limited perspective of their own lifetime,” Kennedy said. “Comparing those help us understand impacts, where they are the biggest, where are the places where we might have the most opportunity to make a difference.”
Kennedy is more optimistic about the possibility for hydropower dams to alter operations for environmental benefits, as they have more flexibility around how much water they release, and when. However, most dams in the watershed are old, defunct and less than 10 feet tall.
“When these dams were put in, we had no idea what impacts they would have,” Kennedy said.
Most of the 3,000 dams in the Connecticut River watershed are not on the river itself, but its dozens of tributaries like the Mill, Fort and Westfield rivers that empty into the great water body. During a heavy rain or snow melt, these dams hold back water and prevent the Connecticut from swelling, as it would do naturally, and flooding adjacent communities.
In general, dams can serve four main functions: flood control, water supply hydropower or recreation. Many defunct dams, once used to power numerous old mills throughout the state, now serve only as a way of holding back popular swimming holes.
“Even if recreation wasn’t a part of the original construction the surrounding of these dams, they may be holding thousands of acres of water that may be used for several purposes,” Dugan said.
Kennedy said there is little “wiggle room” in the study’s many models to alter operations in regards to how and when water is released, or adjusting for seasonal fluctuations.
Christine Hatch, extension associate professor of geosciences at the University of Massachusetts Amherst, said that dams in the watershed date back hundreds of years, so imagining a dam-free Connecticut is difficult.
“There’s a long legacy of them in this region, but there’s also a lot of effort to remove a bunch of them,” Hatch said, “particularly the smaller ones that are no longer serving their intended purpose.”
The computer models help experts decide which river restoration projects will give them the biggest return on an investment. According to Kennedy, removing a dam is by far the most effective way to improve the ecological function of a river, by freeing built up sediment and nutrients and reestablishing flows to minimize excessive growth of plants and algae.
“It’s the easiest, most straightforward, most durable action you can take for a river ecosystem,” Kennedy said.
Hatch said that conversations about dam removal began when concerns about the sustainability of fisheries started to rise. Dams block migratory fish from traveling upstream and spawning, and she says just 7 percent of fish successfully make it past fish ladders.
“They work, but the percentage of fish are terrible,” Hatch said. “It’s kind of amazing that any of them make it up.”
While progress has been made to remove old dams, like the recent demolition of the Upper Roberts Meadow Dam in Leeds, other communities are rallying support to preserve the old structures. In 2014 the Friends of Lake Warner rallied public support to save the lake’s more than 100-year-old defunct dam. Members of the Belchertown Land Trust are close to realizing repairs on the Upper Bondsville Dam that will preserve a small water body on the border of Belchertown and Palmer.
“There’s a lot of emotion about that,” Kennedy said. “People would rather have lakefront property than riverfront property. It’s such a sitespecific thing. When we do take out a dam, we are really careful to have a public meeting, talk with people and find out what their specific values are before we take that path,” Kennedy added. “It’s important to understand both sides whoever you are.”
Public meetings, conversations with stakeholders and community members is an essential part of the dam removal planning process, and sometimes removal isn’t ultimately the best option. Purchasing riverside properties for conservation purposes, restoring floodplain forests and allowing rivers to flood on a seasonal basis are other ways we can improve their ecological health.
“Dams in the Connecticut have definitely impacted ecosystems in a way that may be irreversible,” Kennedy said. “But that’s not to say that we can’t reach a positive state, we have plenty of work to do before we reach that.”
Sarah Robertson can be reached at email@example.com.