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Engineers Try to Restore More Natural Flow to Connecticut

One environmental engineer refers to the 407-mile-long Connecticut River, interrupted by some 4,000 small and large dams, as “probably the most highly dammed river in America.” That, indeed, is both the strength and weakness of the river. The dams provide flood control, hydroelectric power, and water supplies for much of New England, but they also drastically alter this vast ecosystem with a drainage basin extending over 11,250 square miles. This is the quandary being addressed by environmental engineer David Ahlfeld, who is working with UMass engineers Casey Brown and Richard Palmer and a team of students as part of a $350,000 project funded by the Nature Conservancy and carried out in cooperation with the U.S. Army Corps of Engineers and the U.S. Geological Survey.

“The basic question we’re trying to answer is this,” explains Ahlfeld of the Civil and Environmental Engineering Department. “Is it possible to operate the 75 largest dams on the Connecticut and its tributaries in such a way as to continue meeting their intended purposes, but also return some of the original ecosystem function?”

Dr. Ahlfeld will answer this loaded question through a very sophisticated computer “optimization model,” which incorporates data about the river from numerous scientific sources and then quantifies the most advantageous flow release from each dam to maximize all the needs of the dam operators, the recreationists who use the river, the human population that lives along the river, the animals and plants in and near the river, and the ecosystem itself. Among the wildlife that will benefit from this model are myriad floodplain plants and trees, many animal species including fish, mussels, and eels, and numerous aquatic plants.

“What each of these species needs,” observes Ahlfeld, “all comes down to flow – either high flow or low flow – at different times of the year.”

This spring should bring a very big case in point. If we have a rapid snowmelt, resulting in a large runoff and high water flows throughout the river basin, with current protocols dam operators will tend to hold back much of this runoff to minimize flood risk. But is that the most advantageous policy?

“Our optimization model might suggest that releasing some of that runoff from some of the dams would be helpful for everyone and everything on the river, without flooding any of the riverside houses or farms,” says Ahlfeld. “For instance, there are places in the river basin where we have low-lying floodplain forests that ecologically benefit from periods of high water, which drive out invasive and harmful plant species.”

You can see a slice of life from one such floodplain forest if you cross the Sunderland Bridge to South Deerfield. In the Connecticut just to the north there is a long, slender, densely forested island, which, if inundated for about two weeks once each year, would be protected from harmful invasive species.

“So, if we could utilize the big snowmelt this spring to inundate these floodplain forests without flooding riverside land containing human habitats or farms, we’d be utilizing the river flow to help everyone,” Ahlfeld declares. “Conversely, in other seasons it’s beneficial to have lower flows for certain species of fish and mussels.”

Of the 75 or so large dams in the study, some are operated by the Army Corps of Engineers for flood control, some are operated by hydropower utilities, and some are water supply dams. The City of Springfield, for example, has a major dam used for water supply. All these dams hold back the flow of the river, and many are 50 or more years old, with flow regulations instituted decades ago.

“We are trying to bring the most recent science to bear on this basin,” says Ahlfeld. “We engineers will take information from the most informed scientists about what the river ecosystem needs to be healthy and then figure out how we can most efficiently adjust the operation of all these dams to meet the ecosystem’s needs.”

One problem with the current protocols for releasing water along the river is fragmentation, with little coordination among all the different operators about which ones are releasing water, when, and what the net impact is.

“One of the things that we want to show all these stakeholders with our optimization model is that, if they all cooperate, they can improve the whole system without degrading the objectives of each dam operation,” says Ahlfeld. “It’s all interconnected.”

He adds, “The basic problem is that the Connecticut is a much different river than the one existing prior to European settlement, when the ecosystem flowed naturally for migrating fish, floodplain forests, and many other animal and plant species. Once they put the dams in, those systems were interrupted.” (March 2011)