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Connecticut River, Connecticut, Massachusetts, New Hampshire, & Vermont

Integrating many project purposes in a large area

The Connecticut River Sustainable Rivers Program site currently involves 14 U.S. Army Corps of Engineers dams on nine tributaries across four states. This large project entails significant research on the benefits provided by the dams, environmental needs in the river basin, and the effects of potential modifications. A total of 70 reservoirs are being considered for eventual inclusion in the project, making this effort one with the potential to benefit humans and wildlife throughout an entire.

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Connecticut River

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The Connecticut River flows from its source near the Canadian border to Long Island Sound. Land use in the watershed is approximately 77 percent forested, 9 percent agricultural, 7 percent wetlands and water, and 7 percent developed. The Connecticut River is the only major river in the northeastern U.S. without a major port, harbor, or urban area at the mouth. The estuary contains high-quality tidal wetlands selected as Wetlands of International Importance. 

The upper Connecticut River in New Hampshire and Vermont flows mainly through a confined valley. The river in southern Massachusetts and Connecticut flows through the Hartford Basin and the river becomes slow-moving and meandering. South of Hartford, Connecticut, the river crosses the Eastern Border Fault flowing through the Eastern Crystalline Highlands that constricts the river and allows only narrow tidal wetlands. At the mouth, the river flows across a broad coastal plain, forming extensive brackish and salt marshes.

There are 65 major dams on the mainstem of the Connecticut River and its tributaries, which are a primary source of hydrologic alteration in the Connecticut Basin. Major dams are defined as structures capable of storing at least 10 percent of total annual runoff at its location. Although the potential for individual dams in the Connecticut Basin to cause large-scale changes in river flow regimes may be low relative to rivers in other regions, the number of dams per watershed area in the Connecticut is among the highest of all rivers in North America. 

Flow in the mainstem of the Connecticut River is altered mainly by hydropower dams on the mainstem and flood control dams on the tributaries. However, potential future changes in land use and/or climate may become increasingly important factors in determining river flows. 

Floodplain communities are adapted to periodic flooding; thus, they are particularly sensitive to hydrologic alteration and are good indicators of the effects of dams and water withdrawals on high flow events. Dams can affect fish populations through changes in flow regime, habitat quality and connectivity. Extensive research investigating effects of dams on movement of diadromous fish species has been conducted in the Connecticut River, primarily focusing on dams as barriers to fish movement. 

River regulation has often resulted in reductions of freshwater reaching estuaries, causing the mixing zone of fresh and salt water to move farther inland into habitat that may be less suitable for estuarine species. Reductions in freshwater may also increase salinity content in brackish tidal marshes. patterns of hydrologic alteration in the Connecticut River Basin suggest that annual freshwater discharge has not been greatly reduced. Rather, changes in the frequency, magnitude, and duration of flood flows are the main hydrologic alterations that may impact tidal wetlands.

However, the number of dams on the Connecticut River and tributaries and cumulative effects of water storage, withdrawals, and flow fluctuations from hydropower generation appear to be altering the structure and function of riparian and aquatic communities. Studies conducted in the Connecticut Basin and in rivers of the eastern U.S. have determined some links between hydrology and response of physical processes, ecological processes, species and communities. However, more research is needed to determine specific links between altered hydrology and ecological response.

 

Publications

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TitleSiteDate
Connecticut - Potential for experimental flowsConnecticut River2012
Connecticut - Environmental flows science summaryConnecticut River2006
Connecticut - Environmental flows workshop report Connecticut River2006
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