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Ecological impact: River dams in the northeastern U.S. evaluated

Boston (global-adventures.us): River dams can serve many functions, including power generation and flood control, and they have many ecological impacts as well. Water released from dams usually contains very little sediment, leading to scouring of river beds and loss of riverbanks. Older dams often lack a fish ladder, keeping marine life from moving up stream to their natural breeding grounds. Large reservoirs formed behind dams can contribute to seismic activity, due to changes in water load or the height of the water table.

The northeastern U.S. has some of the nation’s most fragmented river systems, with an average of seven dams interrupting every 100 miles (160 kilometers) of river. In a new report titled Northeast Aquatic Connectivity: An Assessment of Dams on Northeast Rivers, a team of biologists and policy experts from throughout the region outlines the ecological impact of these dams, data that can be critical to securing and targeting limited funds for river restoration efforts.

“For the first time, we can easily quantify and compare how removing different dams might affect the ecology of river systems throughout the Northeast, allowing us to more successfully work at the scale of nature,” said Colin Apse, Senior Conservation Freshwater Adviser at The Nature Conservancy and a lead scientist on the project.

Staff members from state and federal wildlife agencies, local universities, The Nature Conservancy and other conservation groups analyzed data sources and used GIS technology to calculate more than 70 different metrics that affect habitat in the Northeast’s vast interconnected river systems.

“Dams and culverts are among the biggest threats to migratory fish in the Northeast,” said Alison Bowden, freshwater conservation director for The Nature Conservancy in Massachusetts. “Removing dams that impact fish populations – particularly in places where those dams are run down and no longer in use − can make a tremendous difference in the health of our rivers,” she said.

The database produced contains information on nearly 14,000 dams in thirteen states and the District of Columbia, and identifies locations where dam removal or fish passage construction would likely have the most significant ecological benefit. An assessment tool can be customized to consider fish like Atlantic salmon, shad and alewife that migrate between fresh and saltwater environments, and resident fish species like brook trout. It allows researchers to evaluate the scale of states, regions or river basins.

Maine and Virginia have the most dams in the top 10 percent regionally for potential benefits for migratory species, although Massachusetts, New Jersey and Delaware also have significant results when river length is considered. All the states in the analysis − from Maine to West Virginia − have one or more dams that rank high for the potential benefits of fish passage restoration, as do each of the major river basins in the region.

Driven by both its numerous coastal streams as well as the Connecticut River basin, Massachusetts is behind only Maine and Virginia in the number of dams in with the highest potential impact on migratory fish. Of the 1,521 Massachusetts dams considered, 161 were in the top 10 percent regionally.

Across the assessment region, dozens of dams have been removed in recent decades, restoring natural habitat to many rivers. But all dams are not created equal, and not all dams need be removed. In some cases, dams play an important role in providing energy, drinking water or recreational opportunity; or dam removal simply isn’t feasible. Community and conservation leaders can use the new tool to consider the ecological benefits of dam removal or fish passage installation. Combined with on-the-ground data about economic and community needs, it will provide a more complete picture to inform local decisions, Apse said.

In many cases, dam removal is a public safety issue. Throughout New England, dams that were constructed during the region’s early industrial years have fallen into disrepair and no longer serve an economic purpose, and many have become dangerous. In 2011, the Massachusetts state auditor identified 100 dams, owned by towns and cities, that are in poor condition or unsafe.

In 2005, much of downtown Taunton, MA was evacuated, and homeowners suffered significant flood damage because a dam on the Mill River failed following a major rainstorm and flooding that led to emergency declarations in more than 40 communities. The combined benefits to public safety and the environment have prompted many Massachusetts lawmakers to support legislation which would create a state loan program to fund dam inspections, repairs and removals.

The Northeast Aquatic Connectivity Assessment report indicates the benefit of removing several dams on the Mill River in Southeast Massachusetts which are slated for removal in the coming years – placing them in the top 10 percent, Bowden said. In fact, the Whittenton Dam, which famously failed seven years ago, is scheduled to come out this summer.

“This ecological data is one piece of the puzzle for communities to use as they decide whether to remove or adapt dams,” Apse said. “It isn’t about removing every dam. It’s about removing the right dams, and using limited funds for the greatest benefit.”

The picture shows the Hoover Dam, a major tourist attraction between Arizona and Nevada, in the Black Canyon of the Colorado River.

By Bernd F. Laeschke

gbusa

Chief Editor at Global Adventures Magazine

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