UMass Amherst Researchers Discover Low Sediment Levels Behind Dams in Northeast US

Research findings will be instrumental to local river restoration and wetlands conservation efforts
All 1700 dams were placed into categories. More than half of the impoundments were “non-sources” of sediment – meaning dam removal would not substantially alter downstream sediment conditions.
All 1700 dams were placed into categories. More than half of the impoundments were “non-sources” of sediment – meaning dam removal would not substantially alter downstream sediment conditions.

AMHERST, Mass.—Researchers in the College of Natural Sciences at UMass Amherst have found that man-made dams built in the Lower Hudson watershed in the northeastern United States do not trap as much sediment from riverways as previously believed. The research findings are good news for communities seeking to remove existing man-made dams that are no longer needed for industrial use, and which can negatively impact wetlands and interfere with local river restoration efforts. More than 600 man-made dams have been removed from New York, New Jersey and the New England region in recent years, and the trend is accelerating. However, dam removals can be contentious because of concerns that removal will release large amounts of sediment trapped behind the structures, and overwhelm downstream river ecosystems.

According to a research paper published by Brian Yellen and Jon Woodruff, assistant professors of geosciences at UMass Amherst, and David Ralston of the Woods Hole Oceanographic Institute (WHOI), the more than 1,700 dams they evaluated in the Lower Hudson watershed only trapped about four years’ worth of sediment—even though the dams have been in place on average for more than 100 years. Most dam-trapped sediment is retained by a few large dams. More than half of the 1700 dams in the Lower Hudson watershed had negligible amounts of sediment. According to the advocacy group, American Rivers, the northeast U.S. has more relic dams than any other part of the country due to its industrial past

“Dams make it hard for fish and other animals that live in rivers to move around,” said Yellen. “Communities want to remove old dams, but some individuals are worried that the mud behind the dams will get washed downstream and hurt fish and turtles and plants. But our studies show that there’s actually not that much mud stuck behind those structures. Hopefully our results will help these communities and their decision-makers continue their efforts to remove dams and restore rivers.”

The research team also created a public-facing tool to help dam owners and engineers who design dam removals to quickly estimate the amount of sediment trapped behind dams. The tool was coordinated by the Hudson River National Estuarine Research Reserve (HRNERR) and was developed collaboratively by UMass Amherst, WHOI, and the nonprofit Consensus Building Institute (CBI).

The team’s research paper is published in the January edition of the peer-reviewed journal Estuaries and Coasts. Research was funded by a National Estuarine Research Reserve grant, which is funded by NOAA, with additional support from the Northeast Climate Adaptation Science Center.