Dams and Sediment in the Hudson (DaSH) - NERRS/NSC(NERRS Science Collaborative)

Dams and Sediment in the Hudson answered key questions about how dam removal will impact conditions in the estuary and offered surprising new findings about tidal marshes in the Hudson River valley. The project used a multidisciplinary approach that combined field observations with an analysis of sediment transport using a proven hydrodynamic model.

Researchers surveyed 17 representative dams in the Lower Hudson River watershed by measuring water depth and sediment thickness and collecting sediment cores. Results were extrapolated to the 1700 registered dams located on tributaries of the Lower Hudson River to estimate the total amount of sediment trapped in the watershed. These observations were complemented by an analysis of sediment discharge data from existing monitoring stations on tributaries to characterize typical sediment input to the estuary and conditions following major storm events. A numerical model of circulation and sediment transport in the estuary was used to evaluate the impact of dam removal scenarios. To understand sediment contributions to tidal wetlands along the Hudson, researchers collected transects of sediment core from 6 representative tidal wetlands and coves. Geochronological data of sediment cores combined with an analysis of historical and aerial photos was used to assess when wetlands began to form and their rates of accumulation.

Results show that dam removals would have a minimal impact on sediment supply to the estuary and tidal wetland growth. Only 10% of dams in the Lower Hudson River watershed are effective sediment traps, and the potential amount of sediment that would be released if all dams were removed represents less than 2 years average sediment input from the watershed. Tidal wetlands along the Hudson were found to be remarkably young and rapidly accumulating sediment despite the presence of dams, growing vertically at rates several times faster than sea level rise.