EVALUATING THE IMPACT OF TRIBUTARY DAM REMOVALS ON TIDAL WETLANDS WITHIN THE HUDSON RIVER ESTUARY

Hundreds of dams built on tributaries of the Hudson River estuary have altered the way that sediment moves through the system. Natural resource managers are now interested in removing some of these dams to improve connectivity of aquatic habitats, restore fish spawning habitat, and reduce risks of dam failures. This project addresses needs identified by managers and regulators to assess the immediate impacts of sediment that is released when a dam is removed, as well as the longer term implications for estuarine sediment budgets and sediment supply to tidal wetlands.

We present results from geophysical surveys and sediment cores from six impoundments within the Stockport Creek watershed, a major tributary to the Hudson River estuary. Our observations detail the amount and type of sediment present in each of these impoundments and relate these findings to corresponding catchment characteristics including surficial geology, land-use, and bedrock lithology. Similar methods applied to the tidal marsh at the mouth of Stockport Creek provide insight into the rates of accumulation and what sediment grain size class plays the most prominent role in allowing these environments to keep pace with sea level rise. Results from estuarine hydrodynamic modeling show effects of hypothetical dam removals on sediment budgets of the lower Hudson, allowing us to test how seasonality and timing of multiple potential dam removals and sediment routing to the estuary may affect estuarine and tidal wetland habitats. Ultimately, the authors plan to provide dam owners and regulators with a tool to plan for sediment considerations when removing small dams.