Watershed Suspended Sediment Supply and Potential Impacts of Dam Removals for an Estuary

Abstract Observations and modeling are used to assess potential impacts of sediment releases due dam removals on the Hudson River estuary. Watershed loads calculated based sediment-discharge rating curves for gauges covering 80% watershed area. The annual average load estuary is 1.2 Mt, which about 0.6 Mt comes from side tributaries. Sediment yield varies inversely with area, regional trends that consistent substrate erodibility. Geophysical sedimentological surveys in seven subwatersheds Lower were conducted estimate mass composition trapped behind dams. Impoundments classified as (1) active traps, (2) run-of-river sites not actively trapping sediment, (3) dammed natural lakes spring-fed ponds. Based this categorization impoundment attributes a inventory database, total impounded estimated 4.9 ± 1.9 Mt. This represents 4 years supply, small compared some individual practically available given current removal rates. More than half dams impound drainage areas less 1 km 2 , play little role downstream supply. In simulated removal, suspended increases modestly near source during discharge events, but otherwise effects minimal. Fine-grained deposits broadly along coarser source, transport distance related settling velocity.