Rapid Tidal Marsh Development on the Hudson during Period of Tributary Damming and Shoreline Modification

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Tuesday, April 14, 2020 from 10:30 a.m. –
12:00 p.m. EST via Webex

Presentation by:

  • Brian Yellen, Ph.D., Assistant Professor, UMass Amherst

Thousands of legacy dams impound streams within the Hudson River watershed. These dams are being removed at an increasing pace to improve aquatic connectivity and public safety, yet the impacts of remobilizing impounded sediments behind these dams on downstream tidal environments remain unclear. Here we present results from surveys of sediments behind small impoundments in three tributary catchments along the Hudson River estuary. We pair results from tributary impoundments with observations of tidal marsh sediments at the mouth of each of the catchments. To generalize the potential impacts of dam removals on sediment dynamics in the estuary, we classify three types of dams: (1) active sediment traps with accommodation space at present; (2) run-of-river dams that contain sediment, but are presently filled; (3) impounded natural lakes where dam removal would not increase downstream sediment transport.

In some tidal marshes, we find that anthropogenic alterations to the estuarine bathymetry or shoreline (e.g. railroad trestles, dredge spoils emplacement) have dramatically increased deposition of fine-grained marsh muds. Marshes have vertically accreted at 1-2 cm/yr, much faster than relative sea level rise, despite the onset of these marshes during the period of peak dam building and potential reduction in sediment supply. This suggests that marsh-building sediment originates predominantly from the main stem of the river, not local tributaries, and that this supply is sufficient to maintain accretion rates much greater than sea level rise. Any increase in sediment supply due to dam removal on these tributaries would have little impact on tidal wetlands along the main channel of the Hudson.

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