EP061-0001
Comparison of longshore and cross-shore sediment transport processes influencing shoreline change

Wednesday, 16 December 2020
Poster
John C Warner1, Christopher R Sherwood2,3, Alfredo Aretxabaleta1, Christie Hegermiller1, Tarandeep Singh Kalra4, Emily Himmelstoss4 and Laura L. Brothers4, (1)USGS Coastal and Marine Science Center Woods Hole, Woods Hole, MA, United States, (2)Organization Not Listed, Washington, DC, United States, (3)U.S. Geological Survey Coastal and Marine Science Center Woods Hole, USGS, Woods Hole, MA, United States, (4)US Geological Survey, Woods Hole, MA, United States
Abstract:
Coastal ocean-facing shorelines experience morphological changes on many time and spatial scales in response to various processes such as wave breaking, overwash, and wave- and wind-driven currents. The nature of coastline response can vary due to the geologic framework of the underlying sub-bottom stratigraphic structure, surficial sediment type, local vegetation cover, etc. These morphologic changes are significant for both understanding coastal community hazards and infrastructure planning for short and long-term shoreline stability.

Here, we investigate the processes that drive coastal change along the shoreline of Cape Cod Bay, MA. This Bay is a semi-enclosed embayment with periodic significant forcing from Nor’easter type storms. These events typically produce remotely generated long period swell that propagates into Cape Cod Bay, as well as winds that generate local seas. In this work, we use the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system to explore the hydro- and morpho- dynamics of Cape Cod Bay and the shoreline. Nor’easter winds drive surface currents into and across the Bay towards the southwest. This sets up a pressure gradient that drives a northern return flow at depth toward Massachusetts Bay. Recent geologic seafloor mapping resolves bedforms and local sedimentary deposits corresponding to these modeled sediment transport pathways. Preliminary findings also suggest that shoreline change along the western section of Cape Cod Bay is controlled by divergences in wave-driven alongshore flows. Meanwhile, shoreline change along the southern portion of the Bay is driven by cross-shore flows contributing to overwash and wave asymmetry. The Cape Cod Canal provides a break in the alongshore flows and sediment transport. Modeled short-term coastal sediment fluxes are compared to short- (<30 years) and long- term (>80 yrs) shoreline change observations to further the understanding of the processes responsible for coastal change in the Bay.

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