Rapid Response: Morphological Change Near Katama Inlet During Hurricane Sandy

Woods Hole Oceanographic Institution, Woods Hole MA

Investigators

Abstract

Intellectual Merit: Hurricane Sandy produced 11-m high waves in 66-m water depth on the continental shelf south of Cape Cod and 5-m high waves in 12-m depth 2 km offshore of the southern shore of Martha's Vineyard, MA. The large waves combined with strong tidal- and wave-driven currents can transport tremendous amounts of sediment along the shoreline, and into the inlet during flood tides. Visual inspection of Katama Bay and Inlet after Hurricane Sandy suggest there were large changes to the ebb shoal, shoreline, inlet, and back bay. A post-Sandy survey of the ebb shoal, inlet channel, and back bay near Katama Inlet will be conducted. When combined with the pre-Sandy survey and observations of tides, waves, and currents that were collected by the investigators before, during, and after Hurricane Sandy, the proposed observations will allow the data and numerical models to be used for addressing the following hypotheses: (i) the timing of storms relative to ebb and flood flows is important to the morphological evolution, and (ii) accretion inside the bay is caused by sand carried alongshore from the west and subsequently transported into the inlet during flood flows. An additional hypothesis is that wave radiation stresses drive water into the inlet, producing stronger flood and weaker ebb flows, further enhancing the transport of sediment into the inlet during storms. Broader Impacts: The project investigators have been providing the local harbormaster, boating organizations, and shell fishermen with updated bathymetric maps to help them with their operations. Improved understanding of, and numerical models for, the processes affecting the morphology would help them with future management decisions as the inlet evolves. For example, the US Army Corps of Engineers has investigated establishing a sustainable breach between Katama Bay and the Atlantic to prevent siltation of the commercial oyster farms in the bay, potentially resulting in several million dollars per year of benefit to the local shell fishing industry. In addition, the results from this study will help harbormasters plan operations as the inlet evolves and currents change in Edgartown Harbor. Moreover, a field-verified modeling system of inlet evolution can be used to simulate a range of nearshore systems, allowing simulations and what-if scenarios in other areas. In addition, the observations will be used by three WHOI-MIT PhD students as part of their dissertation research about the effects of waves on shoreline morphological evolution and on inlet flows.