Hydrodynamics of a multiple tidal inlet system : Katama Bay, Martha’s Vineyard, MA

Abstract

Observations, theoretical models, and a numerical model (ADCIRC) are used to investigate the effects of tides, waves, bay bathymetry, and changing inlet geometry on the hydrodynamics of the multiple-inlet Katama system, Martha’s Vineyard, MA. Momentum fluxes from breaking waves drive water into the inlet, nearly stopping the 2 m/s ebb currents during a hurricane. The evolving morphology of Katama Inlet has a dominant effect on tidal distortion and bay circulation. As Katama inlet lengthened, narrowed, and shoaled between 2011 and 2014, the relative effects of friction (observed and simulated) increased greatly, resulting in reduced circulation energy, an increase in the M6 tidal constituent, and changes in velocity asymmetries that are consistent with an evolution from flood to ebb dominance. The effects of changing inlet parameters (e.g., inlet geometry, bay bathymetry, friction, tidal forcing) are quantified via a lumped element model that accounts for the presence of a shallow flood shoal that limits flow from the ocean into the bay. As the difference in depth between inlet and flood shoal increases, the amplitude and phase of the incoming tide are increasingly modified from predictions without a flood shoal, and flows into the bay are further hindered.