The intertidal zones of the South Atlantic Bight and their local and regional influence on astronomical tides

Abstract

Astronomical tides in the South Atlantic Bight are simulated with a fine-resolution (down to ∼10 m), shallow-water equations, finite element model that fully represents the contiguous geometry of the system, including the: width- and depth-variable continental shelf; inlet-punctuated coastline; and riverine and intertidal character of the estuaries. Tidal levels are analyzed for the entirety of the South Atlantic Bight which produces highly detailed maps (resolution of 10–100 m) of tidal datums (MLW—mean low water, MHW—mean high water) throughout the estuarine rivers and intertidal zones. Model skill (performance) when evaluated over 142 gaging stations is R2 = 92% for tidal datums (MLW and MHW) and less than 10% error for the full astronomical tide signal inside the estuaries, and within 0.01 m s–1 error for M2 shelf velocities. Tidal analysis reveals a sensitivity of the M2-resonant shelf circulation in the South Atlantic Bight with respect to the tidal inlets, estuarine rivers and intertidal zones, primarily from the Florida/Georgia border to Winyah Bay (South Carolina). The inlets generate an ‘openness’ the South Atlantic Bight coastline, but more important are the geometric-dynamic influences of the estuarine rivers (the cause-effect being enhanced resonance due to extended effective shelf width) and intertidal zones (the cause-effect being tidal decay due to energy dissipation). The riverine and intertidal features of the coastline subtly change the mode of tidal propagation over the continental shelf. Dynamically, the standing wave behavior (resonance) of astronomical tides in the South Atlantic Bight is a function of the shelf and coastline geometries. Modeling and assessment of coastal and shelf circulation should consider the domain as a continuum, including high-resolution definition of the coast's estuaries and intertidal zones.