Seasonal morphodynamics of multiple intertidal bars (MITB) on a meso‐ to macro‐tidal beach

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Abstract

Multiple intertidal bar (MITB) beach systems comprise a succession of subdued, shore-parallel sandbars, developed under low energy conditions in meso- to macrotidal settings. Their relatively stable morphologies over long timescales are commonly attributed to a dynamic equilibrium, driven primarily by seasonal morphodynamics. The seasonal behaviour is, however, poorly understood. The relationship between temporal and spatial hydrodynamic forcing and morphological changes were investigated through monthly, DGPS surveys, in Dundrum Bay (Northern Ireland) from April 2019 to March 2020, associated with variations in nearshore wave conditions, simulated using the SWAN wave model. During low-energy, summer conditions, SE waves helped promote MITB stability and a slight increase in bar crest elevation, with the seaward-most bar buffering and preserving the inner bar system through wave dissipation. In the winter, a progressive increase in wave energy, and a switch in wave direction (SW to S), initiated highest rates of cross-shore bar migration and a lowering of bar crests. While the seaward-most bar remained largely submerged, the shoreward-most bar played a key role in protecting the upper-beach and/or foredune. Winter conditions also forced a newly observed meso-scale longshore drift involving offshore sediment transport in the southwestern and onshore transport in the northeast. Cross-shore variability in MITB behaviour at seasonal timescales was, however, primarily driven by local hydrodynamic conditions, including variations in wave energy and direction. Conversely, alongshore variability was largely influenced by the complex nearshore bathymetry, headlands and an active ebb delta, all interacting with changing hydrodynamic forcing. These results challenge the seasonal equilibrium model for MITB systems and highlight longer term patterns of sediment movement.
Original languageEnglish
JournalEarth Surface Processes and Landforms
Early online date17 Nov 2021
DOIs
Publication statusE-pub ahead of print - 17 Nov 2021

Keywords

  • Earth and Planetary Sciences (miscellaneous)
  • Earth-Surface Processes
  • Geography, Planning and Development

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