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Wave, Tide and Topographical Controls on Headland Sand Bypassing
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  • Erin Victoria King,
  • Daniel C Conley,
  • Gerhard Masselink,
  • Nicoletta Leonardi,
  • Robert Jak McCarroll,
  • Timothy Scott,
  • Nieves Garcia Valiente
Erin Victoria King
University of Plymouth

Corresponding Author:[email protected]

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Daniel C Conley
University of Plymouth
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Gerhard Masselink
Plymouth University
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Nicoletta Leonardi
University of Liverpool
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Robert Jak McCarroll
Plymouth University
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Timothy Scott
University of Plymouth
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Nieves Garcia Valiente
Met Office
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Abstract

Embayed beaches separated by irregular rocky headlands represent 50% of global shorelines. Quantification of inputs and outflows via headland bypassing is necessary for evaluating long-term coastal change. Bypassing rates are predictable for idealised headland morphologies; however, it remains to test the predictability for realistic morphologies, and to quantify the influence of variable morphology, sediment availability, tides and waves-tide interactions. Here we show that headland bypassing rates can be predicted for wave-dominated conditions, and depend upon headland cross-shore length normalised by surf zone width, headland toe depth and spatial sediment coverage. Numerically modelled bypassing rates are quantified for 29 headlands under variable wave, tide and sediment conditions along 75km of macrotidal, embayed coast. Bypassing is predominantly wave-driven and nearly ubiquitous under energetic waves. Tidal elevations modulate bypassing rates, with greatest impact at lower wave energies. Tidal currents mainly influence bypassing through wave-current interactions, which can dominate bypassing in median wave conditions. Limited sand availability off the headland apex can reduce bypassing by an order of magnitude. Bypassing rates are minimal when cross-shore length > 5 surf zone widths. Headland toe depth is an important secondary control, moderating wave impacts off the headland apex. Parameterisations were tested against modelled bypassing rates, and new terms are proposed to include headland toe depth and sand coverage. Wave-forced bypassing rates are predicted with mean absolute error of a factor 4.4. This work demonstrates wave-dominated headland bypassing is amenable to parameterisation and highlights the extent to which headland bypassing occurs with implications for embayed coasts worldwide.
Aug 2021Published in Journal of Geophysical Research: Oceans volume 126 issue 8. 10.1029/2020JC017053