A general expression for wave-induced sediment bypassing of an isolated headland

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Robert Jak McCarroll, Gerd Masselink, Nieves G. Valiente, Erin V. King, Timothy Scott, Christopher Stokes, Mark Wiggins


Accurate knowledge of the sediment budget of a coastal cell is necessary for coastal management and predicting long-term coastal change. An important component in the sediment budget of many wave-dominated embayed coastlines is the amount of sediment that bypasses rocky headlands, which present partial barriers to alongshore transport. Despite a recent surge in research interest in headland bypassing, there is as yet no universal method for estimating bypass rates. Here we show, for the first time, that wave-forced bypassing of an isolated headland can be estimated using a parameterisation of wave conditions, shoreface slope, sediment size and headland cross-shore extent. XBeach was used to simulate instantaneous rates of alongshore flux off the apex of an idealised and isolated headland, with >1100 simulations, testing various combinations of wave forcing and morphological factors. The ratio of headland cross-shore extent to surf zone width 〖(X〗_H/X_S) was found to be the critical control on bypass rates. Bypass is predicted as: Q_bypass= Q_0 f(X_H/X_S ); where Q_0 is based on an existing alongshore transport expression (Van Rijn, 2014) and f(X_H/X_S) is a negative exponential function. This formulation was found to accurately replicate bypass rates modelled by XBeach, generally to within a factor of two. Headland shape is a lower-order control on bypass and can be excluded from the parameterisation. This approach was then demonstrated to succesfully estimate bypass rates for a field site, and can be adapted to accommodate time-varying wave conditions and water levels. This new expression can be used to provide a first-pass estimate of wave-forced bypassing rates for a wide-range of headland types. This will be of use to coastal managers, scientists and engineers working on rocky and embayed coastlines.




Earth Sciences, Engineering, Geomorphology, Oceanography, Oceanography and Atmospheric Sciences and Meteorology, Other Engineering, Physical Sciences and Mathematics


coastal sediment budget, embayed beaches, Headland bypassing, sediment transport, wave-dominated coastlines, Xbeach modelling


Published: 2020-07-20 17:38


GNU Lesser General Public License (LGPL) 2.1

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Data Availability (Reason not available):
Data used for the study, including XBeach model outputs, will be made available on Pearl (University of Plymouth data repository), if and when the study has been published.

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