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

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Authors

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

Abstract

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.

DOI

https://doi.org/10.31223/osf.io/67rhx

Subjects

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

Keywords

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

Dates

Published: 2020-07-20 17:38

License

GNU Lesser General Public License (LGPL) 2.1

Additional Metadata

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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