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Effects of Wave Orbital Velocity Parameterization on Nearshore Sediment Transport and Decadal Morphodynamics

1
Department of Physical Geography, Faculty of Geosciences, Utrecht University, 3508TC Utrecht, The Netherlands
2
Deltares, 2600MH Delft, The Netherlands
*
Author to whom correspondence should be addressed.
J. Mar. Sci. Eng. 2019, 7(6), 188; https://doi.org/10.3390/jmse7060188
Received: 24 May 2019 / Revised: 12 June 2019 / Accepted: 15 June 2019 / Published: 19 June 2019
(This article belongs to the Special Issue Dynamics of the Coastal Zone)
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Simple Summary

Sandy coasts evolve as a result of sand transport by waves and tides. Wave-generated flows near the seabed stir the sand into the water column, which can subsequently be transported in cross-shore and alongshore directions. As waves move shoreward into shallower depth, the shape of the near-bed flow changes, which affects the magnitude of sand transport. Until now, computer simulations of decadal coastal development did not contain this shape change adequately and, as a consequence, modelled coasts were predicted to erode or accrete too rapidly. Therefore, we implemented a novel wave shape module based on field data and tested its performance in predicting the decadal evolution of typical, well-monitored sites on sandy Dutch and US East coasts. The modified model now predicts realistic cross-shore profile evolution at both sites without excessive shoreline erosion or accretion. Also, the sand transport rates along the coast are better represented. This opens up the possibility to realistically model coastal evolution on the timescale of decades to a century.

Abstract

Nearshore morphological modelling is challenging due to complex feedback between hydrodynamics, sediment transport and morphology bridging scales from seconds to years. Such modelling is, however, needed to assess long-term effects of changing climates on coastal environments, for example. Due to computational efficiency, the sediment transport driven by currents and waves often requires a parameterization of wave orbital velocities. A frequently used parameterization of skewness-only was found to overfeed the coast unrealistically on a timescale of years—decades. To improve this, we implemented a recently developed parameterization accounting for skewness and asymmetry in a morphodynamic model (Delft3D). The objective was to compare the effects of parameterizations on long-term coastal morphodynamics. We performed simulations with default and calibrated sediment transport settings, for idealized coastlines, and compared the results with measured data from analogue natural systems. The skewness-asymmetry parameterization was found to predict overall stable coastlines within the measured envelope with wave-related calibration factors within a factor of 2. In contrast, the original parameterization required stronger calibration, which further affected the alongshore transport rates, and yet predicted erosion in deeper areas and unrealistic accretion near the shoreline. The skewness-asymmetry parameterization opens up the possibility of more realistic long-term morphological modelling of complex coastal systems. View Full-Text
Keywords: wave parameterization; wave skewness; morphodynamic modelling; sediment transport; delft3d; wave shape wave parameterization; wave skewness; morphodynamic modelling; sediment transport; delft3d; wave shape
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Boechat Albernaz, M.; Ruessink, G.; Jagers, H.R.A.B.; Kleinhans, M.G. Effects of Wave Orbital Velocity Parameterization on Nearshore Sediment Transport and Decadal Morphodynamics. J. Mar. Sci. Eng. 2019, 7, 188.

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