Sediment transport in nonlinear skewed oscillatory flows: Transkew experiments

Abstract

New experiments under sheet flow conditions were conducted in an oscillating water tunnel to study the effects of flow acceleration on sand transport. The simulated hydrodynamic conditions considered flow patterns that drive cross-shore sediment transport in the nearshore zone: the wave nonlinearities associated with velocity and acceleration skewness and a negative mean current, the undertow. Net transport rates were evaluated from the sediment balance equation and show that (1) the acceleration skewness in an oscillatory flow produces a net sediment transport in the direction of the highest acceleration; (2) the net transport in the presence of an opposing current is negative, against the direction of the highest acceleration, and reduces with an increase in flow acceleration; and (3) velocity skewness increases the values of the net onshore transport rates.

Keywords:

• Flow acceleration
• sediment transport
• sheet flow
• wave asymmetry
• wave skewness

Acknowledgements

This work was supported by the European Community's Sixth Framework Programme through the grant to the budget of the Integrated Infrastructure Initiative HYDRALAB III, Contract no. 022441 (RII3). All participants in the Transkew experiments are gratefully acknowledged: André Temperville, Tom O'Donoghue, Hervé Michallet, Paula Freire, Sandra Plecha, Kate Steenhauer, Gustaaf Kikkert, and Noureddine Ait Lafkih. We are also grateful to John Cornelisse and the technical support from Deltares. The ADVP data were provided by Hervé Michallet. The second author was supported by Fundação para a Ciência e a Tecnologia (FCT) through PhD grant SFRH/BD/41827/2007. The work was also carried out within the scope of the research projects SANDEX – PTDC/ECM/70428/2006 and BRISA – PTDC/ECM/67411/2006. Finally, BGR acknowledges additional funding by the Netherlands Organisation for Scientific Research NWO under project 864.04.007.