Sand Transport under Irregular and Breaking Waves Conditions

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Numerical morphodynamic modelling systems used in coastal engineering practice consist of coupled models for waves, currents, sediment transport and bed level change. The sediment transport model usually comprises an advection-diffusion model for the wave-averaged suspended sediment and a practical sand transport formula for bed-load or near-bed total-load, in which the sand transport is empirically related to the local flow and sediment conditions. Well-founded practical models are based on a combination of measurements of net sand transport rates and understanding of the key fundamental processes, which are captured in the model in a parameterised way. However, most practical models are based on measured transport rates and processes from laboratory experiments involving regular, non-breaking waves almost exclusively. The fact that waves are in reality irregular and are breaking in many (if not most) cases of practical interest in coastal engineering, raises the question: what key processes associated with wave irregularity and wave breaking need to be included in a practical sand transport model for the model to be applicable to irregular and breaking wave conditions?The proposed research has two main aims: (1) To substantially improve understanding of the near-bed hydrodynamics and sand transport processes occurring under large-scale irregular and breaking wave conditions and (2) to develop a new practical model for predicting sand transport under waves, accounting for wave irregularity and wave breaking in a way that is well founded on experimental data and understanding of the fundamental processes. The transnational project team involves the Universities of Aberdeen, Liverpool and Twente in collaboration with UK and Dutch industry-based Project Partners. Large-scale experiments will be conducted in the Aberdeen Oscillatory Flow Tunnel and the Large Scale Wave Flume at the Catalonia University of Technology in Barcelona. Physical understanding and data from these experiments, combined with insights from two process-based numerical models, will be used to develop a new practical sand transport model that accounts for wave irregularity and wave breaking. Working with the industry Project Partners, the new model will be implemented in morphodynamic modelling systems used by coastal engineering practitioners and tested for practical applications.