Sand Transport under Irregular and Breaking Waves Conditions

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.

The proposal involves fundamental research leading to the development of a new practical model for predicting sand transport generated by waves and currents on the shoreface and in the surf zone. For the new model to be used for practical application leading to economic and societal impact, it needs to be implemented within morphological modelling systems (e.g. Delft3D, TELEMAC, MIKE) used by coastal engineers to understand and predict coastal erosion and sedimentation due to natural processes and anthropogenic activity. Morphological modelling systems of this kind play a critical role in design and management decisions for the coastal zone, including assessment of the impact of climate change, through increased storminess and rising sea levels, on beach stability, the integrity of coastal structures and the design of beach nourishment schemes. The economic and societal impact of the proposed research therefore lies in the better design and management decisions that result from the use of better-founded, advanced morphological modelling systems for predicting coastal zone dynamics. The improved capability will lead to the design of more environmentally sustainable coastal protection measures and the avoidance of ineffective, failing or expensive design options. In addition, the improved modelling capability will help UK and Dutch coastal engineering consultants to maintain competitive advantage in the global market for coastal engineering expertise. The critical pathway towards realising the economic and societal impact of the research is via take-up of the project's new practical sand transport model by research institutes, consultants and companies engaged in the development and application of coastal morphological models, under contract to government agencies and coastal authorities with responsibility for coastal defence and management. We will facilitate and accelerate the realisation of the research impact by involving these practitioners in the development, initial testing and implementation of the new practical model. We will establish a User Committee comprising the research team and representatives from coastal research and consultancy organisations in the UK and The Netherlands. The role of the Users will be to contribute to the development and take-up of the new practical model. By engaging key users in this way, it is expected that the sand transport model developed within the project will be accepted as the best-founded practical sand transport model for the prediction of sand transport under breaking and non-breaking, regular and irregular waves.