Internal Pressures in Rubble Mound Breakwaters used in Coastal Protection - Recommendations for Assessing Wave Pressures with CFD Models

This paper discusses the use of 2DVertical Computational Fluid Dynamics (2DV-CFD) numerical wave flumes to inform assessments of suffusion risks in permeable structures protecting land reclamation areas. A typical rubble mound breakwater section is presented and key processes during wave interaction with the permeable structure are discussed. Emphasis is given in assessing the influence of the filter layer/geotextile to wave transmission in the breakwater. Results of pressure transmission in the breakwater are presented and compared with empirical methods. Following the analysis of these processes and CFD model results, recommendations are provided, with respect to best practice and limitations of CFD models for assessing suffusion risks, and for their best use. Recommendation include the use of random waves, to capture the effect of groupiness, recommendations for Darcy-Forchheimer coefficient values (A = 150 and B = 2 for armour layer and underlayer, use of existing empirical relations for core layer) and the consideration of internal overtopping to estimate water build-up at the landfill. Assessing suffusion risks at the filtering layer with the help of CFD models should be based on estimates of pressure differences rather than calculation of pressure gradients directly from the model.