The relation between cobble revetments, sand and overtopping: A numerical approach with OpenFOAM®

Abstract

OpenFOAM allowed the author to simulate a large number of scenarios in which the influences of cross-shore profile shape, cobble porosity, cobble diameter and layer thickness on wave overtopping were examined. Four validation runs and six simulations to map the sensitivity are compared with data from two physical experiments conducted in the Delta Flume. The comparison proved the correct working of the model. Then, another 16 simulations with the cobble revetment featuring a variety of porosity, thickness and shape have been completed. The model results show interesting relations when compared with each other. The idea is that a part of the volume of the overtopping wave run-up tongue is sinking into the pores of the cobble revetment and does not overtop. The wave overtopping volume is thus reduced by the total volume of the pores that can be infiltrated over a cycle of a wave. This relation is best captured in a new dimensionless quantity proposed by the author, called the relative pore volume number: n * Rc * sqrt (1+cot^2 (alpha) \ ( Tc/ Hm0^2 ) which accounts for the total accessible pore volume above the waterline. The relative pore volume number has an logarithmic relationship with the dimensionless overtopping rate q / (g*Hm0^3)^0.5 for the parameter space considered in this research. The volume of pores per area above the mean water level is thus related to a reduction in overtopping volumes. The influence factor for roughness of the general formula for predicting the mean overtopping discharge on a slope in EurOtop 2018 by is modified by comparing a fit through the reference curve of all the numerical and physical experiments. The roughness factor can now be predicted as a function of the relative pore volume per area.