Observations and simulations of wave runup during a laboratory dune erosion experiment

Abstract

XBeach, a process-based numerical model designed to simulate morphologic change during extreme storm events, was calibrated and compared to observations from a large-scale laboratory dune erosion experiment. Wave conditions along the tan, wave runup at the beach, and 3-dimensional position of the dune were measured throughout the experiment. Seiching modes in the tank were simulated and matched the observations once the model was calibrated. Simulated waves were sensitive to γ, the ratio of wave height to water depth, and cf., the coefficient of friction. Simulated runup explained 50–87% of the observed variance in observations. However, the magnitude of simulated wave runup was underestimated throughout the experiment. Errors in simulated runup were composed of a high bias and gain error in mean water level, low bias in the infragravity swash, and low bias and gain errors in incident swash. Observed probability density functions of swash were statistically consistent between times when swash was confined to the foreshore and times when swash interacted with the dune. However, simulated probability density functions of swash were statistically different during the collision regime. Despite the systematic underestimation of wave runup, modeled dune erosion compared well with observations after the sediment transport parameters were calibrated. Modeled dune erosion was sensitive to the critical slope parameters over the wet and dry regions of the beach, the depth of the interface between the wet and dry regions of the beach, and the threshold depth for sediment transport and return flow.