Regular and random wave modelling over mild uniform bathymetry using SWASH

Abstract

The modelling of coastal waves is challenging in light of their complex behaviour driven by a range of interacting physical effects such as nonlinear amplification, wave breaking and the influence of bathymetry. However, their accurate modelling and understanding is fundamental in the design of coastal structures. Many numerical models have been established to accurately capture these effects. One notable example is SWASH, which is readily used in industry to provide insight on structural designs. The present study assesses the applicability, validity and accuracy of SWASH to model regular and irregular waves propagating over mild bathymetries from intermediate water depth up to the shoreline. Particular emphasis is placed on the model’s ability to capture the effects of shoaling, wave reflection and breaking with accuracy yet reasonable computational cost. This is addressed through an analysis into the spatial distribution of crest height and wave height statistics. The accuracy of the numerical model is subsequently established through comparisons to equivalent sea-states generated experimentally. SWASH is shown to perform well in modelling sea-states of local steepness $H_s/d<0.3$ with 2% accuracy. However, caution should be taken in modelling steeper sea-states dominated by breaking, where underestimation in normalised crest heights and wave heights of up to 18% are observed compared to experimental measurements.