Prediction of scour depth at breakwaters due to non-breaking waves using machine learning approaches

Coastal structures may cease to function properly due to seabed scouring. Hence, prediction of the maximum scour depth is of great importance for the protection of these structures. Since scour is the result of a complicated interaction between structure, sediment, and incoming waves, empirical equations are notas accurate as machine learning schemes, which are being widely employed for the coastal engineering modeling. In this paper, which can be regarded as an extension of Pourzangbar et al. (2016), two soft computing methods, a support vector regression (SVR), and a model tree algorithm (M5'), have been implemented to predict the maximum scour depth due to non-breaking waves. The models predict therelative scour depth (Smax/H0) on the basis of the following variables: relative water depth at the toe ofthe breakwater (htoe/L0), Shields parameter (theta), non-breaking wave steepness (H0/L0), and reflection coef-ficient (Cr). 95 laboratory data points, extracted from dedicated experimental studies, have been used for developing the models, whose performances have been assessed on the basis of statistical parameters.The results suggest that all of the developed models predict the maximum scour depth with high preci-sion, the M5model performed marginally better than the SVR model and also allowed to define a set oftransparent and physically sound relationships. Such relationships, which are in good agreement withthe existing empirical findings, show that the relative scour depth is mainly affected by wave reflection.