A Genetic Programming based formula for wave overtopping by crown walls and bullnoses

The purpose of this contribution is to propose a new method for the parametrization of the reductive effects induced by crown walls and bullnoses on the average wave overtopping discharge (q) at coastal structures. The method consists of a formula for calculating an influence factor γ*GP to account for the single or combined effects of the structural elements. The formula for γ*GP is conceived to be included in the q formula by EurOtop (2018). The new formula was developed on the basis of the Genetic Programming (GP) technique trained on a database of nearly 1 000 data on wave overtopping at dikes with berms or promenades, crown walls and bullnoses. Part of the data are derived from new experiments carried out by the authors to extend the experience available from the literature and create a database of structure configurations sufficiently wide and appropriately assorted to be used for training the GP. The rough formula for predicting γ*GP obtained by the pure application of the GP was optimized to achieve a greater accuracy in the representation of both the breaking and non-breaking wave conditions. The estimations of q obtained with the new influence factor γ* GP are physically meaningful and satisfactory accurate, and overcome the underestimation bias affecting the predictions from the available formulae.