Wave Overtopping at Sea Dikes on Shallow Foreshores: A Review, an Evaluation, and Remaining Challenges

Wave overtopping is a critical parameter in the design of coastal defense structures. Nowadays, several empirical formulations based on small-scale experiments are available in the literature to predict the mean overtopping discharge at dikes on shallow foreshores. Although the accuracy of the predictions has improved due to each approach's contributions, the formulations' performance depends on their range of applicability. In engineering applications, it is important to know the performance and limitations of the different formulas. This work presents a new experimental dataset focused on very shallow and extremely shallow foreshore conditions for a range of foreshore slopes (i.e., 1/20, 1/35, 1/50, and 1/80) and relative water depths. The recent developments in wave overtopping research on very shallow and extremely shallow foreshore conditions have been reviewed using this dataset to reflect the existing uncertainties and challenges in the wave-overtopping literature. We find that predicting wave overtopping for extremely shallow foreshore conditions still requires improvement. Additional research is needed to understand the (residual) influence on the wave overtopping of the foreshore slope and relative magnitude of the infragravity wave height to the sea-swell wave height at the dike toe, especially for extremely shallow foreshore conditions. The variation in performance of the formulas for different foreshore slopes is demonstrated. Finally, some of the remaining uncertainties that need further exploration are discussed.