Extreme wave runup on a vertical cliff

TL;DR

This study reveals that specific wave groups can cause run-up heights significantly exceeding traditional predictions, indicating the need to reconsider design wave assumptions in coastal engineering.

Contribution

It demonstrates that certain simple wave groups can produce much higher run-ups than linear and weakly nonlinear theories predict, challenging existing design paradigms.

Findings

Run-up heights can exceed initial wave amplitude by a factor of 5.

Certain incident wave frequencies lead to extreme run-up events.

Traditional linear theory underestimates maximum wave impact on vertical cliffs.

Abstract

Wave impact and run-up onto vertical obstacles are among the most important phenomena which must be taken into account in the design of coastal structures. From linear wave theory, we know that the wave amplitude on a vertical wall is twice the incident wave amplitude with weakly nonlinear theories bringing small corrections to this result. In this present study, however, we show that certain simple wave groups may produce much higher run-ups than previously predicted, with particular incident wave frequencies resulting in run up heights exceeding the initial wave amplitude by a factor of 5, suggesting that the notion of the design wave used in coastal structure design may need to be revisited. The results presented in this study can be considered as a note of caution for practitioners, on one side, and as a challenging novel material for theoreticians who work in the field of extreme wave - coastal structure interaction.