What is it about?

After waves break near the shore, they lose energy because of friction. This causes them to become smaller. We have investigated how waves crossing dipping rocky seabed change in height, by adapting equations originally designed for waves crossing horizontal reefs. It turns out, those equations work well compared to a large number of measurements of wave heights over dipping rock surfaces, where the waves approach simply orthogonal to the shore.

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Why is it important?

Predicting changes in wave properties near coasts is usually carried out using sophisticated wave modelling, but for some applications a simpler strategy is needed. For example, if we wanted to develop a computer model for coastal erosion over long periods, we won't know the approaching wave field perfectly so sophisticated wave modelling is unnecessary. The equations and parameters of Sunamura et al. (2014) turn out to work well in predicting wave heights on dipping rock platforms as well as horizontal reefs.

Perspectives

This work started off trying to explain why erosion of a littoral volcanic cone in the Azores that was formed by an eruption in 1957/58 (Capelinhos) has rapidly declined. The modelling in our earlier article suggested that wave attenuation over the widening rock platform left by erosion was not the only cause of the decline. It is satisfying that sometimes a simple approach can work effectively.

Dr Neil C. Mitchell
University of Manchester

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This page is a summary of: Testing the equations for wave attenuation over shore platforms, Geomorphology, December 2022, Elsevier, DOI: 10.1016/j.geomorph.2022.108480.
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