Nearshore wave angles and directional variability during storm events

In nearshore areas, waves change direction due to refraction in shallowing water. Wave angles spatially evolve across this zone, however local variability is challenging to capture with in-situ sensors. In this study, X-band radar (XBR) remote sensing, a phase-resolving numerical model (SWASH), and in-situ observations with acoustic wave and current sensors are combined to assess nearshore wave angles during three storm events. Two new methods of estimating the spatial distribution of wave angles are developed to enable direct comparison of the model results and the remote sensing observations. The results indicate that wave angle estimates from SWASH and XBR are similar and accurate within the directional resolution of in-situ sensors. Differences between the two estimates can occur in areas of high bathymetric variability or regions of low radar backscatter intensity. When waves are breaking over shallow bathymetric features, such as a sand bar, both SWASH and XBR capture a sharp increase in directional spreading. Different types of offshore wave boundary conditions were also investigated, and it was found that when forced with observed directional spectra, SWASH limits the directional spreading compared to when it is forced with bulk wave statistics and JONSWAP spectra. The high spatial variability of local wave angles observed and simulated in this study suggests that wave directions should be more carefully investigated, and may have implications for nearshore sediment transport, morphological change, wave impact forces and wave power estimates.

Automated summary

In this study, X-band radar (XBR) remote sensing, a phase-resolving numerical model (SWASH), and in-situ observations with acoustic wave and current sensors are combined to assess nearshore wave angles. Two new methods of estimating wave angles are developed for comparison between model results and remote sensing observations. The study highlights the importance of understanding wave directions in nearshore areas for sediment transport, morphological change, wave impact forces, and wave power estimates.