Analysis of wave shoaling and shore-breakers on a low tide terrace beach based on in-situ measurements at Xisha Bay on South China coast

Low tide terrace beach is a main beach type along South China coasts with strong tidal actions. How strong tides affect wave transformations on low tide terrace beach still remains unclear. In this study, in-situ measurements are conducted on the low terrace beach at Xisha Bay to provide quantitative descriptions of wave shoaling and shore-breaker phenomena under the tidal effects. It is found that wave breaking is unsaturated on the low tide terrace beach at Xisha Bay. Magnitudes of wave skewness and asymmetry increase as wave shoals and achieve the maximum value at the shore-breaker, and then decrease rapidly. Mean energy dissipation rates of shore-breakers are tide-modulated since the bottom slope changes at the shoreward boundary of wave propagation in a tidal cycle. The remaining wave energy flux at the initialization of the shore-breaker is 1%–12% of offshore wave energy flux, and the energy flux ratio decreases with increasing offshore wave heights. Wave attenuation at shore-breakers can be estimated directly from offshore wave conditions based on findings in this study, favoring designs of seawalls or beach nourishment projects. Field datasets on wave transformations can also be used for verifications of wave numerical models.