Multi-resolution analysis of nearshore hydrodynamics using discrete wavelet transforms

Records of simultaneously measured water level and wave-driven longshore current, originating from spatially co-located devices in close shoreline proximity, have been analyzed using a multi-resolution technique based on discrete wavelet transforms (DWT) to investigate how different spectral components of nearshore hydrodynamics evolve during a storm and how the variations in wave climate are imprinted in the longshore current. The records represent a daily evolution of wave climate and longshore current in the conditions of storm peak. They were sampled every 2 s, which allowed for a very detailed description of their spectral behavior with a method that is capable of identification of non-stationary behavior during a field experiment, which was designed to identify the presence of infragravity waves at a beach with multiple longshore sandbars. The results allowed for decomposition of raw records into orthogonal components containing low, medium and high frequency spectral bands, which made their in-depth analysis possible. The study has demonstrated the usefulness of the DWT for studies on coastal hydrodynamics by extracting spectrally disjoint orthogonal patterns for which physical interpretations were sought. Simultaneously, the paper itself is a pioneering work presenting the first application of DWT to studies on nearshore hydrodynamic processes during storms.