Investigation on the reconstruction of wave bimodal spectrum in the lagoon near islands and reefs

Abstract

Due to the intricate topography and geomorphology of coral reefs, waves propagating from deep water areas to transitional or shallow water near islands and reefs will exhibit features of wave spectra that are very different from those in the deep sea. Thus, a reconstruction of the wave spectra is necessary. In this study, double Gaussian functions are first proposed to identify the characteristic frequencies of wave bimodal spectra, such as peak frequencies corresponding to the low frequency part and high frequency part, and separation frequencies differentiating between the low frequency part and the high frequency part, based on the observed data of wave spectra in the lagoon near islands and reefs of the South China Sea (SCS). The wave bimodal spectra close to the islands and reefs are then rebuilt using the Ochi-Hubble spectrum type. The high frequency and low frequency portions of the bimodal wave spectra are used to determine the significant wave heights, peak frequency and shape characteristics, respectively. The wave motions exhibit basically linear characteristics when two typical sea conditions, such as summer typhoon waves and winter Northeast monsoon waves, are investigated in detail. The superposition of wind waves and swells on the one hand, and the presence of the bottom on the other, have an impact on the generation of the bi-modal spectrum. The bi-modal spectra that were reconstructed and those that were observed have a correlation coefficient that is greater than 90%. The study on the reconstruction of the bimodal spectrum in the paper will provide a reference for the description of the bimodal spectrum near islands and reefs.