Interaction impacts of tides, waves and winds on storm surge in a channel-island system: observational and numerical study in Yangshan Harbor

Abstract

The Yangshan Deep-Water Harbor (YDH) consists of a northern island chain and a southern island chain, with a deep channel between these two chains. It is frequently impacted by storm tides and waves caused by typhoons. The impacts of the interaction of tide, wave, and wind on storm surges in the channel-island system of the YDH were examined, using field data and a wave-current coupled numerical model, during the super typhoon Chan-hom. Field data showed that the tidal amplitude and currents in the Yangshan area nearly doubled and the current directions were reversed. Surge and significant wave height reached 1.3 m and 8 m, respectively, during the typhoon. Model results agreed well with the observations. Model results revealed that the highest water level occurred at high tide, later than the peak surge, which occurred at low tide. The peak surge occurred at the north coast of the northern island chain, due to the backwater of the chain. The surge in the narrow channel was lower than that in the other areas of the YDH. The current direction in the YDH was slightly southward compared with that during an astronomical tide, due to the winds. A peak surge induced by winds occurred first, followed by wave-induced and the air pressure-induced surges. The wave-induced peak surge occurred at the highest water level. The wind-induced peak surge occurred simultaneously with the peak surge of the storm. Wind has a dominant effect on a storm surge, while wave-current interaction has a minor contribution to the total surge. Wind contributed 87.1% towards the peak surge of the storm, followed by a pressure-induced surge (23.7%) and a wave-induced surge (14.4%), during typhoon Chan-hom.