Wave influence on water circulation and self-purification ability in a semi-enclosed sea

Owing to significant variation in waves, studying the effects of waves on water exchange in semi-enclosed seas is challenging, and current knowledge on this subject is insufficient, which hinders effective management of coastal seas. In this study, wave-current coupled and water age models were established to investigate the influence of waves on water exchange in the Bohai Sea, China. The results show that waves do not affect basin-scale circulation in the Bohai Sea, and their effects on water exchange are restricted to nearshore regions, especially in estuaries with subaqueous deltas. Wave-induced age variation is around 5 %, peaking at 16 % nearshore. The wave effects on basin-scale water exchange are an order of magnitude smaller than those induced by winds, yet they govern the exchange process near the Yellow River Estuary. Analysis of age distributions with and without waves indicates that wind fetch and topographic conditions are important factors in determining the wave influence on currents. Wind and storm statistics suggest that north and northeast winds are dominant. Under these conditions, the nearshore regions in the south of the Bohai Sea and downwind areas experience strong wave forces. Due to drastic depth variations at the edges of subaqueous deltas, waves induce a strong longshore current flowing westward into Laizhou Bay, with the wave influence extending nearly 100 km.