Water exchange capability induced by seasonal and regional variability: Assessment of Hong Kong waters

Assessing water exchange capability is an essential step to understand the vulnerability of waterbody to potential pollution. To characterize the spatiotemporal variations of water exchange rate in Hong Kong waters, a three-dimensional hydrodynamic and transport model was implemented. In this study, water residence time (T_re) representing the water exchange rate was <10 days in open waters but exceeded 60 days in weakly-flushed Tolo Harbour. Sensitivity experiments revealed that river discharge accelerated water exchange in western areas, especially during the wet season, causing 45 % ~ 37 % declines in regional T_re. Conversely, tidal currents were the primary limiting factor, particularly during winter. Furthermore, the seasonal reversal of vertical T_re difference in Mirs Bay demonstrated how intrusion water facilitates water exchange by dilution effects. This comprehensive assessment of coastal water exchange capability not only enhances understanding of local marine pollution distribution but also informs coastal management strategies, which can be applied to other coastal water areas.