Impacts of sea level rise on a semi-enclosed bay inside the Pearl River Estuary

Abstract

Sea level rise is a global concern and threat to coastal regions. In the most prosperous estuarine region of China, the Pearl River Estuary, sea level is rising at a rate of 0.01 m/year. The Deep Bay is a semi-enclosed bay connected to the Pearl River Estuary, and its inner bay houses a Ramsar Convention wetland. Previous studies have determined that sea level rises at 0.3 and 0.5m and would respectively cause a 26.2% and 45.7% loss of the intertidal region of Ramsar site. This study employed a three-dimensional coastal model to evaluate the impacts of sea level rise on the hydrodynamics and salinity transport of the bay. The model was validated with observation data in the year of 2007, and hypothetical scenarios for the years 2037 and 2057 are simulated with sea level rises of 0.3 and 0.5m respectively. Simulation results show that the two levels of sea level rise would substantially increase the tidal effect, elevating the tidal prism by 9.8% and 15.0% and magnifying the tidal energy entering the bay by 21.0% and 41.4% respectively. The spatial distribution of salinity in the whole bay would also be substantially changed. The annually averaged salinity levels at bay mouth were 28.3, 28.8, and 29.1 psu respectively in 2007, 2037 and 2057. Those in the inner bay were respectively 9.7, 12.1, and 13.7 psu. Furthermore, the water age at the inner bay would be influenced the most with a 3-day increase. The water exchange ability in inner bay would decrease, potentially stressing the intertidal region with longer residence time of nutrients from the Shenzhen River. However, the current velocity in the intertidal region would decrease by 8.7% and 15.0%, possibly enhancing sediment deposition and thus minimizing the loss of intertidal region during sea level rise.