The role of the Pearl River flow in Deep Bay hydrodynamics and potential impacts of flow variation and land reclamation

Deep Bay (DB) is a semi-enclosed bay that opens to the middle part of the Pearl River Estuary (PRE), the largest estuarine wetland area in the world. Like many rivers around the world, the Pearl River has in recent years experienced more frequent and more severe flow variations. It was hypothesized that Pearl River flow variation would affect the environment of DB, where locates large area of Ramsar wetlands of international importance. The anthropogenic factor of land reclamation was also hypothesized to alter the Pearl River flow and thus affect DB and the PRE environment. Simulations were performed to model water and salt transport processes under different scenarios of Pearl River flow variation and land reclamation. It was found that the Pearl River had a strong governing role on the hydrodynamics of DB, especially in the wet season. The simulation results indicated that in the wet season, the waters at the mouth of DB and DB as a whole were respectively composed of 50–80% and 31–37% of water discharged from the Pearl River. Moreover, it was shown that a 20% increase in Pearl River flow in the wet season would result in 0.2% and 3.3% more Pearl River water flushing into the bay before and after reclamation, respectively. Therefore, reclamation is predicted to stress the coastal ecosystem in DB, as it will enhance the intrusion of pollutants from the Pearl River into the bay head. However, it would benefit the removal and dilution of pollutants directly discharged into the bay from the Shenzhen River. Our results confirm that the hydrodynamic interconnection of bay and estuary in an estuarine system is complex, and should be carefully examined when assessing the environmental impacts of climate change and anthropogenic engineering projects.