Numerical Study On The Effects Of Sea Level Rise On Saltwater Intrusion And Substances Transport In The Pearl River Estuary

The Guangdong-Hong Kong-Macao Greater Bay Area(GBA),located at the Pearl River Estuary(PRE),is the fourth largest Bay Area in the world.It is an important driving force for China's economic development.Affected by the global climate change,the environment of PRE is facing severe challenges due to sea-level rise.The study on the response of saltwater intrusion and substances transport in PRE to sea-level rise is of great practical significance to ensure the sustainable and healthy development of GBA under the background of climate change.In this paper,based on Environmental Fluid Dynamic Code(EFDC),a three-dimensional hydrodynamic numerical model for the integration of river network,estuary and offshore of PRE was established,and the model was used to simulate the response of saltwater intrusion and substances transport process to different sea-level rise in PRE.The innovations of this paper are as follows:1)the model grid depicted the Pearl River network region in detail and extended to the sea area adjacent to the continental shelf;2)the effects of sea level rise on saltwater intrusion were quantified and statistically analyzed;3)conservative tracer was used to analyze the influence of hydrodynamic process on transport of substances quantitatively.Because the central cities of GBA are mainly located in the surrounding areas of the east four outlets of PRE and Lingding Sea,this paper focused on the analysis of those area.In this paper,the responses of saltwater intrusion and substances transport processe to sea-level rise of 30,50,100 and 150 cm in PRE were simulated with 2007 as the baseline.The results showed that sea-level rise has a significant strengthening effect on saltwater intrusion in PRE.When sea-level rises by 100 cm,the length of saltwater intrusion of the east four outlets of PRE will increase by 21.371 km maximally.It was also found that there is a good linear regression relationship between sea-level rise and saltwater intrusion length in each branch during the dry season.During the flood season,sea-level rise would hinder the transport process of land source substances in PRE,and Lingding Sea region is the most significant area of water age growth.In the dry season,water age would increase in some area as a result of sea-level rise,while decrease in other.But the variation amplitude of water age always increases with the increase of sea-level rise.In addition,this study also found that sea level rise will enhance the stratification of PRE.This paper also demonstrated the effectiveness of the plan to cope with sea-level rise that using higher runoff to suppress the saltwater intrusion.By studying the response of salt water intrusion in the dry season to different runoff in PRE under the condition of sea-level rise of100 cm,it is found that the plan has a significant effect.By increasing the runoff,the problem of salinity exceeding the tap water standard in the waterworks was obviously improved.When the threshold of runoff reached 3600 m~3/s,the salinity in Shixi waterworks and Shawan waterworks which are in the upper reaches of the estuary almost did not exceed the standard in the dry season.The saltwater intrusion length of each branch decreased with the increase of runoff threshold,and a good linear relationship was found between them.The linear regression relationships could be combined with the runoff threshold of the load capacity of the water conservancy project in the Pearl River Delta,which could provide the site selection basis for the future construction of waterworks and other projects.