The Salt Flux in the Pearl River Delta, China

The increase of saltwater intrusion in recent years in the Pearl River Delta, has threatened the freshwater supply in the surrounding regions, especially the cities of Zhongshan, Zhuhai, Guangzhou in Guangdong Province and Macau. A numerical modeling system using nested grids was developed to simulate the salinity distribution in the Pearl River delta, and then to investigate the salt transport process and calculate the salt flux for each outlet in the Pearl River estuary. The model forcing functions consist of tidal elevations along the open boundaries and freshwater inflows from the major tributaries in the Pearl River system. The model simulation results are in qualitative agreement with the available field data. The salt flux of the Pearl River delta during the spring tide in dry season is up to 19.5×10⁶ton/ tidal period, while the salt flux during neap tide is only 5.1×10⁶ton/ tidal period, 26.18% of that during the spring tide. The salt flux in Dahu and Guanchong stations are the highest among the stations of the eight outlets, indicating that Humen and Yamen are the most important entries for saltwater intrusion in the Pearl River delta. The most important reason is that the ratio of stream flow to tide flow is different for each outlet. The ratios at Humen and Yamen are the smallest among the eight outlets (<1 for each month), while the ratio at Modaomen is the biggest (>1 for each month), which leads to the lowest salt flux at Modaomen. Salinity distribution in different time periods shows that saltwater intrusion during the spring tide is much more serious than neap tide, and water in many cities during this time period will be unavailable for drinking, irrigation or for ecological purpose.