Analysing the mechanism and proccess of salinity instrusion in the by tidal affected urban region by mathematical modeling: case study in Ho Chi Minh city

Abstract

This study established a 1 dimention mathematical model in the river (Mike 11) connecting with 2 dimentions from the estuaries to the sea (Mike 21) to simulate the proccess, analyze the hydrodynamic mechanism and salinity intrusion (SaI) in space and time in the Ho Chi Minh City (HCMC) area. The simulated results showed that, in the dry season, in the offshore area, salt concentratin often has a high value (over 30 g/l) and does not change much in space and time; the futher into the estuary, the salinity will be affected by the flow of the estuaries and wind, causing the salinity much changing in space and time. In the downstream area of Ho Chi Minh City, the mechanism of salinity intrusion in the river system depends strongly on the interaction between the East Sea tide and the flow from upstream. Accordingly, salinity tends to strongly penetrate into the Thi Vai, Long Tau and Dong Tranh river mouths into the Can Gio ecological area and affect the Dong Nai River. Salinity intrusion is usually at its highest and farest in March and gradually decreases until the beginning of the rainy season. The results also show that the process of discharging water from Dau Tieng Reservoir to flush the salinity in the Sai Gon River has been very effective. Especially, in years of severe drought and salinity such as the dry season of 2016, if the water is not discharged, salinity of 0,25 g/l can instruse nearly to Dau Tieng Reservoir, and exceeded the water supply safety threshold of Tan Hiep water plant (at level of 0,25 g/l) for a long time. These research results will provide comprehensive and reliable scientific information supporting to the management and exploitation of water resources for the sustainable economic and social development of Ho Chi Minh City.