The smaller Tay Ninh cachment and the larger Saigon cachment are located in southern Vietnam and belong to the Dong Nai river basin. The Dong Nai river basin is the largest conglomerate of urbanization and industrialization in Vietnam.
Main source for the water supply is the surface water of the river basin, which is strongly polluted at many locations, in particular in the middle and downstream reaches. The main source of pollution is the waste water from the domestic and industrial sector. The intensive agriculture (irrigation with fertilizers, drainage) and the fishery industry is another significant source of water pollution. Deforestation caused by an increased agricultural land use contributes to the water quality degradation as well as to an increased flood and drought risk and other environmental problems.
According to the Vietnamese Government, a significant improvement of the surface water quality of the Dong Nai basin is one of the national key tasks in the environmental sector. The remarkable socio-economic development of the booming region considerably influences the water quality of the river basin: The surface water of the river basin which is needed for the water supply of the private, commercial, industrial and agricultural sectors is strongly polluted at many locations, in particular in the middle and downstream basin. Therefore, the surface water quality of the Dong Nai river basin needs to be improved as soon as possible.
The catchments are affected by tropical monsoon climate, with a characteristic rainy season from May to November and dry season from December to April. The mean annual rainfall is 1850 mm, whereof 80% falls in the rainy season.
The Tay Ninh river, which is highly polluted, has a catchment of 315 km² and a length of 37 km. The surface width of the river bed ranges from 10 to 40 meters at mean discharge conditions.
The 5500 km² Saigon catchment upstream of Ho Chi Minh City (HCMC, Saigon) is more complex than the Tay Ninh cachment. The whole Saigon river, including the Dau Tieng reservoir in the north has a length of 280 km. The Saigon river originates in Cambodia. In Vietnam it is passing through the provinces Tay Ninh, Binh Phuoc, Binh Duong and HCMC before flowing into Dong Nai river.
The storage capacity of the Dau Tieng reservoir is 1.68 billion m³ at the normal operation water level of 24.4 m.a.s.l.. At this level the area of surface water is 270 km². The Dau Tieng reservoir is the fourth biggest reservoir in Vietnam. The sub catchment area of the Dau Tieng reservoir is 2700 km².
The Saigon river downstream of the Dau Tieng reservoir has a complex semi diurnal tidal regime. The tide affects the river up to Dau Tieng Reservoir. The whole catchment is characterized by high population density, intensive agricultural and numerous industrial areas. The population density rises towards downstream.