Spatio-temporal pattern of water quality in the Saigon-Dong Nai river system due to waste water pollution sources

This paper studies the current status of water quality, using both statistical and modelling approaches, in the waterways of the Saigon-Dong Nai river basin in relation to the nature of its environment and the effect of point and diffuse pollution sources. These sources are located mainly in the urban and industrial areas of Ho Chi Minh City (HCMC) and Dong Nai province. The statistical analysis of monitoring data allows us to determine the state of water quality while the modelling approach provides the means to manage the pollution sources. Both approaches are used in this work. Our statistical analysis of the water quality data collected at many stations from the upper reach of the Saigon and Dong Nai rivers to the urban waterways and the lower end of the rivers near the sea shows a contrast of water quality in different basin areas. These differences are consistent in both dry and rainy seasons and during the high tide and low tide. The results show that several hot spots of some water quality variables require management focus, such as organic waste water pollution at Binh Dien and Thay Cai in HCMC mainly due to local sources. Moderately and highly degraded water quality occurs at Binh Phuoc, Phu An and Cat Lai which are downstream from the industrial areas of Binh Duong (Binh Duong province) and Bien Hoa (Dong Nai province) before entering HCMC. Modelling of some important water quality variables also confirms the spatial extent of the areas where water quality is different as analysed from the statistical analysis of monitoring data. The MIKE-11 modelling system is shown to be a valuable tool for predicting the effect of different sources in HCMC metropolitan area on the waterway areas where water quality is important to protect the ecosystem and people health.