Abstract:
This research was conducted to study water quality of the Chao Phraya river as well as canals in
Bangkok. Upon consideration of monthly precipitation, surface water samples were collected as
representative samples of the wet and dry season. Three sampling locations in the Chao Phraya
river and five sampling sites in the canals were selected according to the population growth rate as
well as the patterns of land use in Bangkok. To compare the impact of land uses on water quality,
kIong Prapa (raw water for water supply production) was selected as a reference point. The
characteristics of river and canal water in this study include physical, chemical, and biological
characteristics. The PCD water quality index, River Pollution Index (RPI) and Dinius' water
quality index were applied to identify the classification and beneficial uses of the surface water.
The results clearly indicated that DO, BOD, and chloride were the major water parameters causing
the degradation of water quality in the dry season. Whereas, the water problems in the wet season
were likely related to SS, turbidity and TCB. The patterns of land use especially commercial,
industrial, as well as residential areas along the Chao Phraya river and canals were the significant
sources of water quality degradation. The application of 3 water quality indices revealed that water
quality index in the wet season generally higher than in the dry season. However, water quality
index in both seasons can be classified into the same classification and beneficial use of the
waters. The scores of PCD water quality index ranged from 13-40, which correspond to a
classification of poor and very poor water quality. The RPI scores varied from 17-24, which
correspond to a classification of poor water quality. While the Dinius's water quality index scores
of 14-37 indicated the beneficial uses of water for recreation, agriculture, industry, navigation, and
transportation of treated waste. The quality of water in klong Prapa was good for water supply
production. Compared to other water quality indices, the Dinius's water quality index was more
suit to be used for water quality management. It is because Dinius's water quality index requires
water quality parameters to be calculated for water quality index score. Thus, the error and
uncertainty from water quality index calculation can be decreased.