Dhaka is situated in central Bangladesh between 23°42' to 23°54' N and 90°20' to 90° 28' E on the upper alluvial deposits upstream of the confluence of two major rivers, the Brahmaputra and Meghana, and covers a total area of 153.84 square km. The landscape of this region represents significant variation in elevation ranges from 1.5 to 15 m with an average of 6 m datum and the drainage pattern is clearly dendritic. The Greater Dhaka urban area is surrounded by the rivers network of Turag, Buriganga and Dhaleshwori in the west and southwest, Balu and Lakhya in the east, and Tongi drainage channel in the north connecting River Balu and Turag. This study examines the present status of surface water pollution and a statistical comparison of the quality of water in different seasons at different locations of the major river around Dhaka city. Water samples have been collected from a part of rivers along different points and analyzed for various water quality parameters (DO, BOD, COD, TDS, TP) during dry and wet periods. A simple ANOVA (analysis of variance) statistical model and Box-Cox normalization were also employed to detect the variation of different water quality variance in the major rivers. Comparisons of abundance values demonstrated high significance level (p ＜ 0.05) between the upstream and downstream at different locations. The study indicates that most of the water quality parameters were generally higher during the dry season especially in the month of January to March. Water quality in the Tongi Railway Bridge and Hagaribagh areas was significantly exceeded the standard limit of USEPA (United States Environmental Protection Agency) and DOE (Department of Environment, Bangladesh) because of the largest amounts of toxic chemicals are released here by the tanneries and leather industries. Tukey- Kramer and Duncan's multiple range tests showed that most of the stations differ from the standard value of DOE and USEPA during the dry season whereas few stations were significantly found during wet season. The result revealed that river Buriganga and Tongi Khal could be treated as polluted because of the present point sources that directly discharge effluents without any treatment. Over a high resolution DEM (Digital Elevation Model) raster river basins were interpolated and presented in this paper.
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