EFFECT OF URBANIZATION ON GROUNDWATER REGIME, DHAKA CITY, BANGLADESH

Groundwater abstraction in Dhaka city has increased more than 700% dur ing the last three decades. Consequently, water level has dropped to 2 0 m below sea level in the south central part of the city, where the g round surface elevation is 5.7 m. The rate of water level decline vari es from 0.75 to 1.5 m/year at different observation points within the city. Iso-conductivity map of the groundwater depicts higher electroly tic conductivity (EC) value (500 to 800 mu S/cm) in the southern part of the city, particularly along the river Buriganga, compared to the n orthern part (100-200 mu S/cm). Contamination in the aquifer of southe rn part is attributed to recharge by polluted water from the Buriganga . Monitoring results of deep tube wells (DTWs) and hand tube wells (HT ws), located in municipal waste and industrial effluent disposal sites , show a marked depth variation in groundwater EC. Higher EC values in the HTWs demonstrates contamination in upper part of the aquifer from the disposal sites. Major ions and trace element concentrations of th e water samples also reveal similar pattern. Increasing trend in the i onic concentrations, particularly Cl- and NO3- as observed in the hist orical record indicates gradual quality deterioration.