Effect of Urbanisation on Groundwater Regime, Dhaka City, Bangladesh

Groundwater abstraction in Dhaka city has increased more than 700% during the last three decades. Consequently, water level has dropped to 20 m below sea level in the south central part of the city, where the ground surface elevation is 5.7 m. The rate of water level decline varies from 0.75 to 1.5m/year at different observation points within the city.

Iso-conductivity map of the groundwater depicts higher electrolytic conductivity (EC) value (500 to 800 μ1S/cm) in the southern part of the city, particularly along the river Buriganga. compared to the northern part (l00-2oo μ1S/cm). Contamination in the aquifer of southern part is attributed to recharge by polluted water from the Buriganga. Monitoring results of deep tube wells (DTWs) and hand tube wells (HTWs), 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 the water samples also reveal similar pattern. Increasing trend in the ionic concentrations. particularly cl^- and N0₃ , as observed in the historical record indicates gradual quality deterioration.