Assessment of long term sustainability of aquifer yield in Dhaka city

Abstract

The present water supply system of Dhaka depends mostly on groundwater. The existing facilities of DWASA cannot keep pace with growing demand of safe water supply. This study investigates the adequacy of current ground water supply system in Dhaka city following standard pump head-flow characteristics. The degree of inadequacy is also investigated for considering upgradation of current system if possible or generation of alternate sources where necessary. A groundwater model has been developed to understand the groundwater flow dynamics and to assess the groundwater resources at the present condition as well as groundwater resources at future development scenarios For the static Pump adequacy study, water supply and distribution network has been generated based on road network map. Network coverage area served by this distribution system has been calculated using GIS. A groundwater model has been developed, the major components of which include evapo-transpiration, unsaturated zone, saturated zone, overland flow and river systems. Technical options/alternatives have been investigated to address the study objectives and finally to make comprehensive water management plans for the study area From the study, existing pump system has been found to be sufficient upto 2015 for Hazaribag, Tejgaon, Ramna, and Mohammadpur with adequate supply and pressure. For Gulshan, Motijheel and Dhanmondi existing system can meet the demand reducing the pump head from 70m to 60m and thereby reducing the system pressure as well. Surface water may be utilized which will improve pressure head. The existing pump systems can’t meet the demand of Shyampur, Sabujbag, Mirpur. From the hydrograph analysis in Mike SHE it is found that Mirpur, Tejgaon and Gulshan are highly vulnerable to aquifer dewatering. The hydrographs estimate that the water table may lower more than 70 meter within 2015 in this areas if this trend continues. According to the analysis in Mike SHE Pheratic surface lowers as much as 60 meter before monsoon and as much as 32 meter after monsoon. Mirpur, Hazaribag, Dhanmondi area has been suffering from the lowest contours of water table. Considering Pump adequacy and model simulation, it can be said that the domestic water supply system comprising mostly of ground water cannot keep pace with growing demand of safe water in Dhaka. The water table as well as current groundwater abstraction is also not sustainable. Therefore, this study is expected to provide a systematic and effective guideline for the analysis of Pump adequacy behavior within the study area for current and future conditions for considering upgradation of current system if possible or generation of alternate sources where necessary.