Prospects of Artificial Recharge for Augmentation of the Upper Dupi Tila Aquifer in Dhaka City, Bangladesh

S. Sultana1 K. M. Ahmed1 and M. B. Mia2
1Department of Geology, University of Dhaka, Dhaka1000, Bangladesh; 2Department of Petroleum & Georesources Engineering, Shahjalal University of Science and Technology, Sylhet, Bangladesh
sarmin029@yahoo.com; kmahmed@univdhaka.edu

Abstract
Dhaka, the 10th largest megacity of the world, is facing severe shortages of water despite receiving a high rainfall in access of 2000 mm/year. Unplanned development activities due to rapid population growth are causing encroachment on retention areas and natural drainage creating obstacles to percolation and infiltration for recharging aquifer. The study is aimed to evaluate the prospects of artificial recharge to enhance the aquifer storage. An attempt has been made to identify zones favourable for the adaptation of site-specific artificial-recharge techniques for augmentation of depleted groundwater through a Geographical Information System.

About 36.33% of the city area allows recharge at present conditions which is insufficient for groundwater recharge. Abundant annual rainfall and the measured onsite parameter of rainwater suggest that the quantity and quality of rain water, if diverted from rooftops, is good enough as source water and the depleted upper aquifer can be served as storage area for artificial recharge. Groundwater elevation contour map of Dhaka city shows major depressions at Gulshan and Shabujbag area due to over abstractions. Analysis of Geotechnical logs suggests that SPT values of different unit both for cohesive and non cohesive nature are also favourable for surface spreading techniques. Moreover the infiltration rate (from 0.409 to 0.4165-m/day) at the pond of Institute of Fine Arts where Madhupur Clay is exposed suggests that it does not create impediment for infiltration.

Hence, based on the clay thickness and compactness, depth to aquifer, groundwater contour, rainfall distribution, lithology and hydraulic properties of Madhupur clay, eight methods for twenty four specific sites have been suggested to increase aquifer storage. Rainwater harvesting, wetland preservation, dredging of some rivers has also been recommended. The current multi-parametric approach using GIS and RS is holistic and will minimize the time and cost especially for site selection of recharge structures.
Key words: Dhaka Megacity; Aquifer; Madhupur Clay Artificial Recharge; GIS.