Groundwater resource assessment using different hydrological methods and GIS techniques for Central Part of Bengal Delta

Abstract

Depiction of terrestrial water flux constituents in respect of geospatial distribution and consecutive disparity are important for water resources assessment. Due to the excessive and indiscriminate withdrawal of groundwater (GW), the water table (WT) in Dhaka area is continuously depleting during the last few decades. The consequences of increasing water scarcity being a grave concern for the policymakers of the country become a serious issue to save Dhaka areas from its possible failure in terms of human survivability and sustainability. These challenges set the urgency and great importance for holistic assessment of GW resources in the present context. GW recharge is estimated using combined Water Balance approach, Groundwater Estimation Committee methodology, and empirical technique. The monsoon and non-monsoon rainfall recharges (RR_M and RR_NM) are found as 63% and 37% in Dhaka City; and 55% and 45% in Dhaka district areas. The contributions for overall GW recharge in Dhaka City and Dhaka district from rainfall (RR_Anl), water bodies (R_SW), return flow (R_RFD), and unaccounted recharge (R_UAc) are 40.2% and 59.1%; 8.6% and 23.26%; 39.1% and 17.64%; and 12.1% and 0% in 1996, respectively. These have been altered as 22.1% and 55.9%; 2.8% and 16.2%; 37.6% and 27.9%; and 37.5% and 0% in 2015, respectively. It is observed that the total GW recharge in Dhaka City and Dhaka district has altered from 590 and 440 mm in 1996 to 730 mm and 422 mm in 2015, respectively. But the water draft due to domestic, private and industrial use in Dhaka City has increased from 726 and 373 mm in 1996 to 1092 and 582 mm in 2015, respectively. The water draft due to irrigation, and private & industrial use in Dhaka district is found as 256 and 110 mm in 1996 to 1369 and 166 mm in 2015, respectively. The seasonal WT fluctuation varies from 1.1 to 2.3 m in falling trend except Dhaka City where no significant variations are observed. The WT in Dhaka City has depleted from 17 m bgl with a rate of 1.5 m/year in 1996 to 63 m bgl in with a rate of 3.2 m/year in 2015. The WT in Dhaka district has been uplifted from 6.4 m bgl with a rate of 0.82 m/year in 1996 and then falling downward at a rate of 0.8 m/year in 2003 and reached to 14.45 m bgl at a rate of 1.52 m/year in 2015. The stage of GW development (SGD) and categorization in Dhaka City fall within 172–208% as ‘vulnerable’ during 1996 which have further aggravated to 229–272% as ‘highly vulnerable’ during 2015. The SGD and categorization in peri-urban area are estimated as 108–112% as ‘overexploited’ during 1996 which has further risen to 150–158% as ‘vulnerable’ during 2015, respectively. But, the condition is better in rural areas where, SGD and categorization are analysed as 61–70% as ‘safe’ in 1996 which has further deteriorated to 108–117% as ‘overexploited’ in 2015.