Assessment of declining groundwater levels due to excessive pumping in the Dhaka District of Bangladesh

摘要

Hydrogeologically, the aquifers of the Dhaka district are located in the B, H and J zones of a total of 15 BWDB-UNDP (1982) groundwater development zones and were considered to have a high groundwater potential. Unplanned and excess groundwater extraction is causing a decline of groundwater potentiometric heads in the area. Groundwater level data from nineteen (19) years of the two aquifers of the Dhaka district have been analyzed to observe how the patterns of water level changes vary throughout the area. The Mann-Kendal (M-K) test with Theil-slope Sen's slope exhibits three categories of groundwater level changes. In densely populated city areas, the trend is extremely negative, with steep declines and annual changing rates that range from - 1.5 m/year to - 2.11 m/year; - 1.01 m/year to - 1.09 m/year in newly urbanized areas; and that range from 0.01 m/year to - 0.36 m/year in the rural areas. The pattern of changing decline trends was observed through six (6) year interval contour maps from 2000 to 2018, and three groundwater zones have been described in the district on the basis of water level changes. This assessment indicated that the dominant groundwater flow direction in the area is in an easterly direction towards urban areas, and that significant groundwater declines are occurring even on the peripheries of the city area. Probable causes of groundwater depletion and approaches to mitigate this issue have been discussed on the basis of geological and hydrogeological studies and investigations in the area.