Geo-Electrical Studies in the High Barino,. Bangladesh for Evaluating Aquifer Geometry of the Area

Abstract

The Barind Tract is one of the major physiographic units of Bangladesh. During the dry period the discharge from shallow and hand tube wells become minimum and some times it becomes completely nil. Out of total 13 Upazillas, comprising the Barind Tract, Sapahar and Porsha Upazillas, situated in the High Ba.rind are adversely affected by water shortage. The Ba.rind region is now in an acute state of deforestation as a result the scarcity of surface water sources and low rainfall. Considering the above hydrogeological problem, geophysical investigation has been carried out in this area and an attempt has been made to study the feasibility of groundwater sources and characteristics of groundwater aquifer; particularly its depth and thickness. The lithological characteristics encountered in different drill holes enabled to divide the subsurface zone into three lithostratigrahic units up to 70 m depth from the ground surface. These are: top sandy and silty clay aquitard unit, fine to coarse sand aquifer unit and silty shale unit at the bottom. The top two layers units were underlain by silty clay unit in places. From the study of 21 deep tube well borelogs, it is evident that the main aquifer does not occur within the upper 300 m, and the composite aquifer, the only exploitable one in the area is present within the depth of 100 m. SLratigraphic panel diagram of the study area is also in good agreement with the geological cross-sections drawn for the study area. Clay-sand interface map also indicates a diverging zone in the study area. While the thickness map of top sandy and silty clay layer indicates an E-W elongated thick zone located in the northeastern portion of Sapaluu· Upazilla. It is observed from the maximum and minimum elevation of groundwater table map that the central pmt of the study area represents a prominent N-S elongated diverging zone. The groundwater flqws radially towards east, west, north and south from the central pm·t of the study area.--------