IJSRP, Volume 4, Issue 8, August 2014 Edition [ISSN 2250-3153]
Manu E., Preko K., Wemegah D.D.
Estimation of groundwater table by hydrogeologists in Ghana over the past decades has proven to be difficult due to the dearth of data on piezometric heads from the very few boreholes present to access this data. The importance of this information in infrastructure planning therefore calls for the need to establish a precise geophysical method that can predict the depth to the water table at a relatively lower cost and higher efficiency as compared with prevailing conventional methods. This paper demonstrates how the ground based ground penetrating radar (GPR) has been successfully used to delineate water table depths and possible ground water flow directions. The MALA GPR equipment with unshielded rough terrain antenna of 25 MHz central frequency in the common offset mode was employed for the data collection. Data was taken along 21 profiles with inter-profile separation of 50 m over the study site of areal extent 1 km2. Water table depths were estimated at an average depth of 21 m in an environment permeated by vertical structures which possibly served as pathways for groundwater infiltration. The general groundwater flow pattern was north-east in the northern and southern parts, and south-west at the central, eastern and western parts of the study area. The contact between the duricrust and the weathered saprolite was found at an average depth of 8 m. GPR-derived groundwater table depths were validated by drilled boreholes which intercepted the groundwater table at an average depth of 20 m within a lithology comprised of sandy clay and granite with varying degrees of weathering. This paper demonstrates the use of GPR as an efficient method for the estimation of groundwater table depth, groundwater flow direction as well as mapping of near surface lithological units; hence, it can serve as a baseline study for future applications.