Geophysical and Hydrogeological Investigation to Characterize the Potential Groundwater Aquifers of Nowshera Area, Khyber-Pakhtunkhwa, Pakistan

Abstract

The sustainable supply of freshwater is a pre-requisite for the sustainable socio economic development of an area as well as its urbanization. Pakistan is among those countries where water scarcity is a big issue. Therefore, the understanding of depositional settings and hydrological properties of the potential aquifer in an area are pre-requisite for urbanization and water abstraction. Nowshera District of Khyber-Pakhtunkhwa Province of Pakistan is situated in semi-arid region where continuous supply of fresh groundwater is very challenging. Geologically, the district is a southern and central part of the Peshawar Basin, which is one of the intermontane basins developed in Northwestern Himalayan Fold and Thrust Belt and has its significance in agriculture, industry, and urbanization in the province. The basin is filled by the Late Quaternary sediments eroded from nearby mountains and hills. About 600 vertical electrical sounding (VES) were acquired at sparsely distributed locations in the Nowshera District. These VES points were processed and interpreted to map groundwater potential and to delineate fresh and saline groundwater layers in the study area. With the help of a combination of geostatistical tools, geophysical data inversion and visualization techniques, the 1D VES data was re-model and visualizes into 2D and 3D spaces. Variogram models were used to differentiate individual aquifer and impermeable layers as well as aquifer characterization. The VES interpretation and borehole data indicate that finer to coarser sediments have been deposited in the study area in different episodes. The fine sediments mainly silty-clay and silty-sand or clayey sand were deposited in lacustrine and flood plain environments. Water channels and streams originating from the surrounding mountains have been acting as transporting and erosional agents, which deposited these sediments into to the middle of the basin. Coarser sediments such as gravels and boulders with intercalated layers of finer sediments were deposited into the basin near the mountain ranges recognized as the alluvial Page | v fan deposits. The admixture of medium to coarse- grained sand and gravels – widely distributed in the study area – formed the main non-leaky confined aquifer zone. The depositional setting of the sediments influences the flow and movement of groundwater. The aquifer hydraulic properties were determined by the integration of pumping test analysis with the VES data acquired in the study area. The results reveal that the aquifer system belonging to the alluvial fan zones has maximum hydraulic transmissivity and hydraulic conductivity whereas the lacustrine zones exhibit very low transmissivities and hydraulic conductivities. However, the aquifer belongs to sandy plain, or flood plain has sufficient transmissivity and hydraulic conductivity. This illustrates that with high concentration of finer sediments and in the absence of recharge boundaries, water transmission is very limited within the lacustrine and sandy plain zones whereas the alluvial fan zones have water conductive strata. Moreover, no saline sediments were found in the study area up to depth of investigation. The measured electrical conductivity values from the water samples taken in more than 2000 wells are in the range of good to mild quality water. This study will be helpful to plan groundwater monitoring and abstraction policy.