Fault Control on Groundwater Flow in An Alluvial Aquifer, Chaman and Khojak Basins, Balochistan, Pakistan

Geological structures such as faults play a critical role in the flow of fluids in a reservoir by affecting its permeability. This study explores the role of the Chaman Fault in the distribution of hydrological division, groundwater separation of the aquifer systems of Khojak and Chaman basins. The Chaman Fault is a left-lateral strike-slip transform plate boundary located at the border city of Chaman, District Killa Abdullah, Balochistan. The Chaman fault plays an important role in the division of groundwater in the subsurface, accommodating the structural compartment of the aquifer system. The studies showed that the strike-slip movement of the fault made the aquifer impervious along the fault line. This assertion may also be confirmed by the drastic change in the water table across the fault. Sharp changes in the groundwater table and Total Dissolved Solids (TDS) were observed during the study. The Karazes which are an indigenous method of irrigation is present in the eastern foothills of Khojak mountains called Khojak basin. Here the water table is as shallow as ≈ 6 meters in comparison to the western side of the fault, where the water table drops to ≈274 meters towards the valley of Chaman basin. The average TDS level on the eastern side of the fault line is 773 mg/L and 1361 mg/L on the western side. Therefore, the Chaman fault is acting as a groundwater barrier which is feeding the Karezes for centuries.