Geophysical Investigation of Fresh-Saline Water Interface: A Case Study from South Punjab, Pakistan

The importance of the study of fresh-saline water incursion cannot be over-emphasized. Borehole techniques have been widely used, but they are quite expensive, intrusive, and time consuming. The electrical resistivity method has proved very successful in groundwater assessment. This advanced technique uses the calculation of Dar-Zarrouk (D-Z) parameters, namely longitudinal unit conductance, transverse unit resistance, and longitudinal resistivity has been employed by using 50 vertical electrical sounding points to assess the groundwater and delineate the fresh-saline water interface over 1045 km² area of Khanewal in Southern Punjab of Pakistan. The x-y plots and maps of D-Z parameters were produced to establish a decipherable vision for the occurrence and distribution of different water-bearing formations of fresh-saline water aquifers through a complicated situation of intermixing of different resistivity ranges for fresh-saline water bodies. This technique is useful to reduce the ambiguity produced by the process of equivalence and suppression which cause intermixing in differentiating fresh, brackish, and saline aquifers during interpretation. The fresh-saline water interface is correlated very well with the previous studies of water quality analysis carried out in Khanewal area. The results suggest that the D-Z parameters are useful for demarcating different aquifer zones. The behavior and pattern of D-Z parameters with respect to occurrence and distribution of different water-bearing formations were effectively identified and delineated in the study area.