Assessment of saline-freshwater interface structure in the Indian coastal delta complexes

The structure of the saline-freshwater interface is important in the context of estimating fresh groundwater reserves and sustainability, saline water intrusion processes and Freshwater discharges into adjoining ocean basins. A method of investigating this structure using self potential and resistivity logs is presented and tested for the Mahanadi-Brahmini-Baitarni delta systems of Orissa on the Indian coast. The method involves establishing a graphical relationship between R. (true water resistivity) and R., (equivalent water resistivity) and the use of scatter trend diagrams between dissolved solids and other ions to derive and estimate ionic components for unknown zones at different depths. A three-dimensional saline-freshwater interface structure map of the study area has been derived and serves as an important tool for: (i) estimation of freshwater resources and withdrawal strategies for future well field development; (ii) understanding the processes and magnitude of saline water intrusion and developing appropriate mitigation strategies; and (iii) identifying areas with active subsurface fresh groundwater discharge channels into adjoining oceanic basins.