In coastal unconfined aquifers, dense seawater forms a dynamic wedge underneath fresh groundwater. Under hydrostatic equilibrium conditions, the depth of the fresh-saltwater interface below sea level $(z)$ is governed by the Ghyben-Herzberg Principle: $$z = \frac{\rho_f}{\rho_s - \rho_f} \cdot h_f$$ Where $\rho_f$ is fresh water density $(\approx 1.000\text{ g/cm}^3),$ $\rho_s$ is seawater density $(\approx 1.025\text{ g/cm}^3),$ and $h_f$ is freshwater table elevation above sea level. Substituting densities simplifies to: $$z \approx 40 \cdot h_f$$ Thus, every meter of freshwater head maintained above sea level supports approximately $40\text{ meters}$ of fresh water column below sea level. Excessive groundwater pumping $(h_f \to 0)$ causes rapid vertical upconing of the saltwater interface toward extraction wells. Coastal aquifers in states like Gujarat, Tamil Nadu, and West Bengal suffer severe saline contamination from heavy agricultural and industrial pumping. Modern coas...