Groundwater flow equation

Summary

The groundwater flow equation is the partial differential equation for the hydraulic head of water in an aquifer. It combines Darcy's law, which gives the flux of water from the gradient of the head, with conservation of mass. Storage comes from the small compressibility of the water and the rock. For a uniform aquifer it is the heat equation for the head, and in steady state it is Laplace's equation. It is the basic model of hydrogeology, used to predict the effect of pumping wells and the spread of contaminants.