Groundwater Flow

This article presents the fundamental equations for groundwater flow: the constitutive equation (the generalized form of Darcy’s law), and the mass balance equation. We restrict this article to isothermal flow of a single fluid, water, through a porous or fractured medium. We consider transient flow with variable density and viscosity through an anisotropic compressible porous medium with variable hydraulic conductivity. When considering compressibility, the approximation is made that the vertical total stress in the porous medium does not vary with time and that horizontal strains in the medium can be neglected. We consider the flow below the water table, called the phreatic surface, to be fully saturated, and above the water table filled by air. Thus, the pores in the soil are assumed to be either filled entirely with water or entirely with air.