In groundwater hydrology, the governing equation of flow in a confined aquifer is derived from a mass-balance (continuity) argument combined with Darcy's law: net mass inflow to an elemental aquifer volume is balanced against the rate of change of water mass held in storage, yielding a diffusion-type partial differential equation (∇²h = (S/T)·∂h/∂t, or equivalently in terms of specific storage and hydraulic conductivity) that relates spatial and temporal variation of piezometric head to the aquifer's storage and transmission properties. The storage coefficient (or specific storage) formalizes how much water a confined aquifer releases from storage per unit head decline, arising from the compressibility of water and of the aquifer matrix rather than from aquifer drainage as in the unconfined case.
In groundwater hydrology, the governing equation of flow in a confined aquifer is derived from a mass-balance (continuity) argument combined with Darcy's law: net mass inflow to an elemental aquifer …