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**Groundwater discharge** is the volumetric flow rate of groundwater through an aquifer.

Total groundwater discharge, as reported through a specified area, is similarly expressed as:

where

*Q*is the total groundwater discharge ([L^{3}·T^{−1}]; m^{3}/s),*K*is the hydraulic conductivity of the aquifer ([L·T^{−1}]; m/s),*dh/dl*is the hydraulic gradient ([L·L^{−1}]; unitless), and*A*is the area which the groundwater is flowing through ([L^{2}]; m^{2})

For example, this can be used to determine the flow rate of water flowing along a plane with known geometry.

The discharge potential is a potential in groundwater mechanics which links the physical properties, hydraulic head, with a mathematical formulation for the energy as a function of position. The discharge potential, [L^{3}·T^{−1}], is defined in such way that its gradient equals the discharge vector.^{[1]}

Thus the hydraulic head may be calculated in terms of the discharge potential, for confined flow as

and for unconfined shallow flow as

where

- is the thickness of the aquifer [L],
- is the hydraulic head [L], and
- is an arbitrary constant [L
^{3}·T^{−1}] given by the boundary conditions.

As mentioned the discharge potential may also be written in terms of position. The discharge potential is a function of the Laplace's equation

which solution is a linear differential equation. Because the solution is a linear differential equation for which superposition principle holds, it may be combined with other solutions for the discharge potential, e.g. uniform flow, multiple wells, analytical elements (analytic element method).

- Freeze, R.A. & Cherry, J.A., 1979.
*Groundwater*, Prentice-Hall. ISBN 0-13-365312-9