Groundwater discharge is the
volumetric flow rate
In physics and engineering, in particular fluid dynamics, the volumetric flow rate (also known as volume flow rate, or volume velocity) is the volume of fluid which passes per unit time; usually it is represented by the symbol (sometimes \do ...
of
groundwater
Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...
through an
aquifer
An aquifer is an underground layer of water-bearing material, consisting of permeability (Earth sciences), permeable or fractured rock, or of unconsolidated materials (gravel, sand, or silt). Aquifers vary greatly in their characteristics. The s ...
.
Total groundwater discharge, as reported through a specified area, is similarly expressed as:
:
where
:''Q'' is the total groundwater discharge (
3·T−1">3·T−1 m
3/s),
:''K'' is the
hydraulic conductivity
In science and engineering, hydraulic conductivity (, in SI units of meters per second), is a property of porous materials, soils and Rock (geology), rocks, that describes the ease with which a fluid (usually water) can move through the porosity, ...
of the aquifer (
−1">·T−1 m/s),
:''dh/dl'' is the
hydraulic gradient (
−1">·L−1 unitless), and
:''A'' is the area which the groundwater is flowing through (
2">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
The discharge potential is a potential in groundwater mechanics which links the physical properties,
hydraulic head
Hydraulic head or piezometric head is a measurement related to liquid pressure (normalized by specific weight) and the liquid elevation above a vertical datum., 410 pages. See pp. 43–44., 650 pages. See p. 22, eq.3.2a.
It is usually meas ...
, with a mathematical formulation for the energy as a function of position. The discharge potential,
3·T−1">3·T−1 is defined in such way that its gradient equals the discharge vector.
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
:
is the hydraulic head
and
:
is an arbitrary constant
3·T−1">3·T−1given 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
In mathematics and physics, Laplace's equation is a second-order partial differential equation named after Pierre-Simon Laplace, who first studied its properties in 1786. This is often written as
\nabla^2\! f = 0 or \Delta f = 0,
where \Delt ...
which solution is a linear differential equation. Because the solution is a linear differential equation for which
superposition principle
The superposition principle, also known as superposition property, states that, for all linear systems, the net response caused by two or more stimuli is the sum of the responses that would have been caused by each stimulus individually. So th ...
holds, it may be combined with other solutions for the discharge potential, e.g. uniform flow, multiple wells, analytical elements (
analytic element method).
See also
*
Groundwater flow equation Used in hydrogeology, the groundwater flow equation is the mathematical relationship which is used to describe the flow of groundwater through an aquifer. The transient flow of groundwater is described by a form of the diffusion equation, similar ...
*
Groundwater energy balance The groundwater energy balance is the energy balance of a groundwater body in terms of incoming hydraulic energy associated with groundwater inflow into the body, energy associated with the outflow, energy conversion into heat due to friction of fl ...
*
Submarine groundwater discharge
*
Discharge (hydrology)
In hydrology, discharge is the volumetric flow rate (volume per time, in units of m3/h or ft3/h) of a stream. It equals the product of average flow velocity (with dimension of length per time, in m/h or ft/h) and the cross-sectional area (in m2 ...
*
Flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications in physics. For transport phe ...
(transport definition)
*
Darcy's Law
References
* Freeze, R.A. & Cherry, J.A., 1979. ''Groundwater'', Prentice-Hall. {{ISBN, 0-13-365312-9
Hydrology
Aquifers