Civil Engineering Reference
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the addition of Equations (6.51) and (6.52) leads to Equation (6.54) when setting
and
.
Most practical problems in rock hydraulics can be solved on the basis of steady-state
seepage fl ow.
Unconfi ned aquifer
The specifi c storage coeffi cient S
0
of an unconfi ned aquifer, that is, a rock mass with free
or phreatic surface, is defi ned as the volume of water V
w
that can fl ow out of or into a
reference volume V if the water table is lowered or raised by one unit:
(6.57)
If H is the thickness of the water-bearing rock formation that is affected by seepage
fl ow, for example, the thickness of an aquifer penetrated by a well, the effective porosity
can be expressed as
(6.58)
The integration boundary h = 0 corresponds to the location of the free surface. If S
0
is
constant the solution of the integral (6.58) yields
(6.59)
The specifi c storage coeffi cient of a homogeneous unconfi ned aquifer can thus be ex-
pressed as
(6.60)
Because the specifi c storage coeffi cient S
0
of a homogeneous unconfi ned aquifer is
equal to in
eff
related to its thickness H, in
eff
in a hydrogeological context is sometimes
denoted as “storage coeffi cient” S.
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