Many aquifers in nature loss or
gain water through adjacent confining beds of relatively low permeability.
However, such leaky aquifers are often only part of multiple-aquifer systems.
When water is withdrawn or recharged in one particular aquifer the head
distribution in the entire system will be influenced. In such a system several
aquifers can be distinguished, each separated from the others by aquitards
(semi pervious layers). These aquifers and aquitards together form a single
leaky system when recharge or discharge at one place influences the head
distribution in all other parts, but is not felt at its boundaries.
In practice, however, the system considered
may be restricted by boundaries with a negligible influence during the period
of interest. When water is withdrawn from one or more layers of a
multiple-aquifer system, the induced drawdown will be dependent on the
hydraulic properties of all aquifers and aquitards. Analytical solutions have
recently been presented for several types of steady-state flow in systems
comprising any number of layers. In an attempt to combine the advantages of an
analytical approach
with the capability of numerical models to include heterogeneity, Hemker
developed a hybrid analytical–numerical solution for transient well flow in
vertically heterogeneous aquifers.
The radial components of flow are treated
analytically, while the finitedifference technique is used to compute the
vertical flow components in the horizontally layered aquifer. The resulting
drawdown equations in the Laplace domain also account for the effects of a
finite diameter pumped well and wellbore storage.
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