Environmental Engineering Reference
In-Depth Information
In the execution part the mesh is computed first in the arrays
x
and
y
. The vector
of distances from the well position is stored in
r
. Then the potential is calculated in
phi
. The reference potential is determined to produce the reference head value
h0
at
the (
i
ref
,
j
ref
) position of the mesh. For the chosen input values, the position of the
reference head has the coordinates (
x
min
,y
min
). The user has to choose different
values if the reference value is to be valid at another location of the model region.
The array of piezometric heads
hc
for the confined aquifer is computed from the
potential using (
14.15
) with a value for reference potential
phi0
calculated before.
The final command initiates the figure plot.
The last commands are valid for the confined aquifer. For the unconfined aquifer
the command sequence needs to be changed only slightly. The potential remains the
same. Only the part in which the head is computed from the potential has to be
altered. The command for
phi0
is concerned, as well as the computation of the head
hu
for the unconfined aquifer. One may use the following commands
phi0 = -phi(iref,jref) + 0.5*K*h0*h0;
% reference potential
hu = sqrt ((2/K)*(phi+phi0));
% unconfined
contourf (x,y,hu);
in order to produce a contour plot, as shown in Fig.
14.3
. The reference head value
needs to be below the aquifer thickness;
H
ΒΌ
6
was used in the computation.
The M-file can be extended to account for situations in which the aquifer
is partially confined and partially unconfined in the model region. To do that, the
M-file must be changed in the part where the head is calculated:
100
80
60
40
20
0
-20
-40
-60
-80
-100
0
20
40
60
80
100
120
140
160
180
200
Fig. 14.3 Drawdown in an aquifer in the vicinity of a pumping well
