Environmental Engineering Reference
In-Depth Information
surf (x,y,hc);
hold on
surf (x,y,hu);
Here the mesh is rectangular and regular, but the
surf
-command can also be
used for irregular meshes.
The next step is to extend the model for situations in which the aquifer is
partially confined and partially unconfined. The potential
(in the M-file:
phi
)
is first evaluated without a constant. Then an appropriate constant
phi0
is added.
The constant is computed differently for the confined and for the unconfined
situation. The confined situation is given if
h0
, the head at mesh position (1,1),
exceeds the aquifer thickness
H
. In order to use this simple criterion, it is required
that the hydraulic head is measured to zero level at the aquifer base (Fig.
13.2
).
The formulae (
13.12
) are applied. The potential for the confined situation gets
another constant, which is
'
2
KH
2
. Inserting this constant the potential becomes
a continuous function at locations with
h ¼ H
, where the conditions change from
confined to unconfined or vice versa. The potential value at these 'critical points' is
given by:
1
1
2
KH
2
'
crit
¼
þ '
0
(13.14)
The formulae for the head thus become:
12
confined
unconfined
11.8
11.6
11.4
11.2
11
10.8
10.6
10.4
10.2
10
0
10
20
30
40
50
60
70
80
90
100
Fig. 13.2 The difference of piezometric head between two specified levels for a confined and an
unconfined aquifer is obviously marginal
