Geoscience Reference
In-Depth Information
z
+
z
+
x
+
x
+
(a)
t
+
= 0.013
(b)
t
+
= 0.518
z
+
z
+
x
+
x
+
(c)
t
+
= 2.274
(d)
t
+
= 4.762
(
aD
)
−
1
Fig. 10.6 Same as Figure 10.4 for an aquifer with
D
c
+
=
0
,
B
+
=
1
.
0
,
=
0
.
36,
n
=
8 and
b
=
1
.
5. (From Verma and Brutsaert, 1970.)
water content to 1
/
2 of its value at saturation. In general, when Ca or (
aD
)
−
1
is small,
the partly saturated zone is relatively thin, and vice versa. As can be deduced from (8.5),
the characteristic negative pressure
H
c
is larger for fine-textured materials, and smaller for
coarse-textured soils. Put in practical terms, capillary flow effects are probably negligible
in a 100 m deep sandy aquifer, but they are likely to be more important ina2mdeep clayey
soil profile.
The remaining two parameters,
B
+
=
B
/
D
and
D
c
+
=
D
c
/
D
, can be used to satisfy the
usual criteria for geometric similarity.
10.1.4 Initial state at the onset of drainage
The maximal outflow rate from an unconfined aquifer into an adjoining stream occurs when
the aquifer is fully saturated. Such a situation can be assumed to exist at the end of heavy or
prolonged precipitation, irrigation or snowmelt, and it can be taken to represent the initial
state of the aquifer when drainage is about to start. As indicated in Equations (10.3), the
