Geoscience Reference
In-Depth Information
0.20
Topp et al. (1980)
Roth et al. (1992)
Dobson et al. (1985)
Data with linear regression line
0.15
0.10
0.05
0.00
0
2
4
6
8
10
Relative Dielectric Constant (-)
fIGURe 25.6
The measured relative dielectric constant and the soil water content compared to different
calibration models.
Roth et al. (1992):
θ = -0.078 + 0.0448ε - 0.00195ε² + 0.0000361ε³
(25.3)
Dobson et al. (1985) and Huisman (2002):
−
−
(
1
n
)
ε
−
n
1
θ
=
ε
s
(25.4)
ε
−
1
ε
−
1
w
w
where ε is the bulk permittivity of a soil-water-air system (assuming that the permittivity of air
equals one), ε
w
and ε
s
are the permittivities of water (81 at 20°) and soil particles (assumed as 5),
respectively, and
n
is the soil porosity. It has to be emphasized that the absolute value of water
content was estimated from field capacity in spring. Therefore, absolute values may be erroneous
to a certain extent, although the measurements of the water content changes as estimated from
lysimeter balance readings are accurate. The equation of Topp et al. (1980) was found to represent
the data best (Figure 25.6).
25.3.3
s
P a t i a l
s
of i l
w
a t e R
c
o n t e n t
v
a R i a t i of n s
25.3.3.1
dye experiment
The spatial variations of the soil water content and resulting flux fields were qualitatively inves-
tigated using dye tracer tests. Due to the destructive nature of the experiment, the tests had to be
conducted at the end of our investigations. The experimental design was chosen according to earlier
investigations from Flury et al. (1994): 50 mm of a 4 gl
−1
Brilliant Blue (Vitasyn Blau AE85) solu-
tion was applied in 4 h. The treated area of 4 m² was horizontally, layer-wise (20 cm) excavated.
Although emphasis was laid on the construction of a
homogeneous
sand tank, the dye penetrated
the substrate irregularly (Figure 25.7). The finger-like flow patterns indicate an heterogeneous flow
field with mobile and immobile soil water regions. The dye pattern supported the need to set up a
heterogeneous numerical model for comparison purposes.
25.3.3.2
Maximum Relection Amplitude
The general suitability of the maximum reflection amplitude as an indicator for the water content
variation and thereby of the variability of the hydraulic functions was shown by Schmalz et al.
