Geoscience Reference
In-Depth Information
the sand tank, whereas no clear trend can be depicted from the radargram as derived 13 h after the
start of irrigation.
25.3.3.3
Simulated Soil Water Content profiles
Spatially distributed soil physical parameter measurements indicated nonuniform depth-dependent
retention characteristics. Optimized van Genuchten parameter values revealed a variation of the
saturated water content, θ
s
, from 0.27 to 0.36, and the residual water content, θ
r
, was found to be
0 in all cases. The range of observed soil hydraulic functions was used to generate layered and
heterogeneous flux fields assuming no spatial autocorrelation for any parameter within one soil layer
because no spatial autodependency could be observed from spatial highly resolved bulk density
measurements. Next to a layer-wise consideration of soil physical properties, we set up a numerical
model in which the independently determined hydraulic properties were randomly distributed over
the numerical mesh holding 4488 nodes. In Figure 25.9 and Figure 25.10 we present the variations
of the soil water content over the entire soil profile and within two selected soil layers. Only in the
heterogeneous case could significant volumetric moisture variations of 0.15 cm
3
cm
−3
be observed.
In a next step the soil water content values along with the NMRA signals of two selected soil
depths were statistically analyzed and box plots of the distributions were computed (Figure 25.11).
It is obvious that there are similarities in the general appearance of the statistical distributions only
between the water content variations and the NMRA distribution assuming a heterogeneous distri-
bution of the soil hydraulic properties (middle graphs in Figure 25.11). When a layer-wise orienta-
tion of the soil physical properties is considered in the soil water status simulations (top graphs in
Figure 25.11), the resulting statistical distribution shows no accordance to the NMRA distribution.
Although it is not possible to directly derive absolute soil water content values from the NMRA
signal, its statistical distribution might be helpful in generating heterogeneous flux fields.
2.5 m
(a)
0.25
0.2
2.0 m
0.15
0.1
0.05
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0
0
0.5
1
1.5
2
2.5
Water Content (m
3
m
-3
)
x-Direction (m)
2.5 m
(b)
0.25
0.2
2.0 m
0.15
0.1
0.05
0.00
0.05 0.10 0.15 0.20 0.25 0.30 0.35
0.40
0
0
0.5
1
1.5
2
2.5
x-Direction (m)
Water Content (m
3
m
-3
)
fIGURe 25.9
Simulated soil water content distributions of the 2.5 × 2 m two-dimensional flux field (left) and
within two depths: 35 cm (thin line) and 125 cm (bold line) 3 h after onset of irrigation. (a) Shows water content
assuming a layered structure and (b) resulted from a random distribution of the soil hydraulic properties.
