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Chapter 4 Temporal stability of soil moisture and its application in model result validation
indicate that these additional sampling locations are also close to the field mean
water content. Therefore, this suggests that the locations with sand contents
representative of the field mean sand contents can be served as time stable
locations for estimations of soil moisture beforehand.
Table 4.3. Mean values of soil texture, bulk density (BD) and hydraulic conductivity (K) in time
stability point (TSP) for four investigated sites.
Parameter UG 79 UG 99 WG HG
Point number 72 41 49 22
Sand (%) 49.0 43.2 50.0 67.8
Silt (%) 34.5 40.5 32.4 21.5
Clay (%) 16.5 16.3 17.2 10.7
BD (g cm -3 ) 0.92 0.94 1.11 1.19
K (cm d -1 ) 164.6 63.6 106.8 141.8
Application of the time stability concept to a hydraulic model
In this part we explore whether time stable points (TSPs) could be used to
identify a certain modeled location. The selected TSP in the previous section is
used to test by the HYDRUS-1D model. This is exemplified by UG 79. Firstly, we
derived the van Genuchten parameters of p72 by ROSETTA, that is, θr=6.3%,
θs=52.3%, α=0.009 cm -1 , n=1.509, Ks=149.9 cm d -1 , and L=0.5, respectively.
Secondly, the Ks from ROSETTA is optimized by the scaled-predictive method.
Here the predictive unsaturated hydraulic conductivity is scaled using a single
measurement at a given water suction, from which Ks is replaced by the
matching water suction (Thomasson et al., 2006). As shown in Fig. 8, there is a
very good match between the measured infiltration rates and the simulated
values via a two-term numerical conic function. According to this, the Ks is
scaled to 164.6 cm d -1 (Table 3). Furthermore, the hydraulic parameters in the
subsoil layer of p72 are also optimized based on the field measured value (i.e.
soil texture and bulk density) in the soil profile combined with the
scaled-calibration method (Thomasson et al., 2006). Remarkably, the modeled
results from TSP match well the measured soil surface moisture in the same
point (Fig. 9). Furthermore, the simulated result from p72 also shows a good
agreement with measured water dynamics in another long-term monitoring
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