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| Titel |
Assessing soil hydrological variability at the cm- to dm-scale using air permeameter measurements |
| VerfasserIn |
K. Beerten, N. Vandersmissen, B. Rogiers, D. Mallants |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250065495
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| Zusammenfassung |
| Soils and surficial sediments are crucial elements in the hydrological cycle since they are the
medium through which infiltrating precipitation percolates to the aquifer. At the same time,
soil horizons and shallow stratigraphy may act as hydraulic barriers that can promote runoff
or interflow and hamper deep infiltration. For most catchments little is known about the
small-scale horizontal and vertical variability of soil hydrological properties. Such
information is however required to calculate detailed soil water flow paths and estimate small
scale spatial variability in recharge and run-off.
We present the results from field air permeameter measurements to assess the
small-scale variability of saturated hydraulic conductivity in heterogeneous 2-D soil
profiles. To this end, several outcrops in the unsaturated zone (sandy soils with
podzolisation) of an interfluve in the Kleine Nete river catchment (Campine area, Northern
Belgium) were investigated using a hand-held permeameter. Measurements were
done each 10 cm on ~ 2 x 1 m or ~ 2 x 0.5 m grids. The initial results of the
measurements (air permeability Kair; millidarcy) are recalculated to saturated hydraulic
conductivity (Ks; m/s) using specific transfer functions (Loll et al., 1999; Iversen et al.,
2003). Validation of the results is done with independent lab-based constant head Ks
measurements.
The results show that field based Ks values generally range between 10-3 m/s and 10-7
m/s within one profile, but extremely high values (up to 10-1 m/s) have been measured as
well. The lowest values are found in the organic- and silt-rich Bh horizon of podzol soils
observed within the profiles (~ 10-6-10-7m/s), while the highest values are observed in
overlying dune sands less than 40 cm deep (up to 10-3 m/s with outliers to 10-1
m/s).
Comparison of field and laboratory based Ks data reveals there is fair agreement between
both methods, apart from several outliers. Scatter plots indicate that almost all points,
regardless the transfer function used, are within 10% (logKs) from perfect correlation.
However, it is not clear yet which transfer function would best fit to the data: both show a
slight systematic offset of ca. 5% (logKs) from the line of perfect agreement. Reasons for the
observed discrepancies can be differences in measurement scale (5-10 times smaller for the
air permeameter compared to constant head core samples) and possibly effects of the soil’s
saturation degree.
Despite the small but systematic offset, we conclude that field based air permeametry is a
relatively cheap, quick and reliable method to map the spatial variability of saturated
hydraulic conductivity in heterogeneous soil profiles.
References
Iversen B. V., Moldrup P., Schjonning P., & Jacobsen O. H. (2003). Field Application of a
Portable Air Permeameter to Characterize Spatial Variability in Air and Water Permeability.
Vadose Zone Journal, 2(4), 618-626.
Loll, P., Moldrup, P., Schjønning, P., & Riley, H. (1999). Predicting saturated hydraulic
conductivity from air permeability: Application in stochastic water infiltration modeling.
Water Resources Research, 35(8), 2387–2400. |
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