|ITEM METADATA RECORD
|Title: ||Assessing soil hydrological variability at the cm- to dm-scale using air permeameter measurements|
|Authors: ||Beerten, Koen|
Mallants, Dirk #
|Issue Date: ||23-Apr-2012 |
|Host Document: ||Geophysical Research Abstracts vol:14|
|Conference: ||EGU General Assembly location:Vienna date:22-27 April 2012|
|Article number: ||EGU2012-7695-2|
|Abstract: ||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 stratigra-
phy 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 -10−7 m/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.
Iversen B. V., Moldrup P., Schjonning P., & Jacobsen O. H. (2003). Field Application of a Portable Air Permeame-
ter 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.
|Publication status: ||published|
|KU Leuven publication type: ||IMa|
|Appears in Collections:||Division of Geology|
|Files in This Item:
There are no files associated with this item.