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| Titel |
Measuring lateral saturated soil hydraulic conductivity at different spatial scales |
| VerfasserIn |
Simone Di Prima, Roberto Marrosu, Mario Pirastru, Marcello Niedda |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141228
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| Publikation (Nr.) |
 EGU/EGU2017-4710.pdf |
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| Zusammenfassung |
| Among the soil hydraulic properties, saturated soil hydraulic conductivity, Ks, is
particularly important since it controls many hydrological processes. Knowledge of
this soil property allows estimation of dynamic indicators of the soil’s ability to
transmit water down to the root zone. Such dynamic indicators are valuable tools to
quantify land degradation and developing ‘best management’ land use practice
(Castellini et al., 2016; Iovino et al., 2016). In hillslopes, lateral saturated soil hydraulic
conductivity, Ks,l, is a key factor since it controls subsurface flow. However, Ks,l data
collected by point-scale measurements, including infiltrations tests, could be unusable
for interpreting field hydrological processes and particularly subsurface flow in
hillslopes. Therefore, they are generally not representative of subsurface processes at
hillslope-scale due mainly to soil heterogeneities and the unknown total extent
and connectivity of macropore network in the porous medium. On the other hand,
large scale Ks,l measurements, which allow to average soil heterogeneities, are
difficult and costly, thus remain rare. Reliable Ks,l values should be measured on a
soil volume similar to the representative elementary volume (REV) in order to
incorporate the natural heterogeneity of the soil. However, the REV may be considered
site-specific since it is expected to increase for soils with macropores (Brooks et al.,
2004).
In this study, laboratory and in-situ Ks,l values are compared in order to detect the
dependency Ks,l from the spatial scale of investigation. The research was carried out at a
hillslope located in the Baratz Lake watershed, in northwest Sardinia, Italy, characterized by
degraded vegetation (grassland established after fire or clearing of the maquis). The
experimental area is about 60 m long, with an extent of approximately 2000 m2, and a mean
slope of 30%. The soil depth is about 35 to 45 cm. The parent material is a very dense
grayish, altered substratum of Permian sandstone that exhibits very low drainage, thus
preventing deep water percolation (Castellini et al., 2016).
In the laboratory, small-scale lateral and vertical saturated hydraulic conductivity, Ks,v,
were determined by the constant-head permeameter method (Klute and Dirksen, 1986) on 20
soil cubes of 1331 cm3 of volume (Bagarello and Sgroi, 2008), allowing determination of
mean Ks anisotropy for the hillslope.
In the field, small-scale Ks,v was determined by infiltration runs of the BEST
(Lassabatere et al., 2006) type carried out using a ring with an inner diameter of 0.15 m. The
BEST-steady algorithm, proposed by Bagarello et al. (2014), was used to analyze the
cumulative infiltration curves in order to decrease the failure rate of the BEST algorithms (Di
Prima et al., 2016). The in situ Ks,l at an intermediate spatial scale was estimated by a trench
test (Blanco-Canqui et al., 2002) carried out on a monolith 50 cm wide, 68 cm long and 34.5
cm deep (the depth to substratum). Finally, the large spatial scale (hillslope-scale) Ks,lvalue
was estimated from the outflow of a 8.5 m large drain and from the perched water
table levels monitored in the hillslope, following the methodology of Brooks et al.
(2004).
Anisotropy was not detected, since the soil cube experiments did not revealed
significant differences between Ks,v and Ks,l values. The differences between the Ks
datasets measured by the cube and the BEST methods were not statistically significant
at p = 0.05. These methods yielded Ks values 6.4 and 5.8 times lower than the
hillslope-scale Ks,l, respectively. The Ks,l value obtained by the trench experiment in
the soil monolith was 1440 mm h−1, which was only 1.5 times higher than the
hillslope-scale Ks,l. Probably, the chosen size of soil monolith was sufficient to properly
represent the spatial heterogeneity of the soil in the hillslope. This finding need to be
confirmed by further trench tests in soil monoliths to be carried out in the studied
hillslope.
References
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