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| Titel |
Quantifying water and air redistribution in heterogeneous sand sample by neutron imaging |
| VerfasserIn |
Jan Sacha, Martina Sobotkova, Vladimira Jelinkova, Michal Snehota, Peter Vontobel, Jan Hovind |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250086945
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| Publikation (Nr.) |
 EGU/EGU2014-890.pdf |
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| Zusammenfassung |
| Significant temporal variation of quasi saturated hydraulic conductivity (Kqs) has been
observed to date in number of infiltration experiments conducted mainly on heterogeneous
soil of Cambisol. The change of quasi-saturated hydraulic conductivity cannot be precisely
described by existing models. The Kqs variations has been recently attributed to a changing
distribution of the entrapped air and water within the sample. It is expected that air
is moved to the preferential pathway and acts as a barrier there. To support this
assumption a ponded infiltration experiment was conducted on a soil sample packed
into the quartz glass column of inner diameter of 34 mm. The sample composition
represents simplified heterogeneity of the natural soil but also allow the easy quantitative
water content determination in individual subdomains of the sample. The matrix
formed by a fine sand was surrounded with regions of coarse sand representing
preferential flow pathways. The Kqs was determined from the known hydraulic
gradient and measured volume flux. The experiment was monitored by neutron
radiography. Volume of water in the sample calculated from neutron projections
matched very well with actually infiltrated volume in the sample during first 40
second after beginning of infiltration. From the acquired radiographic images the
3D tomography images were reconstructed to obtain the spatial distribution of the
water content within the sample. Difference between water volume calculated from
radiography and tomography images was no more than 5%. While the total amount
of water determined by NR within the sample during the quasi steady state flow
remains practically constant (27.9 cm3 at the beginning and 28.6 cm3 on the end
of infiltration) the water content in the coarse fraction decreases (from 0.333 to
0.324) and the water content in the fine fraction increases (from 0.414 to 0.436) in 5
hours. Similarly to previous experiments performed on natural Cambisols, the results
support the hypothesis that the effect of the gradual Kqs variations is caused by the
entrapped air redistribution and the build-up of bubbles in preferential pathways. |
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