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| Titel |
Visualization and quantification of the entrapped air bubbles by neutron imaging |
| VerfasserIn |
Michal Snehota, Vladimira Jelinkova, Martina Sobotkova, Jan Sacha, Milena Cislerova, Peter Vontobel |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082122
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| Zusammenfassung |
| Preferential flow in structured soils may be accompanied by a significant temporal variation
of quasi saturated hydraulic conductivity. These effects, observed in number of experiments
mainly on heterogeneous soil of Cambisol series, are sometimes attributed to a changing
distribution of the entrapped air within the sample.
We have reproduced the variation of the quasi steady state flow during the constant head
ponded infiltration experiment on the packed sample composed of three different
grades of quartz sand, and visualized the water distribution during i) the initial
stages of infiltration by neutron radiography and ii) during the steady state flow by
neutron tomography. Provided that the hydraulic gradient is known, in the case of the
experiment with ponding at the top and the seepage face at the bottom of the sample, the
effective quasi-saturated (or satiated) hydraulic conductivity (KQS) is known. Gradual
decrease of the KQS has been observed during first four hours of the infiltration
event.
Series of neutron tomography images taken during the quasi-steady state stage have
detected trapping of the air bubbles in coarser sand. Furthermore, the volume of a number of
entrapped air bubbles increased during the infiltration event. The fraction of the entrapped air
was calculated for a series of tomography images taken during each experiment. Similarly to
previous experiments performed on natural Cambisols, experimental results support the
hypothesis that the effect of the gradual KQS decrease is caused by the entrapped air
redistribution and the build-up of bubbles in preferential pathways. The trapped air thus
restricts the preferential flow pathways and causes a lower hydraulic conductivity. |
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