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| Titel |
Extended multistep outflow method for the accurate determination of soil hydraulic properties close to water saturation |
| VerfasserIn |
Sascha Iden, Wolfgang Durner |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035291
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| Zusammenfassung |
| Multistep outflow experiments are a well-established method to determine soil hydraulic
properties. In the medium pressure head range where the specific water capacity is
sufficiently high, the method yields reliable results. However, in the pressure head range
corresponding to conditions close to and at water saturation, the method suffers from
considerable uncertainties, in particular with respect to the determination of the hydraulic
conductivity function. This is caused by the insensitivity of the experimental design with
respect to the saturated hydraulic conductivity Ks. It is therefore generally recommended
to perform an additional percolation experiment in order to determine Ks. The
disadvantages resulting from this are an increased experimental cost and the necessity to
combine information from two different experiments. In the case treated in this
study the latter bears the risk of data inconsistency. We present a new experimental
design which combines a water saturated percolation with an unsaturated multistep
outflow experiment in a consecutive manner. The saturated percolation resembles
a falling-head experiment with an initial ponding of 2-4 cm of water at the soil
surface. The onset of unsaturated flow can be identified unambiguously by pressure
head measurements inside the sample. We test this extended multistep outflow
method (XMSO) by inversions using synthetic and real laboratory data. The soil
hydraulic properties are parameterized with free-form functions in order to avoid model
errors in the constitutive relationships and to quantify robustly the uncertainties
of determination close to water saturation. Our results confirm that the XMSO
method allows to identify correctly the soil hydraulic properties in the pressure head
range near and at water saturation. In particular, the saturated hydraulic conductivity
can be determined without bias and with great accuracy. Because of the improved
information content and since the experiment is quick to perform and evaluated
easily by inverse modelling, it can replace the MSO design in future applications. |
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