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| Titel |
A new approach for measuring unsaturated hydraulic conductivity including hysteresis - with suprising insight to non-equilibrium water dynamics |
| VerfasserIn |
U. Weller, M. Köhne, H.-J. Vogel |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250023571
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| Zusammenfassung |
| The unsaturated hydraulic conductivity of soils is in general hard to measure directly and
therefore it is normally determined by inverse modeling of (de)saturation experiments. We
developed a new and rather simple direct measuring method using soil columns where
gravity-flow conditions are established for different but fixed flow rates following a computer
controlled protocol. This is done for wet towards drier conditions by decreasing the flow rate
and vice versa to capture hysteretic effects.
During the measurements we observe a surprising characteristic behavior of the water
potential inside the core which reflects a slow change of hydraulic conductivity with time:
Coming from a high water potential and lowering the flow, the potential first drops, as
expected, but then it gradually rises again with time indicating a decrease of hydraulic
conductivity. This is true over a large range of water potential. When increasing the flow rate
we observe the opposite behavior, i.e. the conductivity is slowly increasing with time with
convergence towards a constant value.
This phenomenology can be explained if we assume that the water content/water potential
relation (ÎΨ) is not a static property but that the system slowly tends towards an
optimal relation expressed by the main drainage and wetting branches of the water
retention characteristic. Then for a rather constant water content (that will give a
constant conductivity) the water potential will change with time towards the optimal
configuration.
This behavior has been described before. There are ÎΨ characterizations that take this
phenomenon into account, but so far it was hard to measure the dynamics of the transition
between non-equilibrium state versus equilibrium. We think that our approach has the
potential to quantify the soil water non-equilibrium dynamics. |
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