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| Titel |
Contact resistance problems applying ERT on low bulk density forested stony soils. Is there a solution? |
| VerfasserIn |
Deborah Deraedt, Camille Touzé, Tanguy Robert, Gilles Colinet, Aurore Degre, Sarah Garré |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106142
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| Publikation (Nr.) |
 EGU/EGU2015-5795.pdf |
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| Zusammenfassung |
| Electrical resistivity tomography (ERT) has often been put forward as a promising tool to
quantify soil water and solute fluxes in a non-invasive way. In our experiment, we wanted to
determine preferential flow processes along a forested hillslope using a saline tracer with
ERT. The experiment was conducted in the Houille watershed, subcatchment of the Meuse
located in the North of Belgian Ardennes (50Ë 1’52.6”N, 4Ë 53’22.5”E). The climate is
continental but the soil under spruce (Picea abies (L.) Karst.) and Douglas fire stand
(Pseudotsuga menziesii (Mirb.) Franco) remains quite dry (19% WVC in average) during the
whole year. The soil is Cambisol and the parent rock is Devonian schist covered with variable
thickness of silty loam soil. The soil density ranges from 1.13 to 1.87 g/cm3 on average. The
stone content varies from 20 to 89% and the soil depth fluctuates between 70 and 130
cm.
The ERT tests took place on June 1st 2012, April 1st, 2nd and 3rd 2014 and May 12th
2014. We used the Terrameter LS 12 channels (ABEM, Sweden) in 2012 test and the DAS-1
(Multi-Phase Technologies, United States) in 2014. Different electrode configurations and
arrays were adopted for different dates (transect and grid arrays and Wenner – Schlumberger,
Wenner alpha and dipole-dipole configurations).
During all tests, we systematically faced technical problems, mainly related to bad
electrode contact. The recorded data show values of contact resistance above 14873 Ω (our
target value would be below 3000 Ω). Subsequently, we tried to improve the contact by
predrilling the soil and pouring water in the electrode holes. The contact resistance
improved to 14040 Ω as minimum. The same procedure with liquid mud was then
tested to prevent quick percolation of the water from the electrode location. As a
result, the lower contact resistance dropped to 11745 Ω. Finally, we applied about
25 litre of saline solution (CaCl2, 0.75g/L) homogeneously on the electrode grid.
The minimum value of contact resistance reduced to 5222 Ω. This improved the
contact resistance substantially, but complicates the execution of a pulse tracer
experiment.
To date we did not find any better solution to this problem and we keep searching a way
to improve the contact resistance in stony forested soils with very low bulk density. We would
like to exchange on these questions with EGU attendees in order to improve the experimental
design or point out a new research path for these specific conditions. This could
lead to enhance the use of ERT in soils with low density and high stone content. |
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