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| Titel |
Time lapse imaging of water content with geoelectrical methods: on the interest of working with absolute water content data |
| VerfasserIn |
Gaël Dumont, Tamara Pilawski, Tanguy Robert, Thomas Hermans, Sarah Garré, Frédéric Nguyen |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250137058
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| Publikation (Nr.) |
 EGU/EGU2016-18245.pdf |
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| Zusammenfassung |
| The electrical resistivity tomography is a suitable method to estimate the water
content of a waste material and detect changes in water content. Various ERT profiles,
both static data and time-lapse, where acquired on a landfill during the Minerve
project.
In the literature, the relative change of resistivity (Δρ/ρ) is generally computed. For
saline or heat tracer tests in the saturated zone, the Δρ/ρ can be easily translated
into pore water conductivity or underground temperature changes (provided that
the initial salinity or temperature condition is homogeneous over the ERT panel
extension).
For water content changes in the vadose zone resulting of an infiltration event or injection
experiment, many authors also work with the Δρ/ρ or relative changes of water
content Δθ/θ (linked to the change of resistivity through one single parameter: the
Archie’s law exponent “m”). This parameter is not influenced by the underground
temperature and pore fluid conductivity (ρ¬w) condition but is influenced by the
initial water content distribution. Therefore, you never know if the loss of Δθ/θ
signal is representative of the limit of the infiltration front or more humid initial
condition.
Another approach for the understanding of the infiltration process is the assessment of the
absolute change of water content (Δθ). This requires the direct computation of
the water content of the waste from the resistivity data. For that purpose, we used
petrophysical laws calibrated with laboratory experiments and our knowledge of the in situ
temperature and pore fluid conductivity parameters. Then, we investigated water
content changes in the waste material after a rainfall event (Δθ= Δθ/θ* θ). This new
observation is really representatives of the quantity of water infiltrated in the waste
material. However, the uncertainty in the pore fluid conductivity value may influence
the computed water changes (Δθ=k*m√(ρ_w ) ; where “m” is the Archie’s law
exponent).
Using these two complementary approaches, we analyzed the effect a major rainfall (20-30
mm in 2 hours) that occurred on the test site, characterized by a vegetalized and relatively dry
zone and a devegatelized and humid zone. We intended to prove that most of the information
contained in the Δθ/θ distribution is the initial water content distribution in the ground. Water
addition in dry zones resulting in large relative changes. The computation of the Δθ is
necessary to demonstrate preferential infiltration through the capping in a restricted zone of
the vegetalized area. |
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