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Article Dans Une Revue Journal of Hydrology Année : 2002

Temporal variations of SP and unsaturated water flow in loam and clay soils : a seasonal field study

Résumé

Accurate assessment of soil–waterfluxes is essential in soil physics due to its direct implications in environmental, agronomical or hydrological applications. Fieldestimations of soil–waterfluxes by ‘classical' hydraulic methods are often difficult to obtain. Moreover ,water fluxes are highly variable in space and time. The obtainment of a reasonable estimate for this variable would require numerous measurement sites. However, such a requirement is rarely met. Thony et al. [CRAcad.Sci.Paris,EarthPlanetarySci.325(1997)317] presented the experimental evidence of a linear relationship between the self-potential (SP) and the unsaturated soil–waterflux. Therefore, this relationship would allow the indirect assessment of the waterflux using electrical measurements. Such an approach would appear much more flexible and easier to perform than the current hydraulic measurements. The aim of this study is to experimentally investigate the existence and robustness of the flux–SP relationship for different soil types and pedoclimatic conditions. The soil–waterfluxes and the SP weremonitored in along-term experiment involving two types of soils, contrasting in hydraulic and electric properties. The soils were placed in lysimeters which were instrumented with tensiometers and TDR probes for monitoring hydraulic heads and moisture content, respectively. Unpolarizable SP electrodes, temperature sensors and suction cups (for collecting pore water) were also installed in the lysimeters. The SP and the fluxes were measured or calculated in the 30–40cm depth section. Results show that the variations of the SP with time were clearly linked to both rainfal levents and evaporation .However, inthelong-term, the linear relationship between the unsaturated waterflux and the SP evolves from strongly correlated to almost not correlated. The slope (sensitivity) of the flux–SP relationship varies with the soil type, decreasing with more electrically conductive soil. Taking into account a varying soil–electrode contact greatly improves theflux–SP relationship at the scale of the rainfal levent, particularly when considering infiltration and drainage phases separately. Nevertheless, at the scale of a year, with alternate drainfalls and evaporation phases, the robustness of the relationship decreases (i.e.thecoefficients of the relationship vary between events). This variability could be related to time variation sin electrical conductivity, not so much to that of thesoil–water, but rather to that of the water from the salted soilmud added to the SP electrodes at the time of installation. This study points out methodological problems associated with the measurement of SP in shallow unsaturated soils overthelong-term and the need for designing specific electrodes for this purpose. However, indeep soils beneath the root zone, environmental conditions generally vary slowly and lightly in comparison to surface horizons. In this case and with our presentset of SP measurement devices, the flux–SP relationship could be more stable than in the surface soil horizons and useful for examining aquifer recharge, capillary rises or contaminant transfert.
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Dates et versions

hal-00108154 , version 1 (19-10-2006)

Identifiants

  • HAL Id : hal-00108154 , version 1
  • PRODINRA : 252173

Citer

Claude Doussan, Laurence Jouniaux, Jean-Louis Thony. Temporal variations of SP and unsaturated water flow in loam and clay soils : a seasonal field study. Journal of Hydrology, 2002, 267, pp.173-185. ⟨hal-00108154⟩
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