Présentations Colloques

    Session 8.07: Hydrogeophysics: innovative non-invasive technologies for groundwater resources exploitation and management
    Mallet (orateur)
    Mapping the soil water content variations in a torrential environment using Slingram electromagnetic technique (EM31)
    Soil water content is a key parameter that controls runoff processes at the watershed scale. Recent studies showed that changes in soil’s water storage was needed to understand the distribution of water residence time and the shape of flood's hydrograph (Davies and Beven, 2015). Identifying the spatial and temporal distribution of soil water content is still challenging especially in sloppy regions with high changes in soil properties and land cover. Hydrogeophysical methods can help to better understand the distribution of runoff generation by mapping soil water holding capacity using the apparent electrical conductivity measurements (Martini et. al, 2016). The present study has been carried out in a 0,86 km2 sub basin of the torrential Draix-Bléone's experimental catchment. Water content changes presents high spatial and temporal variability, controlled by site properties (soil texture and structure, topography, vegetation cover) and climate. The mapping process is complicated because of steep slopes coupled with high erosion rates resulting in a significant gully network. Since the summer 2015, four geophysical surveys were conducted in various moisture conditions and following the same pathway using the Slingram electromagnetic technique (EM31) in horizontal dipole to identify changes in soil properties until 5m. Owing to the marl's structure stability beyond 1m depth (Maquaire 2002), we assume that variations in the soil electrical conductivity between surveys are mainly due to water content variation in the subsurface. First measurements comparison between field campaigns show significant differences between areas with higher values and signal variations in marly's valley bottom and on the footslope than in forested areas. Clay content, soil texture, evapotranspiration and drainage rate are amongst the variables that could explain those changes. A discrete high frequency soil water content monitoring from a set of capacitive sensors is also available to validate the EM signals. Eventually, an integrative hydrogeophysical approach will be proposed to map soil water content over the whole catchment area.


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