Japan Geoscience Union Meeting 2014

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International Session (Oral)

Symbol A (Atmospheric, Ocean, and Environmental Sciences) » A-GE Geological & Soil Environment

[A-GE03_30AM1] Subsurface Mass Transport and Environmental Assessment

Wed. Apr 30, 2014 10:00 AM - 10:45 AM 213 (2F)

Convener:*Yasushi Mori(Graduate School of Environmental and Life Science, Okayama University), Hirotaka Saito(Department of Ecoregion Science, Tokyo University of Agriculture and Technology), Ken Kawamoto(Graduate School of Science and Engineering, Saitama University), Shoichiro Hamamoto(Department of Biological and Environmental Engineering, The University of Tokyo), Ming Zhang(Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology), Chair:Hirotaka Saito(Department of Ecoregion Science, Tokyo University of Agriculture and Technology), Shoichiro Hamamoto(Department of Biological and Environmental Engineering, The University of Tokyo)

10:30 AM - 10:45 AM

[AGE03-03] Self-potential inversion for the estimation of hydraulic conductivity in the presence of unsaturated zone

*Yusuke OZAKI1, Hitoshi MIKADA1, Tada-nori GOTO1, Junichi TAKEKAWA1 (1.Graduate School of Engineering, Kyoto University)

Keywords:Self potential, Inversion, Hydraulic conductivity, Unsaturated zone

Self-potential (SP) is the electrical potential naturally generated in and on the earth. The positive electrical charge in the diffuse layer of the electrical double layer is conveyed by the groundwater flow. The electrical potential is generated when the groundwater flow through the porous medium. This electrical potential directly reflects on the Darcy velocity in the porous material, and therefore the hydraulic conductivity can be estimated from the SP data. The hydraulic conductivity has non-linear characteristics as functions of the water saturation, and so does SP. These features suggest that the effect of the unsaturated zone should be considered for much quantitative analysis of SP. However, the dependency of the SP on the water saturation makes the development of inversion difficult. We solved this problem with the adjoint state method for the calculation of the sensitivity matrix that could save the calculation time. The characteristic of water saturation in SP based on Van-Genuichen model is adapted to our inversion. We applied our inversion to a synthetic SP profile to test the performance of our inversion scheme to compare the results with and without the consideration to unsaturated zone. When the effects of the unsaturated zone are not considered, the value of estimated hydraulic conductivity is underestimated. On the other hands, more accurate image could be derived from the inversion with the consideration to the unsaturated zone. Therefore, our inversion technique would allow us to obtain the accurate hydraulic conductivity structure from SP data at the ground surface, although the SP is affected by the distribution of saturation.