Groundwater Productivity
TANVI ARORA
Abstract
The electrical conductivities of rocks and soils are highly dependent of the water saturation. Variations in electrical resistivity are monitored by time lapse electrical resistivity tomography (TLERT) during a long duration pumping test. This experiment is carried out in the Experimental Hydrogeological ...
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The electrical conductivities of rocks and soils are highly dependent of the water saturation. Variations in electrical resistivity are monitored by time lapse electrical resistivity tomography (TLERT) during a long duration pumping test. This experiment is carried out in the Experimental Hydrogeological Park (EHP) located in Choutuppal, 45 km south-east of Hyderabad. Vadose zone of EHP comprises an uppermost thin layer of red soil (<1m), sandy regolith (1m-3m), saprolite (3 m – 15 m), and then the fissured granite. The pumping test lasts for 5 days and the piezometric variations are between 13 m and 18 m during pumping in CH03 borehole. This fissured granite is characterized by an important horizontal fracture density controlling the flow. An East West profile was laid with 48 electrodes and 3 m spacing interval. CH03, pumping well, was in the center of the profile covering 8 observation wells in both directions. 27 time-lapse datasets were inverted using Res2Dinv adopting least square inversions. The inverted resistivity datasets seem to be correlated with weathered profile and the variations of resistivity may be correlated with variation of hydraulic head. The variations of resistivity are more important close to CH03 and decreases with distance away from it. This behavior is coherent with the depression cone created by the pumping. Moreover, resistivity variations in the vadose zone highlight an influence of the pumping on the water content evolution of this zone. The observed heterogeneous response seems to be correlated with the geological media heterogeneity. TLERT appears to be a powerful tool to follow dynamic behavior of both saturated level and vadose zone for a given event. Grounwater punping monitoring helps to the water content evolution and groundwater productivity.
