HR: 0830h
AN: H31B-0468    [PDF]
TI: Electrical Resistivity Imaging and Depression Focused Recharge
AU: * Bentley, L R
EM: lbentley@ucalgary.ca
AF: University of Calgary, Department of Geology & Geophysics University of Calgary, Calgary, AB T2N 1N4 Canada
AU: Hayashi, M
EM: hayashi@ucalgary.ca
AF: University of Calgary, Department of Geology & Geophysics University of Calgary, Calgary, AB T2N 1N4 Canada
AU: Berthold, S
EM: s.berthold@web.de
AF: Technische Universitat Bergakademie Freiberg, Inst. of Geophysics Technische Universitat Bergakademie Freiberg, Freiberg, 09596 Germany
AB: Seasonal wetlands and small depressions play a fundamental role in recharging regional aquifers in the northern glaciated planes. Water from snowmelt collects in the depressions in the spring and infiltrates into the ground after the soil unfreezes. Infiltrating water leaches salts from the soil beneath depressions. The majority of the infiltrating water moves to the local uplands where it leaves the ground through ET leaving behind zones of evaporitically concentrated salts. A small percentage infiltrates down to the regional aquifer. Leaching and concentrating salts effect the electrical resistivity distribution of the subsurface. Three-dimensional electrical resistivity imaging (ERI) was combined with groundwater and soil measurements to generate a conceptual model of three dimensional fluid flow at San Denis, Saskatchewan. Water chemistry was used to generate a conceptual model of different geochemical zones which could be distinguished by the electrical conductivity of pore water. The Waxman-Smits equation was used to link groundwater electrical conductivity to in situ bulk resistivity. Electrical resisistivity from ERI was then used to map geochemical zones in the subsurface. ERI and chemistry show that infiltrating water reaches a regional aquifer at 20 meters depth. Seasonal wetlands have large zones of high resistivity that reach to the regional water table indicating that salts have been leached out of the tills to the depth of the regional aquifer. Small local depressions also have zones of leached soil beneath them indicating that they contribute to regional groundwater recharge. Since there are millions of small depressions, they may play a fundamental role in groundwater recharge and must be considered in land management. The images show a complex distribution of salts. Most of the salt is located in the upper weathered zone in the glacial tills and the horizontal distribution is controled by the locations of wetlands, steepness of slopes and the depth of the depressions. Adding ERI to the borehole and chemistry data generated a much more detailed and complex picture of water and solute cycling in the near surface.
DE: 0925 Magnetic and electrical methods
DE: 1829 Groundwater hydrology
DE: 1894 Instruments and techniques
SC: Hydrology [H]
MN: 2003 Fall Meeting