Airborne time‐domain electromagnetics, electrical resistivity and seismic reflection for regional three‐dimensional mapping and characterization of the Spiritwood Valley Aquifer, Manitoba, Canada

Abstract

The Geological Survey of Canada commissioned a helicopter‐borne time‐domain electromagnetic (HTEM) survey over a 1062 km2 area of the Spiritwood Valley in southern Manitoba in order to test the effectiveness of airborne time‐domain electromagnetics for mapping and characterizing buried valley aquifers in the Canadian Prairies. The data exhibit rich information content and clearly indicate the broader Spiritwood Valley in addition to a continuous incised valley along the broader valley bottom. We detect complex valley morphology with nested scales of valleys including at least three distinct valley features and multiple possible tributaries. Conductivity‐depth images (CDI) derived from the HTEM decays indicate that the fill materials within the incised valleys are more resistive than the broader valley fill, consistent with an interpretation of sand and gravel. Comparison of ground‐based electrical resistivity and seismic reflection data allow for the evaluation of CDI models. Lateral spatial information is in excellent agreement between data sets. However, CDI results tend to underestimate the dynamic range of electrical conductivity while overestimating depths to valley bottoms; these issues may be associated with system limitations, algorithm limitations or differences between data types. The integrated data sets illustrate that HTEM surveys have the potential to map complicated buried valley aquifers at a level of detail required for groundwater prospecting, modelling and management.