Improved interpretation of groundwater-surface water interactions along a stream reach using 3D high-resolution combined DC resistivity and induced polarization (DC-IP) geoelectrical imaging

Common approaches for characterizing streambed architecture, and its influence on groundwater-surface water (GW-SW) exchanges, are generally limited by their invasiveness and low spatial sampling density, which is a particular issue in streambeds that typically have high spatial heterogeneity. Combined DC resistivity and induced polarization (DC-IP) imaging can provide rapid, non-invasive and continuous information on streambed lithology; however, its full potential remains unrealized, leading to its underutilization for streambed investigations. The objective of this study is to demonstrate the value of DC-IP imaging, in both 3D and high-resolution, for characterizing streambed architecture and interpretating GW-SW exchange patterns. The study focused on a 50 m long stream reach located in Kintore, Ontario, Canada. Traditional methods – streambed temperature mapping, vertical head gradient measurements, streambed porewater quality, and sediment cores – were used to qualitatively identify spatial GW-SW exchanges. Underwater 3D DC-IP surveying was then conducted across the stream reach to obtain high-resolution distributions of resistivity and chargeability. Resistivity first identified three distinct zones along the stream reach: Zone 1 (0–12 m) and Zone 3 (38–50 m) exhibits high resistivity (>100 ohm-m), while Zone 2 (12–38 m) exhibits relatively low resistivity (