Detecting Macropore Fingering Using Temporal Electrical Resistivity Imaging

Abstract

HighlightsSingle macropores can be detected using temporal electrical resistivity imaging under controlled conditions.Macropore flow can be detected based on preferentially wetted fingers of increased conductance.Macropore activation does not appear to require saturated surface conditions to induce preferential flow.Abstract. Riparian soils are uniquely susceptible to the formation of macropores, which are hypothesized to promote fast transport of water and contaminants through upper soil layers. Electrical Resistivity Imaging (ERI) can locate spatial heterogeneities in soil wetting patterns and evaluate differences due to vegetation, thus optimizing the design of riparian buffers. Temporal ERI (TERI) imaging was conducted in a fine and coarse field setting with artificial macropores to evaluate flow under unsaturated simulated rainfall conditions and saturated infiltrometer conditions. While single macropores are detectable using TERI datasets, the results in an average field setting would detect the wetted area surrounding a macropore, not the macropore itself. The results were similar for both the primary fine grain soil site in Oklahoma as well as the coarse grain site in North Carolina. TERI data indicated that without artificial conditions with low noise conditions, a single macropore would not be detected, a wetted zone would be the best detection. In ordinary field evaluation of natural macropores, the TERI technique would detect the wetted zone around a macropore similar to a high hydraulic conductivity zone in a heterogeneous soil matrix. Finally, the results confirmed that macropore activation does not require saturated conditions to generate preferential flow. Keywords: Hydrogeophysics, Preferential flowpaths, Riparian buffers, Temporal electrical resistivity imaging.