LABORATORY ELECTRICAL RESISTIVITY IMAGING OF MACROPORE FLOW

Runoff prevention is essential for water quality in streams and rivers adjacent to agricultural areas to prevent impacts to drinking water resources. Vegetation strips act as buffers to filter contaminants to prevent chemical impacts or algal blooms. In these settings, macropores generated by roots or burrows can strongly affect flow through these buffers by providing a rapid pathway for flow and transport. Electrical Resistivity Imaging (ERI) has been used to delineate preferential flow paths in the subsurface, thus providing data on the appropriate size and location of a buffer zone. What is unclear is how this technology would detect preferential flow due to macropores. Laboratory tank experiments were conducted to test macropore flow concepts under controlled conditions. A 150 cm x 40 cm x 40 cm plexiglass tank on a wooden base was used to measure infiltration in a small-scale, controlled setting. Two 28 electrode ERI setups were placed parallel to each other with a 5 cm electrode spacing. One rail utilized three artificial vertical macropores placed 30 cm apart; the second included seven macropores at a 15 cm spacing. A total of three infiltration experiments were conducted with varying parameters utilizing a rainfall simulator with hour scale rain events. The results were compared against standard soil moisture probes to determine the validity of the ERI flow velocity data.