ERI EVALUATION OF MACROPORE FLOW IN RIPARIAN AREAS

The agricultural industry invests heavily in riparian buffers to reduce non-point source pollution from runoff. Pollution prevention is essential for water quality in streams and river adjacent to major farms that provide potable water and aquatic habitats. Riparian soils are uniquely susceptible to the formation of macropores, which promote fast transport of water and contaminants through upper soil layers. Electrical Resistivity Imaging (ERI) can locate spatial heterogeneities in soil wetting patterns caused by preferential flow through macropores, thus helping in optimizing the design of riparian buffers. Preliminary laboratory experiments were conducted in a 150 cm x 40 cm x 40 cm tank to evaluate flow through artificial macropores of 0.4 cm diameter under steady simulated rainfall. ERI results from the lab indicate a capillary barrier in the tank and no obvious signs of preferential flow. Field scale experiments were conducted in a riparian buffer, on a 1.6 m x 8 m plot with a soil thickness of 30 – 70 cm. The goal in the field was to test flow in unsaturated and saturated macropores. Surface runoff was applied at the upstream end of the plot and the partitioning between surface and subsurface flow measured. Preliminary results from the field show that macropore flow doesn’t significantly affect fluid migration in unsaturated conditions relative to the soil matrix. In saturated surface conditions, macropores can significantly affect fluid distribution in the subsurface.