Application of Electrical Resistivity Monitoring to Determine the Occurrence of Preferential Flow in Unsaturated Soil.
Abstract
Infiltration processes in the vadose zone can be difficult to characterize in the field, which may affect evaluations of contaminant transport. The presence of preferential flow pathways can produce more rapid infiltration rates than would otherwise be predicted using bulk soil properties. Electrical resistivity (ER) geophysical methods are sensitive to changes in water content within a soil matrix and may be used in conjunction with traditional sensing methods to detect the occurrence of preferential flow. Lysimeter soil columns were used as a platform to monitor flow under conditions replicating scenarios of a rising water table and that of gravity driven infiltration to determine associated sensor responses. A rising water table should produce a stable and homogenous wetting front whereas infiltration is potentially unstable and may produce preferential flow. Each lysimeter was suspended from a load cell mass balance system and outfit with moisture probes and matric potential probes along with multiple electrode arrays. ER arrays are designed with a dual configuration allowing for traditional tomographic imaging of different horizontal planes in the lysimeter as well as monitoring the vertical bulk electrical resistivity in the soil matrix. The bulk electrical signal of the soil matrix is sensitive to the interconnectivity of fluid within the pore space and results show that during gravity driven infiltration the water content indicated by the ER signal increases more rapidly than the effective water content reported by the probes. In contrast, during a rising water table scenario the rate at which water content changes is similar for both sensing methods. Furthermore, when comparing the two data sets for a given water content, the downward infiltration case produces lower resistivity values than the upward flow scenario, thus suggesting the downward moving water occurs along isolated pathways separated by drier, high resistivity soil. These results suggest that bulk resistivity measurements could provide relevant insights to the occurrence of preferential flow.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H41J2203H
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGYDE: 1835 Hydrogeophysics;
- HYDROLOGY