Paper No. 42
Presentation Time: 9:00 AM-6:00 PM
ASSESSING THE ABILITY OF ELECTRICAL RESISTIVITY IMAGING TO DISCERN LATERAL CHANGES IN SOIL MOISTURE
ARNOLD, Carl B., HARRIS, Katie M. and DOGWILER, Toby, Southeastern Minnesota Water Resources Center, Department of Geoscience, Winona State University, PO Box 5838, Winona, MN 55987-5838, carlbrunoarnold@gmail.com
The purpose of this study is to determine if lateral variations in soil moisture can be assessed using electrical resistivity imaging (ERI). The experiment was conducted in the Rock Garden at Winona State University in southeastern Minnesota. Initially, three separate ERI surveys were conducted after a prolonged period (several weeks) with no appreciable precipitation. These surveys represented the “dry soil” conditions. The three ERI surveys were Dipole-Dipole, Wenner, and Schlumberger 28 electrode arrays with Induced Polarization data also collected. After completing the “dry soil” ERI surveys, sprinklers were used to create a two hour long simulated rainfall event. The simulated rainfall event was sufficient to saturate the topsoil along the ERI survey line. Immediately after the simulated rainfall the ERI surveys were repeated for the “wet soil” condition. Four soil samples were also collected along the length of the ERI line before and after the simulated rainfall. Each soil sample was analyzed to determine percent water by weight and electrical conductivity.
Based on our results, resistivity values decreased measurably after the addition of the moisture to the soil. Based on comparison of the “dry soil” and “wet soil” ERI surveys, we were able to distinguish changes in resistivity values up to 1 meter below the surface of the soil. Resistivity values decreased in the range of 25 to 200 ohm-m in various portions of the ERI resistivity cross-section. Based on our comparisons we were unable to discern quantifiable differences in the ability of the three ERI arrays to sense the changes in soil moisture.
We conclude that ERI can be successfully used to qualitatively evaluate changes in soil moisture. With additional study and calibration it may be possible to quantify moisture in the soil profile using ERI. Furthermore, our results emphasize that short-term changes in soil moisture can significantly alter the resistivity signature of an earth material.
