A Method for Simultaneous Monitoring of Self-Potential and Soil Suction to Estimate Water Flux in the Vadose Zone

Abstract:

Characterizing water flux within the vadose zone is essential for a multitude of studies and applications related to irrigation, drainage, water management, and containment transport. Although important, current methods used to characterize water flux within the vadose zone (i.e., using soil suction and soil moisture measurements) can be time consuming and are not directly related to water flux. Recent literature has provided evidence that self-potential (SP) is a promising tool to characterize water flux within the vadose zone. SP is the electric potential signal generated by water flux within a porous medium through the electrokinetic phenomenon. To better constrain water flux estimation, it is necessary to determine unsaturated hydraulic conductivity. It has been established that soil water retention curves can be used to predict unsaturated hydraulic conductivity for various suction values. By combining SP and soil suction measurements, it is possible to efficiently and completely describe water flux within the vadose zone. Currently, SP and soil suction are measured via independent methods. Simultaneously measuring SP and soil suction for subsurface in-situ soil measurements with a single probe is an undeveloped and unexplored method for making hydrologic observations. To test the viability of combining these tests, a probe has been built and used to characterize vadose zone water flux in the Dry Creek Experimental Watershed near Boise, ID. The probe, as well as traditional instruments used to characterize water flux, were left in the field for several weeks to record data. The results of the combined SP and soil suction probe were in good agreement with the results from the traditional measurement techniques. From the combined probe, vertical water flux, suction, and hydraulic conductivity could be interpreted. By obtaining these three parameters, a confident and complete interpretation of water flux within the vadose zone could be made. Additionally, due to the combined probe, the data supporting these interpretations were obtained with relatively less work than traditional methods. The results from this study show the potential and benefits for the use of a combined SP and soil suction probe to estimate water flux within the vadose zone.