MODELLING STREAMING POTENTIAL (SP) SIGNALS INDUCED BY WATER MOVEMENT IN THE VADOSE ZONE

Abstract

Field estimation of soil water flux has a direct application for water resource management. Standard methods are often difficult to apply because of the heterogeneity of the subsurface. In the present study, we show that Streaming Potential (SP) monitoring can provide a cost-effective tool to help estimate the nature of the hydraulic transfers (infiltration or evaporation) in the vadose zone. We have modelled the SP response of rainfall infiltration and evaporation in an unsaturated porous medium; our model shows that SP signals of several millivolts are generated, i.e. easily recordable with standard SP equipment and that they allow to characterize the upward or downward water flux. We have compared our model results to SP and hydraulic data sets acquired during both rainfall infiltration and evaporation phases and they confirmed that SP measurements allow effectively to estimate the direction of the water flux at the scale of the electrode separation (usually several decimetres), i.e. at a much larger scale than tensiometric measurements.