Integrated 2D time-lapse resistivity tomography and spontaneous potential surveys demonstrate seasonal, use-related patterns of seepage from a water-supply canal system

The imperative of ensuring structural integrity and maintaining operational safety of hydraulic structures while managing surface water for power generation, food and fiber production, groundwater storage, and preservation of the natural environment drives a worldwide need for locating seepage associated with such structures. This paper is a case study of the geophysical assessment of seepage from the Sutherland Supply Canal and the connecting Paxton Siphon Inlet in subhumid to semiarid western Nebraska, USA. We employed 2D electrical resistivity tomography and self-potential methods to identify and characterize numerous potential seepage zones beneath these structures under both full-canal conditions (August 2023) and subsequent empty-canal conditions (October 2023). Our time-lapse analysis of the two 2D resistivity data sets exhibited a relative increase in the resistivity ratio of the potential seepage zones under empty-canal conditions of up to 700 (i.e., seven times of the magnitude of the resistivity determined in August) and a desaturation of about 26 % relative to saturation under full-canal conditions. These results indicate that a hydraulic connection exists between the canal and the potential seepage zones under it. Furthermore, self-potential data outlined the recharge and discharge zones under the canal according to positive and negative polarity of the drift-referred to base self-potential data. Our integrated time-lapse approach is non-invasive, time- and cost-effective, and easily repeatable; therefore, it is applicable to the assessment of seepage in irrigation canals, siphons, and dams worldwide.