Abstract Preferential flow paths in shallow groundwater systems can be characterized by intensive tracer experiments, but these are expensive and time consuming to carry out. Geophysical surveys, such as ground-penetrating radar (GPR), have also been used to detect the presence of preferential flow paths in these systems, but the results have rarely been compared. Tracer experiments and GPR surveys were combined in two shallow alluvial gravel aquifer systems to better detect the presence of, and characterize, shallow groundwater. The two groundwater systems had differing hydraulic conductivities, dispersivities, and degrees of heterogeneity. Aquifer parameters (flow velocity, hydraulic conductivity, dispersivity) were derived from the tracer data using the method of temporal moments. Preferential flow paths were inferred using data on tracers and pesticide concentrations. The radar image showed preferential flow paths with trends similar to those identified from the tracer experiments and pesticide leaching trials. The combination of these techniques increased the confidence in the final interpretation.

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