Self-potentials (SP) are sensitive to water fluxes and concentration
gradients in both saturated and unsaturated geological media, but
quantitative interpretations of SP field data may often be hindered by
the superposition of different source contributions and time-varying
electrode potentials. Self-potential mapping and close to two months of
SP monitoring on a gravel bar were performed to investigate the origins
of SP signals at a restored river section of the Thur River in
northeastern Switzerland. The SP mapping and subsequent inversion of the
data indicate that the SP sources are mainly located in the upper few
meters in regions of soil cover rather than bare gravel. Wavelet
analyses of the time-series indicate a strong, but non-linear influence
of water table and water content variations, as well as rainfall
intensity on the recorded SP signals. Modeling of the SP response with
respect to an increase in the water table elevation and precipitation
indicate that the distribution of soil properties in the vadose zone has
a very strong influence. We conclude that the observed SP responses on
the gravel bar are more complicated than previously proposed
semi-empiric relationships between SP signals and hydraulic head or the
thickness of the vadose zone. We suggest that future SP monitoring in
restored river corridors should either focus on quantifying vadose zone
processes by installing vertical profiles of closely spaced SP
electrodes or by installing the electrodes within the river to avoid
signals arising from vadose zone processes and time-varying
electrochemical conditions in the vicinity of the electrodes.