Using Electric Resistivity Tomography and Borehole Logs to Detect Sedimentation Changes in a Gravel-Bed Ephemeral Channel

Resumen

Differences in deposit geometry and texture with depth along ephemeral gravel-bed streams strongly reflect fluctuations in bedload, which occur due to environmental changes at the basin scale and morphological channel adjustments. In this study, non-destructive methods, 2D and 3D electrical resistivity tomography(ERT), have been combined with datasets from borehole logs to identify, quantify and analyze the internal geometry of cross-sections of the gravel-bed ephemeral channel, known as Azohía Rambla (southeastern Spain). The electrical survey was performed through longitudinal and transverse profiles in two channel reaches, upper and middle stretches. Both profiles utilized 28 stainless steel electrodes reaching 14-30 m in length and an investigation depth of 3-5 m, approximately. Electrical resistivity values were correlated with data obtained from the samples collected from borehole logs (e.g. sediment strength, grain size distribution, compaction, porosity (ϕ), and hydraulic conductivity (k)). To determine ϕ and K granulometric and morphometric variables, such as shape-sphericity indices, particle sorting, effective grain-sizes and void ratios, were used.