Three‐Dimensional Characterization of Lateral Subsurface Flow in an Alpine Forested Hillslope on the Tibetan Plateau Using Time‐Lapse Electrical Resistivity Tomography

Abstract

Lateral subsurface flow (LSF) is a key component of rainfall-runoff generation on alpine forested slopes, but the influence of weathered bedrock on LSF remains poorly understood due to methodological constraints in monitoring three-dimensional flow dynamics. This study addresses this gap by proposing a standardized morphological interpretation framework for time-lapse 3D electrical resistivity tomography (3D-ERT) inspired by dye-tracing studies, and applying this framework to investigate LSF mechanisms in soil-weathered bedrock systems on an alpine forested slope (NE Tibetan Plateau). During a controlled infiltration experiment, we conducted seven 3D-ERT measurements. The inverted resistivity distributions were temperature-corrected and converted to moisture content. The developed framework was then applied to quantify LSF patterns observed with ERT. Results show that the weathered bedrock layer acts as a permeable conduit, promoting downward leakage of water and limiting storage at the soil-bedrock interface. LSF penetrated vertically into deeper weathered bedrock but remained laterally constrained within the monitoring range, with greater flow distances observed in deeper layers. The soil and weathered-bedrock horizons exhibited contrasting moisture retention and drainage behavior during the initiation and development of LSF events. The emergence of two discrete flow pathways and the different maximum flow distance indicates the heterogeneity of LSF in weathered bedrock layers. Collectively, findings underscore the hydrological role of weathered bedrock in runoff generation on alpine slopes. The proposed ERT interpretation framework complements existing hydrogeophysical approaches by providing standardized morphological descriptors of ERT-inferred wetting patterns, offering a transferable way to characterize the spatiotemporal organization of subsurface flow in data-scarce mountain regions.

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