Integrating geophysical techniques and UAV mapping for the detection and temporal analysis of soil pipes and pipe collapses in agricultural loess landscapes

Abstract Piping erosion represents a persistent and often concealed threat to soil and water resources in agricultural loess landscapes, particularly under semi-arid conditions. Accurate detection and temporal monitoring of soil pipes and pipe collapses (PCs) are essential for effective land management. This study investigates the spatial and temporal dynamics of piping erosion in the Aqchatal catchment, eastern Golestan Province, NE Iran, through an integrated approach combining geophysical surveys and unmanned aerial vehicle (UAV) mapping. The objectives were: (i) to inventory and characterize soil pipes using ground penetrating radar (GPR) and electrical resistivity tomography (ERT); and (ii) to monitor the evolution of PCs from 2018 to 2023 using sequential UAV imagery. Three sets of UAV-derived orthomosaics, together with eight two-dimensional ERT profiles and thirteen GPR profiles, enabled the identification of areas at high risk of piping erosion. UAV analysis revealed recurrent PCs in close proximity to previously documented locations, frequently linked to anthropogenic activities such as agricultural machinery operations. GPR anomalies and ERT measurements indicated the continued susceptibility of areas with previously filled PCs, with possible soil pipes detected at depths of 1–7 m in both geophysical datasets. ERT results further identified resistivity values of 20–30 Ω⋅m for dry clay and silt layers, while values exceeding 300 Ω⋅m corresponded to potential pipe features. The integrated methodology demonstrated high efficacy in detecting and characterizing soil pipes in loess terrain. Based on these findings, targeted management strategies—including the establishment of buffer zones and the installation of informational boards—are recommended to mitigate piping erosion risk. Further assessment of the practical implementation and acceptance of these measures among landowners is warranted.