Agrogeophysical methods for identifying soil pipes

Abstract

Abstract The direct contribution of internal soil piping to soil losses or their collapse to form ephemeral gullies is a vital component in understanding total soil loss from agricultural lands. The generation and evolution of soil pipes occur below the surface, where survey-based measurements and analysis often fail to provide a comprehensive image of these crucial phenomena or their erosional evolution. The distribution of soil pipe collapses does not always correlate with surface flow paths, as indicated by surface topography. This lack of correlation makes inferences from traditional remote sensing or manual surveying of surface features subject to significant uncertainty and lack of correspondence to the actual subsurface flow path. Non-invasive geophysical methods provide a better alternative for high spatial resolution imaging to delineate, characterize, and map the distribution of soil pipe networks. In addition to being non-invasive, geophysical methods are more expedient and lower in cost than invasive techniques. In this paper, the feasibility and efficiency of two geophysical methods, ground penetrating radar (GPR) and electromagnetic induction (EMI), for delineating soil pipes in cross-sectional and plan view maps is presented. The evaluations are based on field measurements at a research site with established soil pipes and ephemeral gullies. Geophysical signatures from the two methods are evaluated using a composite (combined) cross-section plot that includes results of an invasive technique known as cone penetrologger testing (CPL). These signatures are then used to construct plan view maps of the area. The EMI results allow for the delineation of larger zones of fields having soil pipe networks. The GPR data provides a much better resolution. The GPR data can be used to construct maps (depth slices) representing different depths. The results demonstrate the high potential of EMI and GPR as useful tools for studying internal soil pipes.