Piping process: Genesis and network characterization through a pedological and geophysical approach

Abstract

Piping is a soil erosion process initiated by concentrated subsurface water flow, which can develop in both natural and anthropogenic landscapes and causes various environmental impacts. The piping process acts as a relief modifier, leading to soil subsidence on a short time scale. This paper aims to provide a more comprehensive characterization of the piping process in a tropical forested area of Brazil. First, we sought to understand and examine the subsurface environment of the soil, using field description and soil sampling for chemical and physical analyses (pH, CEC, bulk density, total porosity, flocculation degree). Based on this information, we performed geophysical tests using Direct Current resistivity method (DC resistivity), with six lines of electrical resistivity tomography (ERT), to map the pipes and check the connection between subsurface tunnels. Data on the basic properties of the soil aided our interpretation of the geophysical results and the genesis of the piping process. The soil of the study area presented horizons in which textural variations accompanied changes in total porosity, bulk density and flocculation degree. The DC resistivity method efficiently detected the pipes (resistive zones of values >4000 O.m and high contrast with adjacent zones) and revealed the connection and continuity of the pipe network. While various factors may contribute to the subsurface erosive process in the study area, the decisive factor triggering the process seems to be the presence of a permeable layer that lies just above the impermeable layer, which may stop water infiltration and facilitate the lateral water movement.