Piping Erosion in Semi‐Arid Loess Hillslope: The Influence of Soil Characteristics

Abstract

Piping erosion, driven by subsurface flow, has generally received less attention than soil erosion caused by overland flow. This oversight contributes to the growing global problem of soil degradation in various regions. Piping erosion can pose significant geohazards in areas covered by loess, such as the Iranian Loess Plateau (ILP), where it negatively impacts agricultural productivity and human properties. Consequently, identifying the factors influencing this erosion process is essential for developing effective control measures. Therefore, this study aimed to examine the role of soil characteristics and slope positions in the selected area of the ILP prone to piping erosion. In order to achieve this goal, six soil profiles were excavated both inside and outside pipe collapses (PCs) and at various positions on the hillslope (shoulder, backslope, and toeslope). The soil profiles were described following standard pedological methods (the Soil Survey Manual). A total of 28 soil samples were analyzed in the laboratory. Apart from cluster analysis, a comparison of soil properties was done: (1) at various slope positions, and (2) inside and outside PCs. The silt content of the analyzed soils ranges from 57% to 84%, predominantly consisting of medium‐sized silt particles, generally making these soils vulnerable to soil erosion. The sodium (Na+) content tends to decrease in soil profiles inside the PCs, while the exchangeable sodium percentage (ESP) generally increases toward deeper soil layers. This condition may promote preferential flow, particularly in the lower horizons, which acts as a primary driving force for the initiation of piping erosion. Cluster analysis revealed that high content of Na+, Mg2+, and high ESP values are the most significant contributors to piping erosion. Notably, the deepest soil horizons in the pits inside the PCs and across different hillslope positions were grouped into the same cluster, indicating that the C horizons of profiles inside the PCs are the most vulnerable to piping erosion. Variations in vertical soil structure, both within and outside the PCs at different slope positions, suggest that weak soil structure may significantly influence the initiation and enlargement of pipes. The deepest soil horizons of soil profiles inside the PCs have the highest ESP values, indicating their dispersive characteristics. This study has shown that, in loess‐derived soils under semi‐arid conditions, soil properties have a greater impact on piping erosion than hillslope positions. In summary, the study area is characterized by erodible soils, with all hillslope positions being highly susceptible to piping. This research enhances our understanding of piping erosion in loess‐covered regions under semi‐arid conditions and provides a crucial step toward developing effective soil erosion control measures.