How climate-induced wetting–drying cycles contribute to gully erosion: A case study from southern China

Abstract

Collapsing gully erosion developed upon granite residual soil is the most devastating form of soil erosion in southern China. However, despite extensive investigations of the controlling factors of gully erosion, including granite regolith properties (pedon scale), slope geometry and hydraulic conditions (watershed scale), and local climate (regional scale), little is known about the interrelationships among these three-level factors and how these contribute to the initiation of gully erosion. This study presents how the wetting–drying cycles induced by the subtropical climate in southern China alter the properties of granite residual soil, with particular focus on the soil disintegration behavior. The test results indicate a finer texture (clay content increasing by 218%), lower shear strength (effective cohesion and internal frictional angle decreasing 55% and 30%, respectively), and five-times higher permeability for soil subjected to eight wetting–drying cycles. In addition, the wetting–drying cycle triggers more-apparent disintegration behavior, with the disintegration rate improving by 7 times. Such alterations are found to be caused by microstructural alterations including deaggregation and crack initiation, as revealed via scanning electron microscopy and mercury intrusion porosimetry. The implications of the variations of the multilevel soil properties for the development of gully erosion are discussed, with the degraded soil properties lowering the resistance to erosion and the high permeability facilitating soil–water interactions. This study improves the understanding of gully erosion and provides effective technical suggestions.