Characteristics of soil saturated hydraulic conductivity on different positions and their controlling factors of granite collapsing gullies

Abstract

Collapsing gully is a common phenomenon of hydraulic-gravity combined soil erosion in granite hilly area of south China. The study aimed to explore the relationship between soil hydraulics pro-perties and erosion mechanism and the intrinsic controlling factors. The active, semi-stable, and stable types of granite collapsing gullies in southeastern Guangxi were selected to examine the spatial variation of soil saturated hydraulic conductivity and identify the influencing factors. Main results were as follows: 1) Soil saturated hydraulic conductivity of collapsing gullies fluctuated on different positions, with the bottom of collapsing wall showing the minimum value, the top of colluvial deposit showing the maximum, and followed by the top of alluvial fan. 2) All the models being selected to model the soil saturated hydraulic conductivity, including Cosby, Compbell, Julià, and Hypre, performed poor. 3) Results of correlation analysis showed that soil saturated hydraulic conductivity was negatively correlated with capillary porosity and clay content, and positively correlated with non-capillary porosity and sand content. 4) Results of path analysis showed that sand content was the most influencing factor in controlling soil saturated hydraulic conductivity of collapsing gullies, followed by non-capillary porosity and soil bulk density, where sand content and non-capillary porosity exerted a positive effect and bulk density exerted a negative one. Our findings will provide theoretical basis for the mechanistic understanding and prevention of collapsing gullies erosion.