Impacts of soil physical-chemical and mechanical properties on gully erosion development on terrace slopes in dry-hot valley region

Abstract: Gully erosion on land consolidation terrace slopes (LCTSs) is well developed in Jinsha Dry-hot valley region, and has caused serious soil losses. According to the field investigation, the soil erosion modulus caused by gully erosion on LCTSs can up to 8 000 t/(km2?a), which can lead continuous increase of sediment content in Jinsha River and its tributary rivers. Moreover, the development of gully erosion on LCTSs can severely destroy terrace land systems and hamper the exertion of ecological and economic benefits in the study area. In order to explore the key controlling factors of gully erosion development on LCTSs, and to find effective prevention and controlling measurements for gully erosion on LCTSs, a series of field investigations and laboratory measurements have been conducted between March and April 2016. Width, depth, sectional area, density and lacerate-degree of gullies in studied spots had been obtained by directly measuring and calculating based on related theoretical formula. In addition, bulk density, total porosity, capillary porosity, non-capillary porosity, shear strength (including cohesion and internal friction angle) and dispersion rate of studied soil samples were determined by conventional methods in soil science. On the basis of that, in this study, we analyzed the morphological characteristics of gullies on LCTSs, and explored the influence of soil physicochemical properties and mechanical properties on gully erosion development on LCTSs. The results showed that: 1) The non-capillary porosity was the major factor that affected the development of gully morphological characteristics on LCTSs. Non-capillary porosity had significant influence on width, depth, sectional area, density and lacerate-degree of gullies, while the impact manner and degree of non-capillary porosity on above-mentioned morphological characteristics were very different; 2) Soil shear strength only affected depth and sectional area of gullies, and had little influence on width, density and lacerate-degree of gullies on LCTSs. The impact manner of soil cohesion on depth and sectional area was similar, from which both fitting functions were cubic curves. In contrast, soil internal friction angle just affected the gullies' depth, and a quadratic function can be found between soil internal friction angle and gullies' depth; 3) Soil dispersion rate exerted obviously role in the changing of width and lacerate-degree of gullies, among which an exponential growth function can be found between gully width and soil dispersion rate, as well as a power function was built between lacerate-degree of gullies and soil dispersion rate. However, no significant influence had been detected for soil dispersion rate on depth, sectional area and density of gullies on LCTSs; 4) Width and density of gullies were mainly controlled by non-capillary porosity, and soil dispersion rate had more strong effect on lacerate-degree of gullies than other soil properties, while soil physicochemical properties and mechanical properties only had very slightly effect on the depth and sectional area of gullies on LCTSs. According to the above-mentioned analysis, it can be found that the impact manner and degree of soil properties on different morphological characteristics of gullies on LCTSs were very different, and different soil properties also had differential contribution in the development processes of gullies on LCTSs.