Soil Anti-scourability Differences And Its Related Physical Properties On Gullies With Different Degrees Of Activity In Yuanmou Dry-hot Valley Region

Gully erosion is one of primary causes leading to soil and water loss problem also destroying ecological environment in Yuanmou Dry-hot valley. The gully soil anti-scourability (ANS) is an important indicator to reveal the soil erosion mechanism being one of the hotspots and difficulties in the domain of soil erosion. In this thesis, surface soil on different parts (gully head, gully bed and gully watershed) has been selected in three active degree types of gullies (active gully, semi-active gully and stable gully) to verify the ANS under different active degree conditions in Yuanmou Dry-hot valley. Meanwhile, in order to simulate the ANS in different typical periods (the extremely dry season, rainy season and extremely wet season), this study set up three moisture contents (0%,50%,100%) treatment. Furthermore, by using undisturbed soil sample washing test, this paper studies the difference of soil physical and chemical properties under different active degrees of gullies, shows variation of characteristics of gully ANS on different parts, describe dynamic changes of gully ANS under three moisture contents condition, analyzes the influence factors of gully ANS. The main research results for the study are as follows:(1) With the gully active degree changing from active to semi-active to stable, the physical and chemical properties of gully soils change accordingly. The soil in active gully mainly comes from gully bank landslip and slope erosion. It has many features such as high sand content, strong water permeability and low organic matter content. The soil physical and chemical properties vary on different part in semi-active gully. The stable gully soil particles distribute more homogeneous. The soil physical and chemical properties have little difference on different parts under years of physical weathering, water flushing, surface and subsurface biological function. Soil balk density, soil sand content, internal friction angle are highest in active gully and the lowest in stable gully. In general, the above factors show the rank for each gully from high to low is active gully, semi-active gully and stable gully. Conversely, the soil total porosity, field capacity, clay content, silt content and the cohesion show the rank for each gully from low to high is active gully, semi-active gully and stable gully.(2) The sediment on each part (gully head, gully bed, gully watershed) decrease with the runoff time in different active degree gullies. The sediment of all gullies show the rank from high to low is active gully, semi-active gully and stable gully. Meanwhile, the main sediment parts are not consistent in different active degree gullies. The main sediment part is gully head in active gully and semi-active gully, the gully bed is the main sediment part in stable gully.(3) The ANS of surface soil under three moisture contents condition increase with time, and the relationships can be fitted by power function. Under 0% moisture content, the ANS of each part showing the rank from high to low are active gully watershed> gully bed >gully head, semi-active gully watershed>gully bed>gully head, stable gully bed> gully head> gully watershed. Under 50% moisture content, the ANS of each part showing the rank from high to low are active gully watershed>gully bed>gully head, semi-active gully bed> gully watershed> gully head. stable gully head> gully bed> gully watershed. Under 100% moisture content, the ANS of each part showing the rank from high to low are active gully bed>gully watershed>gully head, semi-active gully watershed>gully bed > gully head. stable gully bed> gully head> gully watershed. The research result shows that the ANS on gully head both in active gully and semi-active gully are minimized, the same as gully watershed in stable gully. We all shall strengthen the management and protection for the above parts.(4) Analysis under different moisture content shows that the active gully ANS had significantly positive correlation with the shear strength (Cohesion and internal friction Angle), clay content and biodiversity indicators(richness, Simpson index, abundance), had significantly negative correlation with the sand content. The semi-active gully ANS had significantly positive correlation with richness, Simpson index, abundance, had significantly negative correlation with the sand content. The stable gully ANS had significantly positive correlation with clay content, had significantly negative correlation with field capacity, sand content and biodiversity indicators (richness, Simpson index and abundance). The above results indicate higher shear strength and better soil texture can reduce sediment erosion.