|Other Abstract||A series of easy simulation experimental plots were constructed to study the development processes of gully erosion on land consolidation terrace slopes (LCTSs) based on the field investigation. This study was conducted in Yuanmou Dry-hot Valley Gully Erosion and Collapse Observation Research Station of Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, which was located in Jinsha River Dry-hot Valley Region. This study aimed at revealing the influence of soil types and vegetation conditions on the changing processes of hydrodynamic properties, morphological characteristics and sediment characteristics of gullies on LCTSs, and we studied the changing processes of hydrodynamic properties, morphological characteristics and sediment characteristics on a natural slope which had not been interfered by land consolidation. By comparing the gully development processes on LCTSs with that on a natural slope, the key factors that affect the gully erosion development on LCTSs can be found out. The research results revealed the mechanism of morphological development and sediment yield of gullies on LCTSs and natural slope, which were beneficial to explore the coupling effect of water and soil in mountain area and helpful to take purposeful measures to prevent LCTSs from intense gully erosion. The main conclusions of this study are listed as follows:(1) Classfication criteria for gullies’ morphological development degree on LCTSs, and its main influence factors.According to the field investigations about width, depth, sectional area, areal density and lacerate-degree of gullies, development index of gully erosion Q was considered as the quantitative indicator for division of gullies morphological development degree, and the division criteria were: 0|
2 belonged to extremely intensive development degree.The morphological development degree of gullies on LCTSs was affected by apparent factors and microcosmic factors. Slope type, soil type, vegetation and runoff condition were main apparent factors. Noncapillary porosity, coefficient of uneven distribution of particles, coefficient of curvature, cohesive force, and internal friction angle and dispersion rate of soil were major microcosmic factors.(2) Hydrodynamic properties of gullies on typical LCTSs.Land consolidation changed the varying patterns of hydrodynamic properties over rainfall time, and increased the ratio between runoff erosivity and resistance coefficient. The hydrodynamic properties remained basically stable over the whole test process on the natural slope, however, hydrodynamic properties changed regularly over the rainfall time on LCTSs.Similar change trends with time can be detected for the same hydrodynamic property on LCTSs, and significant difference can also be found for the values of the same hydrodynamic property on LCTSs. Reynolds number, shear stress, stream power and resistance coefficient exhibited to increase firstly and then tended to stable over the whole experimental process on our studied 4 LCTSs. The ratio between shear stress and resistance coefficient were 0.065~0.103, between stream power and resistance coefficient were 0.009~0.012 when gully erosion started on LCTSs.(3) Evolution process of erosion patterns and morphological characteristics on LCTSs.Rill or gully erosion developed in varying degrees on LCTSs, but sheet erosion was the unique pattern on natural slope in our study. The evolution processes of erosion pattern for dry-red soil and entisol were sheet erosion-rill erosion-gully erosion, for vertisols was sheet erosion-slip erosion-rill erosion.The starting time and duration of rill erosion on LCTSs can be affected intensively by soil types and vegetation conditions. The starting time of rill erosion for vertisols was 30 min which was the longest in the 4 LCTSs, in contrast, the starting time were respectively 8~10 min and 5 min for dry-red soil and entisol. As for the duration of rill erosion was 110 min for dry-red soil with vegetation stubble, which was much longer than those of bare dry-red soil, entisol and vertisols.The value of morphological characteristics (length, width, depth, volume and lacerate-degree of gullies) increased in different ways over the experimental time. In the whole experimental process, the volume and lacerate-degree of gullies were all characterized with: entisol >vertisols > dry-red soil, in contrast, the depth of gullies was characterized with: dry-red soil > entisol >vertisols.(4) Sediment yield process characteristics of gully development on LCTSs and natural slope.Land consolidation changed the varying patterns of sediment yielding, and enlarged the amount of sediment. Sediment concentration, transport rate varied depending on rainfall time on LCTSs, but sediment concentration, transport rate did not change with the experimental time and remained at a relatively stable level on natural slope. In whole, the sediment concentration, sediment transport rate and the total amount of erosion of LCTSs were significantly higher than those of natural slope, the former were respectively 10.22~50.20, 16.75~56.00, 10.51~488.06 times as much as the latter.Time changing trends and values of sediment characteristics were significant different among the three soil type LCTSs. It showed a decreasing tendency for sediment concentration and transport rate both in dry-red soil and vertisol. By contrast, sediment concentration and transport rate exhibited to increase firstly and then tended to stable over the test time in entisol. The average value of sediment yield of entisol and vertisol were similar and greater than that of dry-red soil. The sediment concentration, transport rate and total amount of erosion of entisol and vertisol were respectively 3.45~4.91, 2.30~3.56, 1.04~5.27 times as much as dry-red soil.Vegetation stubble can decrease sediment transport rate evidently, but had no significant effects on decreasing sediment concentration and can not change the time trends of sediment concentration and transport rate in this study. Sediment concentration and transport rate all showed to decrease gradually with time under the two vegetation condition LCTSs.(5) Development mechanism of gully erosion on LCTSsThe soil shear strength was the most important soil properties that influenced the hydrodynamic properties, morphological characteristics and sediment yielding process of gullies on our studied slopes. Besides, particle distribution and degree of aggregation of soil can also affect the sediment yield process in this study. The difference of soil properties induced higher soil erodibility (0.456~3.311 g/(N×s)) and critical runoff erosivity(0~1.698 Pa, 0~0.218 N/(m×s)) in LCTSs than those(0.290 g/(N×s), 0.410 Pa, 0.053 N/(m×s)) in natural slope, and changed the dynamic ratio between runoff erosivity and resistance coefficient, which resulted in more severe gully erosion in LCTSs than in natural slope.It was the key factor that affected the evolution processes of erosion modes and morphological characteristics of gully development for the key controlling hydrodynamic properties’ dynamic changing. The key controlling hydrodynamic properties changed from shear stress in the first 30 min to shear stress and runoff power in the last 90 min (30 ~ 120 min).