| On the basis of literatures reviewing on the slope-gully system development from domestic and abroad, the theory of erosion sediment yield of slope-gully system was researched and perfected by aiming at the weak neck and urgent problems to solve in the process of research of slope-gully systems, using slope-gully systems physical model and field crude slope-gully landform, adopting runoff scouring method. According to typical physiognomy of slope-gully systems in Loess Plateau, the slope-gully systems physical model was established. Hydrodynamics characteristic, the process of erosion sediment yield, erosion motivity, the origin of erosion sediment yield were all researched by integrating with rare-earth element tracing technology and adopting scouring method. The adjust-control effect of grassland coverage to hydrodynamics characteristic, the difference of sediment yield process under grassland in slope and gully, the variation of erosion sediment yield process with grassland coverage, the variation of erosion sediment yield process with slope length of slope-gully system were all studied by scouring with field slope-gully systems experiment. Furthermore, according to data of sloping fields reformed to terraced fields collected from field investigation, adjust and control effect of terrace on the process of infiltration , flow generation and sediment yield of slope-gully systems were studied . At the same time, adjust and control effect of check dam on flow generation and sediment yield from the slope-gully systems and its grain composition were studied by the collected data. Based on finite element software, adjust and control effect of check dam on gravity erosion. The following conclusions were obtained:(1) Main runoff dynamic parameters, including Reynolds number, Froude numbers andvelocity in slope-gully systems, varied greatly with runoff discharge and slope position.In this experiment, Reynolds number varied between 342.3 and 858.8, all of which was smaller than 900, and indicated that runoff in the slope-gully system was laminar flow. Froude numbers varied between 1.36 and 8.92 in the erosion processes, and showed that the runoff of the slope-gully systems were turbulent flow.(2) Analysis of sediement source by rare-earth element tracing method indicated that the proportion of sediment from slope was greater than that from gully in the experiment, and sediment from the top two meters on the slope accounted for more than 50% of the total sediment yield. Except for sediment under the runoff discharge of 12L/min, sediment from various element tracing belt in the slope was in the order of La>Ce>Tb >Sm. Sediment from various element tracing belt in the gully was in order of Eu>Yb >Dy, excep for sediment under the runoff discharge of 6L/min and 8L/min. Erosion ratio increased fluctuantly with time under the same runoff discharge. And time sediment reached its peak value decreased with the increase of runoff discharge.(3) The relationship between the erosion rate of the slope-gully systems and the runoff energy consumption or the runoff power per unit width were all established as power function( y = ax~b, where a and b were constants; y was erosion rate of slope-gully systems; x was runoff energy consumption or runoff power per unit width of slope-gully systems). What's more, the correlation between the erosion rate and runoff energy consumption was larger than that the erosion rate and the runoff power per unit width. The relationship between the erosion rate of the slope-gully systems and the runoff shear stress was established as linear function. Result demonstrated that in the process of erosion description with three parameters were in the order of runoff energy consumption > runoff power > runoff shear stress.(4) Reynolds number Re, Fuluode number Fr and velocity of runoff V, were all showed a distinct increscent tendency with the grassland coverage increasing from 30% to 50 %, but were all showed a distinct decreasing tendency with the grassland coverage increasing from 50% to 70 % under the same condition of scouring flow without reference to the grass location of slope and gully in the slope-gully systems. Re, Fr and V were all showd a fluctuant tendency with the time duration, and the change was not very clear under the same condition of scouring flow and grassland coverage. The values of three parameters of Re, Fr and V gradully augmented with the increase of the scouring flow under the same grass coverage. When grassland in gully, the three parameters of Re, Fr and V was slightly larger than that in slope.(5) The gross amount of runoff generation from the slope-gully becomes large with the increasing scouring flow under the same grass coverage without reference to the grass location of slope and gully in the slope-gully systems. The gross amount of runoff generation from the slope-gully shows different change characteristics with the difference of the grass coverage under the same scouring flow. When grassland was in the slope, the change law of the gross amount of runoff generation with different grass coverage was as follows: 0%>50%>30%>original state>70% under the condition of Q=14L/min, 50% >0%> original state > 30% > 70% under the condition of Q=18L/minor Q=22L/min. When grassland was in the gully, the change law of the gross amount of runoff generation was as follows: 0%>50%>30%>original state>70% under the condition of Q=14L/min, original state>70%>50%>30%>0%under the condition of Q=18L/minor Q=22L/min.(6) Sediment yield from the slope-gully systems varied a lot with with the changes of vegetation location. When the grass was located in the slope and the grassland coverage was same, the total sediment yield was showed several changing trendency as follows: 1) for the original state of grass coverage, the total sediment yield decreased firstly and then increased with the increase scouring flow; 2) for the 50 percent of grass coverage, the total sediment yield increased firstly and then decreased with the increase scouring flow; 3) for the other grass coverages, the total sediment yield increases with the increase scouring flow. When the grass was in the slope and the grassland coverage was same, the total sediment yield was showed several change trendency as follows: 1) for the 30 percent or 50 percent of the grass coverage, the total sediment yield decreased firstly and then increased with the increase scouring flow; 2) for the other grass coverages, the total sediment yield increased with the increase scouring flow.(7) Slope length and vegetation cover had deep effect on sediment yield. Results by runoff scouring indicated that sediment yield from long slope was larger than that from short slope. Under the same vegetation cover and same runoff discharge, sediment yield from long slope-gully system was more exquisite than that from short slope-gully system. That is to say, within the range of designed slope length and scouring discharge, sediment yield of slope-gully systems was more exquisite with the augmentation of slope length.(8) Under the same runoff discharge, soil erosion in the slope-gully systems increased firstly and then decreased with the increase of vegetation cover. When vegetation cover on the slope increased from 30% to 50%, sediment yield in the slope gully system increased, and then decreased when vegetation cover increased to 70%. Changes of runoff and sediment yield with vegetation cover on gully showed similar trendComparison of sediment yield with different vegetation cover location indicated that sediment reduction with vegetation cover at the bottom of the slope was much larger than that with vegetation cover at the bottom of the gully.(9) Reforming slopeland to terraced fields improved soil infiltration, reduced nutrient loss, and consequently improved land productivity. At the same time, terrace changed the slope gradient, reduced the runoff yield, and consequently reduced sediment yield and improved stability of slope-gully system.(10) Check dam was effective in reducing soil and water loss, resulted in increasing base flow and decrease in grain composition. Further analysis indicated that with the increase of alluvial height, stability of slope-gully system increased, and gravity erosion or potential was decreased too. That is to say, check dam can adjust and control gravity of slope-gully systems effectively.
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