| Loess Plateau is one of the most serious areas suffering from soil erosion and the most fragile ecological environment area in China and in the world.Soil erosion not only caused the local ecological environment deterioration and declining agricultural productivity,but also blocked downstream rivers because of the large quantity of sediment deposition,which also have the serious impact on the Yellow River and ecological security.Slope-gully system is between slope scale and watershed scale,is important watershed on the Loess Plateau units,is the main source of the sediment of small watershed erosion,also is erosion control and restoration and reconstruction of ecological environment of the basic management unit.Therefore the research of laws of the slope-gully erosion and sediment yield always is an important research topic of Loess Plateau environmental remediation in theory and practice.In this experiment,the width,depth of erosion gully,the runoff velocity and the runoff and sediment yield in the sediment yield process of slope-gully system with three kinds of 45mm/h,85mm/h and 120mm/h was measured,disposed and analysed,which based on the modeling of artificial rainfall hall and the existing ditch system model of Key Laboratory of soil and water loss process and control on the Loess Plateau,Ministry of Water Resources.The temporal and spatial distribution of soil erosion and sediment yield in the slope gully system and the relationship between the spatial and temporal distribution of the runoff and the mechanical parameters of the runoff are discussed.According to the experimental study,the following main results are obtained:(1)In the past,the study on the slope gully system is rarely used to analyze the performance characteristics of hydraulic parameters on the spatial and temporal scales.The correlation analysis between the spatial distribution of erosion and sediment yield are rarer,which is not enough to reveal the real reason for the spatial and temporal variation of sediment yield in the slope gully system.So this research is innovative in the experimental content.(2)When the rainfall intensity is same,the runoff and sediment yield of slope gully erosion isincreasing with the increase of rainfall duration.And the rainfall intensity is bigger,the trend of cumulative runoff and sediment yield increased with the increase of rainfall duration is more obvious.When the rainfall intensity is different,the cumulative runoff of slope-gully would increase with the increase of rainfall intensity,but this speed would not increase indefinitely,but would gradually weaken after the rainfall reaches a certain degree.(3)Under the same rainfall intensity,the greater the rainfall intensity,the greater the Reynolds number.When the rainfall intensity is same,the Reynolds number of slope in the course of slope gully erosion showed a tendency to increase first and then tended to be stable with the increase of rainfall duration.The Reynolds number is an important basis for judging the flow regime.When the runoff is in the laminar flow state,the runoff sediment growth rate is slow.When the runoff is in turbulent flow,the rate of runoff sediment is growing rapidly.From the point of view of space,when the rainfall intensity is same,the Reynolds numbers and runoff sediment ratio reached the maximum value at the turning point of slope and gully slope,and tends to be stable along the slope.(4)From big to small the Froude number under different rainfall intensities are 45mm/h,120mm/h,85mm/h.Thus,with the increase of rainfall intensity,the changes of Froude number is more complex.When the rainfall intensity is same,Froude number showed a trend first increased and then decreased gradually with the increase of rainfall duration.Froude number is an important basis for judging the rapid.In a state of slow runoff,the runoff sediment growth rate is slow.In a state of rapid runoff,the rate of runoff sediment is growing rapidly.From the point of view of space,when the rainfall intensity is same,Froude number showed a gradually increasing trend along the slope firstly,then turn down quickly at the turning point of slope and gully slope,after the emergence of a minimum value began to gradually increase finally.(5)When the rainfall intensity is different,the rainfall intensity is bigger,the Darcy-weisbach number is smaller.When the rainfall intensity is same,with the increase of rainfall duration,the Darcy-weisbach number increases first and then decreases,and finally tends to be stable.Runoff is bound to be affected by resistance in the process of flowing along the slope,and the size of runoff is related to the effective erosion of runoff to the soil.The rate of runoff sediment was relatively stable when the Darcy-weisbach number increased.And the rate of runoff sediment increased gradually when the Darcy-weisbach number decreased.From the point of view of space,when the rainfall intensity is same,the Darcy-weisbach number of gully is smaller than that of slope.From the point of view of gully-slope system. |
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