| Based on the analysis of forces acting on the sediment, and the data of both laboratory and field observation, the processes and features of sediment yield for three main types of soil erosion have been studied and explored. The applications of the theory and method of the cusp-catastrophe of nonlinear science for studying the processes of soil erosion in small watersheds have been discussed. The full text includes four parts are as follows:I The processes of erosion and sediment yield from the overland flowIn this part, the incipient motion characteristic and transport character of sediment on hillslope sediment have been studied from the angle of hydrodynamics. Several main problems such as the critical slope gradient, critical slope length, the stable width of rills, the rill erosion on hillslope, interrill erosion of soil erosion and so on in the research of soil erosion on hillslope have also been analyzed and studied.According to the character of overland flow and the incipient motion of the fine particle of sediments, the visous force has been taken into account for the studying of binding incipient motion of sediment on hillslope, in addition, the effects of exposure degree of sediment particle has been taken into account. By using the method of analysis of forces acting on a single particle of sediment on the hillslope, an equation to calculate the threshold velocity of the sediment on thehillslope is established by using the rolling mode for sediment particle resting on hillslopes. The sediment transport equation for rill erosion on the rillslope is also built by using the incipient velocity equation of overland flow and Meyer-Peter equation form for sediment transport rate, as well as taking the easiest incipient motion diameter of the sediment as the incipient motion diameter. In the calculating of soil erosion on hillslope for stable rill, the dso is taken as the representation diameter of sediment, the equation of sediment transport for rill erosion on hillslope has been obtained. The equation of critical length of rill erosion is produced by the overland flow velocity and incipient velocity equation of slope land sediment. The condition of form rill stable width is the rill flow velocity equal to the threshold velocity of the rill sediment, and the rill stable width equation is produced by the incipient velocity equation of rill sediments. Computational results show that the rill stable width is a function of slope gradient, and it has a critical slope gradient when the rill width increase to maximal value. The critical slope gradient is same as the critical slope gradient of rill erosion. The critical slope gradient has a critical diameter. It is 39.9 degree when the sediment diameter is 0.0185mm. The biggest critical slope gradient is 50.4 degree, and the critical diameter is 0.0198mm. The equations are tested by experiment data, and it shows that the calculated results agree wells with the experiments data.II The soil erosion and sediment yield from wind foerceIn this part, the incipient motion characteristic and transport character of wind sediment have been studied in dynamic method. The exposure degree conception that was used in the water flow was applied for the blown sand initiation, and the exposure degree was analyzed by a statistical method. The threshold wind velocity equation of the non-uniform sediment on plant land and slope land were established, and it was tested by the wind tunnel experiment data. The threshold wind velocity of different slope angle in same wind direction and same slope angle in different wind direction have been analyzed. An equation calculated wind direction was built. The erosion rate equation also is built by using the incipient velocity equation andHecun equation form. The equations are tested by experiment data, and it shows that the calculated results agree wells with the experiments data.Ill The erosion and sediment yield process from freeze-thaw and weatheringBased on the metrical data of freeze-thaw and weathering erosion o...
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