The Coupling Relationship Between The Sediment Yield From Rainfall Erosion And The Topographic Feature Of The Watershed

The small watershed is the basic unit of eco-environment reconstruction and comprehensive controlling of soil and water loss in our country. And it is the research hotspot as to the scientists of soil and water conservation that the law of soil erosion and sediment yield and the development trend prediction of soil and water loss of small watershed. The topographic feature is one of the main factors that influence the process of soil erosion and sediment yield of small watershed. The quantitative parameters of small watershed topographic feature are average watershed slope, average slope length, gully density and so on, which are based on the quantitative method of slope character and do not reflect the essential character of the small watershed topographic feature, which are complex. Based on the fractal character of the small watershed topographic feature, the spatial and temporal variation character of sediment yield of the watershed model, the dynamic developing process and fractal character of the topographic feature of the watershed model, and the coupling relationship between the sediment yield and the topographic feature of the watershed model are 'studied by simulate experiment, fractal theory, high precise photogrammetry and GIS technology. The validation research is conducted in Chabagou watershed where the observation data of rainfall, sediment and runoff for 11 years is collected. The study provides new theory and method for the topographic feature quantitative research in the prediction model of small watershed sediment yield. The following parts are the research results:The temporal variation character of sediment yields of the experimental watershed model. The average sediment transport ratio of every rainfall takes on obvious period character with the developing process of the experimental watershed model. Early developing period (from the first rainfall to the fifth rainfall), active developing period (from the 6th rainfall to the 18th rainfall) and stable developing period (from the 19th rainfall to the 25th rainfall) are defined. In .early developing period and the forepart of active developing period, the temporal variation of sediment concentration and sediment transport ratio of each rainfall can be expressed by power function. In the late part of the active developing period, the temporal variation of sediment concentration and sediment transport ratio of each rainfall can be expressed by exponent function and the variation presents quadratic polynomial function in the stable developing period.The spatial variation character of sediment yields with space of the experimental watershed model. The active position of soil erosion and sediment yield of the experimental watershed model changes from the downside to the upside with the developing process of the watershed model. In the early developing period and active developing period, the downside and middle part of the experimental watershed model are the active positions of soil erosion and sediment yield respectively, and the upside of the experimental watershedmodel in stable developing period of the watershed model. The main gully plays dominant role in the sediment yield process of the experimental watershed model. The proportion that the sediment yield of the main gully accounts for the total sediment yield of the experimental watershed model is from48.7% to 66.6%, and the proportion that deposition sediment yield of main gully accounts for the total deposition sediment yield of the experimental watershed model is from64.9% to 99.4%.The developing process of topographic feature of the experimental watershed model. Expanding the gully width and cutting down the gully bottom are the two chief forms of the topographic feature development. The gully width expanding is conducted mostly in active developing period. The proportion that the main gully area accounts for the total gully area is more than 60%. The gully bottom cutting down is acute in early developing period and the forepart of active developing period. The shape of...