| As a typical and ubiquitous mountain disaster in the nature, soil erosion was regarded as a keystone in the research fieldes of resource and environment now. Based on the Wushui watershed of Hunan province which was taken as a typical example in granite region in the south of Yangtse rive, the law of red soil erosion and runoff & sediment transport were researched on natural sloping plot scale and small watershed scale and middling watershed scale. The coupling relationship among landuse change and runoff and sediment transport were studied based on the landuse change of 30 years from 1978 to 2007. Basic property database were constructed by using ArcGIS, and the storm event distributed hydrological model (PRMS_Storm) with physical mechanism were also built up based on MMS ( Modular Modeling System) . And the model was used to simulate runoff and forecast sediment on Wushui watershed. The purpose of this paper was to provide theory and technique to build monitoring and quantitative evaluation system on the fieldes of soil erosion and sediment and environment, and to guide the ecological construction of soil and water conservation.Based on typical investigation and sampling, five typical landuse types were selected for search, and the differentiation law of physical and chemic property of soil and soil structure and their fractal dimensions were analyzed by the methods of statistical method, elasticity analysis, marginal yield analysis and the fractal theory. The results showed that the differentiation were distinct and influenced by land-use effectively. The fractal dimensions could be used to indicate the characters of soil structure and their stability. The soil structure and stability of woodland were improved, and man-made had made against of them. The results also showed the correlation between the fractal dimensions and indexes of physical and chemic property of soil were different.Sixteen indexes were chosen to analyze the anti-erodibility of different landuse types by the means of index synthesis, PCA and Hierarchical Cluster analysis. And the indexes could be divided into 4 categories, i.e. inorganic colloid, aggregate, water-stable aggregate, organic and micro-aggregate. As a result, the soil anti-erodibility of typical forestland was the best one, the second one was sparse woodland, the third one was dry land, the fouth was wilderness land and the worst was sloping farmland. The results showed these 4 landuse types except the forestland were the major landuse types of soil erosion and water loss under similar condition in watershed researched. Water erosion was the main erosion type in Wushui watershed researched, and gravity erosion such as collapse of mound erosion was also occurred in granite region partly. But the area of erosion was decreasing and erosion intensity was receded since 1978. The natural sloping plots of different land-use were taken as unit of soil erosion and based on observation of 19 single effective rainfall, the differentiation law of surface runoff and erosion under different land-use types were researched. The results indicated that the surface runoff of wilderness land and slope farmland and dry land and sparse-wood land were respectively 13.55,10.99,7.12 and 2.85 times as those of typical forest land. and for the soil erosion modulus, it were in ordere of bareness and wilderness land (7744.2t/km2) > sloping farmland (3826 t/km2) > dry land (942.2 t/km2) > sparse woodland (336.5 t/km2) > typical forestland (10.2 t/km2). The results showed that surface runoff could be store up and soil erosion could be decreased with the cover of vegetation effectually. It could be concluded that the bareness wilderness land and sloping farmland and dry land and sparse woodland were the major landuse types of water loss and soil erosion. Lastly, the multi-factor regression models of surface runoff and soil erosion sediment were built up under single rainfall on natural sloping plot scale by using software of SPSS.The laws of rainfall and runoff and sediment transport were studied on two different spatial scales such as small watershed and middling watershed. By using the fractal theory, the rainfall and runoff daily among same scale watershed and different spatial scale watershed were proved to have similar fraction characters, and the rainfall and runoff daily on watershed scale were also proved to have multi-fraction characters. The results showed that the fractal theory would be used as an available method to quote information and parameter under same scales and different scales, and it also could be used to scaling. Lastly, the multi-factor regression models of runoff and sediment on two spatial scales watershed were built up under single rainfall by using software of SPSS.The size distribution of suspended and bed load sediment and their fraction characters were analyzed on the sloping plot scale and middling watershed scale by using the fractal theory. On the sloping plot scale, the results showed that the differentiation of sediment by erosion under different land-use were distinct, the average d50 of suspended sediment were in order of bareness and wilderness land < sloping farmland < dry land < sparse woodland < typical forestland, and the content of exiguous grain (<0.005mm) were in order of bareness and wilderness land > sloping farmland > dry land > typical forestland > sparse woodland. The maximum of grain size were in order of sloping farmland > dry land > bareness and wilderness land > sparse woodland > typical forestland. The reason could be concluded that the soil anti-erodibility of sloping farmland and dry land were decreased and the component of surface soil grain would be increased gradually because of soil erosion. To the bed load sediment, the content of gruff grain of bareness and wilderness land was dominated, and the proportion of content of bed load sediment and suspended sediment of bareness and wilderness land was 9.42, sloping farmland was 3.61 and dry land was 2.9 correspondingly.On the middling watershed scale such as Wushui watershed, the proportion of size distribution of suspended sediment yearly of clay and silt soil and fine sand and coarse sand were 11%,51%,32% and 6%, the content of silt and small sand were dominated. Since 1981, the content of clay and silt of suspended sediment were decreased and the component of bigger grain was increased gradually. To the bed load sediment, the content of sand and gravel were dominated, the average d50 was 0.847mm. And the results showed that the size distribution of sediment on two different spatial scales was proved to have fraction characters.Then, the dynamic change of landuse and landscape pattern in Wushui watershed from 1978 to 2007 were researched by using ArcGIS and software of FRAGSTATS, and its driving factors including natural resource factors and eco-society factors were analyzed. The coupling relationship among landuse change and runoff and sediment transport of different years were studied, and the multi-factor regression coupling models were also constructed.Lastly, the basic property database of watershed was established by using ArcGIS, the storm event distributed hydrological model ( PRMS_Storm) of Wushui watershed with physical mechanism were built up based on MMS (Modular Modeling System). Then by validation and selection of parameters, the model was used to simulate runoff and forecast sediment on Wushui watershed under typical single rainfall. The average model-fit efficiency of runoff simulation was 0.719, and their percent of pass on forecast runoff peak was 75%. On the sediment transport simulate, the average model-fit efficiency was 0.664, the percent of pass on forecast quantity of sediment was 62.5%, and the percent of pass on forecast sediment peak was 75%. For different rainfall types, the model-fit efficiency of long-time single rainfall was higher than short-time single rainfall usually, and the model-fit efficiency of big rainstorm and rainstorm were higher than downfall and middle rain usually. And the model were simulated and forecasted runoff and sediment under two typical single rainfall in 2007, the results were attained the request of precision.
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