Research Of The Soil Erosion Model Based On GIS: Case Of Wangjiagou Watershed In Western Shanxi Province

According to the spatial scale, almost all of the soil erosion models can be classified as field-scale models; catchment-scale models and region-scale models. Each type of erosion models has its instinctive characteristics. As to the field scale, the analysis of the erosion process on field vertical zones and the interaction between them is very important. In addition to the analysis of soil erosion on hill slopes, effects of runoff and sediment from hill slope on erosion and sediment yield of the followed gully zone and the erosion caused by gravitation are complex and pivotal in the catchments scale. In this scale, the sediment delivery is of significant importance to the erosion modeling. Establishing region scale erosion model, the relationship and the interaction of the subordinate drainages together with the style of the runoff yield and runoff concentration should be taken into account.On the base of reviewing the existing soil erosion and sediment yield models, according to field observation and artificial rainfall data in research region, we analyzed deeply and describe quantitatively factors, which had affected on soil erosion and sediment yield, such as the factor of the rainfall, physiognomy, coverage, cultivation, management, and soil, especially the factor of the special scale. Based on the soil erosion and sediment yield of the hill slop and gully in the Yangdaogou small basin, used the ERODE model as reference, taken small watershed as the basic analysis unit, the Wangjiagou watershed was divided as 40 plots of slope fields, 40 plots of gully fields and 40 basic units, constructed by the proper hillslop and gully, and one channel that used to delivery runoff and sediment. This model includes eight parameters of models, four modificatory coefficients and thirteen relevant equations. The model, based on certain physics process, was designed to estimate single storm responses in runoff and sediment yield. Using 22 natural rainfall data from 1963 to 1968 in Wangjiagou, a lager scale area compared with the Yangdaogou watershed, we tested the model; the prediction precision is above 55%, so this model had a certain practical value.The study indicated the following results:Firstly, We engaged the mathod of watershed divition that was always used in the field of hydrology to simulate the runoff and sediment yield in the lager area based on the laws in certain smaller watershed. Using the fractal theory and taking the fractal dimention that stand for the characteristic of area, one aspect of the physiognomy, we got some result from this method that reflect the influence of the spatial transfer on runoff andsediment yield. This study has some significance on the research of modeling the runoff and sediment yield concerned with the spatial scale transfer and this study can be taken as a valuable attempt on the theory, method and practice to predict the soil erosion in larger catchments based on the experiments and data in small-scale watershed.Secondly, as to model structure, we adopted the small watershed as the basic basin and the hillslop and gully as the subordinate unit, by analysis the relationship of the runoff and sediment between the upper filed and the down zones, then we have build the soil erosion and sediment yield models based on the watersheds and each single storm, which could reflect soil erosion and sediment yield rules of loess Plateau much better.Thirdly, as to research meaning, we made full use of the powerful capability of spatial analysis and data procession, extracted deeper information automatically from the digital elevation model (DEM), such as the mean slope, gully density, degree of cutting, watershed area and the proportion of gully to slope, then analized the interrelation of them, from withch some laws abstained.