Research On Proportions Of Rill And Interrill Erosion From Loess Soil Slopes

The contribution of rill and inter rill erosion have been the difficult problems to slope soil erosion because of the limitations of traditional research methods. Therefore, using new methods and technologies in-depth study on this issue which can help us to get the contribution of rill and inter rill erosion exactly and analysis the variation is necessary. In addition, this can promote the development of the soil erosion theory, construction of soil erosion prediction model and evaluation the environmental effects of soil erosion(the source, estimation and evaluation of the agricultural non-point pollutions) what has an important scientific significance. The study was divided into two parts, indoor and outdoor rainfall simulation. Indoor rainfall simulation experiments were conducted in this study under different slope gradients(10°,15°,20°,25°) and different rainfall intensities(90 mm.h-1,120 mm.h-1). The rill development process, morphological characteristics and variations of rill and inter rill erosion rate were analyzed with the help of the 3D laser scanner. Outdoor rainfall simulation experiments were conducted under the slope length of 5 m and different slope gradients(10°,15°,20°,25°,30°).The 7Be tracer technology was used to calculate the inter rill erosion. While more in-depth study of the relationship between erosion rate variation and cumulative runoff or time was studied under rainfall events. The main research results are as follows: 1. The character of rill erosion on loess hillslopeRunoff generation time and rill occurrence time decreased with the increasing of rainfall intensity and slope degree. The runoff velocity increased with the enlargement of rainfall intensity and slope degree. With the increase of rainfall intensity, slope degree and slope length, erosion rate and runoff velocity increased significantly. The total erosion and runoff increased significantly with the increase of rainfall intensity. Under the slope length of 5 m, total erosion and runoff had no regulation with the increasing of slope degree. Under the slope length of 7 m, total erosion increased with the increasing of slope. The runoff had a runoff critical slope with the increasing of slope. Compared with the rainfall intensity, slope degree showed a larger impact on rill morphology features. When slope degrees are 10°or 15°, slopes influenced mainly by head-ward erosions and vertical erosions, and rills formulated by them have long, narrow and deep features under the slope length of 7 m. When slope degrees are 20°or 25°,slopes influenced mainly by side wall collapse then rills formulated have short, wide and shallow features. 2. The change of sediment particles under the process of the rainfallThe fractal dimension of soil particles was significantly positive correlated with clay and silt content of soil. There was significantly negative correlation between fractal dimension and sand content of soil. The fractal dimension decreased as rainfall intensity increased, and the effects of slope degree and length were not obvious. Under the condition of 5 m slope length, fractal dimension appeared the tendency of first lowering then raising with rainfall duration. Under the condition of 7 m slope length, fractal dimension increased as rainfall duration under 20° slope and 25° slope conditions, while there was no obvious changing regulation under 10° slope and 15° slope conditions. The fractal dimension after rill appeared was lower than that before rill appeared under the 10° slope condition, significantly higher than that before rill appeared under 15°, 20° and 25° conditions. 3. The variations of rill and inter rill erosion rateAs for indoor rainfall simulation, the difference between the test results and the expected of using REE tracer method to research the rill and interrill erosion rate, the specific reason still need further study; The outdoor rainfall simulation used 7Be tracer method to calculate accumulated inter rill erosion in the process of rainfall. It find that inter rill and rill erosion rate with rainfall is not increasing, but first increased, then decreased gradually at the critical point. Multiple regression method was used to fit relationships between erosion rate and slope gradient, rainfall intensity and runoff and we got two power function equations. The fitting equation of indoor and outdoor rainfall simulation were:,; Calculated by the equations of rill and inter rill erosion rate in the RUSLE model, the difference between the calculated values and the measured value was large, which indicating that the equations of rill and inter rill erosion rate in the RUSLE were not applicable to the Loess Plateau.