Experimental Research On Dynamic Processes Of Soil Detachment On Loess HillSlope

Loess Plateau of China is one of the most serious soil erosion areas in the world. Thesevere soil erosion has not only resulted in serious impact on the ecological environment inthe local, but as well posed a great threat on the environment in the lower Yellow River. Rillerosion is one of the main soil erosion processes and the source of sediment yield in loess hillslope. However, Soil detachment capacity by rill flow is the important key parameter in rillerosion.So clarifying the dynamic process of soil detachment by rill flow in loess hill slopecould not only lay the solid foundation for revealing the mechanism of rill erosion andestablishing the process-based model of rill erosion on slope surface，but also it could provideimportant scientific basis for the control of soil and water loss on loess sloping surface,ecological construction and agricultural sustainable development.Based on the basis of analyzing the recent advances of soil detachment by slope runoffand field observation data about rill, with the flume test of rill, controlled sediment feedinghopper with flume test of rill and multi-plot-based experiments of simulated rainfall of theaddition of a steady in-flow at the top of the multi-plot system, the dynamic process of soildetachment by rill flow in loess hill slope, the variation characteristics of soil detachmentcapacity by rill flow in loess hill slope and the coupling relationships between soil detachmentcapacity by rill flow and hydrodynamic parameter were studied. Based on this analysis, theprocess-based model of rill erosion in loess hill slope was developed, and it could lay theimportant foundation for the establishment of the process-based model of soil erosion onslope surface. The main conclusions are as follows:1. Based on analyzing the variation characteristics of soil detachment capacity by rillflow in loess hill slope, the factor model of soil detachment capacity by rill flow wasestablished. Under different flow discharges, soil detachment capacity by rill flow increasedwith slope and they could be well described by linear functions. Under different slopes, soildetachment capacity by rill flow increased with flow discharge and they could be welldescribed by power functions. The factor model of relationship between soil detachmentcapacity by rill flow and the flow discharges and slopes is a binary power function.Flowdischarge has greater influence on soil detachment capacity by rill flow than slope. 2. Based on analyzing the coupling relationships between soil detachment capacity byrill flow and hydrodynamic parameters, the response characteristics between soil detachmentcapacity by rill flow and different hydrodynamic parameters were revealed. Soil detachmentcapacity by rill flow increased with velocity, shear stress, stream power, unit stream powerand unit energy under different flow discharges and slopes. Under different flow discharges,the response relation of soil detachment capacity by rill flow to velocity, stream power, unitstream power, unit energy could be well described by power function, while the responserelation of soil detachment capacity by rill flow to shear stress could be well described bylinear function. Under different slopes, the response relationship of soil detachment capacityby rill flow with velocity, shear stress, stream power or unit energy could be well describedby power function. The response relationship of soil detachment capacity by rill flow withunit stream power could be well described by linear function. Under different flow dischargesand slopes, the response relationship of soil detachment capacity by rill flow with velocityand unit energy could be well described by power function, and the response relationship withshear stress and unit stream power could be described by linear function, and the responserelationship with stream power could be well described by power function or linear function.3. Based on analyzing the hydrodynamic parameter correlated with soil detachmentcapacity by rill flow, the mechanism and dynamic model of soil detachment (soil detachmentcapacity) by rill flow was revealed and established. In the experiments, stream power is thebest hydrodynamic parameter to describe soil detachment (soil detachment capacity) by rillflow. The source of soil detachment (soil detachment capacity) by rill flow is the dynamicaction of the stream power. The dynamic model of soil detachment capacity by rill flow underthe conditions of this study is the linear function or the power function of the responserelationship between soil detachment capacity by rill flow and stream power. The simulationresults of the models are very close, so we can choose according the need.4. Based on analyzing the variations of rill erosion rate and its restriction and influencefactors, a process-based simulation equation of rill erosion was established. Rill erosion rate isrestricted and influenced by soil detachment capacity of rill flow, sediment transport capacityof rill flow and influx of sediment onto rill. The process-based simulation equation of rillerosion is the quaternary power combination equation of logarithm equation of the responserelation of rill erosion rate to soil detachment capacity of rill flow, sediment transport capacityof rill flow and influx of sediment onto rill. The model can predict the variation of the erosionrates by rill flow well in the experiments.