| “Liang-mao slope system in the Loess Hilly Region”whose production and sand production has a direct and significant impact on the slope erosion and the channel erosion below the margin line is the origination of headwater erosion and water flow.The description of the spatiotemporal process of erosion evolution of this special section has not been reported in detail.In view of the above problems,this research uses advanced research techniques-three-dimensional reconstruction technology and intermittent artificial rainfall simulation combining with soil erosion,hydraulics as well as the theory of river sediment transport to express the various erosion processes in the complex soil erosion process chain in an eye-catching graphical form.Evolving morphological parameters are used to elucidate their evolutionary rules and specific characteristics quantitatively.The relationship between the output of corroded material and the amount of morphological change was expounded objectively.The spatial and temporal distribution of the hydrodynamic characteristics of the slope surface was elucidated using the erosion energy and erosion dynamic parameters.The study not only can deepen people’s understanding of the qualitative and quantitative process of soil erosion development,but also has profound academic value and practical guidance value for innovative erosion process research methods and guiding slope and gully treatment guidelines.（1）The evolution process of rill erosion on the loess slope mainly goes through four stages:（1）The evolution stage from sheet erosion to rill erosion,which is often at a distance at the top of the slope has a series of eroded pits which have the shape of beadlike and nearly equal spacing at different distances.The width of eroded pits is about 59cm,the average is about 7cm.The depth is about 14cm with an average of 2.1cm.（2）The rill erosion development stage:the micro rills produced by surface erosion continuously increase in length,width and depth under runoff;（3）The rill network Stage:Bifurcating and merging of rills gradually forms rill network;（4）Undercutting of rills and widening of the trench walls causes rill network developing in length and depth.（2）In this study,the characteristics of fractal rill network development were quantified using the fractal dimension,rill density,degree of rill dissection,and rill bifurcation rate.With the prolongation of the rainfall,the erosion parameters all showed an increasing trend.The rill network developed significantly and showed a development process from the small to the large and from the simple to the complex.By referring to the morphological types of the river system,the loess slope rill network is mainly dendritic.In addition,there are certain differences in the development of rills at different slope locations,and the development of rills is the most intense in the mid-slope of the slope.（3）To obtain the eroded amount through the value of DEM before and after the rainfall runoff erosion process,and then compare it with the actual subsurface rainfall erosion amount.Evaluate the accuracy of the method to obtain the amount of erosion.The calculation shows that the error between the calculated erosion amount and the actual sediment production amount is only 20%at the first test,and the results of other tests fluctuate around10%.Therefore,the technology is eligible enough to be applied for this study.（4）The flow and sediment content increase gradually in the course of the rainfall;Runoff,sediment yield during experiments measured in the slope system were analyzed and found that cumulative runoff,cumulative sediment yield and rainfall duration showed a very significant power relationship;At different stages of the erosion process,the contribution rates of erosion in the surface and rill are different.In the initial stages of the experiment,slope erosion is dominant,and in the middle and later stages,rill erosion is the dominant.Throughout the entire rainfall process,the spatial distribution of the slope erosion is uneven,the erosion in the middle of the slope is the highest,and next is the bottom part of the slope;There is a significant linear correlation between rill erosion rate and fractal dimension,rill density,degreeof rill dissection,and rill bifurcation rate,correlation coefficient are 0.978,0.989,0.980 and 0.916,respectively.Rill density is the optimal descriptive parameter of erosion rate.（5）The change of flow rates at each section in variable slope system as rainfall show the following characteristics:Vbottom rill>Vmiddle rill>Vbottom slope>Vmiddle slope>Vtop slope.The Reynolds number varies from 1489 to 3192 in the mid-slope rill,and the Reynolds number varies from 1639 to 7626 in the rills on the downslope.The flow is turbulent and the turbulence on the bottom section is more severe than middle.The Froude number of the surface runoff of different rainfall events is greater than 1 and there is a trend of gradual increase with the rainfall duration,which means that the flow belongs to the state of rapid flow.The change of the flow resistance coefficient is obviously reduced.The flow shear force,flow power in the mid-slope increase more rapidly than the down-slope section,and rise from35.2Pa、15.1N·m-1·s-1 to 71.3 Pa、45.6 N·m-1·s-1 respectively as rainfall of 180mm.The water flow power can better predict the slope erosion compared with the shear stress of water flow. |
