Experimental Study On Erosion Dynamic Mechanism On The Field Slope In The Loessial Hilly-gully Region

Loess Plateau is one of the most severe soil and water loss regions in China and the world.With the implementation of ecological restoration since 2000,Vegetation restoration measures,such as sealing measures and soil and water conservation projects,have significantly improved the underlying surface conditions in the region,and the sediment transport of the Yellow River has decreased year by year.The measured sediment transport data at Tongguan Station shrank from an annual average of 1.59 billion tons in the early days of the founding of the people's Republic of China to an average of 210 million tons today,a drop of more than 80 percent.The underlying surface condition of vegetation in Huangqiu area has changed from single fragility to complexity and diversity,which has obviously improved the regional vegetation cover conditions and directly affected the regional water cycle intensity and process in the Yellow River Basin.It has significant effects on runoff,erosion and sediment yield and sediment transport in the region.Therefore,the effects of different underlying surface structures on soil and water loss,water and sediment control and their internal regulation mechanism are analyzed in order to scientifically evaluate the vegetation to slope surface.The regulation effect of small watershed and regional water and sediment and the deep understanding of the causes of sediment transport change in the Yellow River basin provide a theoretical basis.By selecting the typical area of the third subsidiary region in loess hilly and gully region,the field rainfall-runoff experimental area was constructed in Luoyugou watershed,Tianshui City,Gansu Province,and different vegetation cover structures were carried out in the field natural environment.Field artificial rainfall experiments with different vegetation cover modes were carried out to study the process of infiltration and runoff sediment production and the variation characteristics of hydrodynamic parameters of different vegetation cover structures and different vegetation cover modes under the action of various rainfall intensities.The response rules of different underlying structural slopes to rainfall,infiltration and runoff sediment production are expounded,and the effect of vegetation on runoff sediment production and its internal regulation mechanism are also revealed.The main results are as follows:(1)the order of influence of different vegetation cover structure on infiltration process is undergroundroot system layer > surface crust > vegetation canopy,and underground root system layer plays a leading role in enhancing soil infiltration.The infiltration capacity of slope surface with different vegetation allocation structure was as follows: shrub-grass mixture > undisturbed grassland > shrub land > bare land.(2)the runoff sediment production process of natural vegetation slope in the field is clarified.The initial time of runoff production was prolonged from single to complex,and shortened with the increase of rain intensity.In the vertical structure of vegetation cover,the surface crust has the best control effect on runoff and sediment production,and the contribution rate of runoff reduction and sediment reduction is43% and 67%,respectively.There was a power function relationship between accumulated runoff and sediment yield in root plot and bare plot.With the superposition of vegetation cover structure,there was a linear function trend between cumulative runoff and accumulated sediment yield.The multi-layer vegetation cover structure can prolong the development period of slope erosion process.Shorten the active period.(3)the runoff velocity on the slope is significantly affected by the vegetation cover structure.The logarithmic function can be used to describe the correlation between the runoff velocity and the vegetation biomass on the slope surface.The more complete the vegetation cover structure is,the better the steady flow effect of the slope surface is.The slope resistance coefficient is affected by vegetation biomass and rainfall intensity,but the effect of vegetation cover structure on resistance coefficient is more significant.(4)there are different critical velocity values of runoff velocity on different vegetation cover slope,the critical flow velocity value and erosion rate change logarithmic function,the larger the critical velocity value is,the stronger the erosion resistance ability of slope surface is,the higher the critical velocity value is,the better the erosion resistance ability is,the higher the critical velocity value is.The critical velocity of slope runoff is related to rainfall intensity and slope biomass,and the effect of vegetation biomass on the critical value of runoff velocity is more significant.(5)there is a logarithmic function relation between the erosion rate and the superposition resistance coefficient of the slope surface.The larger the resistance coefficient,the stronger the anti-erosion ability of the slope surface.The slope resistance coefficient is related to the vegetation cover structure,and the correlation between the resistance coefficient and vegetation biomass can be described by power function.