Influence Mechanism Of Rock Fragment Distribution On Erosion And Sediment Yield Of Red Soil Slope

Red soil is an important soil resource in southern China.It is widely distributed in the terraces and hills of the provinces south of the Yangtze River.It is an important agricultural production base in China.Gravel are often presented in soils owing to the factors of soil genesis,soil erosion,and human activity and appeared in two ways: covering the topsoil and mixing with the soil.The present of gravel changes soil physical and chemical properties.Consequently,surface hydrological process and soil erosion processes.Most of the previous studies on soil erosion processes have removed gravels,which leads to less understanding of the erosion process of gravel-bearing soil.Whether the results have guiding significance is worthy of further study.his paper takes the representative red soil of sloping farmland in the hilly area of South China as the research object,and selects two modes of gravel covering soil surface and soil and stone mixing.Through indoor artificial simulated rainfall test,the effects of different positions of the same gravel on the erosion process of red soil slope under different rainfall intensity(60mm/h and 90mm/h)were studied.The rock fragment covered slopes are recorded as RC0,RC10,RC30,RC50;the soil and rock mixed slopes are recorded as RM0,RM10,RM30,RM50,The main conclusions are as follows:(1)Gravel cover can delay the time of surface runoff,and the mixing of gravel and soil can reduce the initial runoff time.Compared with gravel-covered slopes,soil-rock mixed slopes are more prone to runoff.The runoff rate of the two gravel distribution slopes is larger than the slope without gravels.The stable runoff rate of gravel-covered slope is slightly larger than that of soil-rock mixed slope.(2)Under the same rainfall intensity,the sediment concentration and sediment yield of the two gravel distribution slopes are larger than slopes without gravel.The cumulative sediment yield of gravel-covered slope with the change of gravel coverage is RC10> RC30> RC50> slopes without gravel.With the increase of rainfall intensity,sediment yield increases.(3)Both gravel distribution patterns reduce soil infiltration rates,As the amount of gravel increases,the stable infiltration rate of the soil decreases.Under the same conditions of gravel,the stable infiltration rate of gravel-covered slope is slightly smaller than the stable infiltration rate of soil-rock mixed slope.By comparing the Philip model,the Horton model,and the Kostiakov model,The Horton model can better describe the infiltration process of soil with gravel.(4)Under the same rain intensity,the flow velocity,runoff depth,Reynolds number,flow shear stress and stream power increases with the increase of gravel amounts.whereas the Froude number,the Weisbach resistance coefficient and the Manning roughness coefficient had no significant changes.The runoff depth,Reynolds number,Froude number,flow shear stress and stream power of gravel-covered slope are greater than those of soil-rock mixed slope,whereas Weisbach resistance coefficient and the Manning roughness coefficient are smaller than those of soil-rock mixed slope.flow velocity,runoff depth,Reynolds number,flow shear stress and stream power increases and Froude number decreased with rain intensity increases,Weisbach resistance coefficient and the Manning roughness coefficient had no significant changes.In addition,the flow on the two gravel-distributed slopes belongs to laminar flow and slow flow.(5)When the gravel coverage is less than 10%,the soil crust strength of the slope surface is decreasing.When the gravel coverage is more than 10%,the soil crust strength of the slope is increasing.the soil crust strength increases with the increase of gravel amounts in the mixed slope.The crust strength of soil-rock mixed slope is greater than that of gravel covered slope,especially under heavy rain.(6)The clay on gravel-covered slope and soil-rock mixed slope are mainly transported by runoff in the form of aggregates.The silt are mainly transported by runoff in the form of single particle.There are many aggregates of fine particles in eroded sediment,which are similar to the size of sand particles.The clay,silt and sand on the two kinds of gravel distribution slopes all show clay enrichment,and the silt grains have not changed significantly,basically consistent with the original soil composition.In addition,with the increase of rainfall intensity,the enrichment rate of sand grains increases and that of clay grains decreases.