Riparian Slope Erosion Research Based On The Rainfall Simulation Experimen In Lower Yellow River

Soil erosion is becoming one of a serious ecological and environmental problem in China,which has resulted in a series of negative influences on environment,such as soil degradation,nutrients loss,river pollution,and severely affected the social and economic sustainable development.As the intersection of river and land,riparian zone is an important transition zone between the river ecosystem and the terrestrial ecosystem for material transfer,energy circulation and information exchange.The riparian zone is becoming a hotspot of research gradually in ecology and geography.But influenced by the interaction effect of human activities,the soil and water conservation function of the riparian zone is facing to serious degradation in recent years.The study on affecting of riparian vegetation of hillslope soil erosion processes in the riparian zone is an urgent demand to protect functions and resources.This study took the riparian zone of the Lower Yellow River as research site,and a method of field rainfall simulation was conducted to investigate soil erosion characteristics.The research of characteristics of spatial temporal differentiation of soil erosion on riparian zone of the Lower Yellow River is conducted clearly.The study evaluated the effects of erosive agents(rainfall)and soil surface conditions(slope gradient,vegetation coverage)on soil erosion processes,revealed the process of runoff and sediment producing and its hydrodynamic characteristics.Main conclusions of this study were as follows:(1)The runoff coefficient and erosion rate of riparian slope increased with the growth of rainfall intensity and slope gradients,while they decreased with the growth of vegetation coverages.(2)The soil erosion on the riparian slope of the study area was mainly composed of silt.The sand content in soil erosion of riparian slope increased with the growth of slope gradients,while silt decreased with the growth of slope gradients.There is no significant change in the particle size distribution of soil erosion with different vegetation coverages.The enrichment ratio of fine slit in soil erosion is >1 with different circumstances.(3)The contribution of rainfall intensity,slope gradient and vegetation coverage to soil erosion of riparian slope were 23.6%?7.62% and 45.98%.Based on the analysis of the erosion and sediment yield of different slope and vegetation coverage,when the slope was higher than 15 degrees,the slope sediment yield was affected by slope;when the slope was lower than 15 degrees,the slope sediment yield was affected by vegetation coverage.(4)The most treatments were shown erosion flow regimes usually indicated in sub-critical laminar flow.The flow hydraulics,such as Reynoldsnumber,Froude number,Manning roughness coefficient and Darcy-Weisbach can impacted by rainfall intensity,slope gradient and vegetation coverage,but cannot fitted by a simple function.But the Reynolds number presented significantly positive with rainfall intensity(p<0.01),and the Manning roughness coefficient and Darcy-Weisbach presented significantly positive with vegetation coverage(p<0.01).(5)The hydrodynamic characteristics,such as the flow shear stress,stream power and unit stream power of overland flow on riparian slope increased with the growth of rainfall intensity and slope gradient.The flow shear stress increased with the growth of vegetation coverages,while the stream power and unit stream power decreased with that.Moreover,the average sediment delivery showed a good linear relationship with both flow shear stress,stream power and unit stream power,and both of them had critical value throughout the whole soil erosion process.Stream power can be used to describe the dynamic process of slope erosion.