| Loess plateau soil erosion is the whole of China and the world's most serious soil erosion areas,erosion area accounts for more than 75% over all.Rill erosion of the loess slope is one of the main way of erosion,more than half of the total soil erosion area.Hydrodynamic condition and the bed surface soil conditions are two primary factors of rill erosion,the rill erosion and sediment yield ?vertical and horizontal cross-section shape development and runoff water kinetic parameters are complementary relationship.Systematic analysis of rill water dynamic characteristics and the amount of runoff and sediment yield and cross section morphological factors has a certain value to study the theory of rill erosion.In this article,through indoor scouring experiment,based on the area with abundant and coarse sediment in the middle reaches of the Yellow River in shan xi shen mu county loess and sand in the guan zhong plain yang ling local building two kinds of soil,Respectively studied The loess sand(slope: 3 °,9 °,15 °,traffic: 2.4,3.6,4.8,3.6,4.8 L/min)and building soil(grade 2 °,4 °,6 °,8 °,10 ° and 12 °,traffic: 8,16,24,32,40 L/min)under the condition of discharge and slope completely combination test,rill flow dynamics characteristics,the rill water runoff and sediment yield mechanism and morphology of groove profile and cross section.Mainly draws the following conclusion:(1)The average rill flow velocity,water depth is power function relationship with discharge and slope,compared with slope,the relationship between flow velocity and water depth with discharge is more significant,may be related to bed surface resistance constitutes.Froude number is roughly between 0.96 ~ 1.30,belongs to move flat bed bed surface form transition zone,through analysis and comparison,bed surface energy state is associated with soil clay content and median size.Scope of Reynolds number: 307~1465,rill flow state in the transition zone.Correlation between flow resistance coefficient of lambda and Reynolds number Re is not significant,which compared with rough turbulent flow in open channel flow resistance characteristics.(2)The transverse direction,cross-sectional width depth ratio decreases with the increase of slope,incised and headward erosion is mainly in the development of rill erosion,and collapsed wall erosion is weak.Cross sectional depth ratio and wide is far away from the best cross section of the wide depth ratio,the bed surface has not yet reached a stable state.Cross-sectional shape index eta increases along with the increase of the time of scour and slope,and gradually tend to hydraulic best trapezoid section is corresponding to the width depth ratio.And ? decrease with the increase of the distance from the top,with the increase of flow length,by the broad deep groove profile form gradually narrowed,and also reduce the rill erosion depth.Vertical and horizontal coefficient of surface form ? range of: 0.60 < ?< 11.26.? positively correlated with slope,little correlation with traffic.Roughness coefficient and energy dissipation are good power function relationship with ?.(3)With the increase of slope of section average flow velocity increase volatility.Cross section flow velocity and flow rate and fracture being extremely significant related to the level of 0.001 and correlation with slope.Slope sediment concentration and flow rate and power function description are available,and the relationship between slope and flow erosion and sediment yield were significantly related.Runoff shear stress and the effective stream power and the relationship between erosion and sediment yield amount respectively,the linear and power function form,the effective stream power can better describe the rill erosion and sediment yield.Carrying water saturation coefficient with the increase of slope and the flow,because of its high viscosity test soil,slope of soil transport contribution not as good as the role of the cohesive force of soil particles,carrying saturation coefficient with the slope increased gradually slow down. |
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