Abstract:The flow patterns involved in rill erosion process on loess hillslope are studied by a multi-plot experiments under simulated rainfall with addition of steady in-flow through the tops of the plot. The results showed that: (1) The Reynolds number of rill flow, a judging index of flow pattern, changed under different rainfall intensities and slopes with a overall rise and finally a stabilized trend. A power function equation can be used to describe the two processes. (2) The average Reynolds number of slope rill flow increases with rainfall intensity and slope. Its relation to both rainfall intensity and slope can be described by a logarithmic equation; and to both of the two factors, by a dual power function equation. (3) The rill flow pattern is the laminar flow under different rainfall intensities and slopes. Only under the two of the largest rainfall intensities and slopes, rill flow may be in the transition region. (4) The average Reynolds number, a measure of fluid turbulence, varies between 327 and 457 and remains in the regime of normally considered laminar flow. The change of the Reynolds number, with the amount of the flow, is a significant positive linear correlation.

Abstract:The flow shear stress involved in rill erosion process on loess hillslope and its effect were studied by multi-plot experiments under simulated rainfall with addition of steady inflow through the tops of the plot.The results showed that:(1)The rill flow shear stress increased along with time under different rainfall intensities and the relationship could be described well with a linear equation.The rate of increase was a little less in 6 min after than before.(2)Under different slopes,it increased basically in the same trend and an equation of the straight line could be used to describe the change.The rate of increase appeared difference when runoff began after 12 min.(3)The shear stress of average slope rill flow increased with rainfall intencity and rapidly increased with slope. Its relation to rainfall intensity could be described by a logarithmic equation;to slope,by a power function equation;and to both of the two factors,by a dual power function equation.(4)Under different rainfall intensity and slope,the rill erosion rate increased along with the rill flow shear stress and the relationship could be described well with a linear equation.The shear stress of rill flow,that had significant erosion effect,was one of the important hydraulic parameters and hydrodynamic source of rill erosion.

Abstract:Flow velocity is one of the most basic and important hydraulic parameters. Clarifying the variation of rill flow velocity is of importance to reveal the mechanisms of dynamic rill erosion processes. Rill flow ve-locity on loess hillslope is studied through a multi-plot experiment under simulated rainfall with the addition of a steady in-flow at the top of the multi-plot system. The main findings are as follows:(1)Rill flow veloci-ties for different rainfall intensities decrease with runoff duration, which can be well described by an expo-nential equation.The decrements are great 6 min after runoff generation and then decline. The tendencies arebasically consistent for the decrements at different intensities. (2)Rill flow velocities for different slopes also decrease with runoff duration, which can be described by an exponential equation.The tendencies for the decrements on different slopes are consistent. The decrements are basically consistent during the whole run-off process. (3)The mean flow velocity increases with increased rainfall intensity, which can be well de-scribed by a logarithmic equation, and increases with increased slope steepness, which can be well described by apower equation. A dual logarithmic equation can be used to describe the variation of the mean flow ve-locity with rainfall intensity and slope