Influence Of Surface Roughness On Hydraulic Characteristics Of Overland Flow

Overland flow is the key factor to the slope soil and soil parent materials be destroyed、eroded、transported and deposited. Research on the hydraulic characteristics of overland flow is the basis for the deeper study of the dynamic mechanism of soil erosion. The research of shallow flow by simulating of indoor experiments, is helpful to analysis deeply overland erosion and sediment yield process by the way of dynamics. This study selected several bed condition with different kinds of discharge q(0.04、0.08、0.12、0.16、0.2、0.24 L·s-1·m-1) 、slope gradient S(2°、4°、6°、8°、10°、12°) 、surface roughness d(smooth、0.5~1.25mm、1.25~2.5mm、2.5~5mm、5~10mm) and cover earth bed to analysed the variation of flow velocity(V) 、 runoff depth(h) 、 Reynolds number(Re) 、 Froude number(Fr) 、 resistance coefficient(f)、stream power()and soil detachment rate() with surface roughness、discharge and slope gradient. Main research results included:(1) Under the bed with artificial simulation of surface roughness(fixed bed), flow velocity and resistance coefficient could expressed by surface roughness individually with an exponential function( k).In addition, with the simulated surface roughness increasing, the resistance coefficient exponentially increased, but the average flow velocity exponentially decreased. Flow velocity、runoff depth、Froude number、resistance coefficient and stream power could expressed by surface roughness、discharge and slope gradient with a simple power function( k); Reynolds number could expressed by surface roughness and discharge with power function( k), besides slope gradient have nothing to do with Reynolds number. Furthermore, flow velocity、Reynolds number、Froude number and stream power are negative correlation with surface roughness; runoff depth and resistance coefficient are positive correlation with surface roughness. Resistance coefficient is negative correlation with discharge; the others are positive correlation with discharge. Runoff depth is negative correlation with slope gradient; the remaining parameters are positive correlation with slope gradient.(2) Under the flat bed which covered earth(movable bed), flow velocity、runoff depth、 Reynolds number、Froude number、resistance coefficient、stream power、soil detachment rate and the initial time of runoff could expressed by discharge and slope gradient with a simple power function( k); What’s more, resistance coefficient and the initial time of runoff are negative correlation with discharge and slope gradient, the remaining parameters are positive correlation with the two factors. The initial time of rill could expressed by discharge with a simple power function alone, and the initial time of rill increased with the increase of discharge, but the slope gradient have nothing to do with the initial time of rill. In addition, under the experimental condition, there is a monotonic positive association between soil detachment rate and stream power, this study concluded that the critical value of stream power is 0.03N/(m s), so we can through the stream power of overland flow to determine whether generate soil erosion or not.