| The surface rock layer in the Karst Trough Valley area was exposed,and there were abundant underground fissures.The features of large rock inclination and the development of typical consequent/reverse slope geological structures in the area made the angle between the exposed rock and the slope different,converged the runoff into concentrated flow,made the way of runoff and sediment production and the surface runoff hydraulics characteristics special and resulted in severe soil erosion.In this study,the indoor experiments on the slope in the Karst Trough Valley area with scouring flow method were conducted,and then the hydrodynamics characteristics of concentrated flow and the features of runoff and sediment yield under different flow rates,slopes,angles between rocks and slope were measured based on the angle between the exposed surface rock and the slope,the characteristics of the topsoil and the environmental impact factors that measured in the field investigation.And we discussed the main hydrodynamic indicators that affect the soil erosion rate.This study revealed the change process of soil erosion on the slope surface under the condition of concentrated flow in karst Trough Valley area,which provided a theoretical basis for the establishment of soil erosion model in Karst Trough Valley area.The main results were as follows:(1)Under the condition of 10°slope and 5 L/min inflow,the surface runoff yield increased first and then stabilized with the erosion duration.Under other conditions,the surface runoff yield gradually decreased or increased first and then decreased.The order of surface runoff yield at different angles between rock and slope was:150°>90°>120°>30°>60°>180°.The underground runoff yield showed an increasing trend with scouring duration.It decreased with slope and increased with inflow.The surface-to-underground flow rate ratio gradually decreased with the erosion duration.It was greater than 1 at different angles between the rock and the slope.The sediment yield on the slope decreased with the erosion duration,and its order of magnitude was:150°>30°=120°>180°>90°>60°.Under test conditions,the surface sediment yield increased with increasing slope gradient and inflow.The sediment concentration changed decreased with the scouring time.The sequence of the sediment concentration of the angle between the rock and the slope was:180°>120°>30°>150°>60°=90°,when the rock tendency was consistent with the slope direction,the hydrodynamic indexes were larger.There was a very significant power function positive correlation between slope sediment yield and runoff yield.Among the angles formed by each rock and slope,relative to the included angles of 30°,90°,120°and 180°,the runoff yield at angles in 60°and 150°can predict sediment yield better.(2)Under the experimental conditions,the range of flow velocity was 0.168-0.462 m/s,and it decreased with the erosion duration.There was a significant linear negative correlation between the velocity and the angle between the rock and the slope.The flow velocity increased with the increase of the slope gradient and inflow.The influence of inflow on the velocity was greater than the slope gradient.The Reynolds number of water flow at different angles between rock and slope was significantly affected by slope,flow rate,and the angle between rock and slope.It showed an unspecific change trend with a range of 517.237-3343.686.The relationship between Re and angles between rock and slope was not significant.Fr varied in 0.491-1.157,it decreased with the duration of scouring.When the angle between the rock and the slope was greater than 60°,the Froude number decreased as the angle increased.Under each combination condition,the Darcy-Weisbach friction showed an increasing trend with the scouring duration,and it increased with the slope gradient and decreased with the increase of the inflow.The variation range was 0.617-5.704.The relationship between f and the angle between rock and slope was different for each combination of inflow and slope gradient.The coupling relationship between f and Re was significantly affected by the angle between rocks and slope and the Reynolds number.It was better to describe the f-Re relationship with logarithmic equation when the angle was less than 90°,while it was power function equation when the angle between the rock and slope was greater or equal to 90°.When Re<1791.928,the relationship between f and Re was not significant while f was positively correlated with Re when Re>1791.928 under the experimental condition.(3)With the scour duration going on,the soil erosion rate first decreased and then tended to be stable,the unit flow power gradually decreased,the flow power and the flow shear force fluctuated but the trend was not obvious,the unit energy of the flow cross-section gradually increased.Under the experimental conditions,the soil erosion rate,flow shear force,flow power and unit flow power increased with the change of slopes and discharges,while the unit energy of the flow cross-section increased with the increase of discharges,but the change was not obvious with the slopes.When the rock tendency was consistent with the slope direction,the various hydrodynamic indicators were larger.The relationship between soil erosion rate and flow shear force,flow power and unit flow power was better described by power function equation(R~2=583?0.603),while the relationship between soil erosion rate and unit energy of flow section was better described by linear equation(R~2=0.294).In contrast,it was better to use flow shear force to describe the soil erosion rate on the slope with different angles between rocks and slope in Karst Tough Valley area.(4)The angles between rocks and slope had a significant effect on Manning coefficient of concentrated flow in Karst Trough Valley area.In the process of the experiment,n first increased rapidly and then increased slowly or tended to be stable.The n decreased with the increase of discharge.Meanwhile,the average value of n was in the order:180°>150°>90°>120°>30°>60°.When the angle between rocks and slope was greater than 30°,n was related to h significantly while the relationship between n and h was poor when the angle between rocks and slope was 30°.The relationship between Reynolds number(Re)and n was not significant,while Froude number(Fr)had a significant negative power function correlation with n.The n/h increased first and then decreased with the angle between rocks and slope increased.When the angle between rocks and slope was greater than 30°,n/h and Re had negative correlation with power function;when the angle between rocks and slope was 30°,the relationship between n/h and Re was not significant.The relationship between n/h and Fr was not significant with angle between rocks and slope changed.n/h had a very significant linear negative correlation with the average flow velocity,a significant power function negative correlation with the flow power and a very significant power function negative correlation with the unit energy of the cross section.While the relationship between n/h and soil erosion rate,flow shear force and unit flow power was not significant. |
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