| Runoff scouring experiments were conducted in simulated rainfall hall of Institute of Soil and Water Conservation to study the erosion process on loess slope of different slope gradients and runoff discharges. The hydraulic characteristics, such as flow velocity and flow friction, and soil erosion characteristics were studied. The dynamical mechanics of soil erosion on slope were analyzed by runoff shear stress theory, runoff energy consume theory and unit stream power theory. Some runoff scouring experiments were also conducted on field to study hydraulic characteristics and soil erosion characteristics of grassland. The following conclusions were obtained:1. Extremum phenomena existed in the process of hydrodynamic parameter and soil erosion changing with slope gradient, the critical slope gradient was about 21 ?.The changing tendency of the runoff Reynold's number , flow velocity ,runoffsediment concentration and sediment transport rate versus time was parabola curve in theexperiments, the critical slope gradient was about 21 ?.If slope gradient was lower than 21, these parameters increased with slope gradient increasing, when slope gradient washigher than 21 ?, the parameters decreased with slope gradient increasing.The average flow shear stress and the unit flow energy consume increased in the form of parabola curve with the increase of slope gradient and the maximum value obtained when the slope gradient reached 21".Darcy-Weisbach friction decreased with the increase of slope gradient at first and it reached the minimum value when slope gradient increased to 21?, then it appreciably increased with the increase of slope gradient.2. On the slope of the same gradient, soil erosion and hydrodynamic parameter increased slowly with the flow discharge.In the experiments, the runoff Reynold's number, Froude number, Darcy-Weisbach friction, flow shear stress, flow energy consume and the unit stream power all increased with the increasing of flow descarge. The flow velocity, sediment concentration and sediment transport rate had power relationship with the flow discharge.3. The relationships of the runoff hydrodynamic parameter with slope gradient and flow discharge were subsection power function.Because of the existence of critical slope gradient, the runoff Reynold's number, theflow velocity, the sediment concentration and the sediment transport rate had different formula with the slope gradient and the flow discharge in the different range of slope gradient. We can use subsection power formula to discribe their relationship.4. The relationships of runoff shear stress, the flow energy consume and the unit steam power with the sediment transport rate were found, and the critical dynamical condition of the soil erosion were studied.The occur of soil erosion on slope need certain critical dynamic condition, it had nearly relationship with the flow shear stress, unit flow energy consume and unit stream power. The relationship between the average flow transport rate and the average shear stress was linear. The soil anti-erodebility parameter of the experiments was 178.5g/Pa ?min and the critical shear stress was 0.54Pa.In the experiments, the relationship between the unit transport rate and the unit flow energy consume was linear. The soil anti-erodebility parameter of the experiments was 14.61g/J, the critical energy consume value was 0.37J/min ?cm.The relationship between the unit stream power and slope gradient was parabola and the unit stream power slowly increased with the increase of flow discharge. The unit steam power can be used to predict soil erosion on slope.5. Different part of herbage had different effect on soil erosion on the runoff scouring experiments, the sediment transport rate positive relationship with flow discharge and had negative relationship with vegetation cover degree.Different managements were conducted to study the hydrodynamic characteristics such as flow regime, flow velocity and Darcy-Weisbach friction of field veg... |
PDF Full Text Request