Experimental Study On The Runoff Erosion Process On Slope

Based on the theories such as hydrodynamics, soil erosion and rare-earth elements tracing technology, by using the runoff scouring experiments, the runoff erosion dynamic processes on loess slope of different slope gradients and runoff discharges were systematically studied in the paper. The temporal and spatial variations of the hydraulic characteristics of runoff including flow pattern, flow velocity, flow friction were detailedly observed and analyzed, too. In addition, the dynamic mechanism of runoff erosion on loess slope was analyzed by runoff shear stress theory, runoff energy consumption theory respectively. And the processes of runoff erosion of different sections on the slope were comprehensively studied. The main study contents and results were as follows:1) In the range of the experimental slope gradients and flow discharges, if the slope gradient was 15°,the flow velocities decreased with the increasing scour time, but if the slope gradient was more than or equal to 18°, the flow velocities dramatically fluctuated with the increase of the scour time. In addition, the variation of flow velocity at the upstream section of the slope was more intensive than that at the downstream section of the slope.2) In the range of the experimental slope gradients and flow discharges, the Reynolds number of runoff on the slope varied between 300 and 1000 in the erosion processes, which indicated that the flow patterns of the flow were closedly related with the experimental slope gradients and flow discharges. The results indicated that the Reynolds number of runoff on the slope increased parabolically both with the increasing experimental slope gradients and with flow discharges, and the critical slope gradient was about 24°and the critical flow discharge was between 7.5~8.5 l/min.3) Under the experiment conditions, the flow Froude numbers of the runoff scouring experiments were about between 1 and 14, which indicated that the flow pattern of runoff was supercritical flow. In addiction, the flow Froude numbers of runoff increased fluctuantedly with the slope gradient increasing and decreased with the increase of sour time. However, the effect of the flow discharges on the flow Froude numbers of the runoff was complicated. In other words, under the same slope gradient, the tendency that the flow Froude numbers of runoff increased with the flow discharges was weakened or even counteracted by the erosion resistance came from the slope surface.4) Under the experiment conditions, the Darcy-Weisbach friction increased parabolically with the increasing experimental slope gradients, and the critical slope gradient was about 24°. The effect of flowdischarges on the Darcy-Weisbach friction was unclear or little. In addition, under the same slope gradient, the Darcy-Weisbach friction increased with the increase of the sour time till it reached the biggest value and then decreased with the sour time increasing, which indicated the formation and development processes of the rills on the slopes.5) The study results indicated that the sediment yield, possessing one or two peak values, increased fluctuantely with scour time, and the runoff detachment rate on the slope of the loess soil ,which came from xi'an and with a bigger percent of fine particles, was more than that of the loutuo soil came from Yangling,Shannxi. In addition, the relationship between the detachment rate and runoff shear stress and runoff energy consumption was dotted and the corresponding regression equations was established separately. In comparison, the conclusion that the study on the soil erosion based on the runoff energy consumption theory has a better precision than other hydrodynamic parameters such as shear stress and so on was proposed in the paper.6) In the paper, the relative sediment yield from the different formation position of rill erosion on the slope, the formation and development processes of rill erosion and the variation of runoff sediment transport rate with scour time were studied systematically. The results showed that, under the runoff scouring experiment, the formation section on the slope of the rills was mainly at the top section of the slope with a length of two meters. The development process of runoff erosion on the slope could be explained as follows: firstly, the rill firstly formed at the top section of slope with a length of 0.5 meter. secondly, some small erosion holes formed stochastically at the downstream section of the slope. Then, with the development of the runoff headcut and downcut erosion, the small erosion holes linked together. Through the comprehensive analysis of the sediment yield from the different section along the slope in the same scour time, under the same slope gradients, the sediment yield from the different sections of the slope reached their biggest values when the experimental flow discharge was about 8.5 l/min. In addition, the runoff sediment transport rate increased with flow discharge increasing, however, the effect of the slope gradient on the runoff sediment transport rate was little.