| Combined with runoff scouring method and REE (Rare Earth Element) tracing technology, experiments were conducted to study the critical problem in the water erosion process on the Loess Plateau. After the study and analysis of the flow regime, the rule of dynamics and the resistance variation, the relationship between runoff detachment rate and runoff energy consumption, critical hydrodynamic condition of rill erosion initiation and the soil anti-scouribility, the following conclusions were obtained: 1.Generally, the Reynolds number of the flow varies between the laminar and turbulent flow, which tends to be turbulent flow with large discharge of flow. Roughness coefficients in rills that are easily affected by the slope gradient, are closely related to Reynolds number. That is, the roughness coefficient decreased with the increase of Reynolds numbers on gentle slope and it increased with the increase of Reynolds on steep slope. Flow velocity showed a little increase after a decrease with experimental time length of scouring and the variation of soil-bed irregular in profile and cross section.2.Under the runoff scouring experimental condition, the process of sediment yield on the slope can be divided into the following three stages: interrill erosion stage, intensive rill erosion stage and rill erosion declining stage. The results indicated that under the different flow discharge and slope gradient, the ratio of the amount of sediment yield in the various period to the amount of total sediment yield augments at the beginning and decreases at last during the runoff scouring experiment. Under the same flow discharge, the maximum value of the ratio shows a tendency of appearing in advance with the slope gradient increasing. The intensive rill erosion stage accounts for the main sediment yield, which contribute 52-75% to the total sediment yield in the whole experiment.3.Under the runoff scouring condition, the spatial variation characteristics of the sediment yield on gentle slope (6°, 9°) isn't limited by the runoff process and time variation, and the relative erosion mass of the different section along the slope is similar. Generally, the erosion intensity of the middle section on slope is the minimum; the relative erosion mass at the bottom section of slope decreases with the increasing of the runoff discharge, while the relative erosion mass of the top section increases with the increasing of the runoff discharge. Experiment on the steeper slope (12°) with smaller flow discharge (for example S=12°Q=2.5l/min) indicated that the relative erosion mass of the different section along the slope is similar to that on the gentle slope. With the larger flow discharge, the relative erosion mass decreases with the length of slope increasing. The temporal variation of sediment yield on slope is that the relative erosion mass at the bottom section of the slope decreases with experimental time length of the experiment, while the relative erosion mass on other section increases fluctuantly. The ratio of the relative erosion mass at the bottom section to the total erosion in the initial period of experiment on the same slope gradient tends to decrease with the increasing of the flow discharge with different flow discharge.4. Specified experiments were conducted on the glass flume and the results showed that the runoff on the slope moves in the form of roll waves under the given experiment condition. The number of roll waves and the superposing of roll wave are heavily influenced by the discharge of flow. The larger of flow discharge, the more decrease of the number roll waves. The slope gradient has little effect on the superposing of roll waves down-slope.5.Based on the results of the roll waves studies, the new critical parameter for the rill erosion based on runoff energy consumption is proposed. The critical energy consumption for rill erosion under the given experimental condition is 7.3J. Thus, according to results in the experiment, a new index is put forward to determine the soil anti-scouribilit... |
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