| Rill erosion is one of the most common and important erosion modes of slope farmland in the hilly region of central Sichuan.Runoff directly carries sediment in the whole erosion process,leading to the loss of erosion sediment particles,which makes the soil quality change.On the contrary,the soil particles"redistributed"can also reflect the degree of rill erosion.So in this paper,the purple soil in the central Sichuan hilly area was taken as the research object,laboratory scour experiment and laser diffraction technique were used to research the change characteristics of sediment particles,runoff and sediment yield in rill erosion under the conditions of different flow(4 L/min,6 L/min,8 L/min),slope(10°,15°,20°)and upper fill areas(0.15 m~2,0.3 m~2,0.45 m~2),further clarified the correlation between the two in the process of rill erosion.Finally,it is expected to provide some theoretical basis for rill erosion evaluation and model construction of purple soil slope.The main findings are as follows:(1)Under the conditions of different flow rates,slopes and upper fill areas,the enrichment rate of less than 0.002 mm in the eroded sediment particles was less than 1 at different time periods,and the aggregation rate was significantly less than 1.Under different flow conditions,the enrichment of sediment particles with>0.05 mm was different.Under the condition of 4 L/min flow,enrichment occurred at three different time periods of 0-8,15-30 and 40-60 min,and at 8 L/min,enrichment occurred at 0-8 and 15-30min.When the slope was 20°,the sediment particles of>0.05 mm were enriched in three periods(0-8 min,15-30 min and 40-60 min),15-30 and 40-60 min at 15°,and only 15-30min at 10°.When the upper fill area was 0.15 m~2,the erosion sediment particles of>0.05mm were enriched at 15-30 min.When the upper fill area was 0.30 m~2,they were enriched at 40-60 min,and when 0.45 m~2 it was occurred at 0-8 min.The accumulation of sediment particles of>0.05mm indicates that when the erosion process develops to a certain extent and the sediment carrying capacity of runoff is greater than the gravity effect of sediment itself,it would also be transported and migrated out of the slope.(2)The flow rate and slope had a significant positive effect on the yield of slope.The sediment yield was significantly affected by the slope.When the slope was 20°,the sediment yield rate was significantly higher than that under the other two slope conditions.In addition,during rill erosion,the runoff velocity was positively correlated with the flow rate and slope,and the smaller the flow and slope were,the larger the fluctuation range of the runoff velocity was.The production flow rate,sediment yield rate,sediment concentration and runoff velocity were negatively correlated with the upper fill area.(3)When the flow rate was 4 L/min and 8 L/min,the sediment particles of 0.002-0.05mm and>0.05 mm were significantly correlated with production flow rate,sediment yield rate,sediment concentration and runoff velocity(p<0.01),or significantly correlated(p<0.05).When the slope was 10°and 20°,the correlation between erosion sediment particles<0.002 mm,0.002 mm and>0.05 mm with production flow rate and runoff velocity did not reach a significant level(p>0.05),but the correlation was extremely significant at 15°(p<0.01).When the upper fill area was 0.45 m~2,the sediment particles<0.002 mm were positively correlated with production flow rate,sediment yield rate,sediment concentration and runoff velocity(p<0.05),while the erosion sediment particles<0.002 mm and>0.05 mm were significantly correlated with the four indexes(p<0.01). |
