Influences Of Runoff Path Regulation Measurements On Slope Erosion Process In The Yellow Soil Area Of Eastern Sichuan

Runoff path regulation measures could cut off the slope rainfall runoff line,reduce the kinetic energy of runoff and sediment,and were of great significance for reducing soil erosion and improving water conservation.In this study,the yellow soil slope in the Tianchi Lake watershed in Huaying City,East Sichuan Province was used as the research object,and the method of long-term positioning and observation of runoff plots and artificial rainfall simulation test were used to study the influence of runoff path regulation on the slope erosion process under rainfall conditions.The research results were expected to provide technical support for regional soil erosion control and plantation management.The main conclusions were as follows:（1）From May to October 2019,the 63 natural rainfall data were observed and collected,which showed that the rainfall was mainly concentrated in June,July and August,and the total rainfall in the three months accounted for 62.38%of the rainfall in the entire observation period..Natural rainfall was dominated by medium and small rains,accounting for 76.19%of the total rainfall events.Although there were few events such as heavy rains and torrential rains,the cumulative rainfall accounted for as high as 67.0%.The erosive rainfall index of the yellow soil slope in the study area was drawn as a rainfall standard of 12.0 mm and an I₃₀standard of 10.65 mm/h.While the rainfall standard was considered,the I₃₀standard was preferred.（2）The location observation of runoff plots showed that runoff path regulation could effectively reduce runoff and sediment.Under medium and small rainfall conditions,both the slope runoff rate and the sediment yield rate increased and decreased synchronously with the rainfall intensity,and the peak runoff rate occured slightly later than the peak rainfall intensity.The runoff rate and sediment yield rate of the slopes of the runoff plots as a whole showed as No.1 plot（low vegetation coverage,no runoff path regulation measures）>No.4 plot（low vegetation coverage,runoff path regulation measures）>No.3 plot（high vegetation coverage,no runoff path regulation measures）>No.2 polt（high vegetation coverage,runoff path regulation measures）,indicating that runoff path regulation measures and vegetation cover had more significant effects on runoff and sediment reduction.Under typical natural rainstorm conditions,the average rain intensity during the rainfall process was larger,the initial runoff time on the slope became shorter,and the runoff was larger.At the beginning of rainfall,the runoff rate of each runoff plot was similar,and its change process was basically the same as the change process of rain intensity during the period,and it increased or decreased with the increase or decrease of rain intensity.During the process of sand production,the sand yield rate of No.2,3,and 4 plots changed significantly less than the change of rain intensity.There was a positive correlation between the runoff yield rate and the sediment yield rate of each runoff plot,and the correlation coefficient was significantly smaller than that under small and medium rainfall conditions due to the influence of the underlying surface（slope,vegetation,runoff path,etc.）.（3）Artificial rainfall simulation experiments showed that runoff path regulation measures R1（sparse diamond grid）and R2（dense diamond grid）had a greater impact on the process of runoff and sediment generation on slopes,but different rainfall intensities（60,90,120 mm/h）and slope（25°,30°,35°）conditions were different.The initial runoff time was within the range of 36 to 145 seconds.The initial runoff time of the slope controlled by the runoff path was significantly increased,and the runoff time was delayed by about 2 to 3 minutes.The order of the initial runoff production time of the two treatments and the control group was R0（control slope）<R1<R2 under the rainfall intensity of 60mm/h and 90 mm/h,when the rainfall intensity increased to 120 mm/h the order was R0<R2<R1.The runoff rate increased rapidly at first and then tended to be stable during the process of runoff production,the sediment yield rate decreased with the increase of runoff time.When the slope gradient was small（25°）or the rainfall intensity was small（60 mm/h）,the order of the average runoff and sediment yield rate of slope was R0>R1>R2.When the slope gradient increases to 35°and the rainfall intensity increases to 120mm/h,the runoff and sediment yield rate of R1 and R2 slope was close to or even slightly higher than that of R0 slope.It showed that the flow reduction and sediment reduction effect of the runoff path strength control measures decreaseed with the increase of slope and rainfall intensity.In comparison,the R2 slopes under the conditions of 60 mm/h and 25°had the highest flow and sediment reduction benefits,reaching 17.25%and 21.34%respectively.For R1 and R2 slopes in different combinations of slope and rainfall intensity,the cumulative sediment yield and cumulative runoff were all in a power function relationship.Generally,the benefits of sediment reduction were greater than the benefits of flow reduction,and the performance of this benefit was R2>R1,and both decreased with the increase of rain intensity and slope.In short,the runoff path regulation measures could effectively extend the initial runoff time,reduce the flow and sediment yield,but with the increase of slope and rainfall intensity,this benefit would gradually decrease until it disappeared（35°and 120 mm/h）.Therefore,runoff control measures could effectively improve water conservation and soil and water conservation functions in steep slope areas,but should not be used in the prevention and control of extremely steep slopes and debris flows.