| The high and steep slopes on Loess Plateau are important source areas of soil erosion and natural disasters such as landslides and debris flows on Loess Plateau.This study takes the high and steep slope system as the study object,through indoor simulated rainfall experments,to explore the temporal and spatial variation characteristics of runoff genenration and sediment yield,runoff hydraulic and erosion dynamic parameters and soil moisture content of the studied high and steep slope systems under different steep slope gradients and intermittent rainfall conditions.The main obtained results in the paper are as follows:(1)The runoff genenration and sediment yield characteristics of high and steep slope system under different steep slope gradients and intermittent rainfall conditions are clarified.The initial time for runoff generation of high and steep slope systems with different steep slope gradients was significantly shortened with the increase of slope gradient and number of rainfall event.The accumulated rainfall time for cracks appearing on the slopes of high and steep slope systems decreases with increasing steep slope gradient.The average water depth of gentle and steep slopes increases with the increase of number of rainfall event,and that on steep slopes decreases with increasing steep slope gradient.In addition to the occurrence of cracks,the variation curve of runoff generation rates of high and steep slope systems with different steep slope gradients showed a"rapidly rising-relatively stable" trend.In each field before the crack did not appear on the slope,after the production flow was stable,the production flow rate was 50°>55°>60°>70°>65°,when the cracks appear,the production flow shows a decreasing trend.The total amount of runoff decreases with the increase of steep slope,and increases with the increase of sessions.The steep slope and rainfall events have a greater impact on the sediment production process,and the regularity is not strong.The regularity of the total sediment yield changes with the slope and rainfall events is not obvious.(2)Clarified the spatio-temporal variation characteristics of hydraulic parameters of high and steep slope system and its correlation with runoff and sediment production on slopes.Under intermittent rainfall conditions,the slope velocity of the steep slope section of the high-steep slope system showed an overall increasing trend with the increase of rainfall times and slope The flow pattern of slope runoff is laminar,and the Reynolds number of runoff on steep slopes increases with the increase of rainfall,and decreases with the increase of steep slopes.The runoff flow pattern on the slope is the rapid flow as a whole,and the Froude number of the runoff on the steep slope increases with the increase of the slope,and fluctuates as the rainfall increases.The runoff resistance coefficient of steep slope section fluctuates with the increase of rainfall,but decreases with the increase of steep slope.Under intermittent rainfall,the correlation between slope runoff velocity and slope runoff is insignificant.Reynolds number and drag coefficient are significantly positively correlated with slope runoff,while Frud number and slope runoff are significant.There is a significant negative correlation between production flow.Under intermittent rainfall conditions,the runoff velocity,Reynolds number,Froude number,drag coefficient of slopes are not significantly correlated with the sediment yield of the high and steep slope system(3)The variation characteristics of erosion energy parameters of high and steep slope systems under different steep slope gradients and intermittent rainfall conditions are clarified The runoff shear force increases with the increase of the number of rainfall event,while the runoff power increases totally with the increase of steep slope gradient and number of rainfall event.The runoff energy consumption decreases with the increase of steep slope gradient,while increases firstly and then tends to relative stable with the increase of number of rainfall event At the confidence level of 0.01,the time interval producing runoff amount on slope of high and steep slope systems has a significant linear relationship between runoff shear force,runoff power and runoff ersion energy consumption respectively,while the significant correlation between the time interval slope sediment yield with the above erosion energy parameters do not exist respectively under under different steep slope gradients and intermittent rainfall conditions.(4)The characteristics of soil water content change in high and steep slope systems and the critical characteristics of soil water content when cracks appear.During the first rainfall period,the soil moisture content of the gentle slope section of each high-steep slope system is greater than that of the steep slope section,and the upper layer soil moisture content of the steep slope section satisfies the rule of:downhill>uphill>mid slope.The change curves of average infiltration rate of high and steep slope systems showed a decreasing firstly and then tended to be stable.When cracks appeared on the slope,the average infiltration rate showed an increasing trend,and the average value of average infiltration rate increased with the number of rainfall events.With the increase of steep slope,the amount of average infiltration rate meets the follow rank,i.e 50°>55°>65°>60°>70°.The soil water storage shows an increasing trend with the increase of cumulative rainfall time,in which the increase rate in the first rain is greater than that in other events.The soil water storage volume and cumulative infiltration volume of different steep slopes with high and steep slope systems are significantly correlated at the p=0.01 level.The position of cracks on the slope of the high-steep slope system with a steep slope of 70° is the gentle slope section of the high steep slope,and the position of cracks on the high-steep slope system of other slopes is the upper part of the steep slope section.When cracks occur in high and steep slope systems,the critical values of cumulative infiltration,cumulative rainfall,and water storage decrease with the increase of steep slope.Cumulative infiltration volume accounts for 42.3%to 51.1%of the cumulative rainfall.With the increase of steep slope gradient,it shows fluctuations and has small differences.The slope water storage volume accounts for the cumulative rainfall of 18.7%?41.1%,with the increase of steep slope,showing fluctuations.Cumulative infiltration and cumulative rainfall as a whole is significantly correlated linearly at the p=0.01 level. |
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