Response Of Runoff And Sediment Yield To The Cutting Intensity On Grain-for-Green Slopes

Up to now,the ecological engineering of Grain for Green has been implemented for 20 years in wind-water erosion crisscross region of the Loess Plateau,the vegetation coverage has been significantly improved,and soil erosion has been effectively controlled.In recent years,relevant studies have shown that the growth of vegetation communities has been inhibited,plant diversity has declined,grassland has gradually degraded,ecological service functions have declined because the fencing time is too long in some areas of the area.And due to excessive vegetation cover,the reduced watershed production and soil dry layer have occurred.Relevant research shows that the rational utilization of the vegetation on the slope can maintain the benign development of the ecosystem of the farmland.Combining this area is the main component of agro-pastoral transitional zone and traditional animal husbandry area,the reasonable cutting of vegetation will be an effective means of grassland utilization and management and give play to the ecological and economy benefits of vegetation.However,the primary problem in this area is soil erosion.Studying the characteristics of runoff and sediment yield on the slope and regulating mechanism of vegetation will be the scientific premise for rational utilization of vegetation.In this experiment,study the response characteristics of runoff and sediment yield process,the hydrodynamic characteristics,the regulating effect of vegetation to the cuttinging intensity under different rainfall intensities(60mm/h,90mm/h and 120mm/h)and slopes(10°,20° and 30°).The main conclusions are as follows:(1)About the effect of cutting intensity on the characteristics of runoff and sediment yield on slopes: The runoff rate and erosion rate of different cutting intensity can be demonstrated by the power function equation with the change of rainfall duration,and the demonstration is better under the condition of higher cutting intensity,and the coefficient of determination is higher.The power function relationship between cumulative production flow,cumulative sediment yield and rainfall duration was significant(P<0.05).The effects of rainfall intensity,slope,cutting intensity and interaction between rain intensity and cutting intensity on the runoff yield were significant(P<0.01).Among them,the contribution rate of rainfall intensity and cutting intensity to the change of runoff yield was43.50% and 37.20%,respectively.Under the same rainfall intensity and cutting intensity,the sediment yield of each slope is 20°>30°>10°,and there is a critical slopephenomenon.Rainfall intensity,slope,cutting intensity,interaction between rain intensity and slope,and interaction between rain intensity and cutting intensity all had significant effects on sediment yield on the slope(P<0.05).Among them,the contribution rates of cutting intensity,rainfall intensity and slope factor to the change of sediment yield on the slope were 33.61%,21.05% and 16.40%,respectively.The effect of cutting intensity on the change of runoff yield is slightly greater than the impact on the change of sediment yield.(2)About the effect of the cutting intensity on the hydrodynamic parameters of the slope: Under the same conditions,the average flow velocity is positively correlated with rainfall intensity and slope..Under the same rainfall intensity and slope condition,the average flow velocity increases with the increase of the cutting intensity,and the power function relationship with the rainfall duration is significant(P<0.05).Under the same slope and cutting intensity,the runoff depth,runoff shear stress and stream power increase with the increase of rainfall intensity.The variation of runoff depth and runoff shear stress with the cutting intensity varies with rainfall intensity and slope.Under the same rainfall intensity or slope condition,the resistance coefficient f and the Manning's roughness coefficient n both increase with the decrease of the cutting intensity.The contribution rates of rainfall intensity,slope and cutting intensity and their interactions to the variation of hydrodynamic parameters of each slope are different.(3)About the effect of cutting intensity on the response relationship between hydrodynamic parameters and runoff-sediment: The correlation between flow velocity,runoff depth,runoff shear stress and stream power and runoff yield is significant,and there is a good power function relationship between runoff depth,runoff shear stress and stream power and runoff yield.The correlation between the hydrodynamic parameters of each slope and the sediment yield varies with the conditions of vegetation cutting intensity.The relationship between the hydrodynamic factors and the sediment yield can be described by the power function relationship.The positive correlation between the yield per unit area and the sediment yield per unit area under different conditions was significant(P<0.01),and the linear regression relationship between the unit area flow rate and the sediment yield per unit area was satisfied.The coefficient of determination is 0.704.(4)About the influence of cutting intensity on the regulation effect of vegetation:Under the condition of the same slope and rainfall intensity,the negative correlation between vegetation runoff reduction benefit and cutting intensity was significant(P<0.01),and the correlation coefficient was-0.732.Runoff reduction benefit under variouscutting strength conditions ranged from 13.93% to 79.55%.Under the condition of the same slope and cutting intensity,the negative correlation between runoff reduction benefit and rainfall intensity was significant(P<0.05),and the correlation coefficient was-0.380.Runoff reduction benefit under various rainfall intensity conditions ranged from 40.43% to 69.27%.The sediment reduction benefit can reach a higher level of more than 80% under each test treatment condition.The sediment reduction benefit showed a decreasing trend with the increase of rainfall intensity and cutting intensity.And the sediment reduction benefit under various slope is 10°>30°>20°.Under the condition of the same slope and rainfall intensity,the negative correlation between flow velocity reduction benefit and cutting intensity was significant(P<0.01),and the correlation coefficient was-0.873.The flow velocity reduction benefit under various rainfall intensity conditions ranged from 38.17% to 82.98%.