Study On Erosion Dynamics Process In Slope-gully System Under Different Vegetation Patterns

The Loess Plateau is one of the most serious eroded areas in the world.The fragile ecological environment led to a decline in regional land productivity,which restricted the local agricultural economy and people’s living standards.In the ecological context of returning farmland to forest and grass,vegetation cover and its pattern are important for intercepting sediment and reducing the erosion energy generated by runoff.The slope-gully system is between the slope scale and watershed scale,and is the main source of erosion and sand production in small watersheds.In this study,the runoff plot was constructed in the field environment and the flushing test was adopted.The spatial and temporal characteristics of erosion process,hydrodynamic parameters and erosion energy parameters in slope-gully system under different vegetation patterns(upper slope,middle slope,lower slope,bare slope)were analyzed.Furthermore,the response relationship between erosion dynamic parameters and sediment production and loss were explored.The results can provide theoretical support for optimizing vegetation allocation and formulating scientific for the control measures of soil and water loss in the Loess Plateau.The main conclusions are as follows:(1)The characteristics of runoff and sediment yield in slope-gully system under different vegetation patterns were analyzed.Different vegetation patterns have significant effects(p<0.05)on the initial runoff time,cumulative runoff and cumulative sediment yield of the slope-gully system.The larger the scouring flow of the slopegully system,the shorter the initial runoff time.The initial runoff time of the slopegully system decreases with increasing flow rate.The bare slope has the shortest initial flow generation time under different scouring flows.The sediment reduction benefit of the slope-gully system under different vegetation patterns is better than the water storage benefit.At low scouring flow,the water storage benefit is the best when the vegetation is arranged on the upper part of the slope,reaching 45.79%.At high scouring flow,the water storage benefit is the best when the vegetation is arranged on the lower part of the slope,up to 37.28%.The sediment reduction benefits of different vegetation patterns at different flow rates are arranged as follows: lower slope> middle slope>upper slope.The placement of vegetation in the lower part of the slope exhibits the best interception effect on sediment,up to 89.28% and 74.86%.There was a positive linear correlation between cumulative runoff and sediment yield in the slope-gully system with different vegetation patterns.(2)The spatial and temporal variation of hydrodynamic parameters of slope-gully system under different vegetation patterns were analyzed.At a scouring flow rate of6L/min,all vegetated runoff except the bare slope exhibited laminar flow,while at a scouring flow rate of 12L/min,the runoff pattern of slope-gully system under different vegetation patterns belonged to turbulent flow.The erosion flow is proportional to the runoff velocity.The decrease of runoff velocity in slope-gully system under different vegetation patterns is arranged as follows: middle slope > lower slope > upper slope.The resistance coefficients of runoff plots with vegetation are 1.64-2.15 times and 1.07-1.53 times that of bare slopes under different scouring discharges.(3)The spatial and temporal variation of erosion energy parameters of slope-gully system under different vegetation patterns were examined.The runoff shear force and runoff power of the slope-gully system under different flow and different vegetation patterns fluctuated with increased scouring time and were lowest at the section with vegetation distribution.The decrease of runoff shear force and runoff power at different flow rates were as follows: lower slope > middle slope > upper slope.When vegetation was distributed in the lower part of the slope,the reduction of runoff shear force can reach up to 54.11%-60.13%,and the reduction of runoff power can reach up to 65.15%-75.15%.Vegetation distribution in the middle of the slope has the most significant effect on reducing the unit runoff power at different flow.(4)Different dynamic parameters of erosion have a functional relationship with runoff and sediment yield.The function fitting effect of erosion dynamic parameters and runoff is as follows: runoff power > runoff shear force> Reynolds number> runoff resistance> runoff resistance> Froude number> runoff velocity = unit runoff power.The fitting effect of erosion dynamic parameters and sediment yield is ranked as follows:runoff power > runoff shear force > resistance coefficient > Reynolds number > runoff velocity = unit runoff power > Froude number.The runoff power and the runoff shear force are effective in describing the erosion and sediment production of slope-gully system(5)Planting vegetation on the lower part of the slope can effectively reduce the sediment generation and energy generated during runoff movement in the slope-gully system.Due to the fragile ecological environment of the Loess Plateau and its limited rainfall resources and vegetation restoration capacity,it is recommended to prioritize planting vegetation in the lower part of the slope-gully system to alleviate soil erosion.