| Study on the mechanisms of vegetation spatial configuration on erosion and sediment in the slope-gully system is a key basic scientific issue for understanding the mechanisms of erosion and sediment in the watershed and regulation the sediment source in the watershed-The slope-gully system is an important part in the watershed,its development process of water erosion is the core content of the dynamic mechanism of soil erosion,and it is also the key to water and soil erosion prevention in the watershed.With the continuous development of soil erosion research,the revelation of occurrence and development mechanism of water erosion process in the slope-gully system,the elucidation of regulation mechanism of the vegetation measures on water erosion process in the slope-gully system,the proposal of reasonable regulation methods,which become the focus of current soil erosion research.In this study,the unit slope-gully system was used as the object,using indoor runoff scouring experiments and intermittent simulated rainfall experiments,combined with three-dimensional laser scanning technology and microtopography analysis technology,it was studied the variation process of water erosion dynamics under different vegetation spatial configuration.It was analyzed the effect of vegetation patterns on the runoff and sediment in the slope-gully system from the perspective of hydrology,sediment and microtopography,clarified variation of sediment source under different vegetation pattern conditions,and revealed the erosion dynamics mechanism of vegetation and its spatial configuration in the slope-gully system,as wall as proposed optimal configuration of vegetation for regulation on runoff and sediment in the slope-gully system.The main results are as follows:(1)The study clarified the characteristics of erosion sediment transport processes and the dynamic variation process of hydrodynamic parameters in a slope-gully system with runoff scouring experiments.The results showed that the spatial variation of runoff veocity exhibited a fluctuating state,with runoff resistance.shear stress and runoff power decreasing then increasing with distance between the hydraulic section and the slope top under bare-slope conditions.The most serious erosion observed on the bare underlying surface was recorded on the upper part of the slope and gully.The average runoff velocity inside the gully was largely greater than that over the slope,while erosion power over the slope was generally higher than that in the gully.When the grass strip was planted at about 80%of the slope length,the impact on various hydrodynamic parameters is greatest,the average runoff velocity was at its lowest and decreased by about 22%;runoff resistance increased by 5 times to its largest value.The runoff shear stress and runoff power decreased by 90%and 92%,respectively,with both at their lowest levels,which made water storage function is 12%,sediment reduction function reach 69%.It could better exert soil and water conservation function by direct sediment interception,resulting in the lowest level of erosion in the experiment.(2)The study revealed the regulation mechanism of vegetation spatial configuration on the erosion sediment transport processes and the hydrological processes in a slope-gully system with runoff scouring experiments.The results showed that the runoff and sediment yield increased then decreased with distance between the hydraulic section and the slope top under different vegetation spatial configuration.This variation trend is basically consistent with the variation characteristics of hydrodynamic parameter.The regulation effect of vegetation on erosion sediment transport is achieved through the regulation on the process of water erosion dynamic.In the course of regulation,the vegetation spatial configuration altered spatiotemporal variation characteristics of each hydrodynamic parameter,and thus played a significant effect on hydrological processes.Reasonable vegetation spatial configuration can effectively weaken runoff erosion by increasing the underlying surface runoff resistance and reducing runoff velocity rely on the appropriate position,thus greatly decreasing runoff shear stress and eliminating the separation capacity of runoff scouring on the slope soil.Therefore,the use of grass strips could potentially weaken runoff power effectively and decrease the potential energy of runoff flowing along the slope,eliminating soil erosion to a great extent and thereby achieving better regulation of hydrological processes.(3)The study quantitatively clarified the evolutionary characteristics of erosion sediment and hydrodynamic parameters under vegetation spatial configuration in a slope-gully system with rainfall experiments.The results showed that some vegetation space configuration significantly(p<0.05)influenced both runoff and sediment yield in the slope-gully system.The regulation functions on runoff and sediment with the grass strip on the lower part of the slope were generally clearer than those with grass on the upper part;however,positioning the grass strip closer to the lowermost end of slope the grass strip did not clearly improve the water storage and sediment reduction functions.The optimal position for grass strips in the slope-gully system was identified as 60%of the slope length.In this location,the grass strips could effectively weaken the runoff erosion energy as limiting the acceleration space of runoff and erosion space of sediment,and effectively adjust the sediment concentration,thus further reduced the runoff detachment rate,and decreased average runoff velocity by 46%,with the runoff and sediment reduced by 7.35%and 62.93%,respectively.The water storage function of the grass strip was weak;however,its direct sediment interception function was more effective,the water and soil conservation function was optimal.(4)The study clarified variation regulation of sediment source under different vegetation spatial configuration in a slope-gully system.The results showed that the sediment yield ratio of slope to gully was 3:5 under bare-slope conditions,and erosion sediment yield in the gully region was the main erosion source in the whole slope-gully system,the erosion effect of runoff on the gully was stronger than that of the slope.The sediment yield ratio of slope to gully has changed to some extent under different vegetation spatial configuration,erosion sediment in the gully region was still the main erosion source,which reflected the statement of "water production on the slope and sediment production in the gully" on the Loess Plateau.The variation of sediment yield ratio of slope to gully reflected the variation in regulation scope and effect strength of vegetation spatial configuration.Under the bare slope condition,the sediment from the middle part to the lower part of the gully is the main source of erosion and sediment in the slope-gully system,and the erosion is the most serious in this area.When the grass strip was laid on the lower part of the slope and on the the middle lower part of the slope,such as in Patterns B and C,the whole gully and the middle lower part of the gully were respectively the main region of erosion and sediment in the slope-gully system,where the erosion development has alleviated.As the grass strip moved further to the middle part and middle upper part of slope,it could provide more acceleration space of runoff and erosion space of sediment,which has exceeded the critical value,the main source area of erosion and sediment also gradually moved up,which even extended from the lower part of the gully to the middle part of the slope,the range of eroson expansion,leading to erosion aggravation.Thus,the erosion sediment yield reached the peak within the test range.(5)The study revealed the regulation mechanism of vegetation spatial configuration on the erosion process and erosion pattern in the slope-gully system.The results showed that among many erosive dynamic influencing factors,runoff velocity and sediment concentration,i.e.,runoff shear stress and runoff sediment carrying capacity combined affected the processes of soil erosion and sediment transport in the slope-gully system.The runoff velocity dominated the erosion process.Vegetation spatial configuration controlled largely rill formation and development and density in the slope-gully system,especially on the gully,through their regulation on the runoff velocity and runoff sediment content.Moreover,the role of vegetation not only changed the rill erosion position and degree,more importantly,transformed the main erosion pattern from rill erosion into sheet erosion,and thus the regulation of vegetation on the processes of erosion and sediment transport was realized in the slope-gully system.(6)The study discriminated the soil and water conservation function,regulation efficiency,manner,scope and dynamic regulation approach on water and sediment under different vegetation patterns.The results showed that grass strips have a better direct sediment interception function than water storage function considering the relationship between water and sediment.However,considering the water erosion dynamics,the grass strip could respectively exert runoff retardation sediment interception function on runoff and sediment from up-slope and exert runoff detention elimination energy function on runoff and sediment in the lower part during water erosion dynamic process and erosion sediment process.The regulation scope and strength of the two functions on water erosion dynamics are closely related to the configuration mode.When a grass strip was planted in the middle lower upper part of the slope,it had both the best soil and water conservation effect of runoff retardation sediment interception function and runoff detention elimination energy function.The grass strip could effectively regulate the processes of soil erosion and sediment transport within the slope relying on retardation sediment interception function,and it could reduce greatly the erosion intensity within the range of the slope.Meanwhile,the grass strip could effectively inhibit and mitigate the growth and development of the runoff velocity and "peak discharge" within the gully relying on runoff detention elimination energy function,and it could greatly mitigate the erosion intensity,and thus greatly reduced the sediment yield within the range of the lower part of the slope and the gully.(7)The study proposed and determined the optimal vegetation pattern for regulation on the erosion at low vegetation coverage and revealed the regulation mechanism of vegetation spatial configuration on erosion and sediment in the slope-gully system.The results showed that the relationship between relative position indicator of vegetation and sediment yield met the second power function.The ratio of the distance from the top edge of the grass strip to the slope top to the distance from the bottom edge of the grass strip to the gully bottom is between 0.571-1.200,which is the optimal regulation scope of vegetation on erosion,i.e.,the optimal vegetation spatial configuration mode.When vegetation was planted in the area,it could effectively exert both the best soil and water conservation effect of runoff retardation sediment interception function and runoff detention elimination energy function,and the regulation scope could extend each section from the slope to gully to achieve better effect of erosion reduction.However,when vegetation was planted away from the area,it could not effectively exert soil and water conservation effect,as well as the regulation scope was limited,and thus may even aggravate erosion. |
PDF Full Text Request