Effects Of Different Shrub-Grass Patterns On Soil Erosion Characteristics Under The Flow Driven In Pisha Sandstone Area

The soil erosion in the Pisha sandstone area is serious and the phenomenon of water and soil loss is intense.Therefore,the study of soil erosion and hydraulic erosion dynamic mechanism of different vegetation slopes has important guiding significance for the analysis of sediment production mechanism of slope erosion and establishment of slope hydraulic erosion model.Thus,in order to study the hydraulic parameters,soil erosion and Size selectivity of sediment characteristics and their interrelations of different vegetation patterns under the condition of flow driven,four Shrub grass patterns,i.e.no shrub?GL?,shrub in the upper part of slope?SU?,middle part of slope?SM?and lower part of slope?SL?,were selected as the research objects,and bare slope?BL?was selected as the control,reveal the characteristics and mechanism of soil erosion under different vegetation patterns in the pisha sandstone area,the results showed that:?1?The measures of shrub–grass are effective ways to reduce slope erosion and control flow and sediment.Runoff yeild rate,sediment yeild rate,runoff yeild and sediment yield of different vegetation patterns increase with the increase of flow scouring discharge.The sediment reduction benefit?SRB,67.18%,average,the below same as?of each shrub pattern is better than that runoff reduction benefit?RRB,49.61%?.Under different flow scouring discharge,there are same distribution characteristics of runoff and sediment reduction benefit in different shrub–grass patterns,and the relationship as all follows:pattern SL>pattern SM>pattern SU>pattern GL.Among them,the RRB and SRB of pattern SL reached 66.69%and 83.22%respectively,thus for this study area,the pattern SL is the best vegetation arrangement measure for reduce runoff and sediment yeild of slope.?2?The detachment degree of soil can be significantly reduced by shrub–grass measures.and the soil detachment rate of different shrub–grass patterns increased with the increase of flow scouring discharge.Under the 30 L/min flow scouring discharge,among them,the average soil detachment rate of different shrub–grass patterns is 0.286 g/m²·s,which is 2.08times of that under low flow scouring discharge?15 L/min?.The soil detachment rate of different shrub–grass patterns?i.e.pattern GL,SU,SM and SL?is 49.90%lower than pattern BL.The relationship of soil detachment rate in different patterns of shrub–grass decreased as follows:pattern BL>pattern GL>pattern SU>pattern SM>pattern SL.?3?The fractal dimension of soil particles is significantly different under the measures of shrub–grass.silt and sand are the main components of erosion sediment in the Pisha sandstone area.With the increase of scour time and flow scouring discharge,the sand content(?_sand)and Enrichment Rate(ER_sand)gradually increase,and the sediment show a trend of coarse graining,but there is no statistical significance between different patterns of shrub–grass.Under different flow scouring discharge,there are significant differences in the fractal parameters of sediment particles in different shrub–grass patterns.The average of the fractal dimension?D_??,capacity dimension?D₀?and information dimension?D₁?of the sediment particles are between 2.348².422,0.832⁰.903 and 0.739⁰.874,respectively.In addition,the avrage D_?of sediment particles in different shrub–grass patterns increased as follows:pattern GL<pattern SU<pattern SM<pattern SL as a whole,while the trend of D₀ and D₁ of sediment particles is opposite.?4?During the runoff process,vegetation measures can reduce the flow shear strees,flow stream power and flow unit stream power effectively.The relationship between the hydraulic parameters of runoff in different shrub–grass patterns is as follows:pattern BL>pattern GL>pattern SU>pattern SM>pattern SL.The flow shear stress,flow stream power and flow unit stream power in pattern BL are the highest,reaching 21.503 pa,4.760 w/m² and 0.046 m/s,respectively,compared with the pattern BL,pattern SL reduces 21.01%,50.18%and64.32%,respectively,which is the most effective vegetation pattern to weaken the runoff energy.?5?Hydraulic parameters are positively correlated with soil detachment rate and sediment particles D₀ and D₁,and negatively correlated with sediment particles Dv.Root mass density and sediment particle distribution are closely related to soil detachment rate.The relationship between hydrodynamic parameters,soil detachment rate and sediment fractal parameters is different.Among them,the linear equation or power equations of the hydraulic parameters are both highly efficient in describing the soil detachment rate,while the relationship between sediment fractal parameter and hydraulic parameters is more suitable to be described by exponential equation and logarithmic equation.flow stream power is the best hydraulic parameter to describe soil detachement rate and sediment size selectivity characteristics.The fitting equation between soil detachment rate,hydraulic parameters and sediment fractal parameters is Dr=0.026?^-3.284?^1.664 D_?^1.289 D₁^1.199,which can better simulate the characteristics of soil detachment on the slope surface of Pisha sandstone area.