The Erosion Reduction Effectand Mechanism Of Different Vegetation Allocation Patterns On The Slope Of Minedump

Due to its huge coal reserves,Shenfu Dongsheng Coalfield has become one of the seven largest coalfields in the world.Open-pit mining was the main mining method of Shendong Coalfield.A large amount of spoil ground slag generated during the mining process is piled up into a gangue field and a waste dump,more than a few hundred large and small waste dumps were scattered in the Jinshanmeng Mining Area.The slope of the waste dump was loose,and it is prone to severe soil erosion under climatic conditions such as heavy rain and strong winds.At present,vegetation measures have been widely used in the slope protection of waste dumps and land reclamation in mining areas.Many scholars have done a lot of studies on soil and water conservation on the slope of waste dump,however,the current control erosion benefits and erosion-preventing mechanisms of different vegetation allocation models on waste dump slopes are still unclear.Therefore,this paper taken the slope of open pit mine waste dump site as the research object,and used in-site scouring method.Based on Plot BS（Bare slope）as control,We studied the regulation of runoff and sediment of the waste dump slope,flow hydraulic characteristics of slope and erosion dynamic mechanism of 9 planting patterns（the ratio of the Agropyron planted on the upper slope and Artemisia desertorum on the lower slope was 3:7（CH7）;the ratio of the Agropyron planted on the upper slope and Artemisia desertorum on the lower slope was 7:3（CH3）;Agropyron planted on the whole slope（QC）;Agropyron mixed with Artemisia desertorum in plantation（CG）;the ratio of the no planted on the upper slope and Agropyron on the lower slope was1:3（LC）;Cynanchum chinense planted on the whole slope（ER）;the ratio of the Astragalus adsurgens planted on the upper slope and Agropyron on the lower slope was 1:3（SC）;Agriophyllum squarrosum mixed with Astragalus adsurgens in plantation（SS）;Astragalus adsurgens planted（SD）on the whole slope）.Explain the water reduction and sediment reduction benefits of different vegetation configurations on the slope and the contribution rate of runoff and sediment yield in each discharge stage,and analyze the differences of vegetation root system characteristics and their effects on runoff and sediment yield on different slopes.Revealing the anti-erosion mechanism of different vegetation allocation patterns on the slope of waste dump.The research results can provide some reference and guidance for soil erosion control and ecological restoration in mining areas.Main conclusions are as follows:（1）Under different discharge flow conditions,the runoff rate of each slope shows a sharp rise in the early stage of runoff production,and then shows a trend of stable fluctuation.The erosion rate first increased rapidly and then decreased fluctuately with the prolongation of runoff duration.Under the five kinds of discharge flow conditions of 5²5 L/min,the average runoff rate,average sediment concentration and average erosion rate of bare slopes were distributed between 2.40¹5.16 L/min,0.02⁰.91 g/ml and 279.55¹0900 g/min,respectively.The average runoff rate,average sediment concentration and average erosion rate of vegetation slopes are distributed between 0.07²0.57 L/min,0.001¹.36 g/ml and 0.48¹1162.32 g/min,respectively.Among them,the average runoff sediment of the protected slopes of the non-degraded vegetation configuration pattern are smaller than the unprotected bare slopes,while the average runoff sediment of the degraded vegetation protected slope was larger than the unprotected bare slope.（2）Under different flow rates,the runoff flow patterns of bare slopes are all turbulent.In plot differernt vegetation（QC,CG,ER,SC,SS and SD）,runoff flow pattern of the slope transitions from laminar to turbulent flow with the increase of the discharge flow.Different vegetation allocation modes have different flow patterns of runoff on slopes.With the increase of discharge flow,the runoff flow patterns of each slope change from rapid flow to slow flow.The runoff shear force,stream power and runoff energy of each slope were different with the change process of water discharge duration,while the runoff energy of bare slope was significantly larger than other vegetation protected slopes.Among them,the runoff shear force,stream power and runoff energy of bare slope were distributed in 5.93⁷5.21 Pa,0.002⁰.079N·m^-1·s^-1 and 0.015⁰.116 J,respectively,the runoff shear force,stream power and runoff energy of non-degraded vegetation slopes were distributed in 0.09¹25.38 Pa,0.001⁰.234N·m^-1·s^-1 and 0.004⁰.041 J,respectively.（3）There was no significant relationship between the soil erosion rate of LP and SC slope with the Froude number and drag coefficient.In plot QC,CG,ER,SS and SD,soil detachment rate had a very significant power or exponential function relationship between runoff shear force,stream power,runoff energy,Froude number,Reynolds number and drag coefficient,in which soil detachment rate decreases with the increase of the drag coefficient,that is,the soil detachment rate can be better predicted by hydrodynamic parameters such as runoff shear force and stream power.（4）In plot bare slope,CH7,CH3,QC,CG,LC,ER,SC,SS,SD,the contribution rate of runoff increased with the increase of discharge flow rate at each water release stage（5²5L/min）,and the contribution rate of sediment yield varies fluctuated in each stage of water release,and the contribution rate of each stage of slope in different vegetation allocation modes varied greatly.Among them,The contribution rates of runoff and sediment yield of bare slopes in each discharge stage were 5.46%³5.98%and 7.60%²1.63%,respectively.The contribution rates of runoff and sediment yield of non-degraded vegetation slopes at each stage were 0.21%⁵1.19%and 0.10%⁶0.86%,The contribution rates of runoff and sediment yield of degraded vegetation slopes at each stage were 1.38%³5.57%and 1.83%³5.60%.In all the slopes,regardless of vegetation pattern,erosion rate and runoff rate formed an extremely significant power function relationship.（5）The root characteristics of each slope were significantly different,and the root characteristics of the non-degraded vegetation slopes were larger than that of the degraded vegetation slopes.The biomass density and root diameter of each vegetation slopes were0.15¹.09 kg/m³ and 0.88¹.48 mm,respectively.With the gradual increase of root diameter,the root length density of each protective slope shows the change trend of"increasing first and then decreasing".The total root length density ranged from 634.8 to 3357.83 m/m³;the root surface area density shows the trend of“rise-down-rise-fall”,and the total root surface area density was distributed between 2.6 and 11.39 m²/m³;The root bulk density showed the characteristic of"small on both sides and large in the middle"with the increase of root diameter,and the total root volume density was distributed between 1472.24⁸509.29cm³/m³.（6）Compared with the bare slope,runoff of the non-degraded vegetation slopes of CH7,CH3,QC,CG,LC,ER and SC was reduced by 25.58%,28.95%,20.68%,26.67%,15.39%,30.17%and 42.01%and sediment was reduced by 79.39%,87.44%,84.47%,49.96%,47.31%,54.83%and 89.97%.The runoff and sediment yield of the degraded vegetation SS and SD configuration slopes increased by 6.40%,2.42%and 30.81,21.17%%,respectively.Among them,the straight root system of Astragalus adsurgens and the fibrous root system of the Agropyron ratio of 1:3 configuration mode had the best effect of reducing water and reducing sand,and had the best slope protection ability.The research shows that the slope protection effect of the vegetation mixed configuration was better than that of the single vegetation slope,and the slope protection benefit was different with different proportion factor.The degraded vegetation slope had no protective benefits,which will accelerate the occurrence of erosion.（7）The sediment reduction benefit of different vegetation allocation patterns was affected by the biomass,root length density and root volume density.When the root quality of the plant in the unit soil and the total length of the root system and the root volume were larger,the erosion resistance of the vegetation slope was stronger.When the vegetation on the slope was withered and degraded,the soil and various root indicators were significantly reduced,resulting in increased erosion.