Study On Effect Of Artemisia Ordosica Kraschen Disposition In Preventing Soil Wind Erosion

The problem about preventing wind erosion of vegetation has long been concerned for academia, but the previous studies always focus on the effect that the vegetation coverage to soil drifting,many experts thought that when the vegetation coverage is low, it can't completely fix shifting sand and prevent wind-sand flow.However, in arid and semi-arid region, because of the limit of water conditions, the vegetation coverage isn't very high. To obtain maximum protection benefit and sustainable management objectives,on the condition of ensuring forest diversity and stability, vegetation must have reasonable space layout and continuity time。It is necessary to study forest configstruct and layout, namely,to appropriately ploy plants,it can reduce water competition and control soil erosion on low vegetation coverage. With the common plant Artemisia sphaerocephala as research subject, through the research on the wind field distribution and sediment transport rate, this paper analyzes the mechanism of preventing soil erosion;Through the studies of naturally random distributed Artemisia with different vegetation coverage, evenly distributed Artemisia that simulated with different vegetation coverage, zonal distributed Artemisia with different horizontal distribution,it analyzes wind speed, aerodynamic roughness, near-surface sediment transport rate on different vegetation coverage, and investigates the mechanism of sand-arresting effect and soil erosion control of Artemisia with different horizontal distribution;Through wind tunnel simulation experiment, it analyzes different zonal distributed Artemisia wind control effect. The results are as follows:(1) When wind-sand flow through an individual Artemisia plant,wind speed in the side of it will first increases and then decreases,it will form a wind shadow after the shrub,wind speed behind leeside 1H have the largest decrease,behind it,wind speed increase gradually. Wind-sand flow is deposited both in front and back of the plant, and it erode slightly in both sides of plant. Natural shrub grass vegetations were set several individual plant together to enhance the sand fixing function,and along with the growing of plant to control drift sand gradually.(2) Through the studies of naturally random distributed Artemisia with different vegetation coverage,it is discovered that with other things equal, when vegetation conversation increase, the threshold wind velocity of sand movement increases by exponential function, aerodynamic roughness and friction velocity respectively increases by power function and linear function. Warning coverage in study area is 41.5%-49.4%,critical coverage of soil corrosion is 60%,namely,when coverage of naturally random distributed Artemisia reaches 60%, soil drifting can be controlled basically.(3) The coverage of 50% was a critical point on preventing soil wind erosion.When coeverage degree changes in 0-50%,near-surface wind speed decreased, wind control effect strengthen, roughness increased and near-surface sediment transport rate decreased. When the coverage degree was more than 50% and less than 70%,the wind speed, wind control effect, roughness, near-surface sediment transport rate have no obvious difference. It suggestes that:when the coverage of evenly distributed Artemisia shrub reaches 50%, it can prevent soil wind erosion effectively.(4) Within a certain range, when linage numbers of shelter forest increasing, not only protect distance has been enlarged, but also protective effects has been enhanced that makes a stable protection to ground surface, but the number of rows is not the more the better. The protective effect of three rows allocation was not obvious better than two rows allocation. In practice, two rows allocation is suggested to choose,and its protect distance is 7-10H.(5) Three kind of 2 belts allocation that 1H,2H,3H have no obvious diffent on protect effect in the distance of 7-12H,all can control wind erosion effectively,and reduce wind speed; line spacing of 3H can suspend the attenuation of protection effect in 7-12H,but row middle will be eroded.(6) For one belt with two lines, wind control effect of 4H,6H,8H,10H,12H line spacing is 61.2%,53.3%,45.4%,38.5%,29.2%,surface between two lines is partly eroded.When line spacing increases, area eroded increases, when the spacing increases to 12H, wind erosion area is nearly equivalent to accumulation area; sand-arresting effect behind the belt is obvious,but with line spacing increasing, sand-arresting effect decreases.For 4H,6H,8H,10H,12H line spacing, sediment transport rate that 7H behind the belt decreases 38.92%,35.24%,38.62%,39.69%,43.51%.(7) Through the simulation experimental observation of different zonal distributed Artemisia wind control effect in wind tunnel,we test further the conclusion got in field.The suggestions are as follow:When Artemisia is as artificial vegetation,multi-belt distribution with each belt two lines should be chosed.Consider for the limit of water, the line spacing of Artemisia should be 8H-10H.In this distribution,sand-arresting effect is well, and water consumption will be not exceeding, that avert Artemisia died too earlier.