Research On The Effect Of Wind Prevention And Sand Blocking Of Composite Barriers Based On Climbing Plants

Wind and sand activity is an important symptom of grassland degradation.Currently,fence enclosure is the main technique in the ecological restoration of degraded grasslands.In order to better promote the vegetation restoration of enclosed degraded grassland and soil erosion caused by wind erosion,this research raised a Composite Sand Barrier based on Climbing Plants（CSBCP）.By using indoor wind tunnel,five simulation experiments,which include model A（Fence,β﹝βindicates the permeability of the model﹞:96%～98%）,model B（CSBCPⅠon non-leafy stage,β:59%～64%）,model C（CSBCPⅡon non-leafy stage,β:50%～55%）,model D（CSBCPⅠon leafy stage,β:40%～55%）,and model E（CSBCPⅡon leafy stage,β:30%～35%）,have been respectively carried out under net wind and sand-holding wind conditions of 6 m·s^-1、8 m·s^-1、10 m·s^-1.The main difference among the latter four models is permeability.The flow field structure,wind protection effectiveness,and sand-blocking effect of these models were compared and analyzed to identify the effect of windbreak and sand-blocking of CSBCP.The main findings of this research are as follows:（1）The analysis of the flow field structure of each model showed that the flow field structure of both sides of the enclosure net was similar,and there was no obvious decelerating wind shadow area on the leeward side.However,the overall flow field structure of CSBCP showed a change trend of"decrease-increase（crossing the barrier）-decrease",and there was a wind shadow area on the leeward side.With the increase of wind speed,the range of the minimum acceleration rate deceleration zone on the leeward side of CSBCP on leafy stage increases,while the range of the minimum acceleration rate deceleration zone on the leeward side of CSBCP on non-leafy stage decreases.At the same wind speed,the wind-reduction effect of CSBCP on leafy stage was better than that of CSBCP on non-leafy stage.For the isoline weakening gradient on leeward side,the gradient of model B was similar to that of model D,and the gradient of model C was similar to that of model E.In the measurement range,the protective distance of CSBCP on non-leafy stage was 0.6～15 H（H indicates the height of the barrier）,and the protective distance of CSBCP on leafy stage was 0～15 H.（2）The windbreak efficiency analysis showed that the windbreak efficiency of the fence and CSBCP had a similar change trend under different wind speed conditions.For different wind speed,the average near-surface windbreak efficiency of CSBCP on non-leafy stage（Model B and model C）reached the lowest at 10 m·s^-1 wind speed,with 18.55%and 18.38%,respectively.CSBCP on leafy stage（Model D and model E）were the lowest at 6m·s^-1 wind speed with 44.03%and 45.42%,respectively.The windbreak efficiency of CSBCP on leafy stage increases with increasing wind speed.The windbreak efficiency of CSBCP on non-leafy stage decreases with increasing wind speed.At the same wind speed,the average windbreak efficiency of CSBCP was higher than that of the fence,and the average windbreak efficiency of CSBCP on leafy stage was more than 2 times that of CSBCP on non-leafy stage.（3）The blocking effect analysis showed that the sand-blocking effect of the fence was extremely low and had no sand-blocking function.CSBCP could produce sand deposition in front of the net,and the descending order of the sand interception effectiveness was model E>model D>model C>model B.At different wind speeds,the sand transport rate on the leeward side of CSBCP was lower than the initial sand transport rate throughout.At point 3（6.5 H）,the sand transport rate increases with the increase of wind speed as a whole,and the sand transport rate of CSBCP on leafy stage was extremely low,which makes it easy to form sand accumulation.And there was no obvious pattern at point 2（2 H）.The results of experiments showed that CSBCP could better prevent wind and block sand.The windbreak and sand-blocking effect of the fence can be enhanced by planting climbing plants,and the effect of wind prevention and sand blocking of CSBCP is stronger on the leafy stage than on the non-leafy stage.The lower the porosity of CSBCP,the stronger the effect of wind prevention and sand blocking.And when the porosity reaches 40%～45%,CSBCP can prevent wind and block sand adequately.Therefore,CSBCP can be an important measure to improve the effectiveness of windbreak and sand blocking of fence.In grassland areas with active wind erosion,planting climbing plants along fence can enhance the local ability to block sand and reduce the loss of surface materials caused by wind action.