Study On Characteristics Of Wind-sand Dynamics And Mechanism Of Erosion And Sedimentation Process In Vertical Sand Barriers Of Salix Psammophila

Salix psammophila is a kind of sandy shrub with high resistance and strong sprouting ability,which shows some advantages in controlling wind erosion.At the same time,the branches of Salix psammophila are ideal materials for making sand barriers.Therefore,Salix psammophila is widely planted as an excellent windbreak and sand-fixing plant species in the arid and semi-arid sand areas of northwest China.At present,the research on Salix psammophila sand barriers mainly focuses on the concealed grid Salix psammophila sand barriers,but the strong wind and sand movement will cause different degrees of wind and sand hazards to the region,and the single square sand barrier setting mode of Salix psammophila is no longer satisfied with the multiple wind and sand movement patterns,so it is necessary to study new ways of setting Salix psammophila sand barriers,which is of practical significance to supplement the theory of Salix psammophila sand barrier protection system and regional sand control.In this thesis,we take willow vertical sand barriers as the research object,through setting up field observation tests,collecting and analyzing the data of wind speed,sand transport,and particle size of sand and sand material on the windward and leeward sides of the sand barriers,and carrying out the research on the influence of willow vertical sand barriers on the changes of wind and sand activities and surface morphological characteristics on the near surface.The wind-sand dynamics and surface erosion process around the sand barrier are proposed,and a sand control module is constructed for the sand control of the sand barrier in the Kubuqi Desert.The main findings of the study are as follows:(1)The protection range of Salix psammophila vertical sand barrier is 1H～5H on the leeward side of the sand barrier in the horizontal direction,and depends on the height of the sand barrier itself in the vertical near-surface direction,and the overall impact range is50 cm～120 cm from the surface.(2)The vertical sand barrier changes the motion of the wind and sand flow in transit and increases the jump height of the wind and sand flow near the surface.The overall sand-blocking rate of Salix psammophila vertical barriers ranges from 5.83% to 91.11%.The sand-blocking rate tends to decrease with the increase of porosity when the barrier height is fixed,and to increase with the increase of barrier height when the porosity is fixed.(3)The particle size characteristic curves of the sand material in the wind-sand flow at the vertical ground height on the leeward side of the salix vertical sand barrier are all single-peaked curves,mainly with fine sand and medium sand,in which the content of fine sand is 70.30%～86.74%,and the content of medium sand is 5.45%～27.13%;followed by very fine sand,powder and clay particles,whose percentage contents range from0.62%～5.37%,1.43%～1.88%,respectively.1.43%～1.88% and 0.53%～1.02%,respectively;there is no gravel component.The average particle size of the sand material ranged from2.1 to 2.5(Φ),with good sortability,skewness of incoming symmetry and positive skewness,and kurtosis of medium kurtosis.(4)The near-surface sand accumulation profile of Salix vertical sand barrier is "double peaks and one valley",and the peaks of the two sand accumulation profiles are mainly concentrated in the range of 1 m in front of the sand barrier and 3 m behind the sand barrier.The sand accumulation around the sand barriers with different porosity at 70 cm height and 100 cm height is dominated by sand accumulation.(5)For the construction of sand control module of Salix vertical barrier,for different situations,single row of Salix vertical barrier is recommended for dune leveling module and dune raising module,50 cm height 44% porosity barrier is recommended for dune leveling top module,and the barricade is set up on the windward slope;70 cm height 44%porosity barrier is recommended for dune raising top module,and it is set up on the sand ridge line;the rapid vegetation construction module,it is recommended to use a double row of Salix vertical sand barriers,and to use low height and large porosity sand barriers for the dune pulling area and large height and porosity sand barriers for the accumulation area.