The Study On The Law Of Barchan Dunes' Movement In The Gobi Area In Northern Alxa

The crescent sand dunes in the gobi district have strong mobility and morphological instability.Their rapid activities pose a great threat to the local ecological environment,oasis farmland,and road and mining facilities.The development of resources in the sand areas,environmental protection,wind and sand stabilization projects and other aspects need to grasp the laws of its formation and movement.The black gobi area in the northern part of Alxa has a flat and broad surface,sparse vegetation,and scattered barchan dunes and dune chains on the gravel beds.It is a good observational site for the study of the formation and evolution of barchan dunes in the gobi area.This paper used3 D laser scanning technology is to obtain changes in the shape and position of dunes,and the surface sediments of dunes are measured to determine their grain size composition and change characteristics.The characteristics of dunes movements,morphological changes,and changes in surface sediments are analyzed and studied.Research indicates:1.The annual average moving speed of 3~7m high barchan dunes in the northern part of Alxa is 22.35~26.3m/a,calculated as ridges is21.44~51.96m/a.The higher the height is,the slower the dunes move.The dunes moved more than half of the year in the wind season.Under the long-term effect of unsaturated sand flow,dunes are in a process of reverse evolution.2.The height of dune is linear with the length of the windward slope,the length and width of the left and right wings,and is a power function with surface area and volume.The disturbance of the ENE wind direction to the dunes were characterized by changes in morphology.The maximum wind erosion depth was 0.7m.The sand ridge line shifted towards the windward slope.The offset was logarithmic to the height of the dune.The volume was significantly reduced,and the ratio of the reduction amount to the original volume is logarithmic to height.3.The particle size composition of sand dunes is mainly medium sand andfine sand.The average particle size of dunes is between 1.30 and 1.75?.The finest of the average particle size is in 2016,then the fluctuation follows a downward trend: under the influence of ENE winds and strong winds.The dune size becomes fine,and the average particle size decreases to 1.30? at the end of the observation period.The other particle size parameters do not vary greatly: the sorting coefficient is between 0.79 and 0.86,the skewness is between 0.03 and 0.11,and the kurtosis is between 0.97 and 1.03.4.The particle size distribution pattern of the dune surface is: the average grain size gradually becomes thicker from both sides of the slope to the top of the hill,the windward slope is thicker than the leeward slope,the hill top is thicker than the upturned roof-ridge windward slopes,and the two upturned roof-ridge and the bottom of the windward slope are sensitive to changes of wind,the relationship with the top of the hill is not fixed;the sortability gradually changes deterioration from the top of the hill to the slope of both sides,from the top of the hill to the upturned roof-ridge through the two wings,the sorting performance also deteriorates,and the sorting of the two wings upwind slope is excellent.Corresponding to the leeward slope.