关键词: 塔克拉玛干沙漠, 新月形沙丘, 输沙量垂直分布, 分段拟合函数

Abstract:

In order to study the vertical distribution function of the sand transport rate of wind-sand flow at different height above the barchan dune surface, the sand transport rates of the isolated barchan dune within 100 cm height with 1 cm division in the interior of the Taklimakan Desert were measured. The piecewise fitting results show that: 1) the vertical distribution pattern of sand transport rate at the windward slope base of the dune did not entirely abide by the exponential function but exhibited an “elephant nose effect” similar to the structural characteristics of the wind-sand flow over the Gobi desert surface. The sand transport rate showed a gradually increased trend in the height of 0-3 cm, but above 3 cm it exhibited an exponential function reduction with the height; 2) The sand transport rate within 0-10 cm above the dune crest exhibited an exponential function reduction with the height ,but above 10 cm it showed a quadratic function reduction; 3) The sand transport rate at the left-wing end of the dune showed a power function distribution with the height, but in 0-20 cm at the right-wing end it showed an exponential function reduction and above 20 cm it showed a cubic function reduction; 4) The sand transport rate of wind-sand flow in 0-60 cm height and above 60 cm over the leeward slope base of the dune exhibited a different forms of cubic function distribution respectively and the sand transport rate showed a parabola-shaped vertical distribution. both the dune shapes and the dynamic character of the wind-sand flow affected the vertical distribution of the sand transport rate of wind-sand flow over the barchan dune surface. Since the windward slope base and surrounding zone were a net erosion zone, sand grains were coarse and sand supply was relatively insufficient, unsaturated wind-sand flow formed and the increase in sand transport rate with height did not entirely show an exponential function reduction. The distribution of sand transport rate at the ends of the two wings of the dune was asymmetric, this is mainly because the asymmetric shapes resulted in different proportional saltating and suspending sand amounts and the difference in wind velocity pulse in the horizontal and vertical directions. The difference in wind velocity at the leeward slope base and the crest of the barchan dune resulted in eddy flow and caused part of sand particles from the dune crest to deposit at the leeward slope, part of sand particles was transported in suspension and the transport rate gradually increased with increasing height, when the height reached a threhold (determined by both the dune height and the dynamic intensity of wind-sand flow) the sand transport rate reached a maximum value, and then it gradually decreased, exhibiting a parabolic distribution.

Key words: Taklimakan Desert, barchan dunes, sand flux vertical distribution of wind-sand flow, piecewise function