包兰铁路沙坡头段防护体系前沿栅栏沙丘形态与近地面流场
收稿日期: 2012-12-01
修回日期: 2013-02-14
网络出版日期: 2013-02-14
The Morphology and Near Surface Air Flow Field of Fence Dunes at the Front of the Railway Protective System in Shapotou Section of Baotou-Lanzhou Railway
Received date: 2012-12-01
Revised date: 2013-02-14
Online published: 2013-02-14
防护体系前沿阻沙栅栏不仅是维持栅栏沙丘形态、阻挡流沙进入防护带内的重要屏障，还是栅栏沙丘这一独特沙丘类型形成发育的首要条件。形态测定与流场观测表明，在沙坡头铁路防护体系前沿地带，栅栏沙丘迎风坡平均坡度大于天然沙丘，背风坡坡度小于天然沙丘，背风坡水平长度与迎风坡水平长度之比约为0.7，远大于天然沙丘（0.3）。阻沙栅栏显著影响沙丘表面流场，但栅栏缺失或沙埋后栅栏沙丘与天然沙丘表面流场结构具有很大的相似性。沙丘迎风坡剪切风速均沿坡面至丘顶呈先增大、后减小的趋势，但栅栏沙丘迎风坡脚至中上部剪切风速增长速度较快，中上部至丘顶剪切风速迅速降低而且幅度较大，这种变化对栅栏沙丘的成长具有重要意义。
马晓洁 , 张春来 , 张加琼 , 王焕芝 , 周 娜 . 包兰铁路沙坡头段防护体系前沿栅栏沙丘形态与近地面流场[J]. 中国沙漠, 2013 , 33(3) : 649 -654 . DOI: 10.7522/j.issn.1000-694X.2013.00093
Sand blocking fences at the front of the railway protective system in Shapotou section of Baotou-lanzhou Railway are not only the important barriers that obstruct blown sand flow, but also the prime conditions for the formation and development of the special dunes that we defined as fence dunes in this paper. Observations on dune morphology and air flow field indicate that windward slope of the fence dunes is steeper than that of the natural dunes but leeward slope is gentler than that of the natural dunes. The ratio of the horizontal length of leeward slope to windward slope of the fence dunes is about 0.7, much larger than that of the natural dunes (0.3). Sand blocking fences influence the near surface air flow field significantly. However, if the fences are missing or buried by the accumulated sands, the structure of air flow field over the fence dunes will be similar to that over the natural dunes. Changes of shear wind velocities (u*) along the windward slope of these two types of dunes exhibit a similar tendency that increases from the windward slope toe to the middle-upper slope of the dune and then decreases to the dune top. The only difference is that both increase extent of u* from the windward slope toe to the the middle-upper slope of the dune and decrease extent of u* from the middle-upper slope to the dune top on the fence dunes are larger than those on the natural dunes. This difference is significant in development and growth of the fence dunes.
Key words： fence dunes; dune morphology; near surface air flow field
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