Journal of Arid Environments Journal of Arid Environments ] (]]]]) ]]]–]]] Near-surface airﬂow ﬁeld and aerodynamic characteristics of the railway-protection system in the Shapotou region and their signiﬁcance Chun-Lai Zhang a,b , Xue-Yong Zou a,b,Ã , Xing-Hui Pan a,b , Shuo Yang a,b , Hong-Tao Wang c a MOE Engineering Center of Desertiﬁcation and Blown-sand Control at Beijing Normal University, China b China Center of Desert Research at Beijing Normal University, Beijing 100875, China c Cold and Arid Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou 730000, China Received 13 January 2006; received in revised form 15 November 2006; accepted 14 March 2007 Abstract The effects of near-surface airﬂow on aeolian deposits across the Shapotou region’s railway- protection system were studied. We found that iso-speed lines in the protective belt gradually become less dense with increasing distance along the wind direction due to the inclined topographic relief in that direction and to changes in surface properties (particularly dune undulation). In addition, wind speed at each elevation tends to decrease, with a negative velocity variation coefﬁcient. This coefﬁcient was positive on windward sides of ﬁxed dunes and smaller than that on mobile dunes; its values were negative on the leeward slope of ﬁxed dunes, averaging 1.48% m 1 below a height of 250 cm. Windward wind proﬁles followed a logarithmic relationship but deviated from this relationship leeward. The mean aerodynamic roughness length (z 0 ) of artiﬁcially vegetated surfaces was 0.00543 m, versus 0.000118 m for mobile sands. The average air drag coefﬁcient (C d ) of the artiﬁcial vegetation belt was 1.7 times that of mobile sands. The near-surface airﬂow ﬁeld and aerodynamic characteristics control clay and silt contents in surface soils, which increase greatly (with decreasing median particle size) from the mobile sands upwind of the protective belt to the artiﬁcial vegetation further downwind within the belt, and sorting becomes increasingly poor. Silt content was negatively correlated with, and median particle size and sorting were positively correlated with the relative surface elevation in the protective belt. The relationship between clay content and landform was unclear. Silt content was high and sorting poor in the surface 5 cm; below ARTICLE IN PRESS www.elsevier.com/locate/jaridenv 0140-1963/$ - see front matter r 2007 Published by Elsevier Ltd. doi:10.1016/j.jaridenv.2007.03.006 Ã Corresponding author. College of Resources Science and Technology, Beijing Normal University, 19 Xinjiekouwat Street, Beijing 100875, China. Tel./fax: +86 10 6220 7162. E-mail address: zouxy@bnu.edu.cn (X.-Y. Zou). Please cite this article as: Zhang, C.-L., et al., Near-surface airﬂow ﬁeld and aerodynamic characteristics of the railway-protection system in the Shapotou region and their..., Journal of Arid Environments (2007), doi:10.1016/j.jaridenv.2007.03.006