草原灌木带空气动力学粗糙度研究

Study on the aerodynamic roughness of grassland shrub belt

为了定量研究灌木带修复退化草原的机理,采用集沙仪和风速廓线仪野外采集了不同高度灌木带及退化草原的风蚀物及风速廓线,利用最小二乘法对风速廓线数据进行计算得到了相应的空气动力学粗糙度。结果表明:灌木带对草地的防护机理在于提升了地表的空气动力学粗糙度,降低了近地表的风速,从而导致灌木带相对退化草原的抗风蚀能力增强,大量风蚀物集中在近地表30 cm范围内;距灌木带的距离越远,空气动力学粗糙度呈现下降趋势;同时对不同高度灌木带的研究发现,0.3 m、0.7 m和1.5 m高的灌木带分别在距背风面3 m、5 m和6 m处的空气动力学粗糙度与退化草原的值趋于一致,此距离为该灌木带的有效防风蚀范围,空气动力学粗糙度及有效防护范围均随灌木高度的增加而增大。

In order to carry out a quantitative research on the mechanism of repairing degraded grassland with shrub belt,the wind erosion sediment and wind speed profile with different heights of shrub belt and degenerated grassland had been collected by sand sampler and wind speed profiler.In addition,the corresponding aerodynamic roughness was calculated using the least squares method to calculate the wind profile data.The results showed that the protective mechanism of shrub for grassland was to enhance the aerodynamic roughness of earth surface and reduce the near- surface wind speed,leading to the improvement of ability to resist wind erosion of shrub compared to degraded grassland.A lot of aeolian deposits were concentrated in the near surface within the scope of 30 cm.Aerodynamic roughness appeared a trend of becoming declined with the farther distance from shrubs.At the same time,through studying shrubs of different heights,it was found that the aerodynamic roughness and the value of degraded grassland tended to agree with each other for shrubs with different heights of 0.3 m,0.7 m and 1.5 m high when leeward sides were 3 m,5 m and 6 m,respectively.The distance was an effective wind erosion area of shrub belt,and aerodynamic roughness and effective protective range became enlarged with the increase of the shrub height.This finding has a great significance for the repair of degraded grassland and a reasonable allocation of engineering dimension of shrub belt.