∗ Observations of the CO (J=1-0) line of Comet Hale-Bopp : Pei Chun-chuan, Zeng Qin, Mao Rui-qing, Zhou Yu-lan, Chen Ya-feng, Han Pu, Lei Cheng-ming and Xu Zhi-hai Purple Mountain Observatory, CAS, Nanjing 210008

Abstract

Although the effectiveness of windbreaks in reducing wind speed and sediment transport is highly dependent on the efficiency of individual elements, few field studies have evaluated the effectiveness of single plants typical of arid areas such as Tamarix. A series field experiments were conducted in the Niatak area of Sistan to assess the effectiveness of a single Tamarix tree in reducing wind speed and sediment flux. Wind speed was measured on five occasions at 32 positions around the tree and at heights of z/h = 0.13, 0.5, 1.1, and 2 (where h is the height of the tree). Sediment flux was measured over three dust storm events at 15 positions and at heights of z/h = 0.13, 0.5, 1.1, and 1.8. The results showed a reduction of wind speed and sediment flux of 80–90% at x/h = 1, decreasing to about 5–8% at x/h = 12. There was an acceleration of about 12–20% in wind speed and about 25–35% in sediment flux around the sides of the tree. The tree sheltered a zone of x/h = 7–9 downwind and the pattern of the sediment transport reduction closely conformed to that of the wind speed reduction. The greatest reduction of wind speed and sediment flux was observed on the leeside of the tree at x/h = 0.5 and, 1 and close to the ground surface. The results confirm the effectiveness of Tamarix trees in reducing wind speed and sediment flux, and thus its suitability as a potential control on erosion and sediment transport. Based on the results, designing a windbreak with an optimum inter-rows distance of x/h = 7 and inter-plant spacing of less than 0.5 h is suggested in order to provide maximum control of aeolian erosion.