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Abstract:  
Introduction: Vegetation plays a significant role in controlling aeolian erosion through increasing surface roughness. Although several studies have investigated the effect of vegetation in reducing wind velocity and their interaction with airflow, vegetation effect on wind velocity and airflow requires to investigate. Although researches have been evaluated the reduction effect of windbreaks (artificial or live windbreaks) on wind velocity and turbulence intensity of airflow have not been studies within windbreaks. In this study, variations of wind velocity, turbulence intensity and standard deviation of wind speed are assessed to give valuable knowledge of vegetation function in affecting airflow to researchers.   
Materials and methods: The windbreak is a planted area in Niatak in the Sistan region. It contains of 14 rows of Tamarix tress with a mean height of 4 m which is perpendicular to the prevailing wind direction. The distance between the rows varies between 21 and 32 m and the distance between the trees in each row is about 1.5 m. To assess variations of wind velocity and turbulence intensity, wind velocity were measured upwind, within and downwind of the windbreak at the heights of 20, 80, 200, 360, 450, 570 and 700 cm in wind velocities s of 10.5 and 19.5 m/s. Mean wind velocity and standard devastation of the wind velocity were calculated and turbulence intensity were obtained by dividing standard devastations to wind velocity .    
Results and Discussion: The wind velocity data are normal in the studied wind velocity s (10.5 and 19.5 m/s) and in all locations. The pattern of wind velocity variations is similar in all heights outside and inside of the windbreak and wind velocity changes at the same time in all elevations. Wind velocity fluctuates in a smaller range inside than outside of the windbreak that implies lower wind velocity within than upwind and downwind of the windbreak. The windbreak affect wind velocity within a distance of 50 times of its height for which wind velocity is lower at downwind than upwind of the windbreak. Wind velocity reduced significantly but turbulence intensity and standard devastation increased within the windbreak. The height turbulence intensity and standard devastation were observed at the beginning of the windbreak where wind velocity is lowest. Comparing turbulence intensity between the locations in wind velocities of 10.5 and 19.5 m/s showed that turbulence intensity is similar upwind of the windbreak but a differences appeared in this parameter between the two wind velocities and this difference reduced at downwind of the windbreak. Turbulence intensity and standard devastation were greater in wind velocities of 10.5 m/s than 19.5 m/s. Within the windbreak turbulence intensity in wind velocity of 19.5 m/s is about 20-30% less than that at 10.5 m/s.     
Conclusion: The windbreak affects wind velocity and turbulence intensity significantly. Investigation of wind velocity, turbulence intensity and standard devastation upwind, within and downwind of the windbreak showed that wind velocity is low but turbulence intensity and standard devastation is are greater within than upwind and downwind of the windbreak. Turbulence intensity is influenced by the windbreak because its values in wind velocities of 10.5 m/s than 19.5 m/s is similar upwind and outside the impacted area of the windbreak but different within the windbreak.   
     
Type of Study: Research | Subject: Desert
Received: 2020/07/16 | Accepted: 2020/12/14

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