Sheltering effect of a multiple-row Tamarix windbreak – a field study in Niatak, Iran

Abstract

The Sistan region in southeastern Iran is one of the country's main dust storm areas. To reduce the frequency and intensity of dust storms using efficient windbreaks is critical. In a field study the sheltering effect of a multiple-row windbreak (14 rows of Tamarix aphylla) in the Niatak area was evaluated by obtaining the vertical and horizontal values of Rc(x, z) (wind reduction coefficient) upwind (x=− 100), within (x=100 and 256) and downwind (x=448 and 560) of the windbreak. A slight deflection in the vertical profiles of the sheltering effect at a height ofz/h= 0.2–0.8, a significant increase in the Rc(x, z) values was observed within the windbreak that demonstrated the roughness influence of vegetation. The sheltering effect increased within the windbreak consistent with the increasing aerodynamic roughness length (z0). The greatest Rc(x, z) values was observed at the beginning of windbreak (x= 100), where the largest values of z0 occurred. At downwind distances of x=448 and 560 the values of Rc(x, z) were respectively greater and lower than upwind values, revealing the sheltering effect of the windbreak in an area 50 h beyond the vegetation. Significant sheltered areas (50 h beyond and 1.8 h above the windbreak) and reduced wind speeds (50% at x=100) by the windbreak and the location of minimum wind speed at the beginning of the windbreak demonstrates that the efficiency of the windbreak is optimum. This is mainly attributed to the optimal porosity (39%) and structure of the windbreak (multiple-row design).