Wind fences are artificial structures designed to reduce the hazards caused by wind. Their presence in the airflow reduces the effect of wind velocity not only at the system itself but also at a certain windward and leeward distance.The porosity of the fence was the most influential parameter on the wake characteristics behind the fence, compared to other factors that need to be considered for the fence design.Hence, optimal design of wind fences in most cases is to choose the optimal porosity.

The research of evaluating the optimal porosity of fences for reducing wind erosion was accomplished recently by the researchers of Cold and Arid Regions Environmental and Engineering Research Institute. The researchers defined that the optimal porosity must take into account of its own purposes, required shelter degree and area to be sheltered. Turbulence has profound impacts on the shelter efficiency of high degree. Two concepts that absolute optimal porosity and practical optimal porosity concerning optimal porosity are proposed. Choosing the practical optimal porosity means reducing cost without significant expense of shelter efficiency.The absolute optimal porosity for providing high degree of shelter to abate wind erosion is 0.20 while the practical optimal porosity is around 0.40. If a less shelter degree but over wider area is required, the absolute optimal porosity ranges from 0.05 to 0.10 and the practical optimal porosity is 0.10. For any degree of shelter for abating wind erosion effectively,the fence porosity must be less than or equal 0.40.

The research was subsidized by the Knowledge Innovation Project of the Chinese Academy of Science (KZCX2-YW-329), and the National Natural Science Foundation of China (40638038).