Evaluating the optimal porosity of fences for reducing wind erosion

摘要

Porosity is the most important parameter determining the shelter efficiency of fences.Wind measurements were made around fence models with different porosities in a wind tunnel.The optimal fence porosity is evaluated by means of Gandemer's method that com-bines the effects of wind reduction and turbulence fields on the shelter efficiency for abating wind erosion.Defining the optimal po-rosity 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: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.According to the evaluation in present study,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 effec-tively,the fence porosity must be less than or equal 0.40.