Threshold velocity for wind erosion: the effects of porous fences

Porous fence is a kind of artificial windbreak that has many practical applications. The threshold wind velocities at different distances downwind from Porous fences were measured and the corresponding characteristics of particle movement observed to assess their shelter effect. It is found that the fence's porosity is the key factor that determines the resulting shelter effect. The area near a fence can be typically classified into five regions, each with a different mode of particle movement. Dense fences, and especially solid fences, favor the accumulation of sand upwind of the fences. Fences with porosities of 0.3-0.4 produce the maximum threshold wind velocity; those with porosities of 0.3-0.6 (depending on the fence height) provide the maximum effective shelter distance. It is confirmed that the fence porosities of 0.3-0.4 that have been proposed for practical application in previous research are the most effective for abating wind erosion.