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Impact of plant morphology and density on wind velocity and windborne sediment flux – a wind tunnel experiment

Abbas Miri 1, Deirdre Dragovich1, Zhibao Dong2
1School of Geoscience, University of Sydney, Sydney, Australia, 2Key Laboratory of Desert and Desertification, Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, Lanzhou, China

 

Vegetation plays a critical role in protecting surfaces from wind erosion due to the complex internal and external geometry of plants, and their porous and flexible nature. To better identify potential relationships between vegetation morphology and its impact on wind erosion, the influence of two plant types Cosmos bipinnatus (Plant 1) and Ligustrum lucidum Ait (Plant 2) on wind velocity and sediment mass flux were assessed in different density configurations (low, medium and high) in a wind tunnel. Initially the plants were subjected to a range of wind velocities and plant aerodynamic characteristics obtained. Wind velocity and sand flux density profiles were measured upwind, within and downwind of canopies. Results showed that the two plant types presented different responses to the wind due to differences in their morphology and structure. Both plants re-configured when wind velocity increased and reduced their frontal area and porosity. In high wind velocities the mean values of FA for Plant 2 were higher than Plant 1; and conversely the mean values of OP for Plant 2 were lower than Plant 1. These different plant responses resulted in Plant 1 developing greater permeability and thus having a lesser ability to reduce wind velocity and intercept sediment. Both plants were able to shelter an area vertically from the surface to 1.5h (h is canopy height) above the canopies and horizontally from 5h upwind to 5h behind the canopies. The canopies of Plant 2 were more effective than those of Plant 1 in reducing wind velocity, indicating that Plant 2 presented a greater shelter effect. As a result, Plant 2 had a greater ability to prevent sediment movement within its canopies and to trap more sediment blown over its canopies. Both plants had a greater influence on wind velocity and sediment mass flux at medium and high densities than at a low density. Differences between the two plant types in decreasing wind velocity, producing a shelter effect and trapping blown sediment increased from high to low density. It is concluded that the morphology and structure of plants determines their response to wind and this response affected their efficiency in influencing wind velocity and the sediment transport system. Different plants having different structures thus present different efficiencies.