Aeolian sediment transport over vegetation canopies: A wind tunnel study with live plants

Abstract

This wind tunnel study examines aeolian sediment transport in live plant canopies, whereas most previous studies have used model plants for this purpose. Experiments were performed with three canopy densities of Perennial Ryegrass (Lolium perenne) and with bare sand surfaces. The results suggest that both total sediment mass flux Q and PM10 concentration in the air decreased exponentially with increasing canopy density. In the large-density canopy (frontal area index ¿ = 0.58), Q and PM10 concentration were reduced to 0.01% and 0.4%, respectively, compared to the unplanted configuration. In the medium-density canopy (¿ = 0.16), Q and PM10 concentration were reduced to 6.6% and 48.5%. In the small-density canopy (¿ = 0.03), however, Q and PM10 concentration were increased to 117.5% and 145.6%. This is attributed to elevated shear stress on the sand bed caused by flow acceleration around the tussocks and vortical structures in their lee. Furthermore, the grasses were observed to trigger erosion by oscillating movements at the ground surface. It was also found that the vertical profiles of sediment mass flux in the medium- and large-density canopy strongly deviated from the exponential decay curve of the unplanted configuration, showing a local maximum at approximately twice the canopy height.