Modelling Aeolian Erosion in Presence of Vegetation

Abstract

Soil erosion by wind has many environmental, climatic and health implications. Dust storm represents one of the most dramatic events related to soil erosion. The possible increase of drought events due to climate change may accentuate the frequency and severity of dust storms. Such events have a large environmental cost, especially in agricultural regions. It is therefore necessary to better understand the processes involved in aeolian erosion over heterogeneous surfaces in order to predict dust storms and to identify good landscape management practices to reduce soil erosion. Saltation is a key process in soil erosion as it is the primary driver for dust emission. In the present study, a new saltation model, forced with instantaneous velocity fields and accounting for the presence of vegetation, is introduced in a Large-Eddy Simulation (LES) airflow model. In a first part, the coupled model is tested on a flat erodible surface under various wind conditions. Compared to previous saltation models, the present model is able to simulate explicitly turbulent eddies of the flow and their complete interaction with saltating processes. In the simulations, the saltation intermittency is visualized through the presence of blowing sand structures near the surface, known as aeolian streamers. This is the first time that such structures are reproduced numerically. From a correlation analysis, we confirm previous thoughts that these sand structures are a visual footprint of past turbulent eddies propagating in the surface boundary layer.The standard deviation of the saltation flux associated to these saltation patterns represents about 10 to 20% of the mean saltation flux. In a second part, the sensitivity of soil erosion to different arrangement and type of plants (bushes versus trees) is analyzed and the wind erosion reduction is quantified.