Abstract
Sand fences are widely applied to prevent soil erosion by wind in areas
affected by desertification. Sand fences also provide a way to reduce
the emission rate of dust particles, which is triggered mainly by the
impacts of wind-blown sand grains onto the soil and affects the Earth's
climate. Many different types of fence have been designed and their
effects on the sediment transport dynamics studied since many years.
However, the search for the optimal array of fences has remained largely
an empirical task. In order to achieve maximal soil protection using the
minimal amount of fence material, a quantitative understanding of the
flow profile over the relief encompassing the area to be protected
including all employed fences is required. Here we use Computational
Fluid Dynamics to calculate the average turbulent airflow through an
array of fences as a function of the porosity, spacing and height of the
fences. Specifically, we investigate the factors controlling the
fraction of soil area over which the basal average wind shear velocity
drops below the threshold for sand transport when the fences are
applied. We introduce a cost function, given by the amount of material
necessary to construct the fences. We find that, for typical sand-moving
wind velocities, the optimal fence height (which minimizes this cost
function) is around 50 cm, while using fences of height around 1.25 m
leads to maximal cost.
