| In addition to the well-known soil factors which control wind erosion on
flat, unridged surfaces, two specific processes affect the susceptibility of
tillage ridged surfaces to wind erosion: ridge-induced roughness and ridge-
trapping efficiency.
In order to parameterize horizontal soil fluxes produced by wind over
tillage ridges, eight-ridge configurations composed of sandy soil and
exhibiting ridge heights to ridge spacing (RH/RS) ratios ranging from 0.18 to 0.38
were experimented in a wind tunnel. These experiments are used to develop a
parameterization of the horizontal fluxes over tillage ridged surfaces
based only on the geometric characteristics of the ridges. Indeed, the key
parameters controlling the horizontal flux, namely the friction velocity,
threshold friction velocity and the adjustment coefficient, are derived
through specific expressions, from ridge heights (RH) and ridge spacing
(RS). This parameterization was evaluated by comparing the results of the
simulations to an additional experimental data set and to the data set
obtained by Hagen and Armbrust (1992). In both cases, predicted and measured values are found to be in
a satisfying agreement.
This parameterization was used to evaluate the efficiency of ridges in
reducing wind erosion. The results show that ridged surfaces, when compared
to a loose, unridged soil surface, lead to an important reduction in the
horizontal fluxes (exceeding 60%). Moreover, the effect of ridges in
trapping particles contributes for more than 90% in the flux reduction
while the ridge roughness effect is weak and decreases when the wind
velocity increases. |