Aeolian Sand Transport Rate Over Windward and Lee Slopes of Small Reversing Dunes, Southern Morocco

Several factors affect the aeolian sand transport rate over reversing dunes. In arid zone poor in vegetation, the most important factors are effective wind direction in relation to the dune crest and the inclination of the windward slope. The objective of this paper is to analyze the variation in sand transport rate over such dunes under wind events differing in the direction of the incident wind including winds blowing from the direction of the former lee side. The research was carried out in the dune field of the Coude du Dra region (southern Morocco) where small reversing dunes, up to 3 m high, are numerous. In the case of wind blowing from the direction of low-angle slope, the sand transport rate increased tenfold between dune toe and crest when wind speed was well above the threshold value and around 25 times when wind speed was slightly greater than the threshold value. When the wind direction reversed and the steep lee slope became a windward slope, the sand transport rate at the dune crest was greater than in the previous case. It was caused by strong sand deflation that occurred at the dune crest due to its kinked profile.