Selection of dune shapes and velocities Part 1: Dynamics of sand, wind and barchans

Abstract

Abstract. Almost fifty years of investigations of barchan dunes morphology and dynamics is reviewed, with emphasis on the physical understanding of these objects. The characteristics measured on the field (shape, size, velocity) and the physical problems they rise are presented. Then, we review the dynamical mechanisms explaining the formation and the propagation of dunes. In particular a complete and original approach of the sand transport over a flat sand bed is proposed and discussed. We conclude on open problems by outlining future research directions.

The shape of barchan dunes

“…The insets demonstrate exemplarily that all windward profiles are well represented by with α ≈ 3.0 for dunes and α ≈ 1.8 for heaps (H e , L e are defined in figure 1b). Such collapse of the windward profiles is strongly supported by field data [1,20]. Moreover, the height-length relations for diverse masses and wind speeds can be superimposed on a single master curve by rescaling lengths and heights by their values H c , L c at the shape transition.…”

“…Among the most symmetric structures are isolated heaps and barchan dunes. For a schematic sketch that introduces some of the terminology see figure 1. By identifying and isolating the mechanisms that are essential for dune formation, a mathematical minimal model could recently be formulated [15,16], and was shown to reproduce generically field observations reporting systematic shape variations [20].…”

Factors influencing chloride deposition in a coastal hilly area and application to chloride deposition mapping

“…The wind speed decreases over the downwind slope. This phenomenon has been extensively studied in sand dune formation processes (Andreotti et al, 2002). The elevated wind speed at the upwind slope facilitates atmospheric chloride transport, and a decreased wind speed at the downwind slope facilitates chloride deposition, which may explain the positive partial correlation between D and β sinα from the data.…”

The weather and climate of the tropics: Part 5 ‐ Dry environments

“…Where sandy sediment is in short supply, barchans grow as crescents with an apex across the prevailing wind and horns downwind (Figure 1). They move downwind at between 15 and 60 m yr −1 , strongly dependent on barchan height and develop when the mean wind speed is typically 10 ms −1 or more (Andreotti et al, 2002). The height of these dunes is typically up to 10 m. Strong winds that are variable in direction produce stellate dunes, which may grow to be as much as 250 m high (Williams, 1983).…”