Dynamics of migrating sand dunes interacting with obstacles

Abstract

Wind-and water-driven migrating sand dunes frequently interact with elevated natural and manmade topographical features. The dune-obstacle interaction can alter the migrating behaviour of the dune and, depending on the nature of the obstacle, it may generate various societal and technological risks. Here we study the problem of dune-obstacle interaction in a paradigmatic quasi-2D domain realised in a subaqueous laboratory experiment. Generically, dunes interact with obstacles either by 'crossing' over the obstacle or by being 'trapped'. We describe how the selection of these two distinct dynamical behaviours depends on the size and shape of the obstacle, focusing in particular on the fluid flow in the immediate vicinity of the obstacle. Specifically, we perform a modal decomposition of the measured flow field and we discover that the outcome of the duneobstacle interaction is closely related to the flow structure above the obstacle.

Barchan Dunes Cruising Dune‐Size Obstacles

“…This is in agreement with the findings reported by Bacik et al. (2021) in the 2D case (although in their case the bypass does not exist and the passing over results only from grains' displacements in the vertical direction). Therefore, in order to rationalize the problem, we inquired into dimensionless parameters regrouping the observed behaviors.…”

“…While the size ratio between obstacle and dune is an important parameter affecting the type of interaction, the grain-wall shunning taking place in bypass cases strongly indicates that the transport of grains by the fluid must be taken into account. This is in agreement with the findings reported by Bacik et al (2021) in the 2D case (although in their case the bypass does not exist and the passing over results only from grains' displacements in the vertical direction). Therefore, in order to rationalize the problem, we inquired into dimensionless parameters regrouping the observed behaviors.…”

“…To the authors' knowledge, the only experimental investigation of dunes interacting with large obstacles is the one reported in Bacik et al. (2021) for two‐dimensional (2D) dunes. In that work, the authors carried out experiments in a narrow Couette‐type circular channel, where different 2D obstacles were placed on the bottom and obstructed the dune path.…”

Local Similarity Between Aeolian Barchan Dunes and Their Downsized Subaqueous Counterparts

“…This feature is also known as the selforganization of dune evolution, that is, whether in water or in air, the scattered movement of sand particles can present regular and orderly dune morphology at the macroscopic scale. Therefore, the centimeter-scale dune experiment can be used as a downsized way of studying aeolian dunes (Alvarez et al, 2021;Assis & Franklin, 2020;Bacik et al, 2020;Bacik, Canizares et al, 2021;Charru et al, 2013;Hersen et al, 2002;Y. Zhang et al, 2014).…”

“…This feature is also known as the self‐organization of dune evolution, that is, whether in water or in air, the scattered movement of sand particles can present regular and orderly dune morphology at the macroscopic scale. Therefore, the centimeter‐scale dune experiment can be used as a downsized way of studying aeolian dunes (Alvarez et al., 2021; Assis & Franklin, 2020; Bacik et al., 2020; Bacik, Canizares et al., 2021; Bacik, Caulfield, & Vriend, 2021; Charru et al., 2013; Hersen et al., 2002; Y. Zhang et al., 2014). Compared with field observation and remote‐sensing analysis, the experimental method has the advantages of small spatiotemporal scale (to observe the whole process from origin to extinction), flexibility, controllability, and satisfactory accuracy.…”