Dune-dune interactions in a quasi-2D corridor

Abstract:

Sand dunes often form large collectives known as dune fields. Notwithstanding significant progress in our understanding of single dune dynamics, the morphology of dune fields is still poorly understood. Most importantly, an open question remains whether dune configurations observed in the field are steady or transient.

Recent experiments in our laboratory revealed that two dunes, one directly upstream of the other, can interact at large distances even if they are not in direct contact. The feedback is induced by the wake forming behind the upstream dune. Turbulent fluctuations in the wake enhance sediment flux over the downstream dune and thus increase its migration rate. This change in the migration rate can be described as an effective dune-dune repulsion, which prevents dune collisions on a macroscopic scale.

In this study, instead of probing pairwise interactions, we consider sand dunes arranged in a quasi-2D periodic train. Specifically, we test experimentally how the morphology and migration rate of the corridor depends on the distance between neighbouring dunes. For sparse arrangements, the dunes are dynamically independent but as the gap between the dunes narrows, wake-induced effects ensue. We use a combination of laboratory experiments and mathematical modelling to investigate the physical underpinnings of the inter-dune coupling and explore their consequences for the structural stability of the dune corridor. This work is the first step towards a reduced-complexity model of a dune field that would incorporate the wake-induced dune-dune interactions.