Morphodynamics of barchan-barchan interactions investigated at the grain scale

TL;DR

This study investigates the grain-scale dynamics of binary barchan dune interactions in water, revealing how individual grains move and spread during dune collisions, offering insights into size regulation mechanisms of dunes across planetary environments.

Contribution

It provides a detailed analysis of grain trajectories and diffusion during barchan interactions, advancing understanding of dune size regulation at the grain level.

Findings

Grain trajectories show origin and destination during interactions.

Grains from impacting dunes spread with diffusion-like behavior.

Proposed a diffusion length to quantify grain spreading.

Abstract

Corridors of size-selected crescent-shaped dunes, known as barchans, are commonly found in water, air, and other planetary environments. The growth of barchans results from the interplay between a fluid flow and a granular bed, but their size regulation involves intricate exchanges between different barchans within a field. One size-regulating mechanism is the binary interaction between nearby dunes, when two dunes exchange mass via the near flow field or by direct contact (collision). In a recent Letter (Assis and Franklin, Geophys. Res. Lett., 2020), we identified five different patterns arising from binary interactions of subaqueous barchans, and proposed classification maps. In this paper, we further inquire into binary exchanges by investigating the motion of individual grains while barchans interact with each other. The experiments were conducted in a water channel where the evolution of pairs of barchans in both aligned and off-centered configurations was recorded by conventional and high-speed cameras. Based on image processing, we obtained the morphology of dunes and motion of grains for all interaction patterns. We present the trajectories of individual grains, from which we show the origin and destination of moving grains, and their typical lengths and velocities. We also show that grains from the impacting dune spread with a diffusion-like component over the target barchan, and we propose a diffusion length. Our results provide new insights into the size-regulating mechanisms of barchans and barchanoid forms found on Earth and other planets.