Corridors of barchan dunes: stability and size selection

TL;DR

This paper investigates the stability and size selection of barchan dune corridors, revealing that inherent instabilities in solitary dune models prevent corridor formation, implying additional unknown mechanisms are involved.

Contribution

The study demonstrates that common solitary dune models cannot reproduce dune corridors and identifies fundamental instabilities, suggesting the need for new mechanisms in dune size regulation.

Findings

Solitary dune models do not produce corridor patterns.

Two main instabilities prevent steady-state dune sizes.

Additional unknown mechanisms likely regulate dune size.

Abstract

Barchans are crescentic dunes propagating on a solid ground. They form dune fields in the shape of elongated corridors in which the size and spacing between dunes are rather well selected. We show that even very realistic models for solitary dunes do not reproduce these corridors. Instead, two instabilities take place. First, barchans receive a sand flux at their back proportional to their width while the sand escapes only from their horns. Large dunes proportionally capture more than they loose sand, while the situation is reversed for small ones: therefore, solitary dunes cannot remain in a steady state. Second, the propagation speed of dunes decreases with the size of the dune: this leads -- through the collision process -- to a coarsening of barchan fields. We show that these phenomena are not specific to the model, but result from general and robust mechanisms. The length scales needed for these instabilities to develop are derived and discussed. They turn out to be much smaller than the dune field length. As a conclusion, there should exist further - yet unknown - mechanisms regulating and selecting the size of dunes.