Measurements of the aeolian sand transport saturation length

TL;DR

This study provides direct wind tunnel measurements of the aeolian sand transport saturation length and shows it is largely unaffected by wind strength, highlighting grain inertia as the key limiting factor.

Contribution

The paper offers the first direct measurements of the saturation length and links field data with stability analysis to clarify its dependence on wind conditions.

Findings

Saturation length is nearly independent of wind shear velocity.

Grain inertia dominates the sediment transport saturation process.

Field and wind tunnel measurements are in agreement.

Abstract

The wavelength at which a dune pattern emerges from a flat sand bed is controlled by the sediment transport saturation length, which is the length needed for the sand flux to adapt to a change of wind strength. The influence of the wind shear velocity on this saturation length and on the subsequent dune initial wavelength has remained controversial. In this letter, we present direct measurements of the saturation length performed in a wind tunnel experiment. In complement, initial dune wavelengths are measured under different wind conditions -- in particular after storms. Using the linear stability analysis of dune formation, it is then possible to deduce the saturation length from field data. Both direct and indirect measurements agree that the saturation length is almost independent of the wind strength. This demonstrates that, in contrast with erosion, grain inertia is the dominant dynamical mechanism limiting sediment transport saturation.