From lab to landscape-scale experiments for the morphodynamics of sand dunes

TL;DR

This paper reviews how laboratory and field experiments enhance understanding of sand dune morphodynamics, focusing on key parameters like sediment flux and saturation length, and discusses experimental setups and results across water and wind environments.

Contribution

It provides a comprehensive overview of experimental approaches to studying dune morphodynamics, highlighting the role of key parameters and the consistency between observations and theory.

Findings

Laboratory experiments in water flows serve as good analogues for aeolian dunes.

Dune shape and dynamics are primarily governed by flow and boundary conditions.

Field experiments can quantify mechanisms of dune growth under natural wind regimes.

Abstract

We review the main processes that drive the morphodynamics of dunes, i.e. their growth in height, migration and elongation, and emphasise the contribution of experiments to the understanding of these mechanisms. The main control parameters are the sediment flux $Q$ and the saturation length $L_{\rm sat}$ associated with the spatial relaxation of the flux towards the transport capacity. The other relevant quantities are essentially dimensionless: fluid response to a bed perturbation, dune geometry (orientation, aspect ratio), transport ratios under multi-directional wind regimes. We argue that laboratory experiments dealing with sedimentary bedforms in water flows are good analogues to study the morphodynamics of aeolian dunes at reduced length and time scales, as $L_{\rm sat}$ and $L_{\rm sat}^2/Q$ are expected to be smaller for subaqueous bedload. Besides, dune shape and dynamics are mainly governed by flow and boundary conditions, independent of the transport mode. We discuss different experimental set-ups and results, especially concerning dune pattern orientation and dune interaction. Under natural wind regimes in terrestrial deserts, we show the potential of field experiments in which the control of initial and boundary conditions allows for the quantification of all the relevant mechanisms involved in dune growth. We emphasise the general agreement between observations, measurements and theoretical predictions, which indicates a robust comprehension of the underlying processes. This understanding can serve as a foundation for further investigations, including the interpretation of dune landscapes and the resolution of inverse problems.