Modeling the dynamics of aeolian meter-scale bedforms induced by bed heterogeneities

TL;DR

This paper presents a new model explaining how heterogeneities in desert and beach surfaces influence the formation and evolution of meter-scale sand bedforms, aligning well with observed data.

Contribution

The model introduces a novel approach by incorporating gradual changes in transport capacity over distance, improving understanding of early-stage bedform dynamics.

Findings

Model agrees with high-resolution observations

Predicts stages of bedform development

Explains influence of wind duration and sand flux

Abstract

Desert surfaces are typically non uniform, with individual sand dunes generally surrounded by gravel or non-erodible beds. Similarly, beaches vary in composition and moisture that enhances cohesion between the grains. These bed heterogeneities affect the aeolian transport properties greatly, and can then influence the emergence and dynamics of bedforms. Here, we propose a model that describes how, due to transport capacity being greater on consolidated than erodible beds, patches of sand can grow, migrate and spread to form bedforms with meter-scale length. Our approach has a quantitative agreement with high-resolution spatio-temporal observations, where conventional theory would predict the disappearance of these small bedforms. A crucial component of the model is that the transport capacity does not instantly change from one bed configuration to another. Instead, transport capacity develops over a certain distance, which thereby determines the short-term evolution of the bedform. The model predicts various stages in the development of these meter-scale bedforms, and explains how the evolution of bed elevation profiles observed in the field depends on the duration of the wind event and the intensity of the incoming sand flux. Our study thus sheds light on the initiation and dynamics of early-stage bedforms by establishing links between surface properties, emerging sand patterns and protodunes, commonly observed in coastal and desert landscapes.