A unified model of ripples and dunes in water and planetary environments

TL;DR

This paper introduces a unified hydrodynamic and sediment transport model that explains the formation and differences of ripples and dunes across Earth and planetary environments, revealing a key hydrodynamic response anomaly.

Contribution

It presents a new coupled simulation framework that unifies the understanding of subaqueous and aeolian bedforms across different planetary conditions.

Findings

Identification of two bedform types separated by a wavelength gap

Explanation of the wavelength gap through hydrodynamic boundary layer response

Unified framework for comparing terrestrial and planetary ripples and dunes

Abstract

Subaqueous and aeolian bedforms are ubiquitous on Earth and other planetary environments. However, it is still unclear which hydrodynamical mechanisms lead to the observed variety of morphologies of self-organized natural patterns such as ripples, dunes or compound bedforms. Here we present simulations with a coupled hydrodynamic and sediment transport model that resolve the initial and mature stages of subaqueous and aeolian bedform evolution in the limit of large flow thickness. We identify two types of bedforms consistent with subaqueous ripples and dunes, and separated by a gap in wavelength. This gap is explained in terms of an anomalous hydrodynamic response in the structure of the inner boundary layer that leads to a shift of the position of the maximum shear stress from upstream to downstream of the crest. This anomaly gradually disappears when the bed becomes hydrodynamically rough. By also considering the effect of the spatial relaxation of sediment transport we provide a new unifying framework to compare ripples and dunes in planetary environments to their terrestrial counterparts.