Granular size segregation in underwater sand ripples

TL;DR

This study investigates how underwater sand ripples form and evolve, revealing that granular segregation depends on initial conditions and results in volume segregation, with implications for understanding geophysical patterns.

Contribution

The paper presents new experimental evidence that granular segregation in underwater ripples results in volume segregation, influenced by initial bed preparation and fluid flow, differing from previous surface segregation observations.

Findings

Segregation depends on sand bed preparation.

Final steady state shows volume segregation.

Various exotic ripple patterns are identified.

Abstract

We report an experimental study of a binary sand bed under an oscillating water flow. The formation and evolution of ripples is observed. The appearance of a granular segregation is shown to strongly depend on the sand bed preparation. The initial wavelength of the mixture is measured. In the final steady state, a segregation in volume is observed instead of a segregation at the surface as reported before. The correlation between this phenomenon and the fluid flow is emphasised. Finally, different ``exotic'' patterns and their geophysical implications are presented.