On the formation of current ripples.

J. Bartholdy,B. W. Flemming,A. Kroon,A. Bartholomä,V. B. Ernstsen,C. Winter

doi:10.1038/srep11390

J. Bartholdy, B. W. Flemming + Show 4 more

Open Access

https://doi.org/10.1038/srep11390

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Abstract

For grain sizes finer than coarse sand, the first flow-transverse bedforms to develop are current ripples. Although numerous studies have analysed different aspects of bedform morphodynamics, to date no comprehensive physical explanation for the formation of ripples has been given. We offer such an explanation based on a virtual boundary layer concept, and present a model predicting ripple height on the basis of grain size, current velocity and water depth. The model contradicts the conventional view of current ripples as bedforms not scaling with flow depth. Furthermore, it confirms the dependence of ripple dimensions on grain size, and their relative insensitivity to flow strength.

Highlights

For grain sizes finer than coarse sand, the first flow-transverse bedforms to develop are current ripples
Numerous studies have analysed different aspects of bedform morphodynamics, to date no comprehensive physical explanation for the formation of ripples has been given. We offer such an explanation based on a virtual boundary layer concept, and present a model predicting ripple height on the basis of grain size, current velocity and water depth
When water flowing over sand exceeds the critical shear stress for motion, bedforms develop as a result of dynamic processes acting across the interface between sand and water

Summary

OPEN On the formation of current ripples

Numerous studies have analysed different aspects of bedform morphodynamics, to date no comprehensive physical explanation for the formation of ripples has been given We offer such an explanation based on a virtual boundary layer concept, and present a model predicting ripple height on the basis of grain size, current velocity and water depth. The fact that the model confirms the dependence of ripple size on grain size, in accordance with empirically derived relations[18,19], and confirms the well-known insensitivity to flow strength, supports its validity This leads us to conclude that current ripples are generated and dimensionally scaled as a relatively simple consequence of the virtual boundary layer in association with interactions between well-known properties of the logarithmic velocity profile, grain-size and flow depth. That the nature of this limit is still poorly understood

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