On the dimensional adjustment of subaqueous dunes in response to changing flow conditions: a conceptual process model
Flemming, B.W. (2000). On the dimensional adjustment of subaqueous dunes in response to changing flow conditions: a conceptual process model, in: Trentesaux, A. et al. (Ed.) Marine Sandwave Dynamics, International Workshop, March 23-24 2000, University of Lille 1, France. Proceedings.
In: Trentesaux, A.; Garlan, T. (Ed.) (2000). Marine Sandwave Dynamics, International Workshop, March 23-24 2000, University of Lille 1, France. Proceedings. Université de Lille 1: Lille. ISBN 2-11-088263-8. 240 pp., more
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| Abstract |
Numerous field studies have concerned themselves with the occurrence, dimensions, grain-size characteristics, and the environmental settings of subaqueous dunes. Similarly, laboratory flume studies have mainly looked at the flow conditions producing stable bedforms and the transitions from one bed phase to another as a function of grain size and flow velocity. By contrast, very little is known about the process of dimensional adjustment of dunes to changing flow conditions. Currently, two theories of bedform growth exist, one having dunes grow by the capture of faster migrating smaller dunes by more slowly migrating larger dunes, the other by the stepwise coalescence of smaller dunes into bigger ones scaled to the size of eddies. Both mechanisms are essentially irreversible. The available field evidence clearly contradicts the first theory and supports the second one only in part. The data clearly show bedform amalgamation or coalescence on various scales, both in shallow and deep water, in reversing and unidirectional flows, but also in aeolian dunes, clouds, and snow. Furthermore, there is clear evidence for reversibility of the process. Based on these observations, a conceptual process model is developed which explains the modes of observed dune growth patterns. In this model dune growth proceeds in steps as a function of grain size and flow velocity, the process being inherently reversible. Water depth is a limiting factor, but not otherwise a functional parameter required for bedform generation. Internal sedimentary structures produced in the course of amalgamation or dune splitting is illustrated by theoretical reconstructions and high-resolution seismic profiles. |
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