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Large transverse bedforms and the character of boundary‐layers in shallow‐water environments
Author(s) -
ALLEN J. R. L.
Publication year - 1980
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1980.tb01181.x
Subject(s) - geology , bedform , ripple marks , beach morphodynamics , curvature , transverse plane , flow (mathematics) , waves and shallow water , mechanics , boundary (topology) , sediment transport , geomorphology , geophysics , geometry , ripple , sediment , physics , oceanography , mathematical analysis , mathematics , quantum mechanics , voltage , engineering , structural engineering
Theoretical work, laboratory studies, and field observations indicate that the oscillatory boundary layers generated by the tidal wave differ fundamentally in dynamics and kinematic structure from the unidirectional boundary layers of rivers. Unique to the former are mass‐transport currents attributable to: (1) the wave motion itself, and (2) bed curvature in the presence of the oscillatory flow. The implication of this difference for bed‐material transport is that the larger flow‐transverse bedforms of shallow‐water environments are divisible hydraulically between two major classes: (A) those related to tidal conditions, under which the fluid reverses in direction of flow with each reversal of the tide, permitting the initiation and maintenance of bed features by the spatially reversing, curvature‐related mass transport, and (B) those related strictly to rivers and river‐like flows, in which the fluid motion is unidirectional, and therefore the only mechanisms available for bedform initiation and maintenance are those creating a finite spatial lag between the transport rate and the bed waviness. Forms of Class B are best called dunes and bars, and only those attributable to Class A should be termed sand waves. The latter, restricted to oscillatory boundary layers of tidal origin, apparently correspond to the very much smaller; but also commonly symmetrical, ripple marks produced in wind‐wave oscillatory boundary layers.