Bedform

Bedforms are omnipresent in many environments (e.g., fluvial, eolian, glaciofluvial, deltaic and deep sea), although there is still some debate on how they develop.

Venditti et al. (2006),[8]: 1  based on the earlier model by Liu (1957), proposed that instantaneous initiation is a manifestation of an interfacial hydrodynamic instability of Kelvin-Helmholtz type between a highly active pseudofluid sediment layer and the fluid above it.

In addition, Venditti et al. (2005)[7]: 2  imply that there is no linkage between the instantaneous initiation and coherent turbulent flow structures, since spatially- and temporally-random events should lock in place to generate the cross-hatch pattern.

It is important to note, that laminar-generated bedform studies used the temporally-averaged flow conditions to determine the degree of turbulence, indicating Reynolds number in the laminar regime.

However, instantaneous process, such as burst and sweeps, which are infrequent at low Reynolds number but still present, can be the driving mechanisms to generate the bedforms.

Phase or stability diagrams are defined as graphs that show the regimes of existence of one or more stable bed states.

Bidirectional environments (e.g. tidal flats) produce similar bedforms, but the reworking the sediments and opposite directions of flow complicates the structures.

Current ripples preserved in sandstone of the Moenkopi Formation , Capitol Reef National Park , Utah , United States.
Dimensional phase diagram for combined flows. Relationships of combined-flow bed-phases stability fields in a plot of Oscillatory vs Unidirectional velocity. [ 2 ] : 1
Bedforms formed in sand in channels under unidirectional flow. Numbers correspond broadly to increasing flow regime, i.e., increasing water flow velocity. Blue arrows show schematically flow lines in the water above the bed. Flow is always from left to right.
Parting lineation, from lower left to upper right; Kayenta Formation , Canyonlands National Park .
Megaripple from Utah