Barchan dunes: why they cannot be treated as ‘solitons’ or ‘solitary waves’

Abstract

Schwämmle and Herrmann (Nature, 2003, vol. 426, p. 619) have suggested that two subaerial barchan sand dunes could 'pass through one another while still preserving their shape' in a manner similar to solitons or solitary waves. A wide range of published field and wind tunnel evidence suggests that this assertion should not go unchallenged.

Complex systems in aeolian geomorphology

“…This question has come to a head because recent small-scale flume studies that report barchan-shaped current ripple dynamics (Endo et al, 2004) have been used to justify a type of numerically simulated subaerial dune interaction Herrmann, 2003, 2005) that does not accord with our contemporary understanding and empirical evidence of aeolian dune dynamics in the atmospheric environment (Livingstone et al, 2005). The similarity argument is also assumed as part of a universal scaling law for dunes forming in a variety of materials and fluids, including current ripples (Hersen et al, 2002;Claudin and Andreotti, 2006).…”

Long-time evolution of models of aeolian sand dune fields: Influence of dune formation and collision

“…Most natural dune field interaction functions will not correspond with one of these examples (in particular, see Livingstone et al (2005) for a discussion about the unphysical nature of the soliton example). Instead, a natural dune field interaction function will probably be a combination of these extreme examples, with some regions where f(r) b r, some regions where f(r) N r, and transition points where f(r)=r.…”

How do bedform patterns arise? New views on the role of bedform interactions within a set of boundary conditions

“…The concept originated from CA models of wind ripples (Landry and Werner, 1994), but has been independently proposed for aeolian dunes (soliton model of Schwammle and Herrmann, 2003; 'ejection' of Katsuki et al, 2005a). The exact dynamics of the dune models are doubtful because the downwind dune must emerge from within the separation cell of the upwind dune (Livingstone et al, 2005). A more probable scenario for bedforms with fl ow separation was shown with subaqueous barchan ripples by Endo and Taniguchi (2004), in which the lee eddy of the upstream bedform scours into the stoss slope of the larger downstream bedform, resulting in a scoured trough but also the emergence of a small bedform from the remnant crestline of the downstream bedform.…”