Initiation and inhibition of the formation of asymmetrical sand ripples
Titel:
Initiation and inhibition of the formation of asymmetrical sand ripples
Auteur:
Moss, A. J.
Verschenen in:
Australian journal of earth sciences
Paginering:
Jaargang 22 (1974) nr. 1 pagina's 79-90
Jaar:
1974-04
Inhoud:
Often in nature and sometimes in flumes, asymmetrical sand ripples do not form when considerations of hydraulic variables and grainsize indicate that they should. This paper reports experimental inhibition of ripple formation by allowing small waves, generated from sources both at the surface and on the bed, to pass upstream along a flume. If ripples do not appear on a bed, form drag is greatly reduced and equilibria between flows and particles consequently differ from those existing if ripples are present. Asymmetrical sand ripples are secondary structures, generated immediately downstream of existing ripples, or by modification of either random bed irregularities or protoripples. The latter are transverse patterns of low-amplitude mounds and depressions, evidently stationary, which grow from essentially plane beds, and are enhanced at both peaks and troughs by areally differential erosion and deposition. If it is assumed that a fluid-dynamic lift force is important in moving the bed grains, the formation of protoripples and ripples can be explained qualitatively. Persistence of essentially plane beds, under some conditions, and some differences between ripples and dunes also become explicable.
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