A laboratory study of formative conditions for characteristic ripple patterns associated with a change in wave conditions

A wave-flume experiment was conducted to examine the formative condition for three types of distinctive bedforms that emerged through deformation of existing ripples due to waning wave power. They were ripple marks with: (1) a single secondary crest, (2) double secondary crests, and (3) a rounded crest. Data were analysed using two parameters, kh and d0/λ*, where k is the wave number, h is the water depth, d0 is the near-bottom orbital diameter, and λ* is the spacing of existing ripples. The former quantity, kh, was employed as a surrogate for the degree of flow asymmetry. The result showed that ripples with secondary crests developed under a rather symmetrical flow field with kh ≳ 0·7, if d0/λ* ≲ 1·2, whereas rounded-crest ripples emerged under asymmetrical flow field with kh ≲ 0·7, if d0/λ* ≲ −2·9 kh + 3·2. The number of secondary crests, which initially occurred in each trough, was single if d0/λ* ≳ 0·8, or double if d0/λ* ≲ 0·8. Copyright © 2004 John Wiley & Sons, Ltd.