Xiao, Q.; Li, R.; Li, C., and Fang, X., 2018. Predicting wave-induced ripple geometry and bottom friction factor. In: Liu, Z.L. and Mi, C. (eds.), Advances in Sustainable Port and Ocean Engineering. Journal of Coastal Research, Special Issue No. 83, pp. 148–154. Coconut Creek (Florida), ISSN 0749-0208.
The ripples induced by waves are prevalent in the offshore area. The accurate prediction of the ripple characteristics and bottom friction factors is the foundation of the research on the wave deformation, sediment transport and the evolution of shoreline. In this paper, the formulas commonly used for the calculation of the wave-induced ripples are analyzed and evaluated by using the published experimental data from the laboratory experiment and the field observation. The coordinated property of the bed form and the flow condition is considered, and a new prediction method is proposed to calculate the ripple equilibrium geometry such as length, height and steepness. The discriminant function including the wave critical Shields parameters is introduced to take the effect of the bed load transport into account. The formula of wave friction factor is derived theoretically, and the estimation of roughness height is improved by the sand ripples formulas. The results show that the proposed formulas can give a better description of the ripple characteristics when the bed load sediment move in different state. The critical Shields parameters influence greatly on the calculation ripple geometry. Moreover, the new ripple prediction can be used to calculate bottom friction factors efficiently.