Modelling Dynamic Bed Roughness Associated with Bed Form Development

Abstract

In this study bed form development was quantified and used to calculate a dynamic bed roughness parameter. An algorithm that can be readily implemented into numerical models was developed and evaluated for two scenarios, with distinct flow conditions and sediment carrying capacities. The final bed form height and length and the time for their occurrence were used in an existing bed form development model, which gave the time-dependent ripple dimensions and bed roughness parameters. A good agreement was achieved between measured and predicted results. The variation of the bed roughness, as observed from the flat bed state to the final stage of ripple development, spanned 2 orders of magnitude, irrespective of the flow and sediment transport conditions considered. Implementation of the dynamic bed roughness calculation procedure included herein in numerical models can improve the representation of the sediment-water interface in modelling studies, when compared to the conventional approach based on a constant roughness parameter.