Sand Ripples and Bedforms
Form drag for oscillatory flows over wave-generated sand ripples is important for modeling coastal hydrodynamics and sediment transport processes. A large set of full-scale experiments are conducted in an oscillatory water tunnel, in which form drag is directly measured through a novel pressure-based technique. The measurements suggest that form drag is almost in phase with free-stream oscillatory flow. The maximum form drag is converted to a wave friction factor, and the obtained values are generally within 0.1-0.2. Using measurements and a wave boundary layer model, equivalent sand-grain roughness for sand ripples are calibrated.