Effect of Accelerating on Sediment Incipient Motion over Dunes under Shallow Water Condition

Abstract

Due to the complexity of bed form morphology and dune movement, this paper selected a series of 2-D asymmetric dunes in order to address the development of a flow region associated with velocity profile characteristics and sediment incipient motion under shallow water condition. Experiments were conducted over four asymmetric dunes of one crest length (4 m), two crest height (0.3m,0.4m) and two uniform sediments with mean grain sizes D=0.5 and 0.7 mm at the TianJin Research Institute For Water Transport Engineering, China. By using Acoustic Doppler Velocimeter (ADV), the instantaneous velocities were measured at four cross sections giving a total of 16 measured profiles. The variations of velocity profile along the flow affected by the wavy bottom have been studied. The results show that the effect of flow acceleration plays an important role in governing incipient motion over dunes.