Experimeutal study of the Mechanism of Heterogeneous Sediment Transport in a closed duct.

点击翻译按钮获取中文摘要

We have conducted an experimental study of the nature of bed features in unidirectionary flows as a function of flow strength and sediment sorting by formulating several sediment mixtures with the same mean size of about 4 mm but with wide varying sorting and making series of run at several mean flow velocities over each sediment mixture. In order to conduct this US-Japan cooperative project, a new recirculating flow duct was built at the Environmental Research Center (ERC) in Tsukuba. When the bed shear stress is larger than twice the critical shear stress of the largest grains on the bed, dunes develop on a gravel bed in the closed duct. As the migration rate of dunes are twice the mean travel velocities of sediment, bedload transport rate may be evaluated by the migration rate of dunes. When the bed shear stress is smaller than the critical shear stress of the coarse population among bed material, the fine fraction moves as thin patches or small starved dunes over an immobile coarse substrate. There is a continuous transition between sheets and dunes over a range of botu discharge and proportion of fine grains.