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

我们对单向流动中河床特征的性质作为流动强度和沉积物分选的函数进行了实验研究，通过配制几种平均尺寸约为4毫米但分选变化很大的沉积物混合物，并在每种沉积物混合物上以几种平均流速进行一系列运行。为了进行这个美日合作项目，在筑波环境研究中心（ERC）建造了一个新的再循环管道。当床层剪应力大于床层最大颗粒临界剪应力的两倍时，封闭风道内的砾石床形成沙丘。由于沙丘的迁移速率是泥沙平均移动速度的两倍，因此可以用沙丘的迁移速率来评价河床输沙速率。当床层剪切应力小于床层间粗质种群的临界剪切应力时，细碎组分在不动的粗质基质上以薄斑块或饥饿的小沙丘的形式移动。在细颗粒的流量和比例范围内，在片状和沙丘之间有一个连续的过渡。

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.