Bed Material Movement in Hyperconcentrated Flow

A series of experiments were made in a closed rectangular conduit with bentonite as fine particles and plastic beads as coarse particles. Compared with that in clear water, in bentonite suspensions coarse particles settle more slowly and start moving at a higher flow intensity. Due to the larger threshold velocity and smaller settling velocity, the bed load is smaller and the suspended load is larger. As a result, the total load, consisting of the bed load and the suspended load, is smaller in the low flow intensity region, but larger in the high flow intensity region. The increase of the suspended load favors the transition from dunes to plane bed. So in clay suspension dunes are lower, flatter, and change to plane bed at lower flow intensity. Correspondingly, the form resistance is smaller in clay suspension.