Abstract:

Hyper-concentrated flows occur frequently in desert watersheds， leading to river jamming and causing the severe disasters in desert rivers. But until now it is still unknown about the mechanism on the hyper-concentrated flow induced such a river jamming， mainly because these flows in desert watersheds are too short in duration and too strong in destructive force to be observed in the field. Some studies have used fly-ashes to simulate this process in an experimental water flume. However， these fly-ashes are too small in unit weight to simulate movements for coarser and heavier sands in water flows. Here we let a hyper-concentrated flow （763.7-1 059.54 kg·m^-3）， which was formed by gravity on a 12° slope covered by aeolian desert sands， rush into a water flow in a bending channel with a 3 m width to simulate river jamming by a hyper-concentrated flow. Our results show that coherent vortices at the confluence can cause attached-bank sandbar formation and consequently lead to river jamming. When the ratio of discharge between the hyper-concentrated flow and the flow in the bending channel is larger than 0.5 but less than 6.0， river jamming may occur in the downstream channel to the confluence. Our results also indicate that about 28% of sands supplied by the hyper-concentrated flow are rapidly deposited to form such attached-bank sandbars， which is actually the primary reason of hyper-concentrated flows induced river jamming in desert rivers.

Key words: hyper-concentrated flow, coherent vortices, river jamming, experimental simulation