The Characteristics And Experimental Research Of Gravel Riverbed Under Water Scour

Along with the development of mountainous river water resources in China, the research on water and sediment characteristics of mountainous rivers also appears more important. After building reservoirs or other water retaining structures in the river, the downstream of the coming water and sediment conditions changed, and then the riverbed would suffer water scouring which could cause coarsening. Research on water scour coarsening is a key to the study of riverbed evolution and to solve all kinds of downstream hydropower hubs' problems.First of all, the article analyzes the characteristics of gravel riverbed. Gravel riverbed commonly appears among Mountain Rivers. Different from gravel and sand riverbed or sandy riverbed, gravel riverbed has its own characteristics. The article analyzes the inconstancy of gravel movement, the armoring layer and its formation mechanism, different coarsening types and the downstream fining phenomenon.To study the phenomena above, we designed a flume experiment of gravel riverbed under clear-water scouring. We use continuously graded gravel which has a size range of 3mm to 50 mm as sample. And we present three clear-water scour experiments with the change of flow quality. The experiments are all in a flume which is 17 m long, 0.58 m wide and 0.5m deep. The scouring depth and armoring layer gradation are measured and the process of gravel riverbed armoring under clear-water scour is analyzed.Moreover, starting from incipient velocity, we defined a critical grain size and put forward a new method to predict the gradation of armoring layer which is only applied to gravel riverbed. Validating the method with the data of the experiment and others' data,we can see its good accuracy.