Author(s): K. Kanda; Y. Muramoto; Y. Fujita
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Abstract: Local scours occurring downstream of consolidation works and their adjacent bed protection ones are usually divided into clear-water scour and scour with continuous sediment motion (dynamic scour). In the former type of scour, tractive force on the river bed exceeds the critical tractive force of incipient motion only in a immediately downstream reach of the bed protection works, and in the latter type the tractive force is great enough to carry sand through the length of river bed. Both types of scour are strongly affected by sudden changes in bed roughness of river channels. The scour with continuous sediment motion is predominant during flood; hence analysis of the properties of this type of scour is important for the safety of river structures such as consolidation and bed protection works. Suzuki et al. Conducted a detailed experimental investigation of the process of local scour with continuous sediment motion downstream of consolidation works. But, their study did not deal with the scour under the condition of dynamic equilibrium because the sediment supply from the upstream was not considered. In addition, in downstream reach of bed protection works having protruded spot roughness rapid flows between the protruded spot elements is diffused over the downstream movable bed. It exhibits flow properties similar to those of three dimensional jets, resulting in complex bed profiles with transverse undulations. In consequence, it makes extremely difficult to predict the maximum depth of scour and its location during floods.
Year: 1993