Scouring Processes Of Riverbed Around Spur Dikes

Spur dikes are widely used for dredging waterway and protecting the banks. Most of the previous results are obtained from constant flow and fixed bed experiments in the flumes. By means of movable bed experiments and mathematical model computation, general researches on the scouring processes of riverbed around spur dikes are performed in this paper.The research on length and maximum width of re-circulation is very important for design of spur dikes. A two dimension numerical model is established for the simulation of the flow around spur dike by use of control volume method. Based on previous experimental results and numerical computation, some differences of re-circulation length between laboratory data and field data are discussed and the influence scopes of spur dikes are analyzed.By means of flume experiment, the scouring processes of riverbed are investigated, and the effects of bed variation are discussed emphatically. Local scour on the head of a spur dike is disadvantageous to the structures. Experiments are made to study the influence of head slope on local scour around a spur dike with different head slopes changing from 0 to 6. The test results indicate that a suitable head slope and an adjacent bed protection can prevent the development of the scour hole. A formula of relationship between the maximum depth of a scour hole and head slope is derived from experiment data. Some design principles about head slope and bed protection are suggested for practice engineering.Hydrological conditions in estuaries are very complex and unique. By means of flume experiments on alternating current, the characteristics of spur dikes in tidal current are discussed and the regulations of waterway renovation are investigated. A formula on the expanding ratio of regulated line in estuary is proposed. By use of tests on the alignment of spur dikes in natural broad-shallow river, the design principles of spur dikes both in the shallow water and deep water are proposed, and the engineering value of spur dikes is emphasized. For engineering purposes, several problems about spur dikes are pointed out according to the principles with some engineering examples.