MITIGATION OF LOCAL SCOUR BY USING A TRAINING STRUCTURE PLACED UPSTREAM OF A SPUR DIKE

摘要

Recently, spur dikes are broadly used for environmental and ecological purposes. In order to use spur dikes for a long time, it is necessary to investigate the method to prevent local scour around spur dikes. In this study, a lower-height structure placed upstream zone of the spur dike is considered as a measure of mitigating local scour. This hydraulic structure is called as a training structure. The relative height and location interval of the training structure with the target spur dike were changed and their effects were investigated in a movable-bed condition. Then, the mechanism of reducing local scour by the training structure was evaluated from the flow structures on a fixed bed experimentally and numerically. The scour around the target spur dike becomes smaller with an increase of the height of training structure, but the local scour around the training structure increases. Therefore the height of the training structure is adequate for 0.5 times of the height of the target spur dike. The vorticity is concentrated in the gap when the interval length between training structure and spur dike is too short, but the reduction effect decreases when the interval length is too long. The mechanism of reducing the scour around the spur dike is not attributable to the flow structure on the flat bed but it is subjected to the bed deformation process.