Scour around bridge pier near a bank and its influence on flow pattern

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Local scour around bridge pier near a bank, is pepecuciarly caused by 3D-flow near a bank (vertical flow) and side by side spiral flow, in addition to horse-shoe vortex and forced down flow around free pier, and also due to river bed degradation, flow concentration, etc. Main experimental results are summarised below.1. Side by side spiral flow condition was artificially formed by the effect of air bubbles ejected from lined point sources on the bed longitudinally and laterally. And after verification that this flow condition is close to the existing flow pattern in a river, tha ways of deformation of flow pattern due to the interference with the flow around bridge pier and also the existence of vertical wall were investigated.2. Local scour depth and scoured area around bridge pier are clarified to be remarkably influenced by the position of pier in the side by side spiral flow. It is considered to be significant from the practical point of view that the scouring depth increases almost 20% at some location of bridge pier in side by side spiral flow.3. Side by side spiral flow is forced to be stable near vertical wall where uprising flow along the well except the area of bottom encourages the strenght of spiral motion near the well. Therefore, scouring depth can become maximum around bridge pier installed at proper distance from the wall.4. Some examples of local scour around pier near the wall are described in the cases of compound channel or curved channel, but its generalization is a problem in future.