Civil Engineering Departlmet, M.M.M. Engineering College, Gorakhpur, U.P.
In this paper, local scour caused by the horse-shoe vortex system which forms at the base of the pier has been considered. A formula for the vortex diameter is derived from the analysis of the forces acting on an idealised sediment particle in the scour hole beneath the vortex system by taking into account the strength of scouring vortex at equilibrium condition. The formula relates the vortex diameter to various flow parameters, sediment size and pier diameter. It is assumed that the vortex diameter has a direct relation with the scour depth at the piers. Design criteria are also proposed for clear water scour, live bed scour and field data of different investigators for cohesionless uniform bed materials and cylindrical piers. In the case of non-cylindrical piers, additional multiplying factors to account for pier shape and alignment are applied.
