Time Dependent Local Scour Around Groynes and Bridge Abutments

Scour around any obstruction is the lowering of a portion of the river bed below its natural level. This is caused due to the large scale eddies or a system of vortices which are developed near the obstruction. Local scour occurs around abutments, spur dikes and embankments because of the obstruction to flow caused by such structures. Though the mechanism of scour is difficult to quantify but its study gives considerable guidance in predicting the magnitude of scour around any hydraulic structure. The determination of scour depth is required for the design of any foundation of hydraulic structure for its safety as the development of scour hole is one of the principal causes of failure of any hydraulic structure. A number of scour depth prediction formulae available so far have been analyzed in order to find out appropriate scour predictor around such structures in Bangladesh. By this study it has been tried to evaluate scour development around groynes and bridge abutments from both laboratory and field data and to evaluate recent methods for calculating equilibrium scour and time dependent scour.