Scour Development at Elliptical Guide Banks during Multiple Floods

The scour development at bridge abutments and elliptical guide banks during multiple floods is studied. At the upstream head of the elliptical guide bank, a streamline concentration, a local increase in velocity, vortex structures, and the development of a scour hole were observed. The failure of guide banks as a result of scour leads to the flow redistribution and an unpredicted scour at the alignment of the bridge crossing and can be the reason for failure of piers and abutments. In spite of the importance and complexity of the phenomena, scour at the elliptical guide banks has not yet been studied. The differential equation for the bed sediment movement under clear-water conditions is used, and a method for computing the scour development during multiple floods is presented. The method is confirmed by experimental data. A theoretical analysis of the method suggested was performed, and it was found that the dimensionless depth of scour at the elliptical guide banks depends on the following parameters: the flow contraction rate, the kinetic parameter of the open flow, the kinetic parameter of the flow under the bridge, the ratio of the Froude number to the slope, the dimensionless grain size, the stratified riverbed conditions, the ratio of the local velocity to the velocity at which the sediment movement starts, the relative flow depth, the time interval, the flow unsteadiness, the scour formed during the previous time step, the shape and wall slope of the guide banks, the flow crossing angle, the probability of multiple floods, as well as their sequence and duration