Q. Afflux in rivers with non scourable bed?

Afflux is defined as rise of flood level of the river upstream of a bridge as a result of the obstruction to natural flow caused by the construction of the bridge. It is caused either due to constriction of waterway by approach banks or on account of obstruction to flow caused by piers. Afflux results in increase of velocities in constricted section and at the obstructions. When riverbed has nonscourable strata or material, the increased velocities cannot scour the bed and therefore the boundary remains unchanged. Estimation of afflux under this condition is relatively simpler. When, however, the riverbed is sandy, it can scour easily due to increased velocities at the bridge.