Q. Show Afflux and scour in alluvial rivers?

In case of alluvial rivers, the river bed comprises scourable material like sand. Constriction of bridge waterway causes increase in discharge intensity and increase in velocity which result in bed scour. Scour in riverbed increases the depth of flow and reduces velocity and hence the scouring capacity.

When excess of sediment transporting capacity in the constriction beyond normal capacity in unconstricted reach is neutralised by progressive bed scour during rising flood of a hydrograph, no further scour occurs. This depth with full scour approximates normal scour depth in the same river adjusted for the increased discharge intensity on account of constriction.