ABSTRACT
When a bridge is placed in a river it forms a narrowing of the natural channel and an obstacle to the flow. This results in a loss of energy as the flow contracts, passes through the bridge and then, most significantly, reexpands back to the ful l channel width . To provide the additional head necessary to overcome the energy loss the upstream water level increases above that which would be usually experienced without the bridge. This additional head is called the afflux, and its variation w i t h distance upstream is called the backwater profile. The smaller the opening, the greater the afflux and backwater.
