Q. Describe Principles of river protection works?

Determination of design discharge for a bridge is sometimes required to be based on flood marks left during unprecedented abnormal floods. A flow formula is then used to estimate discharge corresponding to flood marks. The river section is often composite comprising flow section with one or more deep channels and an overbank area carrying spill flow. Allowance for such variation is required to be made in application of the flow formula, suitable procedure for which needs to be known.

Excessive constriction of waterway by approach banks results in rise of water level which is termed afflux. Apart from construction of waterway, afflux is also caused due to pier obstruction. The extent of afflux is an important consideration in fixing bridge waterway.