Correct option is A
The term Afflux refers to the rise in water level upstream of a structure like a bridge or weir when water flows over it. This increase occurs because the structure causes a blockage, leading to a higher water level as the flow passes beneath or over the bridge. The other options are defined as follows:
Free board is the safety margin between the normal water level and the top of the structure.
Scour refers to the erosion of sediment around bridge foundations due to flowing water.
Clerance (likely intended to be "clearance") denotes the vertical space available beneath the bridge for water and traffic.
Therefore, the correct answer is Afflux.
