Q. What do you mean by Scour?

Whenever a bridge crosses a waterway, even a small or intermittent one, scour is a dangerous effect that can damage bridge piers and undermine foundations. Scour is the hole left behind when sediment (sand and rocks) is washed away from the bottom of a river. Scour action is especially strong during floods. Swiftly flowing water has more energy than calm water to lift and carry sediment down the river.