Question

what is the Difference between barrage and dam?

Answer 1

A dam is a barrier across flowing water that obstructs, directs or slows down the flow, often creating a reservoir, lake or impoundment.

A barrage is an artificial obstruction at the mouth of a tidal watercourse used to increase its depth or maintain a separation between fresh and salt water or reduce the risk of tidal flooding up the river.

Answer 2

Dam: Dam is merely a barrier constructed across the river/ flow to stop its flow and store the water by forming reservoirs at up stream side of the barrier.

Barrage: Barrage is also a barrier constructed across the flow to raise and divert the water to an off taking canal or channel.
 for further details read water power and irrigation engineering by Pumia