Floods result in significant economic losses and human misery, necessitating mitigation measures to lessen their effects in places that are vulnerable. The evaluation of the flood peak moderation at a possible downstream damage station in a river system is the main objective of the current study. The flow rate at the damage site is estimated using a downstream flood flow simulation model for a river system that incorporates flows from gauged and ungauged subbasins. The Barak River system in India is used to apply the model, and Badarpurghat selected as a possible downstream damage station. The study reveals that tributaries are having significant impact on the downstream flow and downstream flow can be brought under control during flood seasons by coordinated control of tributaries.