Control of Water Level: A weir increases the level of a river or channel , generating a head that makes it easier to divert water into a reservoir or canal.

Water flow is regulated by altering the peak's height, which guarantees a consistent & regulated supply for irrigation or other purposes.

Control of Sediment: The weir reduces the amount of silt that enters the canal and preserves its efficiency by slowing the water flow and allowing sediment to settle upstream.

Flood Control: The weir helps control surplus water during high flow situations by channeling it into overflow channels to stop flooding downstream.

The weir is an essential part of Irrigation Engineering and diversion because of these purposes.