WEIR
An impervious barrier which is constructed across a river to raise the water level on the upstream side is known as a weir. Here the water level is raised up to the required height and the surplus water is allowed to flow over the weir. Generally it is constructed across an inundation river.

 BARRAGE

When adjustable gates are installed over a weir to maintain the water surface at different levels at different times is known as a barrage. The water level is adjusted by operating the gates or shutters. The gates are placed at different tiers and these are operated by cables from the cabin. The gates are supported on piers at both ends. The distance between the pier to pier is known as Bay.

Weir-

1. It is a solid construction put across a river to raise the water level in the river.
2. Less costly.
3. No control over the water level.
4. No attention is required at the time of flood.
5. After long time, silting problem is there.

Barrage-

1. No solid construction is put across the river. Heading up of water is effected by the gates.
2. More costly.
3. Better control over the water levels.
4. At the time of flood, the gates are raised and lowered.
5. No silting problem.

Causes of failure of Weirs & their Remedies