A solid obstruction put across river to raise its water level and divert water into canal (low head structure) Vertical drop wall or crest wall Upstream, downstream cut off wall at the ends of impervious floor

The only difference between a weir and a barrage is of gates, that is the flow in barrage is regulated by gates and that in weirs, by its crest height. Barrages are costlier than weirs. Weirs and barrages are constructed mostly in plain areas. The heading up of water is affected by gates put across the river. The crest level in the barrage (top of solid obstruction) is kept at

Common causes of failure of weirs include: Excessive and progressive downstream erosion, both from within the stream and through lateral erosion of the banks Erosion of inadequately protected abutments

When the angle between the headwork axis and the river axis exceeds 10°, the problem arises of concentration of flow on one side and island formation due to heavy silting within the guide bank on the other side. If the river axis is to the right of headwork axis, the concentration of flow is generally generally on the left side with consequent tendency to form an island

Bligh's Creep Theory: Design of impervious floor for sub surface flow: It is directly depended on the possibilities of percolation in porous soil on which the floor (apron) is built. Water from upstream percolates and creeps (or travel) slowly through weir base and the subsoil below it. The head lost by the creeping water is proportional to the distance it travels (creep length) along the base of the