Types of wier:
1. Gravity wier:
Uplift pressure due to the seepage of water below the floor is resisted (entirely) by the weight of floor.
2. Non-gravity floor:
it has less thicker floor resistance is offered by the bending action of reinforced concrete floor.
Types of Gravity Weir
- Vertical drop weir
- Masonary or concrete slope weir
- Dry stone slope weir
- Parabolic weir
Vertical drop weir
- Most basic type and most wiedly used in small weirs
- Vertical drop weir or crest wall
- Upstream and downstream cut off wall at the end of impervious floor.
- Launching apron for scouring prevention
- Graded inverted filter at downstream floor end to relieve the uplift pressure.
Masonary or concrete slope weir:
- Suitable for soft sandy foundation.
- Generally used where the difference in wier crest and d/s river is limited to 3m
- Hydraulic jump is formed on slopping crest
Dry stone slope wier:
- Body wall or weir wall
- u/s and d/s rock fill laid in form of glacis with few interveining core walls.
- similar to spillway section of a dam
- body wall designed as low dam
- cistern to dissipate the energy
- u/s and d/s protection works are similar to that of vertical drop weir.