Weir:
- Weir is a crest wall constructed across a river to divert raise water of river into canal.
- Crest wall constructed across a river raises the water. And the small part is done by shutter sometimes if provided on the top of crest wall.
Types of Weir:
Weirs are classified as follows:
- Gravity Weir
- Non-gravity weir
1.Gravity Weir:
- When the weight of weir balances uplift pressure caused by the head of water seeping below weir then it is called as gravity weir.
2.Non gravity weir:
- In this, weight of concrete slab with the weight of divide piers resists the uplift pressure largely.
- Non gravity weirs has following types:
- Vertical drop
- Rock fill
- Concrete
A.Vertical drop:
- This type consists of horizontal floor and a masonry crest with vertical or nearly vertical downstream face and One provides shutters at the crest.
- Most of storage is done by raised crest and some storages by shutters provided over the crest.
B.Rock fill:
- One calls it as dry stone slope weirs.
- It is suitable for fine sandy foundation stone which one uses mainly for construction of such type of weirs and hence requires large quantities of stone.
C.Concrete:
- These are suitable for permeable foundations.
- In such weirs sheet piles are provided on both upstream and downstream floors, in order to destroy the energy of water.
Component Parts:
The component parts are as follows:
- Body of weir
- Upstream Apron
- Upstream curtain wall
- Downstream apron
- Downstream curtain wall
- Crest
- Shutter
1.Body of weir:
- One generally makes it of masonry.
- Its function is to raise water level on upstream side.
- It should be strong enough to resist water pressure.
2.Upstream apron:
- It protect it during floods from eroding action.
- Its length depends upon discharge of river and weir’s length.
- It also help to prevent leakage in subsoil and it minimizes uplift water pressure if any exist.
3.Upstream curtain wall:
- One provides it to reduce the uplift pressure.
- Its length depends upon the nature of soil.
4.Downstream apron:
- Downstream apron serves like energy dissipators.
- These are provided for destroying kinetic energy and thus prevent downstream side from erosion.
- Its length depends upon the height of fall nature of soil discharge etc.
5.Downstream curtain wall:
- It protect downstream floor from uplift pressure.
- Its length depends upon the length of weirs.
6.Crest:
- It is the top of the weir.
- It must be strong and durable as it has to resist water pressure oftenly during floods.
- During flood, water flows over from the crest.
7.Shutter:
- Shutters are provided at the top.
- It also helps in raising the water level on upstream of river.
- Shutters must be strong to resist water pressure.
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