What is Weir?

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:

1. Gravity Weir
2. 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:

1. Vertical drop
2. Rock fill
3. 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:

1. Body of weir
2. Upstream Apron
3. Upstream curtain wall
4. Downstream apron
5. Downstream curtain wall
6. Crest
7. 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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