Components of diversion headworks

Components of Diversion Head Works:

The various components of diversion headworks are as follows:

1. Weir or Barrage
2. Divide wall
3. Fish ladder
4. Under sluice
5. Silt excluder
6. Canal Head Regulator
7. River training works
   1. Guide bund
   2. Marginal bund

a. Weir or Barrage

• Weir is a structure constructed across a river to raise its water level and divert it into the irrigation canal.
• Weir is provided with shutters on the crest.
• A part of raising water is carried out by shutters.
• It is usually aligned at right angle to the direction of flow of river.

• Barrage is a structure constructed across a river to raise its water level and divert it into the irrigation canal.
• The crest of barrage is low.
• The raise of water level is done with the help of gates.
• It is costlier than weir.

b. Divide Wall

• It is also called divide groyne.
• It is a long masonry or concrete wall which is constructed at right angle to the axis of the weir.
• It separates under sluice from the rest of the weir.
• It extends from upstream to downstream of the weir. 

c. Fish Ladder

• Due to construction of weir or barrage, fish are not able to migrate from upstream to downstream of weir and vice versa.
• So to enable fish to migrate, fish ladder is provided.
• The velocity of flow in fish ladder is maintained at less than 3 to 3.5 m/s.

d. Under Sluice

• It is also called scouring sluice.
• It is the opening provided in the weir wall with their crest at lower level.
• These openings are controlled by gates.
• They are located at same side as off-taking canal.

e. Silt Excluder

• They are silt control devices.
• They exclude silt in water from entering into the canal.
• They are provided on river bed in front of head regulator.
• It consists of number of rectangular channels.
• It rests on the floor of under sluice pocket.

f. Canal Head Regulator

• It is a structure constructed at the head of canal.
• It is present at upstream of weir or barrage.
• It consists of number of spans separated by piers.
• Piers support the gate provided for regulation of water to the canal.
• The spans are 6 to 8 metres.
• The steel gates are used which are operated manually.

g. River Training Works

• River training works are various measures adopted on a river or stream to stabilize the river channel along a certain cross section and alignment.
• They are adopted for alluvial soil because they frequently change their courses.

The following river training works in diversion headworks are used:

1. Guide bund
2. Marginal bund

i. Guide Bund

• It is also called guide bank.
• They are earthen or rock-fill embankments provided to control the flood water of alluvial river.
• It is provided to prevent river from changing its course and to keep the construction work area straight and non-twisted.
• Guide bund was first designed in India by Bell. So, it is also called Bell's bund.

ii. Marginal Bund

• It is also called a levee.
• It is an earthen embankment provided to control the flood water from a river within an allowable cross section.
• Spreading of flood water beyond the marginal bund is prevented by its construction.