Diversion Headworks MCQ Quiz - Objective Question with Answer for Diversion Headworks - Download Free PDF

Concept:

Head Sluices (or Canal Head Regulator): A head sluices or canal head regulator (CHR) is provided at the head of the off-taking canal, and serves the following functions:

• It controls the entry of the silt into the canal.
• It regulates the supply of water entering the canal.
• It prevents river floods from entering the canal.

Silt Ejectors (or Silt extractors): These are the devices that extract the silt from the canal water after the silted water has traveled a certain distance in the off-take canal. These works are, therefore, constructed on the bed of the canal, and a little distance downstream from the head regulator.

Under-Sluices (or Scouring Sluices): The under sluices are the openings that are located on the same side as the off-taking canal and are fully controlled by gates, provided in the weir wall with their crest at a low level. Their main functions are:

• It helps in controlling the silt entry into the canal.
• It scours the silt deposited on the river bed above the approach channel.
• It passes the low floods without dropping the shutter of the main weir.
• It preserves a clear and defined river channel approaching the regulator.

Divide Walls: Divide wall is a masonry or concrete wall constructed at the right angle to the axis of the weir. Its main objective is to form a still and comparatively less turbulent water pocket in front of the canal head regulator so that the suspended silt can be settled down which then later be cleaned through the scouring sluices from time to time.

Explanation:

Distributary head regulator

• Controls water flow from the main canal into distributary channels.

• Maintains proper distribution of water according to demand.

• Prevents excess water entering distributaries, avoiding flooding.

• Essential for managing irrigation systems efficiently.

Additional Information

Canal escape:

• Removes surplus water from a canal to a natural drain or water body.

• Protects canal banks from erosion and overtopping.

• Used during floods or heavy rain to maintain canal safety.

• Acts as a safety valve for the canal system.

Cross regulator:

• Installed across the canal to maintain water level upstream.

• Controls discharge and flow distribution downstream.

• Helps in diverting water and regulating flow in branch canals.

• Not used for controlling off-taking channel supply.

Canal fall:

• Provides a controlled vertical drop in a canal on steep slopes.

• Prevents erosion by dissipating energy of flowing water.

• Maintains the canal bed profile and water flow.

• Does not regulate flow to off-taking channels.

Concept:

Head Sluices (or Canal Head Regulator): A head sluices or canal head regulator (CHR) is provided at the head of the off-taking canal, and serves the following functions:

• It controls the entry of the silt into the canal.
• It regulates the supply of water entering the canal.
• It prevents river floods from entering the canal.

Silt Ejectors (or Silt extractors): These are the devices that extract the silt from the canal water after the silted water has traveled a certain distance in the off-take canal. These works are, therefore, constructed on the bed of the canal, and a little distance downstream from the head regulator.

Under-Sluices (or Scouring Sluices): The under sluices are the openings that are located on the same side as the off-taking canal and are fully controlled by gates, provided in the weir wall with their crest at a low level. Their main functions are:

• It helps in controlling the silt entry into the canal.
• It scours the silt deposited on the river bed above the approach channel.
• It passes the low floods without dropping the shutter of the main weir.
• It preserves a clear and defined river channel approaching the regulator.

Divide Walls: Divide wall is a masonry or concrete wall constructed at the right angle to the axis of the weir. Its main objective is to form a still and comparatively less turbulent water pocket in front of the canal head regulator so that the suspended silt can be settled down which then later be cleaned through the scouring sluices from time to time.

∴ The correct combination is 1-C, 2-D, 3-B, 4-A.

Concept:

The efficiency of a silt ejector is given by the percentage reduction in silt intensity from upstream to downstream of the ejector:

\( \eta = \frac{I_u - I_d}{I_u} \times 100 \)

• \( I_u \) = Silt intensity upstream of the ejector
• \( I_d \) = Silt intensity downstream of the ejector

Concept:

Divide wall

• The dividing the river width into two portions; one is called the weir portion, and the other portion from which the canal takes off is having openings and is called the 'under-sluice-pocket' or 'under sluices' or 'weir scouring sluices'.
• If there are two canals, taking off from each flank, then there will be two divide walls and two under sluices. 

Explanation:

Canal-regulator:

• Canal Regulators are required on a channel to regulate the supply of water.

• For effecting control of flow on the irrigation system some structures are required to be constructed at the barrage and also on the off-taking distributary canals and these structures are : 1. Canal Head Regulator  2. Canal Cross Regulator

​Canal Cross Regulator: 

• It is a control structure constructed across a canal to regulate the level of the water upstream of the cross regulator.
• It is general practice to provide a cross regulator in the main canal downstream of the off-taking canal.

• The functions of cross regulator:
  (a) To allow the desired discharge in the off-taking canal that is situated upstream of the cross regulator,
  (b) To release water from the canals by operating along with escapes,
  (c) To maintain the water surface slopes in appropriate conjunction with the flow control over falls so the canals may attain their regime slopes and cross sections,
  (d) To control the discharge released by one canal into another canal or lake.

​Canal Head Regulator: 

• A canal head regulator which is located just upstream of a barrage (or placed appropriately near about a reservoir) is provided to help,
  (a) regulate the discharge flowing into the off-taking canal, and
  (b) control the entry of sediment into the canal.

• A head regulator is generally aligned at an angle of 90° to 110° to the axis of the barrage in order to minimize the entry of sediment entering into the channel, besides
  preventing backflow and stagnant pools in the under-sluice pocket that lies in the vicinity of the regulator.

 ​

Explanation:

Canal head work

• Any hydraulic structure constructed at the head of the canal to regulate the flow of water is called canal head work.

Functions

• It regulates the supply of water into the canal.
• It controls the entry of the silt.
• It prevents the river flood from entering the canal.

Depending upon the stages (reaches) of the river, the location of head work is:

• Trough stage or alluvial stage
• Boulder stage
• Rocky stage
• Delta stage

​

Trough stage or alluvial stage

In this stage, the cross-section of the river is made up of alluvial sand and silt. The bed slope and velocity are small. It is Most suitable because

• The demand for irrigation water is high.
• Seepage losses are less.

Both rocky and delta stage is not suitable for canal head work.

Explanation:

Components of Head Works

Following are the parts/components of headworks

• Weir
• Under Sluices
• Canal Head Regulators
• Fish Ladder.
• Divide Wall.
• River Control Works

Concept:

Head Sluices (or Canal Head Regulator): A head sluices or canal head regulator (CHR) is provided at the head of the off-taking canal, and serves the following functions:

• It controls the entry of the silt into the canal.
• It regulates the supply of water entering the canal.
• It prevents river floods from entering the canal.

Silt Ejectors (or Silt extractors): These are the devices that extract the silt from the canal water after the silted water has traveled a certain distance in the off-take canal. These works are, therefore, constructed on the bed of the canal, and a little distance downstream from the head regulator.

Under-Sluices (or Scouring Sluices): The under sluices are the openings that are located on the same side as the off-taking canal and are fully controlled by gates, provided in the weir wall with their crest at a low level. Their main functions are:

• It helps in controlling the silt entry into the canal.
• It scours the silt deposited on the river bed above the approach channel.
• It passes the low floods without dropping the shutter of the main weir.
• It preserves a clear and defined river channel approaching the regulator.

Divide Walls: Divide wall is a masonry or concrete wall constructed at the right angle to the axis of the weir. Its main objective is to form a still and comparatively less turbulent water pocket in front of the canal head regulator so that the suspended silt can be settled down which then later be cleaned through the scouring sluices from time to time.

Explanation:

Divide wall: 

This is much like a pier and is provided between the sets of under sluice or river sluice or spill bays. It separate under sluices from the main weir. The main functions of a divide wall:

• It separates the turbulent floodwaters from the pocket in front of the canal head.
• It helps in checking parallel flow (to the axis of the barrage) which would be caused by the formation of deep channels leading from the river to the pocket in front of the sluices.

Head regulator: 

A head sluices or canal head regulator (CHR) is provided at the head of the off-taking canal, and serves the following functions:

• It controls the entry of silt into the canal.
• It regulates the supply of water entering the canal.
• It prevents river floods from entering the canal.

Components of Diversion headwork are as follows:

Concept:

Silt Control Devices: The entry of silt into a canal, which takes off from a diversion head works, can be reduced by constructing certain special works which are called silt control works or silt control devices. These works may be classified into the following two types:

Silt Excluders:

• Silt excluders are those works which are constructed on the bed of the river at upstream of the head regulator.
• The clearer water enters the head regulator and consequently the silted water enters the silt excluder. In this type of works, the silt is, therefore, removed from the water before it enters the canal.

Silt Ejectors:

• Silt ejectors, also called silt extractors, are those devices that extract the silt from the canal water after the silted water has travelled a certain distance in the off-take canal.
• These works are, therefore, constructed on the bed of the canal, and a little distance downstream from the head regulator.

Explanation:

Components of Head Works

Following are the parts/components of headworks

• Weir
• Under Sluices
• Canal Head Regulators
• Fish Ladder.
• Divide Wall.
• River Control Works

Concept:

Divide wall

• The dividing the river width into two portions; one is called the weir portion, and the other portion from which the canal takes off is having openings and is called the 'under-sluice-pocket' or 'under sluices' or 'weir scouring sluices'.
• If there are two canals, taking off from each flank, then there will be two divide walls and two under sluices. 

Explanation:

Main Canal Head Regulator:

(i) It is a masonry or concrete structure, constructed at the head of the canal taking off from the river.

(ii) It is constructed upstream of the under sluices and located in one bank.

(iii) Its alignment is kept at an angle varying from 90° to 120° with the axis of the weir. (So, the Minimum Angle between the axis of weir and canal head regulator is 90°)

(iv) The head regulator consists of a number of spans separated by piers and each span is fitted with a steel gate which can be moved up or down.

(v) In the grooves made in the piers, with the help of either manual labour or winches.

(vi) In old regulators, the spans use to be quite small, but the modern trend is to use larger spans of 8 to 18 m.

Following are the functions of a main canal head regulator.

(i) To open or close the discharge in the canal and when require.

(ii) To check the silt entrance into the canal.

(iii) To prevent river floods from entering the canal.

Concept:

In the design of straight glacis fall, the clear length of the crest is calculated as per the table given below;

Hence option (2) is correct.