Diversion Networks: Functions, Types and Components | Civil Engineering Optional Notes for UPSC PDF Download

What is Diversion Headworks?

Functions of Diversion Headworks

1. Control Water Quantity: Regulates the amount of water diverted into the canal.
2. Mud Regulation: Controls the amount of mud entering the canal.
3. Water Level Regulation: Manages the water levels in the river, ensuring a consistent flow into the canal.
4. Increase Irrigable Land: By raising the outflow level of the canal, more land can be irrigated.
5. Fluctuation Reduction: Reduces water level fluctuations in the river.
6. Water Storage: Although not the main function, it stores some water to compensate for dry periods.

Components of Diversion Headworks

1. Weir or Barrage

   • Weir: A solid wall built across a river to raise the water level upstream, allowing excess water to flow over it.
   • Barrage: An advanced weir with adjustable gates to control water levels.

2. Divide Wall
   A long wall perpendicular to the weir or barrage, made of stone, bricks, or concrete, to:

   • Prevent cross currents or eddy currents.
   • Ensure a straight approach at the canal head.
   • Prevent overturning of the weir or barrage.
     

3. Scouring Sluices or Under Sluices

   • Openings at the bottom of a weir or barrage with movable gates to allow sand to flow through, preventing silt buildup.

4. Fish Ladder

   • Facilitates the free movement of fish across the weir or barrage, with baffle walls to limit water speed.

5. Canal Head Regulator

   • Built at the canal head to control water flow, consisting of piers and gates operated by mechanical devices.
     

6. Silt Excluder

   • Prevents heavy silt from entering the canal by directing it through tunnels from the head regulator to the divide wall.

7. Dyke or Marginal Embankment

   • An earth embankment parallel to the river bank to:
     • Protect agricultural land.
     • Prevent flooding of towns and villages.
     • Restrict flood or storage water to specific areas.

8. Guide Bank

   • Structures on both sides of the barrage to prevent erosion, ensure a straight water path, and control water speed near the structure.

Types of Diversion Headworks

1. Temporary Diversion Headworks: Comprise bunds or temporary structures across a river to raise the water level for canal diversion. These need reconstruction after floods.

2. Permanent Diversion Headworks: Include weirs or barrages built across a river to permanently raise water levels for canal diversion.

Selection of Site for Diversion Headworks

• The river should be straight and narrow.
• The river banks should be well-defined.
• The structure should not flood valuable land nearby.
• The site should be elevated and easily accessible by road.
• Building materials should be readily available near the construction site.

Types of Diversion Network

• Diversion Headworks: (a) Temporary Spurs or Bunds: These are temporary structures constructed annually after floods to divert the required water supply from the river into a canal. (b) Permanent Weirs and Barrages: These are permanent structures built across a river to divert water into a canal system. 
• Storage Headworks: Storage headworks involve the construction of a dam across a river. The primary purpose is to store water during periods of excess supply in the river and release it when the demand exceeds the available supply. The diversion headworks are designed to divert a specific quantity of water from the river into a canal system, while storage headworks are used to regulate and store water for later use, providing a more consistent supply.