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For 4th Semester Polytechnic CE Students
Written by Garima Kanwar | Blog: Rajasthan Polytechnic
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Subject: Water Resources Engineering, CE 4005 Same as CV 4005
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5. Diversion Head Works & Canals 🌊🚧
Diversion head works and canals are critical components of the water supply and irrigation infrastructure. Their primary role is to capture and control water from rivers, lakes, or reservoirs and direct it to areas requiring irrigation or other uses.
Key topics include:
- Weirs, Barrages, Canals, Cross Drainage Works, Canal Regulators and their functions.
5.1 Weirs 🌊
A Weir is an artificial barrier built across a river or stream to control the flow of water. It's typically used for raising the water level and diverting water into a canal or reservoir.
Weir Components:
- Crest: The horizontal top of the weir that controls the water level. The height of the crest is adjustable in some weirs, using gates to raise or lower the water level.
- Weir Wall (Body): This is the main structure of the weir. It retains water and directs it towards the canal.
- Still Basin: The area below the weir where the water calms down after it flows over the crest. This is important for reducing turbulence before the water enters the canal.
- Approach Channel: A channel that directs water to the weir. It’s designed to ensure that water flows smoothly towards the weir and doesn’t get diverted elsewhere.
Types of Weirs:
- Broad Crested Weir: Wide-top weir used on large rivers with high flow rates.
- Sharp Crested Weir: A narrow crest, commonly used in small streams and for measuring flow.
- V-Notch Weir: A V-shaped notch used for precise measurement of low flow in small streams.
- K.T. Weir: A specific type used for diverting water to canals, designed with adjustable gates to control flow more efficiently.
5.2 Diversion Head Works 🚧💧
Diversion head works are the systems of structures designed to divert water from rivers into canals or reservoirs for irrigation and other purposes. The design is crucial for regulating the amount of water flowing into the system to ensure consistent supply.
Layout of Diversion Head Works:
- The approach channel carries water from the river to the diversion point. It's designed to direct the water in a controlled manner towards the main diversion structure.
- Weir or Barrage is placed across the river to raise the water level and divert it into the intake structure. These structures control the water level and prevent overflow.
- The canal intake is the entry point where the water is taken from the river into the irrigation canal. It includes controlling gates and other mechanisms to regulate the flow.
Components of Diversion Head Works:
- Sluice Gates: Adjustable gates that control the volume of water entering the canal.
- Sediment Traps: Some diversion systems include systems to settle out the sand, silt, and debris from the water to avoid clogging the canals.
- Trash Rack: A mesh structure that prevents large debris from entering the canal intake.
- Intake Canal: A smaller channel that carries the diverted water into the main canal system.
5.3 Barrages 🌊🔧
A Barrage is a type of low dam built to regulate the flow of a river and to raise the water level for storage and diversion. Unlike weirs, which generally control only the flow, barrages also help in adjusting the water levels more precisely.
Components of Barrages:
- Crest: The top of the barrage structure, often equipped with adjustable gates to raise or lower the water level.
- Gate: Movable barriers used to control the water flow. Gates open or close depending on the water level in the river and the canal.
- Approach Channel: The water path leading to the barrage.
- Sluice Gate: These gates are used to allow excess water to escape, especially during high flow periods, preventing overflow of the canal system.
Difference between a Weir and a Barrage:
- Weir: Typically has a fixed crest and is used to raise the water level or divert a small amount of water to a canal.
- Barrage: More complex with adjustable gates, allowing for more precise control over large volumes of water. Barrages are used in places with high and fluctuating river flows.
5.4 Canals 🚜💧
Canals are artificial watercourses that are created for the purpose of irrigation, navigation, or water transport. They are key to managing the water diverted from rivers, providing water to fields, or draining excess water from an area.
Classification of Canals:
- Main Canals: These are the primary watercourses that receive water directly from the diversion headworks and distribute it to smaller branch canals.
- Branch Canals: These canals receive water from the main canals and distribute it further to smaller distributaries or irrigation networks.
- Distributary Canals: Small canals that split from branch canals and irrigate smaller plots of land.
Canal Cross Section:
- Embanked Canals: These canals are built above the ground level (embankments) and are commonly used in areas with flat terrain.
- Cutting Canals: These are dug into the ground when the terrain is raised, creating a cutting or trench to hold the canal.
Partial Embankment and Cutting:
- Combination Systems: In some areas where the ground elevation changes drastically, canals may have both embankments and cuts. This helps maintain a steady flow despite varying terrain.
Balancing Depth:
- The balancing depth refers to the optimal depth that should be maintained in the canal to balance water flow efficiency and reduce erosion or water wastage.
5.5 Canal Lining 🏞️🌿
Canal Lining involves placing a durable surface material inside the canal to prevent water seepage and to reduce erosion. It ensures that the water remains in the canal and doesn’t percolate into the surrounding soil, especially in arid regions.
Purpose of Canal Lining:
- Water Conservation: By preventing seepage, lined canals ensure that the water reaches the intended areas without loss.
- Prevent Soil Erosion: Lining protects the canal from erosion, especially during high-flow conditions.
- Reduced Maintenance: With a lined canal, the frequency of repairs and cleaning is reduced, making maintenance cost-effective.
Materials Used for Lining:
- Concrete: Used in high-flow and industrial canals because of its durability.
- Bricks or Stone: In older systems or rural areas, where construction material is locally available.
- Plastic or PVC: Used for smaller-scale, temporary canal systems or for irrigation systems in urban environments.
Advantages:
- Increased Efficiency: Helps in improving the water conveyance efficiency by minimizing water loss.
- Longer Lifespan: Protects the canal structure and reduces wear-and-tear caused by water flow and sediment.
5.6 Cross Drainage Works 🚧🌊
Cross Drainage Works are structures designed to maintain the natural flow of watercourses beneath or over a canal, preventing any blockage or disruption in drainage systems.
Types of Cross Drainage Works:
- Aqueduct: An aqueduct allows water to flow over a canal or road, typically used when there is a stream or river at a higher elevation than the canal.
- Siphon Aqueduct: Water flows under the canal through a series of pipes. This is used when the watercourse is at a lower level than the canal.
- Super Passage: A structure that allows one canal to pass over another canal without affecting the flow of either.
- Level Crossing: A crossing where the two drainage systems meet at the same level.
These works help ensure that natural drainage systems are not disrupted by the canal and maintain proper water flow.
5.7 Canal Regulators 🔧💦
Canal Regulators are mechanisms used to control and monitor the water flow through canals. Proper regulation ensures that the water is evenly distributed across all fields and sections of the canal network.
Types of Canal Regulators:
- Head Regulator: Installed at the beginning of the canal to control how much water enters the canal from the river. It's crucial for regulating the inflow.
- Cross Regulator: Positioned at different points along the canal network to ensure water is evenly distributed between branches and distributaries.
- Escape: Used to release excess water from the canal, especially during high water levels, to prevent flooding.
- Falls and Outlets: These are structures that allow water to exit the canal system for irrigation purposes or to drain excess water.
Summary 📝
- Diversion Head Works (weirs, barrages, intake systems) are the structures that capture water from natural sources and direct it towards canals.
- Canals (main, branch, distributary) are used to convey this water to fields or urban areas.
- Cross Drainage Works (aqueducts, siphons, etc.) maintain natural watercourse flows under or over canals.
- Canal Lining helps prevent water loss and ensures long-term efficient use of canal infrastructure.
- Canal Regulators ensure proper management of water flow through the system, preventing wastage and inefficiency.
Together, these components ensure that water is effectively diverted, transported, and distributed for agriculture, industries, and other human uses.
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