3. Dams and Spillways, Water Resources Engineering, CE 4005 Same as CV 4005

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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

Branch: Civil Engineering 🏗️
Semester: 4th Semester 📚

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3. Dams and Spillways 🏞️💧

Dams and spillways are crucial components of water resources engineering, used to store water, prevent flooding, and regulate water flow for irrigation, hydroelectric power generation, and other purposes. Let's understand their concepts in detail.

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3.1 Dams and Its Classification 🏞️

A dam is a structure built to control the flow of water, typically to create reservoirs for storing water, prevent flooding, or generate hydroelectric power. The classification of dams depends on factors like material, design, and function.

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3.1.1 Earthen Dams 🌾🌍

Earthen Dams are made primarily of natural materials like soil, clay, and rocks. They are the most common type of dam, particularly for agricultural and flood control purposes.

• Structure: Composed of compacted soil or earth, earthen dams have a wide base and narrow top. They are typically sloped on both sides to prevent erosion.
• Advantages: Low cost, can be constructed in locations with a lot of earth material, and have good flexibility to withstand pressure.
• Example: The Oroville Dam in California is an earthen dam and is one of the largest in the U.S.

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3.1.2 Gravity Dams (Masonry and Concrete) 🧱🏗️

Gravity Dams are designed to resist water pressure through their own weight. They are made from masonry or concrete materials and are generally used in areas where water flow is high.

• Masonry Gravity Dam: Made of stone or brick masonry and designed to withstand the horizontal force of the water.

• Concrete Gravity Dam: Built with concrete, these are used for large-scale water storage and hydroelectric power generation.

• Structure: These dams have a thick base and taper towards the top, creating a triangular profile. The dam relies entirely on its weight to hold back the water.

• Example: The Hoover Dam in the U.S. is a famous concrete gravity dam built for hydroelectric power generation.

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3.2 Earthen Dams 🌍💧

Construction of Earthen Dams:

• Materials Used: These dams are constructed with materials such as clay, silt, sand, and gravel. The inner core is often made of impervious material to prevent water seepage.

• Types of Earthen Dams:

  1. Homogeneous: Made from a single material throughout the dam structure.
  2. Zoned: Different materials are used in different zones of the dam (impervious core, transition zone, and permeable outer shell).

• Functioning: The weight and the structure of the earth materials hold back water and prevent leakage. Proper compaction is essential to ensure the dam's strength.

• Advantages:

  1. Economical to build.
  2. Can withstand seismic activity better than concrete dams.
  3. Easier to repair.

• Disadvantages:

  1. Prone to erosion if not maintained properly.
  2. Can be damaged by heavy rainfall or floods.

• Example: Kakrapar Dam in India is an earthen dam used for irrigation and flood control.

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3.3 Spillways 🌊🚰

Spillways are structures used to allow excess water to flow out of a dam. The main function of a spillway is to prevent the dam from overtopping, which could lead to catastrophic failure.

• Purpose: To safely release water when the reservoir is full or when heavy rainfall causes the water level to rise rapidly.

• Types of Spillways:

  1. Overflow Spillway: Water flows over the top of the dam structure.
  2. Side Channel Spillway: Water flows off the side of the dam structure.
  3. Shaft Spillway: Water is directed downwards through a vertical shaft.

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3.3.1 Definition of Spillways 💦

A spillway is a device used to release surplus water from a reservoir in a controlled manner to prevent overflow and the potential for dam failure.

• Importance: Spillways play a crucial role in maintaining the safety and integrity of dams by ensuring water is safely released during floods or when the reservoir reaches its full capacity.

• Example: The spillway of the Oroville Dam in California is designed to release excess water safely during heavy rainfall.

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3.3.2 Energy Dissipaters 🔋💧

When water is released from a dam through a spillway, it can create dangerous erosive forces and cause damage to the surrounding environment. Energy dissipaters are used to reduce the kinetic energy of the water as it flows out of the spillway, thus preventing erosion and protecting downstream areas.

• Types of Energy Dissipaters:

  1. Still Basin: A large basin designed to slow down the water and reduce its energy.
  2. Baffle Blocks: Blocks placed in the path of the water to reduce its speed.
  3. Troughs or Chutes: Smooth channels through which the water flows slowly.

• Example: The Energy Dissipation System at the Three Gorges Dam in China helps reduce the force of water flow as it exits the spillway.

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Diagram: Gravity Dam and Spillway

Here’s a simple diagram illustrating a Gravity Dam and its associated spillway. The spillway allows for excess water to flow safely, and the energy dissipater slows down the water’s speed to prevent damage.

     |--------|           |-----------------------|
     |        |           |                       |
     | Gravity|           |      Spillway          |
     |  Dam   |           |                       |
     |        |           |                       |
     |        |           |-----------------------|
     |________|           |       Energy          |
       | | |              |     Dissipater        |
       | | |              |                       |
       | | |              |_______________________|
       | | |
       | | |
       | | |
       ------

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Summary 🏞️💧

• Dams are critical for water management, controlling floods, storing water for irrigation, and generating hydroelectric power.
  • Earthen Dams are cheaper, flexible, and used in agricultural or flood-prone regions.
  • Gravity Dams are heavy, solid structures made from concrete or masonry and are used for large-scale water storage and power generation.
• Spillways ensure that excess water is safely released from a dam to prevent overflow and maintain dam stability.
• Energy Dissipaters are used in spillways to reduce the force of water and prevent downstream erosion.

Understanding the different types of dams, spillways, and their components helps in the safe and efficient management of water resources.

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