A Comprehensive Guide to Dam Types, Structures, and Control Elements

Posted on Aug 25, 2024 in Geology

DAMS

Definition

Dams are water reservoirs designed to store water. Their functions include:

  • Supplying water for consumption
  • Controlling flow to prevent flooding
  • Harnessing water power for energy transformation (electrical, mechanical, etc.)

Classification of Dams

Types of Dams by Structure:

  • Gravity dams
  • Lightweight gravity dams (buttresses)
  • Arch dams

Types of Dams by Material:

  • Concrete dams
  • Embankment dams
  • Mixed dams

Types of Dams by Application:

  • Filter dams
  • Storage dams
  • Flood control dams
  • Diversion dams
  • Energy production dams

Gravity Dams

These dams feature an isosceles triangle profile, with a wider base to withstand greater water pressure. The weight of the material counteracts the reservoir pressure, transferring the thrust to the ground. The soil must support the weight of both the reservoir and the dam.

Forces Acting on Gravity Dams:

  1. Own weight
  2. Hydrostatic pressure
  3. Subpresión (uplift pressure)
  4. Sediment or silt thrust
  5. Seismic force
  6. Weight of water on the upstream face
  7. Negative pressure correlation between the mantle and the downstream water face
  8. Water discharge friction on the face
  9. Impact of waves and floating bodies
  10. Ice pressure
  11. Earthquake effects

Advantages of Gravity Dams:

  • Most common type
  • High durability
  • Low maintenance

Disadvantages of Gravity Dams:

  • Require a large amount of material
  • Limited wall height

Lightweight Gravity Dams (Buttresses)

These dams utilize ribs to lighten the concrete slabs that hold back water. The pressure is channeled into buttresses, which transfer the load to the foundation. Columns further reduce the concrete weight.

Advantages of Lightweight Gravity Dams:

  • Reduced material usage
  • Suitable for locations with limited construction materials

Disadvantages of Lightweight Gravity Dams:

  • High project implementation costs (require skilled labor)
  • Require a stable rock foundation
  • Complex behavior in the crown liner and thermal expansion

Arch Dams

These dams are characterized by their curved, thin structure, often reinforced with steel bars or cables. The reinforcements distribute the load to both the foundation and the arch itself. They are typically built in narrow, deep gorges.

Types of Arch Dams:

  • Constant radius arch dams: Feature a vertical upstream face with a consistent radius of curvature.
  • Variable radius arch dams (dome or double curvature): Have curves with radii that decrease systematically with depth below the crest.

Advantages of Arch Dams:

  • Require the least amount of concrete
  • Ideal for tall, narrow gorges

Disadvantages of Arch Dams:

  • Complex calculation and construction
  • Require stirrups and very hard, stable rock
  • Difficult material transportation and placement

Concrete Dams

These dams utilize concrete, a compact, dense, and easily moldable material with high compressive strength. They are the most widely used type today.

Advantages of Concrete Dams:

  • Durable and strong
  • Versatile in design

Disadvantages of Concrete Dams:

  • Expensive and time-consuming to build
  • Require skilled labor and specialized machinery
  • Poor tensile strength, requiring reinforcement

Embankment Dams

These dams are constructed using natural materials like earth and rock, compacted to create a barrier. They are often zoned, with different materials used for permeability control.

Types of Embankment Dams:

  • Earth dams: Composed of over 50% earth or a mixture of earth, gravel, and sand.
  • Rockfill dams: Primarily constructed using coarse stone.
  • Earth-rockfill dams: Combine both earth and rock, with an impermeable core and permeable outer layers.

Advantages of Embankment Dams:

  • Cost-effective
  • Relatively easy to construct
  • Don’t require highly skilled labor
  • More adaptable to different foundation conditions

Disadvantages of Embankment Dams:

Relatively small in size Lower resistance compared to concrete dams Vulnerable to overtopping

Mixed Dams

These dams combine concrete with other materials like rubble, fill, soil, and clay. They are typically gravity dams with large, low-rise walls.

Advantages of Mixed Dams:

  • Rapid construction
  • Relatively inexpensive
  • Safe as long as water levels remain below the crest

Disadvantages of Mixed Dams:

Highly dangerous if overtopped

Parts of a Dam or Reservoir

Reservoir:

The volume of water held back by the dam.

Lake:

The portion of the valley inundated by the reservoir.

Closure:

The specific location where the dam is constructed.

Dam Components:

1. Faces:

The two vertical or near-vertical surfaces of the dam: the upstream face and the downstream face.

2. Crest:

The top surface of the dam, often featuring a walkway or road.

3. Abutments:

The sides of the dam that connect to the valley walls, crucial for arch dams.

4. Foundation:

The base or floor upon which the dam wall rests.

5. Spillway:

A channel designed to safely discharge excess water from the reservoir, either freely or in a controlled manner.

6. Hydraulic Structures:

Structures like intakes, outlets, and gates used to manage water flow within the dam system.

7. Bottom Outlet:

Channels used for releasing water from the lower levels of the reservoir for purposes like sediment flushing or irrigation.

8. Locks:

Watertight compartments used to raise or lower boats and ships to different water levels in a navigation channel.

9. Control Tower:

A structure housing equipment and personnel for monitoring and controlling dam operations.

10. Fish Ladder:

A structure with a series of pools that allow fish to migrate upstream, bypassing the dam.

Penstocks:

Pipes used to convey water from the reservoir to turbines for hydropower generation.

Control Gallery:

A network of tunnels within the dam wall for accessing and monitoring instrumentation and drainage systems.

Cleaning Gallery:

A gallery specifically designed for accessing the bottom outlet to remove accumulated sediment.

Drains:

Channels or pipes installed within the dam to collect and direct seepage water downstream, reducing uplift pressure.

Hydraulic Jacks:

Outlets used to extract water for human consumption or other purposes.

Control Elements

These systems ensure the structural stability and safe operation of a dam.

Pendulum:

Direct and inverted pendulums measure horizontal movements within the dam structure, providing data on its stability.

Deformeters:

These instruments measure relative displacement between blocks at joints, helping monitor expansion joints, cracks, and overall dam movement.

Drain Head Meters:

Used to monitor water pressure in the foundation drains, providing information on drainage effectiveness and seepage behavior.

Geodetic-Topographic Control of Crest Movement:

A system using fixed and mobile stations with precise surveying equipment to monitor even minute movements in the dam’s crest.

Leakage Flumes:

Structures that collect and measure seepage water, providing early warning signs of potential issues within the dam.

Other Gauges:

  • Millimeter scales
  • Temperature sensors
  • Extensive tape measures
  • Vibrating wire piezometers
  • Pneumatic piezometers
  • Vibrating wire extensometers
  • Potentiometric extensometers