Dams and Water Management Quiz

Dams and Spillways

• Dams and spillways are critical components in water resource management.
• Dams store water, control floods, and generate hydroelectric power.
• Spillways release excess water to prevent structural failure.
• Dam design integrates engineering, geology, and hydrology for functionality and safety.
• These structures are crucial for global challenges like water scarcity, renewable energy demand, and climate resilience.

Importance and Relevance

• Dams provide water for agriculture, drinking, and industrial use.
• Many dams generate hydroelectric power, a renewable energy source.
• Spillways protect downstream areas from flooding.
• Dams support local economies through irrigation, navigation, and tourism.
• Dams are relevant for managing water availability and increasing climate variability.

Issues from Improper Construction

• Structural Failures: Inadequate geological surveys can lead to foundation instability or leakage, risking collapse.
• Flood Risks: Poorly designed spillways may fail to manage excessive inflow, causing catastrophic flooding.
• Environmental Impact: Faulty planning can lead to excessive sedimentation, habitat loss, and ecosystem imbalance.
• Economic Loss: Dam failures result in costly repairs, loss of agricultural productivity, and community displacement.
• Human Safety: Neglecting seismic considerations can cause dam failure in earthquake-prone areas.

Terminology and Basic Aspects of Dam Construction

• Crest: The top of the dam.
• Abutments: The parts of the dam that rest on the side slopes of the valley
• Freeboard: The vertical distance between the top of the dam and the water surface.
• Heel: The upstream end where the dam meets the foundation.
• Toe: The downstream end of the dam's base.
• Headwater: The water upstream.
• Tailwater: The water downstream.

Types of Dams and Their Functions

• Concrete Dams: Large structures built across rivers, streams, or other bodies of water to store, control, or divert water, which are comprised of gravity dams, arch dams, and buttress dams.
• Masonry Dams: Impervious barrier against reservoir water leakage.
• Rock-fill Dams: Primarily made from rock or gravel, with a core of impermeable material to prevent water seepage through.
• Earth Dams: Embankment dams made of earth, clay, sand, and gravel.

Spillways and Gates

• Normal Spillways: Gravity spillways or overflow spillways, crucial for safely releasing excess water.
• Pipe Spillways: Discharge structure made of a pipe passing through the dam body, suitable for low headwater projects.
• Tunnel Spillways: Tunnel punctures the upper end, functioning as an intake and discharging water from the lower end.
• Glory Hole (Shaft) Spillways: Vertical or inclined shaft for free-flowing or pressured water.
• Side Channel Spillways: Water flows from the reservoir through a separate channel.

Outlet Works

• A portion of the reservoir water is diverted through tunnels, channels, or conduits to supply irrigation canals, water schemes, or hydroelectric plants.
• The water diversion structure is termed the outlet.

Gates of Different Types and Their Functions

• Plain Gates: Move translationally along slots in piers across the spillway crest (e.g., lift or slide type).
• Radial Gates: Rotate on hinges (e.g., in normal position).

Geomorphology and Dam Design

• Dams are designed to meet safety standards while minimizing cost.
• Factors like river valley shape, foundation materials, and availability of construction resources are critical to optimal design.

Factors Affecting Dam Construction

• River Valley: Wide, shallow valleys are better for embankment dams; narrow valleys favor concrete dams.
• Foundation: Depth to bedrock and material properties are vital for structural integrity.
• Materials: Availability of suitable materials (rock, soil, cement) affects feasibility and cost.

Geological Evaluation for Dam Sites

• Site Assessment: Geological surveys identify potential issues like fault lines, weak rock formations, or unstable slopes.
• Material Testing: Analysis of soil, rock, and other materials verifies design specifications.
• Monitoring: Continuous monitoring tracks structural performance and integrity.

Causative Factors of Dam Disasters

• Geological Causes: Weak or porous foundation rocks, laminated or weak rocks, faulted or cavernous foundation, and landslides.
• Other Causes: Faulty spillway design, drainage issues, natural calamities, and poor construction materials.

Preliminary Investigation and Selection of a Dam Site

• Purpose: Identify geological weaknesses to ensure feasibility and minimize costs.
• Key Tasks: Mapping geological features, remote sensing analysis, fault, shear zone analysis, slide scar, slope characteristic comparison, and comparison of site options.

Detailed Investigation of a Dam Site for Design Purposes

• Purpose: Provide surface and subsurface data for dam design and cost estimation.
• Key Tasks: Create maps, conduct trenching, drilling and core logging, assess rock types, perform lab tests, and analyze faults, folds, and cavities.

Source of Building Materials for Different Types of Dams

• Building materials are critical to dam safety, durability, and efficiency.
• Appropriate materials are identified and sourced for various dam types.

Building Materials for Concrete Dams

• Aggregate materials (sand, pebbles, gravel, and crushed rock) are crucial for concrete dams.
• Testing (e.g. crushing strength, impact resistance, shape, and size) of aggregate materials are performed.

Building Materials for Dams

• Concrete and Cement: Use sand, pebbles, gravel, and crushed rock as aggregates; tested for crushing strength, impact resistance.
• Rock and Earth Fill: Durable rock-fill materials sourced from quarries.
• Earth Dams: Clayey soils and sand are used for impermeable cores.

Rip-rap for Dam Slope Protection

• Purpose: Protect dam slopes from erosion.
• Material Selection: Hard, durable rocks from riverbeds, terraces, or quarries are preferred with a compressive strength of 350 KG/CM2 or more.
• Alternative Materials: Concrete blocks, if durable rocks aren't available.

Impervious Core Materials for a Dam

• The selection of suitable materials for rock-fill and earth dams is important for structural integrity.
• Ideal material composition: Well-graded mixture of sand, gravel and fines mixed with suitably plastic tough clay.
• Alternative Materials examples: Crushing crushed soft rocks.

River Diversion and Construction Work

• Temporary rerouting of rivers is common during construction.
• Methods include cofferdams (temporary walls), tunnels, and channels.

Foundation Preparation

• Site clearing, excavation to required depth, leveling, and compaction of soil are necessary.
• Soil testing and drainage considerations help ensure stability.

Construction Approaches for Different Types of Dams

• Construction approaches vary depending on dam type (gravity, arch, embankment).
• Concrete, curved concrete structures, and compacted earth are used for different dam types.

Main Dam Types and Construction Approaches

• Gravity Dams: Large concrete blocks poured in sections, precise placement of concrete.
• Arch Dams: Concrete poured in curved sections using natural valley shape to distribute water pressure; strong foundation critical.
• Embankment Dams: Layers of earth or rock-fill; impervious core to prevent leakage; proper soil selection and compaction.
• Buttress Dams: Variation of gravity dams; buttresses support the face; reduced concrete volume.

Other Considerations

• Cofferdams: Temporary structures to divert water flow during dam construction, allowing access to the excavation area.
• Diversion Structures: Channels or tunnels to redirect water flow around the construction site.
• Grouting: Injection of grout to seal cracks and improve foundation stability.
• Monitoring and Instrumentation: Sensors and monitoring systems to track dam behavior.

Post-Construction Work

• Seepage: Common post-construction problem; tracer studies and grouting address seepage paths and leaks.
• Drainage Issues: Blockage of drainage holes or malfunctioning grout curtains lead to uplift pressure.
• Landslides and Earthquakes: Reservoir filling can trigger landslides or earthquakes, causing damage; geological studies mitigate risks.
• Scouring: Cavity formation from downstream spilled water; need for flexible measures.