Dam Classification and Spillway

Dam Classification and Spillway

• Dams have existed since ancient times, used by all advanced civilizations for water management
• The Roman dam at Cornalvo in Spain has been used for almost two millennia
• The Grand Anicut dam on the Kaveri River in Tamil Nadu, South India was established in the 1st or 2nd century
• Civilizations developed in river valleys, using water supply systems and irrigation
• Modern dams are often multi-purpose, serving multiple functions including power generation
• Dams control river flow by completely blocking the river valley
• This creates a reservoir, a large artificial lake, which stores water for various uses
• Reservoir storage is divided into maximum pool, normal pool, live storage, minimum pool, and dead storage
• Spillways are critical dam structures, allowing excess water to pass over or through the dam to prevent flooding
• Additional structures needed for a dam include outlets, gates and valves, service roads, reservoirs, bridges, energy dissipaters and diversion structures
• Dams have advantages like balancing water supply and demand, providing water storage for long periods, regulating river flow for navigation and irrigation, and preventing floods

Advantages of Dams

• Temporal and quantitative balancing between available water and demand
• Water storage for days, weeks, months, years, and multi-year periods for power generation
• Regulation/balancing of river flow (such as navigation, low flow augmentation)
• Water supply and irrigation purposes
• Flood control

Disadvantages of Dams

• Interference with natural fauna and flora in the dam valley
• Interference to landscapes through dams and reservoirs
• Alteration of groundwater water levels
• Impact on fish populations
• Influence on sediment balancing
• Displacing people from land inundated by reservoirs
• Change in water temperature and quality

Reservoir

• A reservoir is a large artificial lake created by constructing a dam across a river
• Any body of water can be termed a reservoir
• In water resource engineering, a reservoir is a relatively large body of water stored on the upstream side of a dam
• Reservoirs and dams work together

Types of Reservoirs

• Single-purpose reservoir: A reservoir designed for only one purpose
• Multi-purpose reservoir: A reservoir designed for multiple purposes

Storage Components of Reservoirs

• Maximum pool level
• Normal pool level
• Live storage
• Minimum pool level
• Dead storage
• River bed
• Spillway
• Outlet

Dead Storage

• The portion of the capacity which is accumulated by silt and sediment
• Water in this area is not normally used or withdrawn

Active Storage

• The portion of the capacity that normally stores and withdraws water for beneficial uses

Surcharge Storage

• Storage required as a reserve between full reservoir level and maximum water level (for flood peaks)

Bottom Outlet

• Outlet for discharging water and flushing sediment in the reservoir

Service Outlet

• It is used to discharge the required amount of water to downstream beneficiaries

Types of Dams

• Storage Dam: used to store flood water in dry seasons
• Diversion Dam: used to raise water level, not store water
• Detention Dam: used to temporarily hold flood water before gradual release
• Debris Dam: used to retain debris and allow more clear water to pass
• Coffer Dam: constructed to divert water during construction

Classifications of Dams (Hydraulic Design)

• Overflow dam: designed to allow surplus water over a crest made from a material that is resistant to erosion
• Non Overflow dam: not designed to be overtopped; materials could include earth, or rock fill

Classifications of Dams (Construction Material Used)

• Concrete dam: made of masonry or concrete
• Earth fill dam: made of earthen material
• Rock fill dam: made of rock
• Timber dam: made of timber
• Steel dam: made of steel

Rigid Dams

• Constructed of rigid materials like concrete, masonry, steel, or timber
• Little deflection or deformation under pressure

Non Rigid Dams

• Constructed of non-rigid materials like earth or rock fill
• Tend to have more settlement and deformation under pressure

Characteristics of Concrete Gravity Dams

• Constructed from mass concrete or masonry
• Dissimilar face slopes (downstream and upstream)
• Hard, rigid structures with stability based on their weight
• Require a sound rock foundation

Advantages of Concrete Gravity Dams

• Good for narrow valleys, and suitable for wide valleys (excluding arch and cupola)
• Smaller construction fill volume compared to embankment dams
• Construction can occur regardless of weather conditions
• Smaller free board (1-1.5m)
• Can be constructed as overflow dam, hence saving costs

Disadvantages of Concrete Gravity Dams

• Sensitive to settlement, requiring a strong rock foundation
• Can be affected by earthquakes
• Construction requires significant technical personnel, equipment, and form work
• Difficult heightening
• Interference with natural landscape

Characteristics of Concrete Arch Dams

• Upstream curvature
• Constructed from concrete material
• Stability achieved through a combination of arch and gravity action
• Utilizes arch strength to resist loads
• Requires strong abutment rock mass

Characteristics of Concrete Buttress Dams

• Require one-third to one-half the concrete needed for gravity dams (economical for dams over 14m)
• Retain 30-60% more concrete compared to gravity dams
• Eliminate uplift pressure

Characteristics of Embankment Dams

• Constructed from naturally excavated and placed materials without binding material
• Suitable for rock or compressible soil foundations
• Can accommodate some settlement
• Typically involve earthfill, rockfill, or hydraulic fill

Earth Fill Dams

• Embankment dams primarily made of compacted earth, potentially with horizontal layers.

Rock Fill Dams

• Embankment dams containing more than 50% compacted or dampened rock.

Hydraulic Fill Dams

• Embankment dams built from dredged material including earth, sand, gravel, or rock brought together by flowing water.

Phase of Engineering Activity for Site Investigation and Construction

• Reconnaissance survey
• Preliminary and feasibility studies
• Final investigation and basic design
• Construction
• Operation

Selection of Sites and Type of Dams (Influencing Factors)

• Topography (valley form): Narrow U-shaped valleys are suitable for overflow dams, while V-shaped valleys are better for arch dams
• Foundation (stability, impermeability): Strong rock foundations are crucial
• Geology (layers, fishers): Consider the type and characteristics of soil strata
• Required height: Dams' heights depend on their purpose
• Purpose of the dam: Determines the type and capacity of the dam
• Climate (ice): Consider ice conditions at the site, especially for reservoir design
• Flood spillway
• Availability, quality, and nature of construction materials
• Construction needs, including resources, equipment, personnel, and logistical factors
• Landscape: Consider the dam's visual impact on the environment
• Cost (economics)

Topography

• Narrow U-shaped valleys are suitable for overflow dams
• Narrow V-shaped valleys are better suited for arch dams
• Low, rolling plains are suitable for earth fill dams with separate spillways

Geology and Foundation Conditions

• Solid Rock Foundations: are ideal for most dam types, as they offer high bearing strength and resistance to erosion. If seams and fractures exist, they need special treatment to prevent seepage through the cracks.
• Gravel Foundations: can support lower dams (up to a height of 15m), but not high concrete gravity dams.
• Silt and Fine Sand Foundations: suggest earthen or low gravity dams (up to 8m) due to potential seepage issues.
• Clay Foundations: can cause significant settlement, and are typically not suitable for concrete gravity or rock-fill dams. Additional treatment may be possible with earthen dams.
• Non-uniform Foundations: special design and solutions must be considered when dealing with various unstable foundations.

Availability of Materials

• Materials for dam construction should be available locally
• Good soil may necessitate an earth dam
• Concrete dams are likely where cement, sand, and stone are readily available
• Materials from farther distances might favor hollow dam designs (like buttress dams)

Explore the fascinating world of dams and spillways, from ancient structures like the Roman dam at Cornalvo to modern multi-purpose dams. Learn about the various types of storage in reservoirs and the critical role spillways play in flood prevention. This quiz offers insights into water management techniques that have shaped civilizations.