11 Advantages and Disadvantages of Arch Dam | Types of Arch Dam | Hoover Dam (USA) |
What is an Arch Dam? |Advantages and Disadvantages of Arch Dam | Biggest Arch Dams in The World |Hoover Dam (USA) | Uses of Arch Dams |Construction of An Arch Dam
What is an Arch Dam?
An arch dam is a concrete dam with a design that curves upstream. It is a concrete or masonry construction that bears load mostly through lateral thrust into its abutments, allowing it to be thinner than a gravity dam.
The arch dam is constructed so that the force of the water against it, known as hydrostatic pressure, forces against the arch, straightening it slightly and strengthening the structure as it pushes into its base or abutments.
An arch dam works best in tight canyons or gorges with steep walls of stable rock to support the structure and pressures.
Because they are thinner than any other style of dam, they require far less building material, making them cost-effective and practicable in distant places.
Modern arches are typically curved in both plan and section. Some of the early arch dams were conservatively proportioned, thus their resistance was primarily due to weight. Hoover Dam is a noteworthy example of this arched gravity type.
Hoover Dam (USA)
Hoover Dam is a concrete arch-gravity dam in the Colorado River’s Black Canyon, on the border between Nevada and Arizona.
It was built during the Great Depression, between 1931 and 1936 and dedicated on September 30, 1935, by President Franklin D. Roosevelt.
Its construction required a major effort involving thousands of employees and cost over a hundred deaths.
Originally known as Boulder Dam since 1933, it was renamed Hoover Dam in 1947 by a joint vote of Congress in honor of President Herbert Hoover.
The Hoover Dam is the height of a 60-story structure. When it was finished in 1935, it was the world’s tallest dam. Its foundation is as thick as two football fields.
Each spillway, which is designed to allow floodwaters to pass without causing damage to the dam, can manage the volume of water that rushes over Niagara Falls.
Two spillways safeguard the dam from over-topping. The spillway exits are behind each dam abutment, nearly parallel to the canyon walls.
The spillway entry configuration resembles a traditional side-flow weir, with four 100-foot-long (30-meter) and 16-foot-wide (4.9-meter) steel-drum gates on each spillway.
The gates are raised and lowered in response to reservoir water levels and flood conditions. The gates cannot completely prevent water from accessing the spillways, but they can keep the lake level at an extra 16 feet (4.9 meters).
Four reinforced-concrete intake towers above the dam transfer water from the reservoir into massive steel pipes known as penstocks.
Water plunges 500 feet (150 meters) via the pipes to a hydroelectric power plant at the dam’s foot, the water spins 17 Francis-type vertical hydraulic turbines, which turn a series of electric generators with a total power capacity of 2,080 megawatts.
The Metropolitan Water District of Southern California, the city of Los Angeles, and other southern California destinations receive over half of the generated electricity, with the remainder going to Nevada and Arizona.
Hoover Dam use an arch to carry water pressure and other pressures to the abutments. An arch dam is ideal for tight canyons with strong flanks that can withstand the thrust created by the arch movement. The portion of an arch dam is roughly triangular, like that of a gravity dam, although it is much thinner.
In the vertical plane, the arch dam might have a single or double curvature. In general, double-curvature arch dams are more cost-effective and are implemented in practice.
Design & Load of An Arch Dam
The design of an arch dam is a time-consuming and difficult task. It begins with a basic dam architecture that is progressively developed until the design objectives are met while adhering to the design criteria.
Arch dams are subjected to time-varying external loadings as well as hostile conditions that degrade their physical qualities. Damage to such dams increases over time, and concrete disintegration is unavoidable.
The following are the primary loads for which an arch dam is designed:
- The Dead Load
- The Reservoir’s Hydrostatic Load and the Tailwater
- Temperature Load
- Earthquake Impact
Types of Arch Dam
Constant Radii Arch Dam
The dam’s upstream face has a constant radius, resulting in a linear shape face throughout the dam’s height.
However, the radius of the inner curves decreases as we walk down from top elevation to bottom elevation, forming a triangle in cross-section.
Variable Arch Dam
The radius of the dam arch’s inner and outer faces varies from bottom to top. The radius of the arch is greatest at the top and smallest at the bottom. As we proceed upward, the middle angle of the arch widens as well.
Constant Angle Arch Dam
This is the most cost-effective method of construction, however, because the third type of arch dam incorporates overhangs at the abutment portions, a stronger foundation is necessary.
The constant angle arch dam has the same size of the central angles of the horizontal arch rings at all heights.
Advantages and Disadvantages of Arch Dam
Advantages of Arch Dam
- Arch dams are particularly well suited to gorges when the length is short in comparison to the height.
- The section of an arch dam is substantially less for a given height than that of a matching gravity dam. As a result, an arch dam uses less material and is thus less expensive.
- Uplift pressure issues are minor due to the substantially narrower base width.
- Because cantilever movement transfers just a small portion of the water load to the foundation,
Disadvantages of Arch Dam
- Arch dams demand expert labor.
- An arch dam’s design is also extremely complex.
- It needs a strong rock abutment capable of withstanding arch thrust.
- It is not appropriate in locations where strong abutments are not present.
Uses of Arch Dams
Arch dams are used in shallow to deep water depths, ranging from feet (for small arch dams) to hundreds of feet. The dam’s performance depends on soil conditions and rock formations.
- In shallow river valleys, the site can be excavated and sloped for the foundation structure.
- As the site is above isochronal soil, an arch dam is not used.
- Small arch dams are used for irrigation canalization, as well as both domestic and storm drainage systems.
- Narrow canyons with steep walls are best suited for arch dams.
- Any place where a river flows between steep rock walls is also ideal for an arch dam.
- Arch dams are more common and successful than gravity dams in tight seams of bedrock.
- Highway and railway tunnels, as well as water canals are also commonly designed using arch dams.
- They are particularly suitable for the construction of a large hydroelectric station at a narrow point in a river.
Construction of An Arch Dam
An arch dam’s construction is dependent on the type of rock and soil found at the site.
Locating an appropriate site is critical when constructing an arch dam.
For a constant radius arch dam, the rock around the site can be made ready for excavation using explosives.
The sidewalls of the valley are then embedded with concrete in order to reinforce the structure and increase its stability.
If a variable radius arch dam is being constructed, it is necessary to make deep excavations in the rock bed of the site and slope them toward one another to create a strong wall.
In some cases, it may be necessary to build earthwork on top of this wall to further strengthen it.
A series of forms are then inserted into the excavated rock, and these forms will be used to shape the arch dam.
The process of making concrete is almost identical for either type of arch dam.
Consequences of Dam Failures
Dam failures tend to occur when the water pressure in a dam exceeds its design pressures.
An arch dam karst environment with a weak rock foundation that slips or fails will collapse under the pressure.
The effects of dam collapse are far-reaching when the dam is constructed near populated areas.
Many people have been killed due to landslides and floods triggered by a dam failure.
This incident happened in 1972 with the collapse of the Tadoba-Andhari Dam that destroyed a small town called Poladpur in Maharashtra India.
Another incident occurred near Koyna, India, which resulted in over 1000 deaths and over 2000 injuries.
Recently, the failure of the Xiaolangdi Dam in China caused over 40 casualties and the collapse of a valuable historical bridge.
The Biggest Arch Dams in The World
| Name | Height | Type | Country | River | Year |
| Jinping-I Dam | 305 m (1,001 ft) | Concrete arch | China | Yalong | 2013 |
| Xiaowan Dam | 292 m (958 ft) | Concrete arch | China | Lancang | 2010 |
| Xiluodu Dam | 285.5 m (937 ft) | Concrete arch | China | Jinsha River | 2013 |
| Enguri Dam | 271.5 m (891 ft) | Concrete arch | Georgia | Enguri | 1978 |
| Vajont Dam | 261.6 m (858 ft) | Concrete arch | Italy | Vajont | 1959 |
| Mauvoisin Dam[5] | 250 m (820 ft) | Concrete arch | Switzerland | Dranse de Bagnes | 1957 |
| Laxiwa Dam | 250 m (820 ft) | Concrete arch | China | Yellow River | 2009 |
| Deriner Dam | 249 m (817 ft) | Concrete double-arch | Turkey | Çoruh River | 2012 |
Arch Dam FAQs
What is difference between Arch Dam and Gravity Dam?
Gravity dams are the most common type of dams. It is a concrete dam that relies on the weight of its material to carry out the pressure exerted by water on the dam.
As opposed to gravity dams, arch dams are typically constructed in narrow gorges with abutments that are capable of resisting thrust and horizontal forces from the arch.
In the past few years, there has been a growing tendency to construct concrete arch dams instead of gravity dams. This is mostly because of their low cost in comparison to gravity dams. Moreover, they reduce risk due to uplift pressures.
However, this comes with a drawback. They require a very detailed design that is complex and cannot be handled by laymen. Arch dams also carry the risk of failure, given that they are built on a steep slope and depend solely on their structure to carry out loads.
How does Arch Dam work?
The water pressure acts on the arch, which is then transferred to the abutments. The force of the water compresses the dam and transfers extra pressure to the abutment below it.
What is an arch dam structure?
An arch dam is a concrete dam that relies on its shape and structure to carry out loads of water pressure and other pressures from its reservoir to its abutments.
How an Arch Dam is constructed?
An arch dam is a concrete dam that relies on its shape and structure to carry out loads of water pressure and other pressures from its reservoir to its abutments.
What are the types of Arch Dam?
There are three types of arch dams: constant radius, variable radius and constant angle types. While a gravity dam is a concrete dam that relies mainly on its weight to support itself, an arch dam is a concrete dam whose structure bears most of the load.
How is an arch dam designed?
Arch dams are designed based on engineering methods that involve the evaluation of forces and loads, selection of appropriate materials and analyses of the zone’s elevation and cross sections.
What are the loads for which an arch dam is designed?
The arch dam is constructed on a steep slope so that it can transfer water pressure through its structure to resist internal pressures within the reservoir.
What is the advantage of Arch Dam?
Arch dams are suitable for construction of narrow gorges with abutment areas that can resist thrust and horizontal forces from the arch.
Why is there less cost for an arch dam?
Arch dams require less material, and thus cost less than a gravity dam.
How does the arch come into existence?
The angle at which an arch is built upon the vertical plane depends on how many times it will be turned in a circle around its horizontal axis. When the material is poured, the concrete is not forced to run under the arch.
What are the major problems with Arch Dam design?
With arch dams, it is hard to calculate and predict load forces exerted by water pressure on the dam.
What are reasons for which an Arch Dam can fail?
The main reason for failure of an Arch Dam is due to overloading, providing inadequate strength and stability of its abutments and insufficient quality of materials used in its construction.
