What is a dam?
A dam is a wall of solid material built across a river valley or catchment to block the flow of the river.
The dam wall creates a lake and allows water to continue flowing down steam of the dam. Dams
create a permanent supply of water for the community to use. The dam must be watertight so it is
safe and stops water from escaping downstream and the walls must be strong enough to resist water
pressure. The higher the dam, the greater the depth of water stored behind it, and the greater the
water pressure on the dam wall.
A dam must have a way of releasing water in controlled amounts so people can use it. Water is
released into a network of pipelines that supply homes, businesses and farms with water.
If it rains heavily, or if the river floods, water can escape over a concrete ‘spillway’ and into the river
downstream. A spillway is usually built at the side of the dam wall. Dams also can have large steel
release gates or come valves to allow water to flow out when required. If the dam is built of concrete,
water can even flow over the dam wall.
Some dams are constructed to provide flood mitigation while others are for drinking water storage
and others to produce Hydro electricity.
How are dams built? Each dam is different – some are small and deep, some are shallow and wide. It all depends on the size of the river and shape of the valley. Dams can be made from different materials. There are two main types of dams.
Concrete dams are made of strong, solid concrete walls that resist the pressure of water;
Earth and rock fill dams have a solid core of clay in the middle to prevent water leakage, and
an outer layer of rock for strength.
Dams and the environment
A dam built across a river will impact the river valley. Plants, animals, roads, farms and sometimes
even towns will be flooded. The flow of a river downstream will also be disrupted, and fish and wildlife
may be threatened. This is why all modern dams undergo strict environmental controls to minimise
their environmental impact.
Some ways to reduce the environmental impact of dams are:
Working with the local community to relocate houses and roads
Keeping trees and vegetation in the valley to stop soil erosion into the dam lake
Preventing noise, dust and pollution during construction
Relocating wildlife or special cultural sites in the catchment area
Building water ‘ladders’ around the dam wall so fish can swim upstream or downsteam
After the dam is built, regularly releasing water to keep the river healthy
Types of Dams
FIVE BIGGEST DAM IN INDIA
Tehri Dam(uttaranchal)
Bhakra Nangal Dam(himachal pradesh)
Bhakra Nangal Dam is a gravity dam across the Sutlej river Himachal Pradesh. Bhakra Nangal is the largest dam in India, with a height of 225 meters and second largest Dam in Asia. Its reservoir, known as the “Gobind Sagar Lake” it is the second largest reservoir in India, the first being Indira Sagar dam.
Sardar Sarovar Dam also known as “Narmada Dam” is the largest dam to be built, with a height of 163 meters, over the Sacred Narmada River in Gujarat. Drought prone areas of Kutch and Saurashtra will get irrigate by this project. The gravity dam is the largest dam of Narmada Valley Project with power facilities up to 200 MW. The dam is meant to benefit the 4 major states of India Gujarat, Madhya Pradesh, Maharashtra and Rajasthan.
A dam is a wall of solid material built across a river valley or catchment to block the flow of the river.
The dam wall creates a lake and allows water to continue flowing down steam of the dam. Dams
create a permanent supply of water for the community to use. The dam must be watertight so it is
safe and stops water from escaping downstream and the walls must be strong enough to resist water
pressure. The higher the dam, the greater the depth of water stored behind it, and the greater the
water pressure on the dam wall.
A dam must have a way of releasing water in controlled amounts so people can use it. Water is
released into a network of pipelines that supply homes, businesses and farms with water.
If it rains heavily, or if the river floods, water can escape over a concrete ‘spillway’ and into the river
downstream. A spillway is usually built at the side of the dam wall. Dams also can have large steel
release gates or come valves to allow water to flow out when required. If the dam is built of concrete,
water can even flow over the dam wall.
Some dams are constructed to provide flood mitigation while others are for drinking water storage
and others to produce Hydro electricity.
How are dams built? Each dam is different – some are small and deep, some are shallow and wide. It all depends on the size of the river and shape of the valley. Dams can be made from different materials. There are two main types of dams.
Concrete dams are made of strong, solid concrete walls that resist the pressure of water;
Earth and rock fill dams have a solid core of clay in the middle to prevent water leakage, and
an outer layer of rock for strength.
A dam built across a river will impact the river valley. Plants, animals, roads, farms and sometimes
even towns will be flooded. The flow of a river downstream will also be disrupted, and fish and wildlife
may be threatened. This is why all modern dams undergo strict environmental controls to minimise
their environmental impact.
Some ways to reduce the environmental impact of dams are:
Working with the local community to relocate houses and roads
Keeping trees and vegetation in the valley to stop soil erosion into the dam lake
Preventing noise, dust and pollution during construction
Relocating wildlife or special cultural sites in the catchment area
Building water ‘ladders’ around the dam wall so fish can swim upstream or downsteam
After the dam is built, regularly releasing water to keep the river healthy
Types of Dams
Dams can be grouped according to the type of material of which they are constructed as follows; concrete dams are further grouped according to how they achieve their strength and stability.
CONCRETE DAMS
CONCRETE DAMS
- Concrete Gravity Dams
- Concrete Arch Dams
- Concrete Buttress Dams
- Earth Dams
- Earth and Rock Fill Dams
- Concrete Faced Rock Fill Dams
Concrete Gravity Dams rely on the weight of the concrete of which they are built to resist the forces (gravity, water pressure, earthquake) to which they are subjected.
Concrete Arch Dams and Buttress Dams can be built using a smaller amount of concrete than that required for a Gravity Dam and, as a result, are cheaper to build. This is possible because Arch and Buttress Dams are designed to transfer some of the loads (forces) on them to the foundation on which they are built ie the strength of the foundation is used to help resist the loads which could not be resisted simply by the weight of the dam wall alone. In all cases the impermeable membrane of concrete dams is the whole dam wall.
Concrete Arch Dams and Buttress Dams can be built using a smaller amount of concrete than that required for a Gravity Dam and, as a result, are cheaper to build. This is possible because Arch and Buttress Dams are designed to transfer some of the loads (forces) on them to the foundation on which they are built ie the strength of the foundation is used to help resist the loads which could not be resisted simply by the weight of the dam wall alone. In all cases the impermeable membrane of concrete dams is the whole dam wall.
Fill or Embankment Dams are grouped according to the material of which they are constructed which, in turn, relates to the type of impermeable membrane used. Earth Dams are built of homogeneous, impermeable earth material so that the impermeable membrane is the whole dam wall.
Earth and Rock Fill Dams have a relatively narrow, impermeable earth or clay core inside the dam but most of the dam is constructed of permeable rock fill which, by itself, would be incapable of retaining water. The impermeable membrane in these dams is the clay core
.
Concrete Faced Rock Fill Dams are constructed of permeable rock fill, the impermeable membrane being a concrete slab constructed on the upstream face of the dam wall. This type of dam has become increasingly popular over the last 25 years or so. A recent example is the proposed 205 m high Bakun Dam in Malaysia, originally put on hold due to the Asian financial crisis. Three Australian concrete faced rock fill dams (CFRD) built in 1970-71 (Pindari, Kangaroo Creek and Cethana) played a significant role in the development of the CFRD type of dam design.
Tehri Dam(uttaranchal)
Tehri Dam located on the Bhagirathi River, Uttaranchal Now become Uttarakhand. Tehri Dam is the highest dam in India,With a height of 261 meters and the eighth tallest dam in the world. The high rock and earth-fill embankment dam first phase was completed in 2006 and other two phases are under construction. The Dam water reservoir use for irrigation, municipal water supply and the generation of 1,000 MW of hydroelectricity.
- Height: 260 meters
- Length: 575 meters
- Type: Earth and rock-fill
- Reservoir Capacity: 2,100,000 acre·ft
- River: Bhagirathi River
- Location: Uttarakhand
- Installed capacity: 1,000 MW
Bhakra Nangal Dam is a gravity dam across the Sutlej river Himachal Pradesh. Bhakra Nangal is the largest dam in India, with a height of 225 meters and second largest Dam in Asia. Its reservoir, known as the “Gobind Sagar Lake” it is the second largest reservoir in India, the first being Indira Sagar dam.
- Height: 226 meters
- Length: 520 meters
- Type: Concrete gravity
- Reservoir Capacity: 7,501,775 acre·ft
- River: Sutlej River
- Location: Punjab and Himachal Pradesh
- Installed capacity: 1325 MW
Hirakud Dam(Orissa)
Tehri Dam -Uttaranchal
Tehrhhhhi Tehri hDah
- Height: 60.96 meters
- Length: 25.8 km
- Type: Composite Dam
- Reservoir Capacity: 4,779,965 acre·ft
- River: Mahanadi River
- Location: Orissa
- Installed capacity: 307.5 MW
Nagarjuna sagar Dam(Andhra Pradesh)
Da
- Height: 124 meters
- Length:1,450 meters
- Type: Masonry Dam
- Reservoir Capacity: 9,371,845 acre·ft
- River: Krishna River
- Location: Andhra Pradesh
- Installed capacity: 816 MW
Sardar Sarovar Dam(Gujrat)
Sardar Sarovar Dam also known as “Narmada Dam” is the largest dam to be built, with a height of 163 meters, over the Sacred Narmada River in Gujarat. Drought prone areas of Kutch and Saurashtra will get irrigate by this project. The gravity dam is the largest dam of Narmada Valley Project with power facilities up to 200 MW. The dam is meant to benefit the 4 major states of India Gujarat, Madhya Pradesh, Maharashtra and Rajasthan.
- Height: 163 meters
- Length:1,210 meters
- Type: Gravity Dam
- Reservoir Capacity: 7,701,775 acre·ft
- River: Narmada River
- Location: Gujarat
- Installed capacity: 1,450 MW
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