Construction of Dams

ENVIRONMENT MANAGEMENT

Unit X

Social Issues & Environment By:

Sunny Advani

Sukhada Desai

Contents:

What is a Dam?History of DamsWhy are Dams built?Construction of DamProblems associated with DamsRehabilitation & ResettlementCase Study: Aswan High Dam

What is a Dam?

A dam is an obstacle built across a river or a lake to hold back water. The reservoirs which form behind them are used to store water which is used for four major uses:

(i) to ensure a regular water supply for industrial and domestic use, (ii) for irrigation, (iii) for flood control, (iv) for hydroelectric power.

History of Dams

The word dam can be traced back to Middle English, and before that, from Middle Dutch, as seen in the names of many old cities For instance the Dutch capital Amsterdam (old name Amstelredam) started with a dam through the river Amstel in the late 12th Century, and Rotterdam started with a dam through the river Rotte

History of Dams….

The oldest surviving and standing dam in the world is believed to be the Quatinah barrage in modern-day Syria. The dam is assumed to date back to the reign of the Egyptian pharao Sethi (1319–1304 BC), and was enlarged in the Roman period and between 1934-38. It still supplies the city of Homs with water.About 2000 years ago the Romans built two dams near Merida in Spain to provide water for the town. They are still used today to provide water for irrigation

Why are Dams built?

Power generation : Hydroelectric power is a major source of electricity in the world. Many countries have rivers with adequate water flow, that can be dammed for power generation purposes. For example, the Itaipu on the Parana River in South America generates 14 GW and supplied 93% of the energy consumed by Paraguay and 20% of that consumed by Brazil as of 2005.

Why are Dams built?….

Water supply : Many urban areas of the world are supplied with water abstracted from rivers pent up behind low dams or weirs. Examples include London - with water from the River Thames and Chester with water taken from the River Dee. Other major sources include deep upland reservoirs contained by high dams across deep valleys such as the Claerwen series of dams and reservoirs.


Stabilize water flow / irrigation: Dams are often used to control and stabilize water flow, often for agricultural purposes and irrigation. Others such as the Berg Strait dam can help to stabilize or restore the water levels of inland lakes and seas, in this case the Aral Sea.Flood prevention :Dams such as the Blackwater dam of Webster, New Hampshire and the Delta Works are created with flood control in mind.


Land reclamation: Dams (often called dykes or levees in this context) are used to prevent ingress of water to an area that would otherwise be submerged, allowing its reclamation for human use.Navigation: Dams help make inland waterways accesible to ships and barges.For example, to make the Ohio river in the east-central United States navigable throughout its length, engineers constructed a sreies of 13 dams.

Construction of Dams

Siting a Dam

Planning a Dam

Building a Dam


Siting a Dam: During this process the engineer must consider the purpose of the dam & how much water the reservoir needs to hold.He must also find out the amount of water which flows down the river during the rainy season and in times of drought, and whether more water can be brought from streams in the neighborhood.


Planning a Dam: The engineer then needs to decide what type of dam can be conveniently and economically built across the outlet. Modern dams fall into two categories:

1.Embankment Dams

2.Masonry Dams

Embankment Dams

Generally these are built in valleys which are wide and shallow, and when the rock in the walls of the valley are not hard enough to support the weight of a concrete dam.A couple of examples of embankment dams are: the High Island Dam in Hong Kong, the Mica Dam in Canada and the Marchlyn Dam in North Wales made of rock , the 154m high Goschener Dam in Switzerland made of broken stone, and the Aswan High Dam in Egypt.

Masonry Dams

Gravity: A dam which holds its place against the horizontal push of the water by its own weight is called a gravity dam. Examples are the Claerwen Dam in Wales and the Lower (original) Aswan Dam in Egypt.

Masonry Dams

Arch: An arch of brick or stone can carry the weight of the masonry above it by transmitting the thrust through the abutments to the ground. A well known example, the Lumiei Dam in Italy is 449 feet high and made of concrete.

Masonry Dams

Buttress: This type combines the principles of both the gravity and arch dams. It consists of a series of buttresses placed at intervals and connected by horizontal arches. Loch Sloy Dam in Scotland is an example.

Masonry Dams

Barrage: In narrow bays and in the mouths of rivers, the water flows in as the tide rises and flows out again as the tide falls. It is possible, by damming the river, to make use of the moving water to generate electricity. This type of dam is called a barrage. The Rance Barrage in western France is 804 metres long and lies across the mouth of the Rance River.


Building a Dam: Once the detailed plans have been drawn up and a cost benefit analysis has been approved, the dam can be built. Consideration must then be given to the financial implications of building the dam.

Problems associated with Dams

Loss of WaterSiltingErosionRisk of DisasterEcological Disruptions


Loss of Water: The reservoir provides for evaporation and more area of seepage from below compared with the stream that preceded it. For example, evaporation from lake Powell removes about 270,000 cubic metres of water per year,enough to serve the water needs of a city with the population of half a million.


Silting: Consider the physical events that take place during the life of the dam & its reservoir. Most of the sediments that enters the reservoir from the runoff that feeds it settles to the bottom before it can get a chance to spill over the dam.

Thus the reservoir gradually fills up. Rates of buildup can reach 10cm, or 0.1 meter, per year.


Erosion: The water that flows over the dam is quite free of sediment. Even water that is discharged from outlet below the surface carries less sediment that would have been present before the dam was built.

As the water now moves more rapidly in the stream below, it starts to scour out the stream bed because it has an unused capacity for carrying sediment. This causes soil erosion.


Risk of Disaster: This causes soil erosion.Areas near rivers (their flood plains) are attractive for farming, industry, & commerce especially when flood control promises to make the region safe.

But unusually heavy rainfall can fill and overflow the reservoir, which then can no longer limit the flow. In such cases, the population in the flood path is vulnerable to disaster.


Ecological Disruptions: Building a dam changes the ecology of the surrounding area.

1.Dams alter the water temperatures and affect the microhabitats. Among the most affected animals are fishes.

2.Dams prevent nutrient-laden silt from flowing downstream.

3.Dams also cause havoc on human populations.

Rehabilitation & Resettlement

The policy prescribes four ways in which an affected person could be compensated:

1.Free choice

2.Resettlement to the Host Area

3.Relocation within the same Chiefdom

4.Remain in situ


1. Free choice: in this option the affected persons chose their own destination and were compensated for structures and a 20 % inconvenience allowance, but lost their fields.

2. Resettlement to the Host Area: through this option the affected person was paid compensation for his/her structures plus a 10 % inconvenience allowance and got land as replacement for his/her fields.


3. Relocation within the same Chiefdom: this option allowed for affected people to receive compensation for their structures and a 10 % inconvenience allowance and land as replacement for their fields. If the person's land was not affected, he/she received only compensation for structures.


4. Remain in situ: whereby the person's structures are not affected but their fields would be affected. The affected people would receive either cash compensation for the development of their remaining fields or development assistance to improve their remaining fields.

Case Study: Aswan High Dam

Egypt's High Dam across the Nile at Aswan is a stupendous piece of civil engineering. It was completed in 1970 after a decade of construction and an expenditure of over 1 billion dollars. It was undertaken as a joint venture between Egypt and Russia using plans drawn up by a West German firm.Construction began in 1960 with the excavation of a diversion canal to take the water away from the construction site, later it became a source of power.

Case Study: Aswan High Dam….

The dam has caused problems, as well as almost fulfilling its major purposes. Great Britain's Economist magazine has blamed the High Dam for :

1.causing the erosion of the Egyptian coastline

2.killing the sardine industry

3.depriving the delta of the yearly silt that gave Egypt the world's most fertile soil

4.spawning a plague of the dangerous bilharzia parasite

References:

1. The World's Rivers: The Nile. Julian Waterhouse 1995

2. Oxford Junior Encyclopedia. 1955 edition

3. Children's Britannica 1989 edition

4. Egypt's Dream Fulfilled Time-Life Books

5. Keller, Edward. Environmental Geology. Upper Saddle River: Prentice-Hall, Inc., 2000.

6. Pearce, Fred. The Dammed: Rivers, Dams, and the Coming World Water Crisis.

KOYNA-DAM

NARMADA DAM

SARDAR SAROVAR DAM

List of largest dams

Dams in Nagpur

Wakeshwar, Telhara,Surabard,Salaimendha ,Zilpi,Anjangaon ,Khadki ,Nandira,Paradgaon,Khapari ,Nandera ,Wadgaon ,Nishanghat ,Ukarwahi ,Wadad ,Botezhari ,khandezhari,Nawegaon ,Urkudapar ,Wani ,Pirawa ,Chichala,Satighat ,Gothangaon ,Karhandala ,Nanda ,Raibasa ,Mahurkund ,Nagalwadi ,Paradsinga ,Ranwadi ,Kotwalbardi ,Zilpa ,Dhotewada ,Junewani ,Madhuganga,Dongartal ,Mahurnala ,Sheonibondki ,Khumari ,Chorbahuli ,Khidki ,Bhagimahari ,Suwardhara ,Kanhadevi ,Adegaon ,Kathalabodi ,Sirsi ,Chinoda

,Undri ,KhumarNallah

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Documents

Construction of Dams