2. outin
INTRODUCTION
Dams in the 20-21 century
Types of Dams
How do dams work?
benefits of dams?
Dams and climate risk
Costs of dams?
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OUTLINE:
3. *.The International Commission on Large
Dams (ICOLD) defines a dam as ‘an artificial
barrier that has the ability to impound water,
wastewater, or any liquid-borne material, for
the purpose of storage or control of water’.
*.Dams are made from earth, stacked
rock or concrete, and are usually
constructed across rivers to store water
in the reservoir that is formed behind
the dam as a result of the river being
blocked.
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4. Dams in the 20th century And Some Facts
Today, around 3 800 km3 of fresh water is withdrawn annually from the world’s lakes,
rivers and aquifers.2 This is twice the volume extracted 50 years ago.
For thousands of years, dams have been used to store water and to create energy.
However, 90 percent of global dam investments have been made after (1949-1950,
both in terms of the millions of small or medium sized dams and the thousands of
dams higher than 50m
The last century saw a rapid increase in large dam building. By 1949 about 5 000 large
dams had been constructed worldwide, three-quarters of them in industrialized
countries. By the end of the 20th century, there were over 45 000 large dams in over
140 countries.
As dam building accelerated after the 1950’s, opposition to dams became more
widespread, vocal and organize
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5. Dams in the 20th century And Some Facts
The top five dam-building countries account for nearly 80% of all large dams
worldwide. China alone has built around 22 000 large dams, or close to half the world’s
total number. Before 1949 it had only 22 large dams. Other countries among the top
five dam building nations include the United States with over 6 390 large dams; India
with over 4 000; and Spain and Japan with between 1 000 and 1 200 large dams each
Approximately two thirds of the world’s existing large dams are in developing countries
. An estimated 1 700 large dams have been under construction in other parts of the
world in the last few years. Of this total, 40% are reportedly being built in India
Since average construction periods generally range from 5 to 10 years, this indicates a
worldwide annual average of some 160 to 320 new large dams per year.
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6. TYPES OF DAMS
Almost each dam that has been constructed all over the world is unique. This is so
because a particular type is chosen because of the considerations of many factors,
as discussed in subsequent sections. In fact, dam engineering brings together a
range of disciplines, like structural, hydraulics and hydrology, geotechnical,
environmental etc
Though each situation demands a unique proposal for the type of dam, a broad
classification based on the construction material can be made in dividing the
types of dams that have been commonly constructed as:
1. Embankment dams, which are constructed of earth fill and/or rock fill,
2. Concrete dams, which are constructed of mass concrete.
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9. How do dams work?
Dams store water in the reservoir formed behind the dam
The stored water can be used for various consumptive
purposes, including use as water for irrigation, or as sources of
drinking water for urban and regional towns and cities.
The stored water can also be released from the reservoir
during the times that natural flows in downstream rivers are
inadequate to help meet a variety of environmental objectives
Depending on the catchment area for the dam, the water
stored in dam reservoirs is usually easier to treat to a drinking
water standard than other sources of drinking water, such as
run of river supplies. This is because the long time spent in
storage usually improves the quality of the water stored in the
reservoir
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10. benefits of dams?
Water supply for domestic, irrigation and industrial use
Meeting the agricultural demand for food supply
Flood control
Hydropower
Recreation
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11. Water supply for domestic, irrigation and
industrial use
Dams can provide a cost-effective supply of water for domestic, irrigation and
industrial use, when compared to other sources of water, such as recycled water,
groundwater, desalination and demand management on a cost-benefit analysis.
When determining the suitability of dams all water source options should be
assessed based on a cost-benefit analysis
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12. Meeting the agricultural demand for
food supply
The water stored in dams is critically important to
many towns in rural and regional Australia, as they are
often the main source of water supply. The dams have
enabled many regional and rural towns to prosper and
develop economically-important agricultural industries.
The 2014 Agricultural Competiveness Green Paper
identifies 27 potential new dam sites in Australia that
would help develop new food growing regions.
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13. Flood control
Whilst not always their primary purpose,
dams provide the opportunity to
attenuate flood flows, by their ability to
store large volumes of water and then
constrain the rate of outflow to
downstream rivers through spillways or
other release structures.
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14. Hydropower
Hydroelectricity is electrical energy generated
when water that flows down rivers, streams or
waterfalls is channelled through water turbines.
In Australia, hydroelectric power is most
commonly generated from water is that is stored
in dams and then released from the dam
through water turbines In 2011, hydroelectricity
produced 67 per cent of Australia’s total clean
energy generation
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15. Recreation
Dams provide opportunities for communities to
undertake various recreational activities, such as
sailing, boating and fishing. From a public
health perspective it is highly preferable if this
onwater recreational activity occurs on dams
that store water that is not going to be used as
a source of drinking water.
Dams can also promote local tourism.
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16. Dams and climate risk
There is a complex relationship between climate, weather, rainfall and stream
flows into dams
The proportion of total rainfall from heavy falls will increase in the 21st century
over many areas of the globe
A one-in-twenty year maximum daily rainfall event is likely to become a one-in-
five to one-in-fifteen year event by the end of the 21st century in many regions
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