Multipurpose
reservoirs
Water
supply
Flood
control
Soil
erosion
Environmental
management
Hydroelectric
power generation
Navigation
Recreation
Irrigation
ü
The multipurpose
nature of these facilities dictates that the agencies which manage them are
responsible for balancing competing demands.
ü
For example, managers
responsible for hydroelectric power generation often want to keep lake levels
as high as possible, since the water stored in the reservoir serves as a kind
of "fuel" for their
generators.
ü
However, managers
responsible for flood control often want to keep lake levels as low as possible
to provide the maximum amount of storage capacity for rainwater runoff.
Water supply
ü
Water supply is the provision of
water by public utilities, commercial organizations, community endeavors or by
individuals, usually via a system of pumps and pipes.
ü
Irrigation is covered separately.
Flood control
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Floods are caused by many factors:
heavy rainfall, highly accelerated snowmelt, severe winds over water, unusual
high tides, tsunamis, or failure of
dams, levees, retention ponds, or other
structures that retained the water.
ü
Flooding can be exacerbated by
increased amounts of impervious surface or by other natural hazards such as
wildfires, which reduce the supply of vegetation that can absorb rainfall.
ü
Periodic floods occur on many
rivers, forming a surrounding region known as the flood plain.
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During times of rain, some of the
water is retained in ponds or soil, some is absorbed by grass and vegetation,
some evaporates, and the rest travels over the land as surface runoff.
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Floods occur when ponds, lakes,
riverbeds, soil, and vegetation cannot absorb all the water. Water then runs
off the land in quantities that cannot be carried within stream channels or
retained in natural ponds, lakes, and man-made reservoirs.
ü
About 30 percent of all
precipitation becomes runoff and that amount might be increased by water from
melting snow.
ü
River flooding is often caused by
heavy rain, sometimes increased by melting snow.
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A flood that rises rapidly, with
little or no advance warning, is called a flash flood.
ü
Flash usually result from intense
rainfall over a relatively small area, or if the area was already saturated
from previous precipitation.
Soil erosion
ü
In geomorphology and geology,
erosion refers to the actions of exogamic processes (such as water flow or
wind) which remove soil and rock from one location on the Earth's crust, then
transport it to another location where it is deposited.
ü
Eroded sediment may be transported
just a few millimeters, or for thousands of
kilometers.
ü
While erosion is a natural process,
human activities have increased by 10-40 times the rate at which erosion is
occurring globally.
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Excessive (or accelerated) erosion
causes both 'on-site' and 'off-site' problems.
ü
On-site impacts include decreases
in agricultural and (on natural
landscapes) ecological collapse, both
because of loss of the nutrient-rich upper soil layers. In some cases, the
eventual end result is desertification.
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Off-site effects include
sedimentation of waterways and eutrophication of water bodies, as well as
sediment-related damage to roads and houses.
ü
Water and wind erosion are now the
two primary causes of land degradation; combined, they are responsible for
about 84% of the global extent of degraded, making excessive erosion one of the
most significant environmental problems world-wide.
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Intensive agriculture, deforestation,
roads, anthropogenic climate change and urban sprawl are amongst the most
significant human activities in regard to their effect on stimulating erosion.
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However, there are many remediation
practices that can curtail or limit erosion of vulnerable soils.
Environmental resource
management
ü
Environmental resource management
is the management of the interaction and impact of human societies on the
environment.
ü
It is not, as the phrase might
suggest, the management of the environment itself.
ü
Environmental resources management
aims to ensure that ecosystem services are protected and maintained for future
human generations, and also maintain ecosystem integrity through considering
ethical, economic, and scientific (ecological) variables.
ü
Environmental resource management
tries to identify factors affected by conflicts that rise between meeting needs
and protecting resources.
ü
It is thus linked to protection and
sustainability.
Hydroelectricity
ü
Hydroelectricity is the term
referring to electricity generated by hydropower; the production of electrical
power through the use of the gravitational force of falling or flowing water.
ü
It is the most widely used form of
renewable, accounting for 16 percent of global electricity generation â€'3,427
terawatt-hours of electricity production in 2010, and is expected to increase
about 3.1% each year for the next 25 years.
ü
Hydropower is produced in 150
countries, with the Asia-Pacific region generating 32 percent of global
hydropower in 2010.
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China is the largest
hydroelectricity producer, with 721 terawatt-hours of production in 2010,
representing around 17 percent of domestic electricity use.
ü
There are now four hydroelectricity
plants larger than 10 GW: the Three Gorges Dam and Xiluodu Dam in China, Itapúa
Dam across the Brazil/Paraguay border, and Guru Dam in Venezuela.[1]
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The cost of hydroelectricity is
relatively low, making it a competitive source of renewable electricity.
ü
The average cost of electricity from a
hydro plant larger than 10 megawatts is 3 to 5 U.S. cents per kilowatt-hour. It
is also a flexible source of electricity since the amount produced by the plant
can be changed up or down very quickly to adapt to changing energy demands.
ü
However, damming interrupts the
flow of rivers and can harm local ecosystems, and building large dams and
reservoirs often involves displacing people and wildlife.
ü
Once a hydroelectric complex is
constructed, the project produces no direct waste, and has a considerably lower
output level of the greenhouse
gas carbon dioxide (CO
2) than fossil fuel powered energy
plants.
Navigation
ü
Navigation is a field of study that
focuses on the process of monitoring and controlling the movement of a craft or
vehicle from one place to another.
ü
The field of navigation includes
four general categories: land navigation, marine navigation, aeronautic
navigation, and space navigation.
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It is also the term of art used for
the specialized knowledge used
by
navigators to perform navigation tasks.
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All navigational techniques involve
locating the navigator's position compared to known locations or patterns.
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Navigation, in a broader sense, can
refer to any skill or study that involves the determination of position and
direction.
ü
In this sense, navigation includes
orienteering and pedestrian navigation.
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For information about different
navigation strategies that people use,
visit
human navigation.
Irrigation
ü
Irrigation is the artificial
application of water to the land or soil.
ü
It is used to assist in the growing
of agricultural crops, maintenance
of landscapes, and re-vegetation of
disturbed soils in dry areas and during periods of inadequate rainfall.
ü
Additionally, irrigation also has a
few other uses in crop production, which include protecting plants against
frost, suppressing weed growth in grain fields and preventing soil
consolidation.
ü
In contrast, agriculture that
relies only on direct rainfall is referred to as rain-fed or dry land farming.
ü
Irrigation systems are also used
for dust suppression, disposal of sewage, and in mining.
ü
Irrigation is often studied
together with drainage, which is the natural or artificial removal of surface
and sub-surface water from a given area.
ü
Irrigation has been a central
feature of agriculture for over 5000 years, and was the basis of the economy
and society of numerous societies, ranging from Asia to Arizona.
Channel improvement.
At
the diversion structure, a headwork regulates the flow into a canal.
This canal, which takes its supplies
directly from the river, is called the main canal and usually direct irrigation
from the waters of this canal is not carried out.
This
acts as a feeder channel to the branch canals, or branches.
3
Branch
canals generally carry a discharge higher than 5 m /s and acts as feeder
3
channel
for major distributaries which, in turn carry 0.25 to 5 m /s of discharge.
The
major distributaries either feed the water courses or the minor distributaries,
3
which
generally carry discharge less than 0.25 m /s.
Though irrigation canals may be
constructed in natural or compacted earth, these suffer from certain
disadvantages, like the following
•
Maximum
velocity limited to
prevent
•
Seepage
of water into
the ground
•
Possibility of
vegetation growth in
•
Possibility of bank
failure,iesofburrowing either animals
All these reasons lead to adoption of
lining of canals, though the cost may be prohibitive.
Hence, before
suggesting a possible lining for a canal, it is necessary to evaluate the cost
vis-Ã -vis the savings due to reduction in water loss through seepage.
Apart from avoiding all the
disadvantages of an unlined canal, a lined canal also has the advantage of
giving low resistance and thus reducing the frictional loss and maintaining the
energy and water surface slopes for the canal as less as possible. This is
advantageous as it means that the canal slope may also be smaller, to maintain
the same discharge than for a canal with higher friction loss. A smaller canal
slope means a larger command area.
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