Chapter: Environmental Science and Engineering
Water Resources
WATER RESOURCES
Water is an important component of all living
beings. Nearly 80% of earth’s surface is covered by water.
Uses of Water
Due to
its unique properties, water is of multiple uses for all living organisms.
Water is absolutely essential for life.
Most of
the life processes take place in water contained in the body.
Uptake of
nutrients, their distribution in the body, regulation of temperature, and
removal of wastes are all mediated through water.
Human
beings depend on water for almost every developmental activity.
Water is
used for drinking, irrigation, and transportation, washing and waste disposal
for industries and used as a coolant for thermal power plants.
Water
shaped the earth's surface and regulates our climate.
Hydrological cycle
1.
Evaporation
2. Precipitation
3. Transpiration
The
transformation of water from liquid to gas phases as it moves from the ground
or bodies of water into the overlying atmosphere. The source of energy for
evaporation is primarily solar radiation.
Evaporation often implicitly includes transpiration from plants, though together they are specifically referred to
as evapotranspiration. Total
annual evaporation amounts to approximately 505,000 km3 (121,000 cu
mi) of water, 434,000 km3 (104,000 cu mi) of which evaporates from
the oceans.
Condensed
water vapor that falls to the Earth's surface .Most precipitation occurs as rain, but also
includes snow, hail, fog drip, graupel, and sleet. Approximately
505,000 km3
(121,000 cu mi) of water
falls as precipitation each year, 398,000 km3 (95,000 cu mi) of it
over the oceans.
The
transformation of water vapor to liquid water droplets in the air, creating clouds and fog.
The
release of water vapor from plants and soil into the air. Water vapor is a gas
that cannot be seen.
The
runoff produced by melting snow.
The
variety of ways by which water moves across the land. This includes both surface runoff
and channel
runoff. As it flows, the water may seep into the ground,
evaporate into the air, become stored in lakes or reservoirs, or be extracted
for agricultural or other human uses.
The flow
of water from the ground surface into the ground. Once infiltrated, the water becomes
soil moisture or groundwater.
The flow
of water underground, in the vadose zone and aquifers. Subsurface water may return to the
surface (e.g. as a spring or by being pumped) or eventually seep into the
oceans. Water returns to the land surface at lower elevation than where it
infiltrated, under the force of gravity or gravity induced pressures. Groundwater tends to
move slowly, and is replenished slowly, so it can remain in aquifers for
thousands of years.
The state
change directly from solid water (snow or ice) to water vapor.
Flow chart
OVER UTILIZATION OF SURFACE AND GROUND WATER
With
increasing human population and rapid development, the world water withdrawal
demands have increased many folds and a large proportion of the water withdrawn
is polluted due to anthropogenic activities.
Out of
the total water reserves of the world, about 97% is salty water and only 3% is
fresh water. Even this small fraction of fresh water is not available to us as
most of it is locked up in polar ice caps and just 0.003% is readily available
to us in the form of ground water and surface water.
Effects of over exploitation of water
Subsidence: When ground water withdrawal is
more than its recharge rate, the sediments in the aquifer (a layer of rock that is highly permeable and contains
water) get compacted, a phenomenon knows as ground subsidence. It results in
sinking of overlying land surface. Due to this structural damage in buildings,
fracture in pipes etc., occurs.
Lowering of water table: Mining
of groundwater is done extensively for irrigating crop fields. However, excessive mining would cause
lowering of water table.
Water logging: When excessive irrigation is
done with brackish water it raises the water table gradually leading to water-logging and salinity problems.
FLOODS AND DROUGHT
Heavy
rainfall often causes floods in the low-lying coastal areas.
Prolonged
downpour can also cause the over-flowing of lakes and rivers resulting into
floods. When annual rainfall is below normal and less than evaporation, drought
conditions are created.
Causes of flood and drought
Deforestation,
overgrazing, mining, rapid industrialization, global warming etc., have
contributed largely to a sharp rise in the incidence of floods.
Deforestation
leads to desertification and drought too. When the trees are cut, the soil is
subject to erosion by heavy rains, winds and sun.
The
removal of thin top layer of soil takes away the nutrients and the soil becomes
useless. The eroded soils exhibit droughty tendency.
Preventive measures
Clear
knowledge in control of drought and desertification can be very useful for
dealing with the problem.
Carefully
selected mixed cropping helps to optimize production and minimize the risks of
crop failures.
Social
forestry and Wasteland development can prove quite effective to fight the
problem, but it should be based on proper understanding of ecological
requirement and natural process.
CONFLICTS OVER WATER
Indispensability
of water and its unequal distribution has often led to inter-state or
international disputes. Issues related to sharing of river water have been
largely affecting our farmers and also shaking our governments. Many countries
are engaged in bitter rivalries over this precious resource. For instance,
Argentina
and Brazil, dispute each other's claims to the La Plata river, India and
Pakistan fight over the rights to water from the Indus, Mexico and USA have
come in conflict over the Colorado river, India and Bangladesh are fighting for
Bhrahmaputra river, and
Iran and
Iraq contest for the water from Shatt-Al- Arab River.
Within
India, water conflicts are still being continues between the states. For Eg.,
Sharing
of Krishna water between Karnataka and Andhra Pradesh, Sharing of Siruvani
water between Tamilnadu and Kerala, and others. Sharing of Cauvery between
Karnataka and Tamilnadu
On June
2,1990, the Cauvery Water dispute Tribunal was set up which through an interim
award directed Karnataka to ensure that 205 TMCF of water was made available in
Tamil Nadu's Mettur dam every year, till a settlement was reached.
In
1991-1992 due to good monsoon, there was no dispute. In 1995, the situation
turned into a crisis due to delayed rains and an expert Committee was set up to
look into the matter which found that there was a complex cropping pattern in
Cauvery basin.
Samba
paddy in winter, Kuravai paddy in summer and some cash crops demanded intensive
water; thus aggravating the water crisis.
Proper
selection of crop varieties, optimum use of water, better rationing are
suggested as some measures to solve the problem
BIG-DAMS –BENEFITS AND PROBLEMS
Dams are
built across the river in order to store water for drinking, agricultural,
industrial purpose. Now days they are mainly used for the hydropower
production.
1 Benefits
River
valley projects with big dams play a key role in the development process due to
their multiple uses.
These
dams aim at providing employment for tribal people and raising the standard and
quality of life. Dams can help in checking floods and generate electricity and
reduce water and power shortage, provide irrigation water to lower areas,
provide drinking water in remote areas and promote navigation, fishery.
2 Problems
The
impacts of big dams can be upstream as well as downstream levels. The upstream
problems include the following:
Displacement
of tribal people
Loss of
forests, flora and fauna
Changes
in fisheries
Saltation
and sedimentation of reservoirs
Loss of
non-forest land
Stagnation
and water logging near reservoir
Breeding
vectors and spread of vector –borne diseases
Reservoir
induces seismicity causing earthquakes
Microclimatic
changes
Growth of
aquatic weeds
3 Downstream problems include the following
Water
logging and salinity due to over irrigation
Microclimatic
changes
Reduced
water flow and slit deposition in river
Flash
foods
Salt
water intrusion at river mouth
Loss of
land fertility
Outbreak
of vector-borne diseases like malaria.
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