Chapter: Environmental Science and Engineering

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Water Resources

Water is an important component of all living beings. Nearly 80% of earth’s surface is covered by water.

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

 

Evaporation

 

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.

 

Precipitation

 

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.

 

Condensation

The transformation of water vapor to liquid water droplets in the air, creating clouds and fog.

 

Transpiration

The release of water vapor from plants and soil into the air. Water vapor is a gas that cannot be seen.

 

Snowmelt

The runoff produced by melting snow.

 

Runoff

 

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.

 

Infiltration

 

The flow of water from the ground surface into the ground. Once infiltrated, the water becomes soil moisture or groundwater.

 

Subsurface Flow

 

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.

 

Sublimation

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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