Water Resources | Revision Notes
Water is one of the most important resources on the Earth. Although 71% of the total surface of the Earth is covered with water, only 1% of freshwater is available for direct human use. Evaporation of water from oceans and precipitation in the form of rainfall—parts of the water cycle—ensure the continuous availability of freshwater. However, water is becoming a scarce resource. India is facing an acute shortage of water supply. India receives about 4% of the global precipitation and ranks 133 in the world in terms of availability of water per person in a year.
Reasons for Scarcity of Water in India
The following reasons can be attributed to the scarcity of water in India:
- A large and growing population has resulted in the scarcity of water resources in the country.
- To provide food resources for such a vast population, water resources are overused to irrigate agricultural fields. Indiscriminate use of wells and tube wells has led to a considerable decline in the water table.
- The establishment of various industries has resulted in the further exploitation of water resources. The discharge of industrial effluents has also degraded the quality of water.
- In India, generation of hydroelectricity on a large scale has also put pressure on the water resources.
- Urban centres have multiplied in the country. Many houses and housing societies have their own independent boring devices. This has further depleted the water table.
- In India, many places or regions may have sufficient water resources but may still suffer from water scarcity. This may be because of the deterioration in the quality of drinking water. Disposal of household and industrial wastes and the use of insecticides and pesticides in agriculture may result in worsening of the quality of water.
Negative Impact of Building Big Dams
At present, many big dams are constructed in our country. These are called multipurpose dams as they help in the generation of electricity and provide water for irrigation and industrial uses. Recently, these multipurpose dams have come under attacks from environmentalists because of the following reasons:
- Damming of rivers and regulating their flow result in excessive sedimentation at the bottom of the reservoir. This may hamper aquatic life and their migration to other water bodies.
- Building of dams result in the submergence of land and vegetation. This results in the decomposition of vegetation.
- Construction of large dams results in the displacement of villagers and communities. The villagers have to give up their lands and their means of livelihood.
- Large forest areas are also submerged because of the building of dams. This threatens our biodiversity.
- As dams provide water for irrigation, intensive irrigation leads to salinity of soil.
- Frequently, the water in large dams is used for the benefit of the urban population and the rural population is often left out. This further widens the gap between the rich and the poor.
- Dams which were initially built to control floods are now causing floods because of sedimentation. In case of excessive rainfall, the release of water from dams often floods the area, causing damage to lives and property.
- Land degradation, water-borne diseases and pollution are some other effects of building large dams.
It has been stressed that it is more beneficial to build small check dams and small reservoirs in order to deal with the problem of water scarcity. It not only provides water for irrigation at the time of need but also recharges groundwater.
Hydraulic Structures in Ancient India
- Dams, lakes and reservoirs were built at the time of the rule of Chandra Gupta Maurya.
- Evidences of irrigation works have been found in Kalinga (Odisha), Nagarjunakonda in Andhra Pradesh, Santhebennur in Karnataka and Kolhapur in Maharashtra.
- Bhopal Lake was built in the 11th century.
- In the 14th century, a tank in Hauz Khas was built in Delhi by Iltutmish.
Rainwater harvesting is a technique of collecting and storing rainwater for domestic use. It is done in the following ways:
- Rainwater on the rooftop is first collected using a PVC pipe. Water is then filtered by using sand and bricks.
- Water is then taken down either to a sump (a hollow structure or a depression where liquids collect) for immediate use or to a well or any other structure which is dug in the premises of a house.
- Water from this well can be used later for domestic consumption. It also recharges the water table.
Technique of Rainwater Harvesting
India has a long tradition of water harvesting. The technique differed from regions to regions and was also called by different names. Rain roof water harvesting was practised in Rajasthan and in Bengal. Long canals were taken out from large rivers which received water during flooding of the river (inundation canals) in dry regions of western India. Agricultural fields were converted into rain-fed storage structures. This helped the soil to gain moisture. In Rajasthan, many houses had underground storage tanks (known as ‘tanka’). Rainwater from the sloping roofs of the house was collected into these underground tanks through pipes.
Rainwater harvesting is one of the most important methods to deal with the scarcity of water. It not only provides water for domestic use during the summer but also recharges the water table.