Class 10 Geography · Chapter 3 NotesWater Resources

Three-fourths of the earth's surface is covered with water, but only a small proportion of it is freshwater that can be put to use. This usable freshwater is mainly obtained from surface run-off and groundwater. Both are continually renewed and recharged through the hydrological cycle. In this cycle, water evaporates, forms clouds, returns as precipitation, and then flows over the land or seeps into the ground. Because water keeps moving through this cycle, it is called a renewable resource. However, the availability of water resources varies over space and time, mainly due to variations in seasonal and annual precipitation. This is why some regions have plenty of water while others face shortages.

• Freshwater sourcessurface run-off and groundwater
• Renewal processhydrological cycle
• Water is renewable, but its availability varies from place to place and season to season

Water scarcity is often linked only with low rainfall or drought-prone areas, but the chapter shows that this is not the full picture. In most cases, scarcity is caused by over-exploitation, excessive use and unequal access to water among different social groups. A region may receive ample rainfall and still suffer from scarcity if its population is large, if water is polluted, or if some groups cannot access it. Growing populations need more water for domestic use and for producing more food. To expand irrigated areas for dry-season agriculture, water resources are over-exploited. Irrigated agriculture is the largest consumer of water. Industrialisation and urbanisation add further pressure, as industries and dense urban settlements are heavy users of water and energy.

• Main causesover-exploitation, excessive use, unequal access
• Agriculturelargest consumer of water; irrigation expands dry-season farming
• Industry and citiesheavy water users; groundwater pumping depletes fragile resources
• Pollutiondomestic and industrial wastes, chemicals, pesticides and fertilisers make water hazardous

The chapter mentions two important government programmes. Atal Bhujal Yojana (Atal Jal) is being implemented in 8220 water-stressed Gram Panchayats of 229 administrative blocks or talukas in 80 districts of seven states: Gujarat, Haryana, Karnataka, Madhya Pradesh, Maharashtra, Rajasthan and Uttar Pradesh. These selected states account for about 37 per cent of the total number of water-stressed blocks in India. One key aspect of Atal Jal is to bring behavioural changes in the community, from consumption to conservation and smart water management. The Jal Jeevan Mission (JJM) aims to enable every rural household to get an assured supply of potable piped water at a service level of 55 litres per capita per day on a long-term basis, by ensuring functional tap water connections.

• Atal Bhujal Yojana (Atal Jal)community behaviour change towards conservation
• Jal Jeevan Mission (JJM)55 litres per capita per day of potable piped water for rural households

From ancient times, India has built hydraulic structures such as dams of stone rubble, reservoirs, lakes, embankments and canals. A dam is a barrier across flowing water that obstructs, directs or retards the flow, often creating a reservoir, lake or impoundment. Dams were traditionally built to impound rivers and rainwater for irrigation. Today, dams serve many purposes: electricity generation, water supply for domestic and industrial use, flood control, recreation, inland navigation and fish breeding. When many uses of the impounded water are integrated, the project is called a multi-purpose river project. Examples include the Bhakra-Nangal project in the Sutluj-Beas basin, used for hydel power and irrigation, and the Hirakud project in the Mahanadi basin, which integrates water conservation with flood control. After Independence, Jawaharlal Nehru called dams the 'temples of modern India'.

• Dambarrier across flowing water creating a reservoir
• Multi-purpose projectintegrates irrigation, power, water supply, flood control, recreation, navigation and fish breeding
• ExamplesBhakra-Nangal (Sutluj-Beas), Hirakud (Mahanadi)

In recent years, multi-purpose projects and large dams have faced scrutiny and opposition. Regulating and damming rivers affects their natural flow, causing poor sediment flow and excessive sedimentation at the bottom of the reservoir. This results in rockier stream beds and poorer habitats for aquatic life. Dams fragment rivers, making it difficult for aquatic fauna to migrate, especially for spawning. Reservoirs on floodplains submerge existing vegetation and soil, leading to decomposition over time. Ironically, dams built to control floods have sometimes triggered floods due to sedimentation. Floodplains are deprived of silt, a natural fertiliser, causing land degradation. Multi-purpose projects have also been linked to earthquakes, water-borne diseases, pests and pollution from excessive water use. Irrigation has changed cropping patterns towards water-intensive commercial crops, causing salinisation of soil.

• Sedimentation reduces reservoir capacity and harms aquatic habitats
• River fragmentation affects fish migration and spawning
• Submergence of vegetation and soil; loss of silt in floodplains
• Social and ecological effectsdisplacement, water-borne diseases, salinisation

In ancient India, people had in-depth knowledge of rainfall regimes and soil types, and developed many techniques to harvest rainwater, groundwater, river water and flood water according to local ecological conditions. In the hill and mountainous regions of the Western Himalayas, people built diversion channels called 'guls' or 'kuls' for agriculture. Rooftop rainwater harvesting was commonly practised to store drinking water, particularly in Rajasthan. In the flood plains of Bengal, people developed inundation channels to irrigate fields. In arid and semi-arid regions, agricultural fields were converted into rain-fed storage structures that allowed water to stand and moisten the soil, such as the 'khadins' in Jaisalmer and 'johads' in other parts of Rajasthan. In Bikaner, Phalodi and Barmer, almost all houses traditionally had underground tanks or tankas for storing drinking water.

• Guls or kulsWestern Himalayas diversion channels
• Khadins and johadsRajasthan rain-fed storage structures
• Tankasunderground tanks in Bikaner, Phalodi and Barmer
• Inundation channelsflood plains of Bengal

In the semi-arid and arid regions of Rajasthan, particularly in Bikaner, Phalodi and Barmer, almost all houses traditionally had underground tankas for storing drinking water. A tanka could be as large as a big room; one household in Phalodi had a tank 6.1 metres deep, 4.27 metres long and 2.44 metres wide. Tankas were part of a well-developed rooftop rainwater harvesting system and were built inside the main house or courtyard. They were connected to sloping roofs through a pipe. Rain falling on rooftops would travel down the pipe and be stored in the tankas. The first spell of rain was usually not collected, as it cleaned the roofs and pipes. Rainwater from subsequent showers was collected. This water could be stored till the next rainfall, making it a reliable source of drinking water in summers. Rainwater, or palar pani, is considered the purest form of natural water. Many houses also built underground rooms adjoining the tanka to beat the summer heat.

• Tankaunderground tank for storing rainwater
• First spell of rain not collected; later showers collected
• Palar panipurest form of natural water
• Underground rooms near tankas kept houses cool

Today, rooftop rainwater harvesting is being successfully adapted in many parts of rural and urban India. In Gendathur, a remote village in Mysuru, Karnataka, nearly 200 households installed rooftop rainwater harvesting systems. The village receives an annual precipitation of 1,000 mm, and with 80 per cent collection efficiency and about 10 fillings, every house can collect and use about 50,000 litres of water annually. From the 200 houses, the net amount of rainwater harvested annually amounts to 1,00,000 litres. In Shillong, Meghalaya, rooftop rainwater harvesting is common even though Cherapunjee and Mawsynram, about 55 km away, receive the highest rainfall in the world. Nearly every household in Shillong has a rooftop rainwater harvesting structure, and 15-25 per cent of total household water requirement comes from it. Tamil Nadu is the first state in India to make rooftop rainwater harvesting compulsory for all houses, with legal provisions to punish defaulters. In Meghalaya, a 200-year-old bamboo drip irrigation system taps stream and spring water using bamboo pipes.

• Gendathur, Karnataka200 households, 1,00,000 litres harvested annually
• Shillong15-25 per cent of household water from rooftop harvesting
• Tamil Nadufirst state to make rooftop rainwater harvesting compulsory
• Bamboo drip irrigationMeghalaya, 200-year-old system