Water Resources – NDA Geography Notes

India receives a good amount of rain every year. But this rain is not evenly spread: some regions get too much, others get very little. Most of the rain also falls in just three to four months during the monsoon. For the rest of the year, rivers run low and water becomes scarce.

This chapter is about how India manages its water. It covers sources of water, types of irrigation, major multipurpose dam projects, river water disputes, and rainwater harvesting. NDA tests this chapter through dam-river matching, canal identification, tank irrigation reasons, and specific questions about projects. These questions appear regularly and reward precise factual knowledge.

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Sources of Water in India

India gets water from three main sources. Rainfall provides an average of about 1,170 mm per year, but most of it falls during the Southwest Monsoon (June to September). The rest of the year is mostly dry. Rivers carry water from mountains and rain-fed areas to drier regions, supplying both surface water and groundwater. Groundwater is stored in underground layers called aquifers and drawn up by tube wells and bore wells for irrigation and drinking.

Groundwater demand increased greatly with the Green Revolution, because high-yield crops need far more water than traditional varieties. Replenishable groundwater reserves are highest in states like Uttar Pradesh, Bihar, and West Bengal, not in Sikkim, Nagaland, or Tripura.

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Irrigation in India

India’s agriculture depends heavily on irrigation. Only about 30% of India’s net sown area receives reliable rainfall. The rest needs artificial irrigation. India uses three main types.

Canal Irrigation

Water is brought to fields through channels dug from rivers or reservoirs. This is most suitable in flat, alluvial plains where water flows easily. Canal irrigation is most developed in the Northern Plains: the Ganga-Yamuna plains, Punjab, and Haryana.

Bhakra Canal is the most important canal in Haryana in terms of area coverage. [NDA 2015-I] Western Yamuna Canal is another important canal in Haryana, drawing water from the Yamuna at Yamunanagar. Canals and bore wells can be dug most easily in the soft alluvium of the Northern Plains. [NDA 2012-II]

Well and Tube Well Irrigation

Water is drawn from underground by wells or tube wells. This is most suitable where groundwater is plentiful and accessible, and most common in the Northern Plains, where the alluvial soil is soft and groundwater is close to the surface. The deltaic regions of Mahanadi, Godavari, and Krishna also support well irrigation well.

Tank Irrigation

Tanks are small reservoirs built by constructing a low embankment across a stream. They collect rainwater during the monsoon and store it for use in summer. Tank irrigation is most common in Peninsular India, especially in South-Central India. [NDA 2011-I]

Why is tank irrigation practised in Peninsular India? [NDA 2011-I]

The terrain is uneven and rocky, making canals hard to build. Hard, impervious rocks prevent rainwater from percolating into the ground, leaving insufficient shallow groundwater for wells. Rivers are seasonal, flowing only during the monsoon. Undulating terrain helps accumulate rainwater in natural depressions. And many streams become torrential in the rainy season and can easily be dammed.

Tank and well irrigation are negatively related, where tanks are common and wells are rare. Tank irrigation is found in areas with impervious rock layers where water cannot seep down to form aquifers. That is the very condition that makes well irrigation impossible.

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Multipurpose River Projects

India has built many large dams on its rivers that serve more than one purpose, hence the name multipurpose projects. Their purposes include irrigation, hydroelectric power generation, flood control, navigation, drinking water supply, and recreation and fisheries. Jawaharlal Nehru called these multipurpose dams “temples of modern India”, believing they would bring development, electricity, and food security to the nation.

Dam / Project	River	State	Key Notes
Bhakra Nangal	Sutlej	HP / Punjab	Feeds Bhakra Canal; most important in Haryana [NDA 2015-I]
Hirakud Dam	Mahanadi	Odisha	One of longest earthen dams; near Sambalpur [NDA 2006-I]
Nagarjuna Sagar	Krishna	AP / Telangana	One of world’s largest masonry dams [NDA 2016-I]
Srisailam Dam	Krishna	AP / Telangana	Major hydroelectric project on Krishna
Gandhi Sagar	Chambal	Madhya Pradesh	[NDA 2007-I]
Rana Pratap Sagar	Chambal	Rajasthan	Hydroelectric project [NDA 2014-II]
Ukai Dam	Tapti (Tapi)	Gujarat	NOT a hydroelectric project: thermal power station nearby [NDA 2014-II]
Tehri Dam	Bhagirathi	Uttarakhand	Highest dam in India
GB Pant Sagar	Rihand	Uttar Pradesh	—
Tawa Reservoir	Tawa (Narmada tributary)	Madhya Pradesh	Near Pachmarhi [NDA 2006-I]
KRS (Krishnarajasagara)	Cauvery	Karnataka	Irrigates large parts of Karnataka
Mettur Dam	Cauvery	Tamil Nadu	Forms Stanley Reservoir
Ranjit Sagar Dam	Ravi	Punjab	NOT on Beas [NDA 2007-I]
Bagalihar Dam	Chenab	J&K	All three on Chenab only [NDA 2020-I]
Dulhasti Dam	Chenab	J&K	—
Salal Dam	Chenab	J&K	—
Bhavani Sagar Dam	Bhavani	Tamil Nadu	—
Damanganga Reservoir	Damanganga	Dadra & Nagar Haveli	—

Neyveli is NOT a hydroelectric project. It is a thermal power plant using lignite coal. [NDA 2014-II] Papanasam and Rana Pratap Sagar are hydroelectric projects.

★ IMPORTANT Four dam-river pairs NDA tests as traps: Ranjit Sagar = Ravi (not Beas). Hirakud = Mahanadi (not Damodar). Alamatti = Krishna (not Cauvery). Mettur = Cauvery (not Krishna). Neyveli = Thermal (not hydroelectric). [NDA 2007-I | NDA 2007-II | NDA 2014-II]

Hydroelectric projects on the Chenab: Bagalihar, Dulhasti, and Salal are all on the Chenab River in J&K. [NDA 2020-I] The Salal Power Project is also on the Chenab River. Under the Indus Waters Treaty, India has the right to build run-of-the-river power projects on the western rivers including the Chenab.

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The Cauvery Water Dispute

The Cauvery water dispute is one of India’s oldest and most complex river water conflicts. The states involved are Kerala, Karnataka, Tamil Nadu, and the Union Territory of Puducherry. Tamil Nadu argues it needs water for the Cauvery delta farmers who grow paddy. Karnataka argues it needs water for its growing population and agriculture. The dispute went through decades of legal battles, with the Supreme Court of India eventually issuing an award on how to share the water.

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River Water Interlinking

Some rivers in India have surplus water while others face serious shortage. The National River Linking Project proposes to transfer water from surplus river basins to deficit basins through a network of canals and tunnels. The Ken-Betwa Link Project in Madhya Pradesh is the first river interlinking project to receive approval and begin construction. It will transfer water from the Ken River (a Yamuna tributary) to the Betwa River, helping water-scarce districts in Madhya Pradesh and Uttar Pradesh.

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Rainwater Harvesting

Rainwater harvesting means collecting and storing rainwater for future use before it flows away as runoff. It is especially important in cities where concrete surfaces prevent water from entering the ground, in dry regions where groundwater is scarce, and in areas that face seasonal water shortage.

Traditional Systems of Rainwater Harvesting in India

System	Region	Description
Johad	Rajasthan	Traditional earthen check dam to store rainwater
Kundi / Tanka	Rajasthan	Underground tank to collect and store roof water
Kul	Himachal Pradesh	Diversion channel from glacial streams to fields
Baoli (Stepwell)	Rajasthan / Delhi	Ancient stepwell for collecting groundwater
Ahar Pynes	Bihar	Traditional surface water channels
Bamboo drip	Northeast India	Uses bamboo pipes to channel spring water to fields
Zabo	Nagaland	Community rainwater harvesting system in hills

Not suitable for urban rainwater harvesting: A gully plug is a watershed management technique used in rural and hilly areas to check soil erosion. It is not suitable for urban settings. Rooftop recharge pits, recharge wells, and recharge trenches are the appropriate urban methods.

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Challenges of Water Resources in India

Floods affect regions like Assam, Bihar, and coastal Odisha every year. The Brahmaputra and Kosi are the most flood-prone rivers. Droughts recur in Rajasthan, parts of Maharashtra, Andhra Pradesh, and Karnataka. Groundwater depletion from heavy tube well use, especially after the Green Revolution, has lowered the water table in many states. Pollution in rivers like the Ganga and Yamuna is severe from cities and industries.

Safety of large dams: Genuine threats include urbanisation near dam sites, flash floods in the catchment area, and seismic activity in the surrounding area. All three are recognised dam safety concerns.

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