Water Resources – NDA Geography Notes

Introduction

India receives a good amount of rain every year. But this rain is not evenly spread. Some regions get too much rain. 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.

Understand the Topic

Sources of Water in India

India gets water from three main sources:

Rainfall — India gets an average of about 1,170 mm of rain per year. But most of it falls during the Southwest Monsoon (June to September). The rest of the year is mostly dry.

Rivers — Rivers carry water from mountains and rain-fed areas to drier regions. Both surface water and groundwater are used from river systems.

Groundwater — Water that seeps into the ground and is stored in underground layers called aquifers. Tube wells and bore wells draw this water up for irrigation and drinking.

Groundwater in India: Tube wells are used to exploit groundwater. Demand for groundwater increased greatly with the Green Revolution — because high-yield crops need more water. Replenishable groundwater reserves are highest in states like Uttar Pradesh, Bihar, and West Bengal — NOT in Sikkim, Nagaland, or Tripura. [NDA tested via CDS]

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.

Three main types of irrigation:

1. 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:

• Northern Plains — Ganga-Yamuna plains, Punjab, Haryana
• Punjab and Haryana get water through canals from the Bhakra Nangal project on the Sutlej

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 — water is taken 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]

2. 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.

Well irrigation is most common in the Northern Plains — where the alluvial soil is soft and groundwater is close to the surface.

3. 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 | NDA tested via CDS]

Why is tank irrigation practised in Peninsular India?

There are several reasons: [NDA 2011-I | NDA tested via CDS]

• The terrain is uneven and rocky — canals are hard to build
• Hard rocks make it difficult to dig wells (little percolation of rainwater)
• Rivers are seasonal — they only flow during the monsoon
• Undulating terrain helps in accumulating rain water in natural depressions
• Rocky and impervious surface layers mean insufficient shallow groundwater
• Many streams become torrential in the rainy season and can be easily dammed

Tank irrigation and well irrigation are negatively related — where tanks are common, wells are rare. This is because:

• Tank irrigation is found in areas with impervious rock layers (water cannot seep down to form aquifers)
• Well irrigation requires good groundwater reserves (which impervious rocks prevent)
• Tank irrigation developed earlier than well irrigation in these areas
  [NDA tested via CDS]

Not suitable for urban rainwater harvesting: Gully plug is NOT suitable for urban areas — it is a rural/watershed management technique. Rooftop recharge pits, recharge wells, and recharge trenches are suitable for urban rainwater harvesting. [NDA tested via CDS]

Multipurpose River Projects

India has built many large dams on its rivers. These dams serve more than one purpose — hence they are called multipurpose projects.

The purposes include:

• Irrigation — providing water for farms
• Hydroelectric power generation
• Flood control
• Navigation
• Drinking water supply
• Recreation and fisheries

Jawaharlal Nehru called these multipurpose dams “temples of modern India” — because he believed they would bring development, electricity, and food security to the nation.

Important Multipurpose Projects:

Dam/Project	River	State	Key Notes
Bhakra Nangal	Sutlej	Himachal Pradesh/Punjab	India’s largest dam project; 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	Andhra Pradesh/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	Built by MP government [NDA 2007-I]
Rana Pratap Sagar	Chambal	Rajasthan	Hydropower project [NDA 2014-II]
Ukai Dam	Tapti (Tapi)	Gujarat	NOT a hydropower project — thermal power nearby [NDA 2014-II]
Tehri Dam	Bhagirathi	Uttarakhand	Highest dam in India
GB Pant Sagar	Rihand	Uttar Pradesh	[NDA tested via CDS]
Tawa Reservoir	Tawa (Narmada tributary)	MP	Near Pachmarhi [NDA 2006-I]
KRS Dam (Krishnarajasagara)	Cauvery	Karnataka	Irrigates large parts of Karnataka
Mettur Dam	Cauvery	Tamil Nadu	Forms Stanley Reservoir
Ukai Reservoir	Tapti	Gujarat	NOT Amravati (Amravati is in Maharashtra) [NDA 2006-I]
Bhavani Sagar Dam	Bhavani	Tamil Nadu	—
Damanganga Reservoir	Damanganga	Dadra & Nagar Haveli	[NDA tested via CDS]
Rihand Valley Project	Rihand	Uttar Pradesh	[NDA tested via CDS]

Neyveli is NOT a hydroelectric project — it is a thermal power plant (uses lignite coal). [NDA 2014-II]

Papanasam and Rana Pratap Sagar are hydroelectric projects. Ukai is associated with a thermal plant nearby, not hydroelectric. [NDA 2014-II]

Key Dam-River Matching (tested repeatedly):

From NDA and CDS papers:

• Bhakra Nangal = Sutlej [NDA tested via CDS]
• Hirakud = Mahanadi (NOT Damodar) [NDA 2007-I]
• Gandhi Sagar = Chambal (in MP) [NDA 2007-I]
• Ranjit Sagar = Ravi (NOT Beas) [NDA 2007-I]
• Nagarjuna Sagar = Krishna [NDA 2016-I]
• Ukai = Tapti (NOT Amravati lake) [NDA tested via CDS]
• Tehri = Bhagirathi
• GB Pant Sagar = Rihand (in UP) [NDA tested via CDS]
• Dul Hasti = Chenab (NOT Mahanadi or Chandra)
• Tawa Reservoir = Tawa River, near Pachmarhi (MP) [NDA 2006-I]
• Damanganga = Dadra and Nagar Haveli [NDA tested via CDS]
• Salal Power Project = Chenab [NDA tested via CDS]

Note on Dul Hasti: CDS 2014-I match says Dul Hasti = Chandra (River Chandra is a tributary of Chenab). This is an important nuance. At NDA level, Dul Hasti is associated with Chenab system.

Hydroelectric Projects on the Chenab:

Bagalihar, Dulhasti, and Salal are all on the Chenab River in J&K. [NDA 2020-I]

Salal Power Project is on the Chenab River. [NDA tested via CDS]

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The Cauvery Water Dispute

The Cauvery water dispute is one of India’s oldest and most complex river water conflicts.

States involved: Kerala, Karnataka, Tamil Nadu, and Union Territory of Puducherry. [NDA tested via CDS]

Both Karnataka and Tamil Nadu claim water from the Cauvery for their farmers. 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 has gone through decades of legal battles, with the Supreme Court of India eventually giving an award on how to share the water.

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River Water Interlinking

Some rivers in India have surplus water. 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
• Dry regions where groundwater is scarce
• 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: Gully plug is a watershed management technique used in rural/hilly areas to check soil erosion. It is not suitable for urban settings. [NDA tested via CDS]

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Challenges of Water Resources in India

Floods: Some regions like Assam, Bihar, and coastal Odisha face severe floods every year. Brahmaputra and Kosi are the most flood-prone rivers.

Droughts: Rajasthan, parts of Maharashtra, Andhra Pradesh, and Karnataka face recurring droughts.

Groundwater depletion: Heavy use of tube wells — especially after the Green Revolution — has lowered the water table in many states.

Pollution: Rivers like the Ganga and Yamuna carry heavy pollution from cities and industries.

Safety of large dams: Potential threats include urbanisation near dam sites, flash floods in the catchment area, and seismic activity in the surrounding area. All three are genuine threats to dam safety. [NDA tested via CDS]