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Latest Geography NCERT Notes, Solutions and Extra Q & A (Class 8th to 12th)
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Class 11th Chapters
Fundamentals of Physical Geography
1. Geography As A Discipline 2. The Origin And Evolution Of The Earth 3. Interior Of The Earth
4. Distribution Of Oceans And Continents 5. Geomorphic Processes 6. Landforms And Their Evolution
7. Composition And Structure Of Atmosphere 8. Solar Radiation, Heat Balance And Temperature 9. Atmospheric Circulation And Weather Systems
10. Water In The Atmosphere 11. World Climate And Climate Change 12. Water (Oceans)
13. Movements Of Ocean Water 14. Biodiversity And Conservation
Indian Physical Environment
1. India — Location 2. Structure And Physiography 3. Drainage System
4. Climate 5. Natural Vegetation 6. Natural Hazards And Disasters: Causes, - Consequences And Management
Practical Work In Geography
1. Introduction To Maps 2. Map Scale 3. Latitude, Longitude And Time
4. Map Projections 5. Topographical Maps 6. Introduction To Remote Sensing

Chapter 3 Drainage System

Introduction To Drainage System

We often observe water flowing through natural channels like rivers, streams, and temporary channels during the rainy season. These channels play a vital role in carrying away excess water. If a region lacks such well-defined channels or if they become blocked, it often leads to extensive flooding.

The flow of water through clearly defined pathways is known as **drainage**. A **drainage system** refers to the network of these channels within a specific area. The specific arrangement or shape of this network is called the **drainage pattern**. The pattern that develops in a region is shaped by numerous factors, including:

Rivers flow in a particular direction primarily dictated by the **slope** of the land. Water is pulled downwards by gravity, so rivers follow the path of least resistance along gradients. For example, rivers originating in the Himalayas and the Western Ghats often flow eastward towards the Bay of Bengal because the general slope of the land in the Indian subcontinent, particularly the Peninsular Plateau, is from west to east.

A river, along with its tributaries (smaller streams that flow into the main river), collects water from a specific geographical area. The area from which a river system collects water is called its **catchment area**. The entire area drained by a river and all its tributaries is known as a **drainage basin** or **river basin**. The boundary line that separates one drainage basin from an adjacent one is called a **watershed** or drainage divide.

While the terms river basin and watershed are related, there is a distinction based on size. River basins are typically used for larger river systems covering extensive areas, whereas watersheds are generally applied to smaller areas drained by rivulets or smaller streams. Despite the difference in scale, both river basins and watersheds are considered unified geographical units. Actions taken in one part of a basin or watershed can directly impact other parts and the system as a whole. Because of this interconnectedness, drainage basins and watersheds are often considered appropriate units for planning and management at various scales (micro, meso, or macro).

Drainage patterns vary depending on the underlying geological structure and topography. Some important drainage patterns include:

The Indian drainage system can be classified in several ways. Based on the direction of water discharge into the sea (orientation to the sea), it is divided into:

  1. The **Arabian Sea drainage**: Rivers that discharge their waters into the Arabian Sea. This includes about 23% of India's drainage area. Major rivers in this category include the Indus, Narmada, Tapi, Mahi, and Periyar.
  2. The **Bay of Bengal drainage**: Rivers that discharge their waters into the Bay of Bengal. This constitutes nearly 77% of India's drainage area. Major rivers here include the Ganga, Brahmaputra, Mahanadi, Krishna, and Kaveri.

These two major drainage divisions are separated by a water divide formed by geographical features like the Delhi ridge, the Aravalli range, and the Sahyadris (Western Ghats).

Another classification is based on the size of the drainage basin:

Based on their origin, nature, and characteristics, the Indian drainage system can also be broadly classified into the **Himalayan Drainage** and the **Peninsular Drainage**. Although this classification is widely accepted, it has some limitations, such as classifying older rivers originating in the northern Peninsula (like Chambal, Betwa, Son) as part of the Himalayan system due to them being tributaries of the Ganga. This book follows the Himalayan and Peninsular drainage classification.


The Himalayan Drainage

The **Himalayan drainage system** comprises rivers that originate in the Himalayan mountains. This system has evolved over a long geological history, intricately linked to the formation and uplift of the Himalayas themselves. The main river basins included are the Ganga, the Indus, and the Brahmaputra.

A key characteristic of Himalayan rivers is that they are **perennial**, meaning they have water throughout the year. This is because they are fed by two sources: precipitation (rainfall and snowmelt during the monsoon season) and the melting of glaciers and snow cover in the mountains, which provides water during the dry seasons.

In their mountainous course, these rivers are in a **youthful stage** of erosion. They flow through steep gradients and have significant erosive power. They carve out dramatic landforms like deep **gorges** (cut simultaneously with the uplift of the Himalayas), steep-sided **V-shaped valleys**, rapids, and waterfalls (Figure 3.3). (This refers to Figure 3.3).

Photograph showing rapids in a river, illustrating turbulent, fast-flowing water typical of a steep gradient mountainous section.

As these rivers descend into the plains, their gradient decreases, and the dominant processes shift from erosion to **deposition**. In the plains, they form various depositional features such as flat alluvial valleys, oxbow lakes (cut-off meander loops), flood plains (areas inundated during floods, built by sediment), and braided channels (channels splitting and rejoining around sandbars). Near the river mouths, they often form large **deltas**. In the mountainous regions, the river courses are often highly winding (tortuous). However, in the plains, they develop strong meandering tendencies (loop-like bends) and frequently shift their channels, particularly during floods. The River Kosi in Bihar is infamous for its frequent course changes, earning it the moniker 'sorrow of Bihar'. This is due to the large amount of sediment the Kosi carries from its upper mountainous reaches, which gets deposited in the plains, blocking the channel and forcing the river to find new paths.

The amount of water discharged by rivers, especially those influenced by monsoons and snowmelt like the Kosi, fluctuates significantly throughout the year. Discharge is maximum during the rainy season and when snowmelt is high. The positive effects of flooding can include replenishing soil moisture and depositing fertile silt on floodplains. However, negative effects are often devastating, including loss of life, damage to property and infrastructure, disruption of agriculture, and spread of diseases.

Evolution Of The Himalayan Drainage

There are varying scientific viewpoints on the detailed evolutionary history of the Himalayan rivers. However, a widely accepted geological hypothesis suggests that a vast, single river system, sometimes referred to as the **Shiwalik** or **Indo-Brahma** river, once flowed along the entire length of the Himalayas from Assam in the east to Punjab and further west into Sindh (now in Pakistan), discharging into the Gulf of Sindh during the Miocene geological epoch (approximately 5 to 24 million years ago). Evidence supporting this theory includes the remarkable continuity of alluvial deposits found in the Shiwalik hills, composed of sands, silts, clays, boulders, and conglomerates, which are indicative of a large river system.

It is believed that this mighty Indo-Brahma river system was later broken up or 'dismembered' into the three main river systems we see today:

  1. The **Indus** system and its major tributaries in the western part.
  2. The **Ganga** system and its Himalayan tributaries in the central part.
  3. The **Brahmaputra** system (along its course in Assam) and its Himalayan tributaries in the eastern part.

This breakup is thought to have occurred due to geological uplifts and downthrusts. A major factor was likely the **Pleistocene upheaval** in the western Himalayas, including the uplift of the **Potwar Plateau** (and the connected Delhi Ridge). This uplift created a new water divide that separated the Indus and Ganga drainage systems, causing the Indus to flow westward and the Ganga eastward. Similarly, a **downthrusting** or sinking of the area known as the **Malda gap** (between the Rajmahal hills of the Peninsula and the Meghalaya plateau) during the mid-Pleistocene period diverted the courses of the Ganga and Brahmaputra river systems, directing them to flow towards the Bay of Bengal instead of potentially continuing westward.


The River Systems Of The Himalayan Drainage

The Himalayan drainage system is composed of numerous rivers, but the three major river systems that shape the landscape and support life in the North Indian plains are the Indus, the Ganga, and the Brahmaputra.

The Indus System

The **Indus River System** is one of the largest river basins globally, covering an area of approximately 1,165,000 sq. km, with about 321,289 sq. km located within India. The total length of the Indus is around 2,880 km, of which about 1,114 km flows through India (specifically through Jammu and Kashmir).

The Indus, also known as the Sindhu, is the westernmost of the major Himalayan rivers in India. It originates from a glacier near Bokhar Chu, located in the Tibetan region of the Kailash Mountain range at an altitude of 4,164 meters. In Tibet, the river is called ‘Singi Khamban’ or ‘Lion’s mouth’.

From its source, the Indus flows northwestward between the Ladakh and Zaskar ranges, passing through the Ladakh and Baltistan regions of India (Union Territory of Ladakh). It cuts through the Ladakh range near Skardu, forming a spectacular, deep gorge near Gilgit (now in Pakistan-administered Kashmir). The Indus enters Pakistan near Chilas in the Dardistan region.

Within India, the Indus receives several Himalayan tributaries, including the Shyok, Gilgit, Zaskar, Hunza, Nubra, Shigar, Gasting, and Dras. After entering Pakistan, it flows southward and receives the Kabul river on its right bank near Attock. Other notable right-bank tributaries from the Sulaiman ranges are the Khurram, Tochi, Gomal, Viboa, and Sangar. The Indus continues its southward journey, receiving the collective waters of the five main rivers of Punjab (the 'Panjnad') a little above Mithankot in Pakistan. The Panjnad is formed by the confluence of the Satluj, Beas, Ravi, Chenab, and Jhelum rivers. Finally, the Indus discharges into the Arabian Sea, east of the city of Karachi in Pakistan. In India, the main stem of the Indus only flows through the Ladakh region.

Major Tributaries of the Indus in India:

The Ganga System

The **Ganga River System** is the most significant river system in India, not only due to its large basin size but also its immense cultural and economic importance, considered a sacred river. The Ganga originates from the Gangotri glacier near Gaumukh (3,900 m) in the Uttarkashi district of Uttarakhand. At its source, it is known as the **Bhagirathi**. The Bhagirathi flows through narrow gorges in the Central and Lesser Himalayas. At **Devprayag**, the Bhagirathi merges with the **Alaknanda** river; from this confluence onwards, the river is called the **Ganga**.

The Alaknanda originates from the Satopanth glacier above Badrinath. The Alaknanda itself is formed by the confluence of the Dhauli and Vishnu Ganga rivers at Joshimath (or Vishnu Prayag). Other important tributaries join the Alaknanda before Devprayag: the Pindar river meets at Karna Prayag, and the Mandakini or Kali Ganga meets at Rudra Prayag.

The Ganga enters the plains at **Haridwar**. From Haridwar, the Ganga flows initially southward, then southeastward, and finally eastward across the vast North Indian Plain. Its total length is approximately 2,525 km. This length is shared by the states of Uttarakhand (110 km), Uttar Pradesh (1,450 km), Bihar (445 km), and West Bengal (520 km).

The Ganga basin within India covers a huge area of about 8.6 lakh sq. km. The Ganga river system is the largest in India, encompassing numerous perennial rivers (from the Himalayas) and non-perennial rivers (from the Peninsular plateau joining from the south).

Major Tributaries of the Ganga:

The Ganga continues flowing eastward into West Bengal, where it splits into two main distributaries: the **Bhagirathi** (which flows southward through West Bengal as the Hooghly river) and the **Padma** (which flows into Bangladesh). The Padma river eventually merges with the Brahmaputra (known as Jamuna in Bangladesh) and then the Meghna river, forming the world's largest delta, the Sunderbans, before finally discharging into the Bay of Bengal near the Sagar Island.

Key Tributaries in detail:

The 'Namami Gange Programme' is a comprehensive initiative launched by the Indian government in 2014 to address pollution, conserve, and rejuvenate the River Ganga. Its main pillars include developing infrastructure for sewage treatment, riverfront development, cleaning the river surface, promoting biodiversity, afforestation, public awareness campaigns, monitoring industrial waste discharge, and developing 'Ganga Grams' (villages along the river) for sustainable practices.

The Brahmaputra System

The **Brahmaputra** is one of the largest rivers in the world, with its source in the Chemayungdung glacier of the Kailash range near Mansarovar lake in Tibet. From its origin, it flows eastward for about 1,200 km in a flat, dry region of southern Tibet, where it is known as the **Tsangpo** ('the purifier'). The Rango Tsangpo is a major right-bank tributary in Tibet.

The Brahmaputra makes a dramatic turn to the south near Namcha Barwa (7,755 m peak) and cuts a deep gorge through the Central Himalayas. It emerges from the foothills in India west of Sadiya town in Arunachal Pradesh, where it is known as the **Siang** or **Dihang**. Flowing southwest through the Assam valley (for about 750 km), it receives its main left-bank tributaries, the Dibang (or Sikang) and the Lohit. From this confluence onwards, the river is known as the **Brahmaputra**.

Major tributaries of the Brahmaputra in the Assam valley:

The Brahmaputra enters Bangladesh near Dhubri and flows southward. In Bangladesh, it is joined by the Tista river on its right bank and is then known as the **Jamuna**. The Jamuna finally merges with the Padma river (the main channel of the Ganga in Bangladesh) and further downstream with the Meghna river, forming the Sunderbans delta before emptying into the Bay of Bengal.

The Brahmaputra is notorious for its high incidence of **floods, channel shifting, and bank erosion**. This dynamism is a result of the large volume of water and enormous sediment load carried by its many tributaries, particularly those originating in the Himalayas, due to heavy rainfall in the catchment area and the easily erodible nature of the terrain.


The Peninsular Drainage System

The **Peninsular drainage system** is considered geologically **older** than the Himalayan one. Evidence for this includes the mature nature of Peninsular rivers, characterized by broad, largely eroded, and shallow valleys, and the generally stable courses they follow.

The Western Ghats, running close to the western coast of India, act as the main **water divide** for the Peninsular rivers. Most major rivers originating in the Western Ghats flow eastward across the plateau and discharge into the Bay of Bengal. In contrast, rivers originating on the western slopes of the Western Ghats are short, fast-flowing rivulets that drain into the Arabian Sea.

Most of the major Peninsular rivers flow from west to east, except for the **Narmada** and **Tapi** rivers, which are notable exceptions that flow westward through rift valleys and discharge into the Arabian Sea. Several rivers originating in the northern part of the Peninsula, such as the Chambal, Sind, Betwa, Ken, and Son, are part of the Ganga river system (Himalayan drainage) because they are tributaries of the Ganga.

Major independent river systems of the Peninsular drainage (flowing directly into the sea) include the Mahanadi, Godavari, Krishna, and Kaveri, all flowing eastward, and the Narmada and Tapi flowing westward.

Peninsular rivers typically have a **fixed course** with an absence of significant meanders (except in their lower plains sections). A key characteristic is their **non-perennial flow**, meaning they are largely dependent on monsoon rainfall and their water levels fluctuate significantly between the wet and dry seasons. Only some larger Peninsular rivers have relatively continuous flow, but their volume decreases considerably outside the monsoon period. The Narmada and Tapi are exceptions in that they flow through fault-guided valleys, but their flow is also seasonal.

The Evolution Of Peninsular Drainage System

The present configuration of the Peninsular drainage system has been shaped by three significant geological events in the distant past:

  1. **Subsidence of the Western Flank:** During the early Tertiary period, the western part of the Peninsula is believed to have tilted and subsided (sunk) below sea level. This submergence disturbed the original symmetry of the drainage, which might have flowed equally in both east and west directions from a central watershed.
  2. **Himalayan Uplift and Trough Faulting:** The uplift of the Himalayas in the north subjected the northern flank of the Peninsular block to stress, leading to subsidence and the formation of trough faults (rift valleys). Rivers like the Narmada and Tapi flow through these faults. The movement within these trough faults filled them with eroded material over time. This fault-guided course is why these rivers are exceptions to the general eastward flow and why they typically form estuaries (rather than large deltas with extensive alluvial deposits) at their mouths because they flow through resistant bedrock in their lower reaches and the coast is more stable or possibly slightly subsiding.
  3. **Tilting of the Peninsular Block:** A slight tilting of the entire Peninsular block occurred, from northwest to southeast. This tilting directed the majority of the Peninsular river systems towards the Bay of Bengal, establishing the dominant east-flowing drainage pattern observed today.

River Systems Of The Peninsular Drainage

Here is a brief overview of the major independent river systems of the Peninsular drainage:

The Mahanadi

The **Mahanadi** river originates near Sihawa in the Raipur district of Chhattisgarh. It flows eastward through Odisha and discharges into the Bay of Bengal. It is 851 km long, and its catchment area is approximately 1.42 lakh sq. km. About 53% of its basin lies in Madhya Pradesh and Chhattisgarh, and 47% in Odisha. Some navigation is possible in its lower course. The Mahanadi forms a large delta before entering the Bay of Bengal.

The Godavari

The **Godavari** is the **largest** river system of the Peninsular India, sometimes called the **'Dakshin Ganga'** (Ganga of the South) due to its size. It originates in the Nasik district of Maharashtra. It flows eastward across the Deccan Plateau and discharges its water into the Bay of Bengal. Its total length is 1,465 km, with a large catchment area of 3.13 lakh sq. km. The basin is spread across Maharashtra (49%), Madhya Pradesh and Chhattisgarh (20%), and Andhra Pradesh (31%). Its main tributaries include the Penganga, Indravati, Pranhita, and Manjra. The Godavari forms a picturesque gorge south of Polavaram in its lower reaches and is known for heavy floods. It is navigable only in its deltaic region. Below Rajamundri, the river divides into several branches, forming a large delta.

The Krishna

The **Krishna** is the second largest east-flowing Peninsular river, rising near Mahabaleshwar in the Sahyadri (Western Ghats). Its total length is 1,401 km. Major tributaries include the Koyna, Tungabhadra, and Bhima. The Krishna basin's catchment area is spread across Maharashtra (27%), Karnataka (44%), and Andhra Pradesh and Telangana (29%). It also forms a delta before entering the Bay of Bengal.

The Kaveri

The **Kaveri** (Cauvery) river originates in the Brahmagiri hills (1,341m) of Kodagu district in Karnataka. It is 800 km long and drains an area of 81,155 sq. km. The Kaveri is unique among major Peninsular rivers because it carries water throughout the year with relatively less fluctuation compared to others. This is because its upper catchment receives rainfall during the southwest monsoon (summer), while its lower part receives rain during the northeast monsoon (winter), ensuring a more consistent flow. The Kaveri basin is spread across Kerala (3%), Karnataka (41%), and Tamil Nadu (56%). Its important tributaries are the Kabini, Bhavani, and Amravati. The Kaveri also forms a delta in its lower course before reaching the Bay of Bengal.

The Narmada

The **Narmada** river is one of the few major Peninsular rivers that flows westward. It originates on the western flank of the Amarkantak plateau (1,057 m). It flows through a prominent **rift valley**, bounded by the Satpura range to the south and the Vindhyan range to the north. The Narmada creates scenic features like a picturesque gorge in marble rocks and the Dhuandhar waterfall near Jabalpur. It flows for about 1,312 km before meeting the Arabian Sea south of Bharuch, forming a broad, 27 km long **estuary** instead of a delta. Its catchment area is approximately 98,796 sq. km. The Sardar Sarovar Project, a major dam and irrigation project, is constructed on this river.

The Tapi

The **Tapi** (Tapti) is another important westward-flowing river, also flowing through a rift valley parallel to the Narmada. It originates from Multai in the Betul district of Madhya Pradesh. It is 724 km long and drains an area of 65,145 sq. km. Its basin is located primarily in Maharashtra (79%), with smaller portions in Madhya Pradesh (15%) and Gujarat (6%). Like the Narmada, the Tapi forms an estuary at its mouth into the Arabian Sea.

Luni

The **Luni** is the largest river system in Rajasthan, located west of the Aravalli range. It originates near Pushkar from two branches, the Saraswati and the Sabarmati, which merge at Govindgarh. It is then known as the Luni and flows westward out of the Aravallis towards Telwara, then turns southwest to join the Rann of Kachchh. The Luni is an **ephemeral** river, meaning it flows primarily during the rainy season and often disappears into the sand before reaching the sea. It is a river of the inland drainage system in a region characterized by low precipitation and high evaporation, making it water-scarce.


Extent Of Usability Of River Water

India's rivers carry a significant volume of water annually, crucial for agriculture, domestic use, and industry. However, this water is distributed unevenly throughout the year and across different regions. Perennial rivers, mostly from the Himalayas, have consistent flow, while non-perennial (Peninsular) rivers have very low flow during the dry season. During the monsoon, many rivers experience floods, with large quantities of water flowing unused into the sea. Paradoxically, while some areas face devastating floods, others concurrently suffer from drought. This highlights not just an issue of water availability but also one of effective water management, storage, and distribution.

Addressing the simultaneous problems of floods and droughts requires integrated water resource management strategies. One proposed measure is the large-scale inter-linking of rivers, aiming to transfer surplus water from water-rich basins (often in the north, during monsoon) to water-deficit basins (often in the south or west, during dry periods). India has explored or implemented various smaller inter-basin transfer schemes, such as the Periyar Diversion Scheme, Indira Gandhi Canal Project, Kurnool-Cuddapah Canal, and Beas-Satluj Link Canal. A larger, more ambitious proposal involves linking major Himalayan and Peninsular rivers, but this faces significant engineering, environmental, social, and financial challenges, including the difficulty of lifting water from lower plains to higher plateaus and the potential environmental impacts.

Another major challenge facing India's river systems is **pollution**. Rivers are polluted by various sources:

This pollution degrades water quality, harms aquatic life, and makes river water unsafe for human use, exacerbating water scarcity. Initiatives like the Ganga Action Plan and efforts to clean the Yamuna aim to reduce pollution levels through wastewater treatment, controlling industrial discharge, and public awareness campaigns. Preventing pollution requires stringent regulations, effective enforcement, adequate treatment infrastructure, and changes in public behavior to treat rivers as vital and vulnerable ecosystems.

Several factors pose problems in effectively using river water in India, including uneven seasonal flow (high during monsoon, low otherwise), pollution, sediment load (reducing storage capacity in reservoirs), uneven spatial availability, interstate river water disputes (over sharing resources), and encroachment on river channels by settlements.


Exercises

Multiple Choice Questions

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State The Differences Between The Following

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Answer The Following Questions In About 30 Words

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Answer The Following Questions In Not More Than 125 Words

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Project/Activity

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