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Introduction

The proper channel of the flow of water is known as the ‘drainage of the region’, and the network of all those drainages is considered the 'drainage system’.

It is usually the result of the different factors of the geological period including the structure and nature of the rocks, the topography of the region, the slope, and the flow of the running water. Moreover, the drainage of a single river and its tributaries is known as a ‘drainage basin’. and the elevated structure dividing two drainage basins is called a ‘water divide’. The largest basin of the world is the Amazon River, whereas that of India is of the Ganga River.

There are primarily four drainage patterns, including:

• Dendritic: This drainage pattern resembles the branches of a tree, with rivers flowing in multiple directions. An example is seen in the rivers of the northern plains.
• Radial: In this pattern, rivers originate from a central point, such as a hill, and flow outward in all directions. An illustration is of rivers originating from the Amarkantak range.
• Trellis: This pattern features primary tributaries of a river flowing parallel to each other, with secondary tributaries joining them at right angles.
• Centripetal: In this pattern, rivers discharge their waters from various directions into a central lake or depression.

Drainage System of India:

India's drainage system can be categorized into two primary divisions based on where the water flows: the Arabian Sea drainage and the Bay of Bengal drainage. These two drainage systems are separated by geographical features such as the Delhi ridge, the Aravallis, and the Sahyadris. Approximately 77% of the drainage in India is oriented towards the Bay of Bengal, while the remaining 23% discharge their water into the Arabian Sea.

Another classification of Indian drainage is based on the mode of origin, nature, and characteristics. This classification divides the drainage into two categories: the Himalayan drainage and the Peninsular drainage. Rivers in the Himalayan region and those in the Peninsular region have different origins and characteristics, originating from distinct physiographic regions of India.

The Himalayan rivers

• Himalayan rivers flow perennially, receiving water from both rainfall and melted snow from the mountains.
• Their journey through the Himalayas involves carving deep gorges and valleys due to ongoing erosion caused by the mountain's uplift.
• In the upper courses, these rivers create steep valleys, rapid currents, and cascading waterfalls.
• As they progress into the middle and lower courses, particularly the plains, they form features like meanders, oxbow lakes, and depositional features in floodplains.
• The Kosi River, known as the "sorrow of Bihar," frequently changes its course due to the large amount of sediment it carries from upstream.
• Sediment buildup can block the river's flow, prompting it to shift its path, which can have significant impacts on the surrounding regions.

The Peninsular River:

• The Peninsular drainage system predates the Himalayan one.
• Most Peninsular rivers are seasonal, relying heavily on regional rainfall for their flow.
• Peninsular rivers tend to have shorter and shallower courses compared to those originating from the Himalayas.
• With the exception of the Narmada and Tapi rivers, the majority of major Peninsular rivers flow from west to east towards the Bay of Bengal.
• Rivers like the Chambal, Sindh, Betwa, Ken, and Son, originating in the northern part of the Peninsula, are part of the Ganga river system.
• Other significant Peninsular rivers include the Mahanadi, Godavari, Krishna, and Kaveri.
• The Western Ghats serve as a divide, directing the flow of major Peninsular rivers towards the Bay of Bengal and smaller streams towards the Arabian Sea.

1. Himalayan Drainage System:

• The Himalayan drainage system comprises three major river systems: the Indus, the Ganga, and the Brahmaputra.

• Indus River System

• Area: Covers a total area of 11,65,000 sq.km, with 3,21,289 sq.km in India.
• Length: Stretches for 2,880 km in total, with 1,114 km within India.
• Alias: Also known as "Sindhu," it is the westernmost among India's Himalayan rivers.
• Origin and Course: Begins from a glacier near Bokhar Chu in the Tibetan region, at an altitude of 4,164 m in the Kailash mountain range. Flows northwestward, entering India in Ladakh (Leh), where it forms a scenic gorge. Along its journey, it's joined by several Himalayan tributaries like the Shyok, Gilgit, Zaskar, Hunza, and Nubra. Passes through Baltistan and Gilgit, emerging from the mountains at Attock, where it merges with the Kabul River on its right bank. Continues southward, receiving the Panjnad near Mithankot in Pakistan, which comprises the Satluj, Beas, Ravi, Chenab, and Jhelum rivers. Eventually empties into the Arabian Sea.
• Tibetan Name: Known as "Singi Khamban" or "Lion's mouth" in Tibet.

Main Tributaries of the Indus River

• Satluj

• Origin: Begins at "Rakas tal" near Mansarovar in Tibet.
• Course: Runs nearly parallel to the Indus for about 400 km before entering India. Passes through Shipki La in the Himalayan ranges and enters the Punjab plains. Meets the Beas river in Hari-ke-Patan, Amritsar, Punjab, before flowing into Pakistan. Supplies water to the Bhakra Nangal project canal system.

• Beas

• Origin: Starts at Beas Kund near Rohtang Pass in Himachal Pradesh.
• Course: Flows through Kullu valley, forming gorges at Kati and Largi in the Dhauladhar range. Enters Punjab plains, meeting Satluj near Harike, Punjab. Entirely flows within India.

• Ravi

• Origin: Originates west of Rohtang Pass, Kullu Hills, Himachal Pradesh.
• Course: Flows through Chamba valley, draining the area between Pir Panjal and Dhauladhar ranges. Enters Punjab plains, running along Indo-Pakistan border before entering Pakistan. Joins Chenab near Sarai Sidhu.

• Chenab

• Origin: Formed by Chandra and Bhaga streams meeting at Tandi near Keylong, Himachal Pradesh. Also known as Chandrabhaga.
• Course: Largest tributary of Indus, flows around 1180 km before entering Pakistan.

• Jhelum

• Origin: Springs at Verinag in the south-eastern part of Kashmir valley, foothills of Pir Panjal.
• Course: Flows through Srinagar, enters Wular Lake before entering Pakistan through a deep narrow gorge. Joins Chenab at Jhang, Pakistan.

Right and Left Bank Tributaries:

• Right Bank Tributaries of the Indus River: Nubra River (main tributary of Shyok River), Shyok River, Gilgit River, Hunza River, Kabul River, Khurram River, Gomal River, Viboa River, Tochi River, and Sangar River
• Left Bank Tributaries of the Indus River: Zanskar River, Suru River, Kishanganga (Neelam) River, Jhelum River, Chenab River, Ravi River, Beas River, Satluj River, and Panjnad River.

Indus Water Treaty: 

The Indus Water Treaty (IWT), signed between India and Pakistan on September 19, 1960, stands as a significant agreement aimed at regulating the sharing of water resources from the Indus River and its tributaries. Serving as a cornerstone for confidence-building measures between the two nations, the treaty strategically divides the Indus River system into two distinct segments. The eastern rivers, which include Satluj, Beas, and Ravi, fall under India's jurisdiction, granting it rights to utilize their waters. Conversely, the western rivers, comprising Chenab, Jhelum, and Indus, are designated for Pakistan's use. According to the treaty terms, India is allocated 20% of the water from the Indus river system, while Pakistan receives the remaining 80%. This allocation framework seeks to ensure equitable distribution and management of the vital water resources shared by the two countries, contributing to regional stability and cooperation.

• The Ganga River System:

The Ganga River System, considered India's national river, encompasses the largest river system in the country, consisting of both perennial and non-perennial rivers originating from the Himalayas and the Peninsula, respectively. Spanning approximately 2525 km in length, the Ganga traverses through India and Bangladesh, covering a basin area of about 8.6 lakh sq.km within India alone. Originating from the Gangotri glacier near Gaumukh in Uttarakhand, it commences as the Bhagirathi and converges with Alaknanda at Devprayag, forming the Ganga. Alaknanda, originating from the Santopanth glacier above Badrinath, flows through five significant confluences known as the Panch Prayag. After emerging from the mountains at Haridwar, the Ganga initially flows southward, then southeastward up to Mirzapur, before turning eastward across the Bihar plains. Upon reaching Farakka in West Bengal, it bifurcates into the distributary Bhagirathi-Hooghly, which eventually joins the Bay of Bengal near Sagar Island. In Bangladesh, the primary branch becomes the Padma, merging with the Jamuna river, then with the Meghna to form the Meghna river, finally emptying into the Bay of Bengal. The Ganga-Brahmaputra delta, known as the Sundarban Delta, is the world's largest and fastest-growing delta, renowned for its Royal Bengal tiger habitat. Additionally, the Ganga's right bank tributaries include the Yamuna, Tamas, Son, and Punpun, while its left bank tributaries comprise the Ramganga, Gomati, Ghaghara, Gandak, Kosi, and Mahanadi.

• The Ganga River System is India's national river, representing the largest river system in the country.
• It consists of both perennial and non-perennial rivers originating from the Himalayas and the Peninsula, respectively.
• With a length of approximately 2525 km, the Ganga flows through India and Bangladesh, covering a basin area of about 8.6 lakh sq.km within India.
• Originating from the Gangotri glacier near Gaumukh in Uttarakhand, it starts as the Bhagirathi and merges with Alaknanda at Devprayag to form the Ganga.
• Alaknanda, originating from the Santopanth glacier above Badrinath, flows through five significant confluences known as the Panch Prayag.
• After emerging from the mountains at Haridwar, the Ganga initially flows southward, then southeastward up to Mirzapur, before turning eastward across the Bihar plains.
• Upon reaching Farakka in West Bengal, it bifurcates into the distributary Bhagirathi-Hooghly, which eventually joins the Bay of Bengal near Sagar Island.
• In Bangladesh, the primary branch becomes the Padma, merging with the Jamuna river, then with the Meghna to form the Meghna river, finally emptying into the Bay of Bengal.
• The Ganga-Brahmaputra delta, known as the Sundarban Delta, is the world's largest and fastest-growing delta, renowned for its Royal Bengal tiger habitat.
• Additionally, the Ganga's right bank tributaries include the Yamuna, Tamas, Son, and Punpun, while its left bank tributaries comprise the Ramganga, Gomati, Ghaghara, Gandak, Kosi, and Mahanadi.
  
  
• The Brahmaputra River System

The Brahmaputra River, a transboundary river flowing through China, India, and Bangladesh, originates from the Chemayungdung glacier in the Kailash range near Mansarovar Lake. Initially named "Tsangpo," meaning "the purifier," it travels approximately 1,200 km eastwards through the dry and flat terrain of southern Tibet, where the Rango Tsangpo serves as its major right-bank tributary. Upon emerging from the Central Himalayas near Namcha Barwa, the river transforms into a turbulent force after carving a deep gorge. In India, it adopts the name "Siang" or "Dihang" upon entry west of Sadiya town in Arunachal Pradesh. Continuing southwest, it is joined by significant left-bank tributaries, Dibang or Sikang and Lohit, thereafter being referred to as the Brahmaputra.

• The confluence of Dihang, Lohit, and Dibang forms the Brahmaputra in Assam, where it features a braided channel throughout its length, creating numerous riverine islands.
• Majuli in Assam stands as the world's largest river island, nestled within the Brahmaputra.
• Upon entering Bangladesh near Dhubri, the Brahmaputra heads southward. Here, the Tista/Teesta river joins on its right bank, transforming the river into the Jamuna. It then bifurcates, with the majority of its flow continuing as Jamuna to merge with the Padma (Ganga) river.
• The lesser eastern branch, known as the lower or old Brahmaputra, curves southeast to merge with the Meghna River near Dhaka.
• The Padma and Meghna converge near Chandpur, collectively forming the Meghna as they flow into the Bay of Bengal.

Right and Left Bank Tributaries:

Major left-bank tributaries of the Brahmaputra include Burhi-Dihing and Dhansiri, while significant right-bank tributaries comprise the Subansiri (Gold river), Kameng, Manas, and Sankosh. The Brahmaputra River is notorious for floods, channel shifting, and bank erosion, primarily due to the large size of its tributaries and the substantial sediment load carried, owing to heavy rainfall in its catchment area.

2. Peninsular Drainage System

The Peninsular rivers are distinctive for their fixed courses, lack of meanders, and non-perennial water flow, with exceptions like the Narmada and Tapi rivers.

Major West Flowing Peninsular Rivers:

Narmada:

• Origin: Arises from the western flank of the Amarkantak plateau in Madhya Pradesh.
• Course: Flows westward through a rift valley between the Vindhyan and Satpura ranges. Notable attractions include the Marble Rocks near Jabalpur and the Dhuandhar Falls.
• States: Flows through Madhya Pradesh and Gujarat.
• Endpoint: Empties into the Arabian Sea near the Gulf of Khambhat, forming a broad estuary.
• Length: Approximately 1,312 km.
• Notable Feature: Hosts the Sardar Sarovar Project and Kanha National Park.

Tapi/Tapti:

• Origin: Begins in Multai, Betul district, Madhya Pradesh.
• Course: Also flows in a rift valley parallel to the Narmada, albeit shorter in length.
• States: Passes through Madhya Pradesh, Maharashtra, and Gujarat.
• Endpoint: Drains into the Arabian Sea near the Gulf of Khambhat.
• Length: Around 724 km.
• Notable Feature: Houses the Ukai Dam.

Mahi:

• Origin: Springs from the Vindhyan Range, Madhya Pradesh.
• Course: Flows northwest into Rajasthan, then southwest through Gujarat.
• Endpoint: Empties into the Arabian Sea near the Gulf of Khambhat.
• Notable Features: Features the Mahi Bajaj Sagar Dam and Kandana Dam.

Sabarmati:

• Origin: Arises in the Aravalli Range, Udaipur District, Rajasthan.
• Course: Travels southwest across Rajasthan and Gujarat.
• Endpoint: Meets the Gulf of Khambhat of the Arabian Sea.

Luni:

• Origin: Begins in the Pushkar valley of the Aravalli Range near Ajmer.
• Course: Initially known as Sagarmati, it merges with Sarasvati to become Luni, the largest river in the Thar Desert.
• Endpoint: Turns brackish below Balotra and disappears into the Rann of Kutch.
• Also known as Lavanavari or Lavanavati, meaning "Salt water" in Sanskrit.

Major East Flowing Peninsular Rivers

East flowing rivers in the Peninsular region follow a west-to-east course, driven by the land gradient, ultimately draining into the Bay of Bengal. These rivers carry substantial sediment loads, resulting in the formation of deltas along the east coast, contrasting with estuaries formed by west-flowing rivers.

Mahanadi:

• Origin: Begins near Sihawa in the Raipur district of Chhattisgarh.
• Course: Flows through Odisha before emptying into the Bay of Bengal.
• Length: Extends for 851 km, with a drainage basin shared by Maharashtra, Chhattisgarh, Jharkhand, and Odisha.
• Features: Flows north initially, then east, joined by the Jonk and Hasdeo rivers before entering Odisha. Notable for the Hirakud Dam near Sambalpur, the largest earthen dam globally.

Godavari:

• Origin: Emerges from the Western Ghats near Nashik in Maharashtra.
• Course: Flows eastward into Telangana, then southeast through Andhra Pradesh, forming a vast delta with the Krishna river.
• Length: Stretches for 1,465 km, with drainage shared by Maharashtra, Madhya Pradesh, Chhattisgarh, Odisha, and Andhra Pradesh.
• Features: Known as the "Dakshin Ganga" or Ganga of the South. Notable for its delta, termed the Rice Granary of South India. Features the Sir Arthur Thomas Cotton Dam below Rajahmundry.

Krishna:

• Origin: Originates near Mahabaleshwar in Sahyadri, Maharashtra.
• Course: Empties into the Bay of Bengal at Hamsaladeevi, Andhra Pradesh.
• Length: Spans 1,401 km, with a drainage basin shared by Maharashtra, Karnataka, Andhra Pradesh, and Telangana.
• Features: Significant tributaries include Tungabhadra, Dhudhganga, Koyana, Ghatprabha, Musi, and Bhima.

Kaveri/Cauvery:

• Origin: Springs from the Brahmagiri range of the Western Ghats in Karnataka.
• Course: Flows through Karnataka and Tamil Nadu.
• Length: Approximately 800 km, with a basin shared by Tamil Nadu, Karnataka, Kerala, and Puducherry.
• Features: Forms the Shivasamudram Falls, the second largest waterfall in India. Important tributaries include Kabini, Bhavani, Amravati, and Hemavati. It is known for its consistent water flow throughout the year due to rainfall from various monsoon seasons.

Significance of India’s drainage system

India's vast river drainage system holds immense significance, both historically and ecologically. Spanning across the country like lifelines, these rivers have shaped India's civilization, culture, and economy for millennia.

Firstly, these rivers have been integral to the development of ancient civilizations such as the Indus Valley Civilization, which flourished along the banks of the Indus and its tributaries. The Ganges, Yamuna, Brahmaputra, and other rivers have been revered as sacred by millions, shaping religious practices and rituals deeply ingrained in Indian society.

Economically, India's rivers have played a pivotal role in agriculture, providing fertile plains through which they flow. The annual monsoon rains replenish these river basins, ensuring a bountiful harvest for millions of farmers. Additionally, these rivers serve as vital transportation routes, facilitating trade and commerce throughout history.

Ecologically, the river systems support diverse ecosystems, harboring a rich variety of flora and fauna. Wetlands, floodplains, and mangrove forests along the riverbanks provide crucial habitats for numerous species, contributing to India's biodiversity.

However, the significance of India's river systems extends beyond its borders. Several major rivers, such as the Ganges and Brahmaputra, originate in the Himalayas and flow through neighboring countries like Nepal and Bangladesh, fostering transboundary cooperation and diplomacy.

Furthermore, these rivers also pose significant challenges, including pollution, over-extraction of water, and the impacts of climate change. Addressing these issues requires concerted efforts at the national and international levels to ensure the sustainable management of these vital resources

In conclusion, India's vast river drainage system is not only a physical feature of the landscape but also a symbol of the country's cultural heritage, economic prosperity, and ecological diversity. Recognizing its significance and safeguarding its health is essential for the well-being of present and future generations.