Chapter Notes

Drainage

The term drainage describes the river system of a particular area. It's like the network of veins in a leaf, where small streams flow from different directions, join together to form a main river, and finally drain into a large body of water like a lake, sea, or ocean.

The entire area of land that is drained by a single river system is called a drainage basin. If you look at a map, you'll see that elevated areas, like a mountain or an upland, act as barriers that separate two drainage basins. This kind of upland is known as a water divide.

Drainage Systems in India

India's drainage systems are primarily shaped by the major landforms of the subcontinent. Because of this, we can divide Indian rivers into two main groups:

• The Himalayan rivers
• The Peninsular rivers

These two groups of rivers are very different from each other, not just because they originate in different regions but also in their characteristics and behavior.

Characteristics of Himalayan Rivers

• Perennial Flow: Most Himalayan rivers are perennial, meaning they have water throughout the year. This is because they are fed not only by rainfall but also by the melting snow and glaciers from the high mountains.
• Long Courses: These rivers travel a long distance from their source in the mountains to the sea.
• Formation of Gorges: Major rivers like the Indus and the Brahmaputra originate north of the mountain ranges and have carved out deep gorges by cutting through the mountains over millions of years.
• Erosional and Depositional Features:
  • In their upper courses (in the mountains), the rivers flow swiftly and perform intense erosion, carrying huge loads of silt and sand.
  • In their middle and lower courses (on the plains), the rivers slow down and form features like meanders (S-shaped curves), oxbow lakes, and other depositional features in their floodplains. They also form large, well-developed deltas at their mouths.

Characteristics of Peninsular Rivers

• Seasonal Flow: A large number of Peninsular rivers are seasonal. Their flow depends entirely on rainfall. During the dry season, their water levels drop significantly, and some smaller rivers may even dry up.
• Shorter and Shallower Courses: Compared to the Himalayan rivers, Peninsular rivers have shorter and less deep courses.
• Origin and Flow Direction: Most of the major rivers of peninsular India, such as the Mahanadi, Godavari, Krishna, and Kaveri, originate in the Western Ghats and flow eastwards into the Bay of Bengal. However, some, like the Narmada and Tapi, originate in the central highlands and flow westwards.

The Himalayan Rivers

The three major Himalayan river systems are the Indus, the Ganga, and the Brahmaputra. These rivers are very long and are joined by many large and important tributaries. A river along with all its tributaries is called a river system.

The Indus River System

• Source: The Indus river originates in Tibet, near Lake Mansarowar.
• Course: It flows west, entering India in Ladakh, where it forms a stunning gorge. It flows through Baltistan and Gilgit and emerges from the mountains at Attock. From there, it flows south through Pakistan and finally reaches the Arabian Sea, east of Karachi.
• Tributaries: In the Kashmir region, it is joined by the Zaskar, the Nubra, the Shyok, and the Hunza. The major tributaries—the Satluj, the Beas, the Ravi, the Chenab, and the Jhelum—join together before entering the Indus near Mithankot in Pakistan.
• Basin: The Indus basin is vast. A little over a third of it is in India (in Ladakh, Jammu and Kashmir, Himachal Pradesh, and Punjab), with the rest located in Pakistan.
• Length: With a total length of 2900 km, the Indus is one of the longest rivers in the world.

The Ganga River System

• Source: The headwaters of the Ganga are called the 'Bhagirathi' and are fed by the Gangotri Glacier. The Bhagirathi is joined by the Alaknanda at Devaprayag in Uttarakhand to form the Ganga.
• Course: The Ganga emerges from the mountains onto the plains at Haridwar. It then flows eastwards across the northern plains. At Farakka in West Bengal, which is the northernmost point of the Ganga delta, the river splits.
• Distributary and Mainstream:
  • The Bhagirathi-Hooghly, a distributary, flows south through the deltaic plains to the Bay of Bengal.
  • The mainstream flows south into Bangladesh, where it is joined by the Brahmaputra. Downstream, this combined river is known as the Meghna.
• Tributaries:
  • From the Himalayas (Left Bank): Major rivers like the Yamuna (which originates from the Yamunotri Glacier and meets the Ganga at Allahabad), the Ghaghara, the Gandak, and the Kosi. These rivers often cause destructive floods in the northern plains but also enrich the soil.
  • From the Peninsular Uplands (Right Bank): The Chambal, the Betwa, and the Son. These rivers come from semi-arid areas, have shorter courses, and carry less water.
• Delta: The delta formed by the Ganga and the Brahmaputra is known as the Sundarban Delta. It is the world's largest and fastest-growing delta and is named after the Sundari tree that thrives in its marshland. It is also the home of the Royal Bengal tiger.
• Length and Features: The Ganga is over 2500 km long. The plain from Ambala to the Sunderban has a very gentle slope—a fall of just one meter for every six kilometers. This gentle gradient is why the river develops large meanders.

The Brahmaputra River System

• Source: The Brahmaputra rises in Tibet, east of Mansarowar lake, very close to the sources of the Indus and the Satluj.
• Course: Most of its course lies outside India. It flows eastwards, parallel to the Himalayas. Near Namcha Barwa (7757 m), it takes a sharp 'U' turn and enters India in Arunachal Pradesh through a gorge.
• Names: The river is known by different names in different regions:
  • Tsang Po in Tibet
  • Dihang in Arunachal Pradesh
  • Jamuna in Bangladesh
• Characteristics:
  • In Tibet, the river carries a smaller volume of water and less silt because it flows through a cold and dry area.
  • In India, it passes through a region of heavy rainfall. As a result, the river carries a large volume of water and a considerable amount of silt.
• Features and Impact: In Assam, the Brahmaputra has a braided channel and forms many riverine islands. During the rainy season, the river frequently overflows its banks, causing widespread floods and devastation in Assam and Bangladesh. Unlike other north Indian rivers, it deposits huge amounts of silt on its bed, causing the riverbed to rise and the channel to shift frequently.

The Peninsular Rivers

The main water divide in Peninsular India is the Western Ghats, which runs parallel to the western coast. The drainage basins of the peninsular rivers are smaller compared to their Himalayan counterparts.

East-Flowing Rivers

Most of the major peninsular rivers—the Mahanadi, the Godavari, the Krishna, and the Kaveri—flow eastwards and drain into the Bay of Bengal. These rivers form deltas at their mouths.

West-Flowing Rivers

The Narmada and the Tapi are the only long rivers that flow west and form estuaries. There are also numerous small, short coastal rivers that flow west from the Western Ghats into the Arabian Sea.

The Narmada Basin

• Source: Rises in the Amarkantak hills in Madhya Pradesh.
• Course: It flows westwards in a rift valley, which is a long, narrow valley formed due to faulting in the Earth's crust.
• Features: The Narmada creates many picturesque locations, including the 'Marble rocks' gorge near Jabalpur and the 'Dhuadhar falls'. Its tributaries are very short and join the main stream at right angles.
• Basin: Covers parts of Madhya Pradesh and Gujarat.

The Tapi Basin

• Source: Rises in the Satpura ranges in Madhya Pradesh.
• Course: It also flows west in a rift valley, parallel to the Narmada, but is much shorter in length.
• Basin: Covers parts of Madhya Pradesh, Gujarat, and Maharashtra.

The Godavari Basin

• Source: Originates from the slopes of the Western Ghats in the Nasik district of Maharashtra.
• Characteristics: At about 1500 km, the Godavari is the largest Peninsular river. Its drainage basin is also the largest among the peninsular rivers.
• Dakshin Ganga: Because of its great length and the large area it covers, it is also known as the Dakshin Ganga.
• Tributaries: Its major tributaries include the Purna, the Wardha, the Pranhita, the Manjra, the Wainganga, and the Penganga.
• Basin: Covers parts of Maharashtra (about 50% of the basin), Madhya Pradesh, Odisha, and Andhra Pradesh.

The Mahanadi Basin

• Source: The Mahanadi rises in the highlands of Chhattisgarh.
• Course and Length: It flows through Odisha to reach the Bay of Bengal and is about 860 km long.
• Basin: Its drainage basin is shared by Maharashtra, Chhattisgarh, Jharkhand, and Odisha.

The Krishna Basin

• Source: Rises from a spring near Mahabaleshwar.
• Course and Length: The Krishna flows for about 1400 km to the Bay of Bengal.
• Tributaries: The Tungabhadra, the Koyana, the Ghatprabha, the Musi, and the Bhima are some of its tributaries.
• Basin: Its drainage basin is shared by Maharashtra, Karnataka, and Andhra Pradesh.

The Kaveri Basin

• Source: The Kaveri rises in the Brahmagiri range of the Western Ghats.
• Course and Length: It reaches the Bay of Bengal south of Cuddalore in Tamil Nadu and is about 760 km long.
• Tributaries: Its main tributaries are the Amravati, Bhavani, Hemavati, and Kabini.
• Basin: Drains parts of Karnataka, Kerala, and Tamil Nadu.
• Features: The river forms the second biggest waterfall in India, the Shivasamudram Falls, which is used to generate hydroelectric power.

Lakes

Lakes are not only tourist attractions but are also incredibly useful to human beings in many ways.

Formation and Types of Lakes

India has many different kinds of lakes. Some are permanent, while others are seasonal, containing water only during the rainy season.

• Ox-bow lakes: Formed when a meandering river cuts off one of its loops.
• Lagoons: Formed in coastal areas by spits and bars, which trap seawater. Examples include Chilika lake, Pulicat lake, and Kolleru lake.
• Glacial Lakes: Most freshwater lakes in the Himalayan region are of glacial origin. They were formed when glaciers dug out a basin, which later filled with snowmelt.
• Tectonic Lakes: The Wular lake in Jammu and Kashmir, India's largest freshwater lake, was formed as a result of tectonic activity.
• Salt Water Lakes: The Sambhar lake in Rajasthan is a salt water lake, and its water is used for producing salt.
• Human-made Lakes: Damming rivers for hydroelectric power generation has also led to the formation of large lakes, such as Guru Gobind Sagar (Bhakra Nangal Project).

Importance of Lakes

Lakes are of great value for several reasons:

• They help regulate the flow of a river, preventing flooding during heavy rains and maintaining water flow during dry seasons.
• They can be used for developing hydel power.
• They moderate the climate of their surroundings.
• They maintain the aquatic ecosystem.
• They enhance natural beauty, help develop tourism, and provide recreation.

Role of Rivers in the Economy

Rivers have been fundamentally important throughout human history.

• Basic Resource: Water from rivers is a basic natural resource, essential for various human activities.
• Settlements: Riverbanks have attracted settlers since ancient times, and many of these settlements have now grown into big cities.
• Economic Significance: For a country like India, where agriculture is the main source of livelihood for most people, rivers are crucial for irrigation, navigation, and hydro-power generation.

River Pollution

The increasing demand for water from rivers is negatively affecting its quality.

• Causes:
  1. Water Diversion: Growing domestic, municipal, industrial, and agricultural demand leads to more and more water being drained out of rivers, reducing their volume.
  2. Pollution: A heavy load of untreated sewage and industrial waste is often emptied directly into rivers.
• Impact: This not only pollutes the water but also affects the river's natural self-cleansing capacity. For example, the Ganga can naturally dilute and assimilate pollution within 20 km of large cities, but increasing urbanization and industrialization prevent this from happening.
• Conservation Efforts: Concern over rising pollution has led to the launch of various action plans. The river cleaning program in India began with the Ganga Action Plan (GAP) in 1985. In 1995, this was expanded to cover other rivers under the National River Conservation Plan (NRCP), with the goal of improving the water quality of the country's major rivers.