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This revised chapter on NCERT Class 11 Geography India Physical Environment Chapter 3: Drainage System Notes provides a clear overview of India’s river systems, drainage patterns, and major river basins. These notes simplify complex concepts into easy-to-understand pointers. It is basically designed for exam preparation and quick revision of drainage basins, Himalayan and Peninsular rivers, and their evolution. You can also download a free PDF for effective exam preparation.
Contents
- 1 Introduction
- 2 Drainage Patterns
- 3 Classification of Drainage Systems
- 4 Evolution of the Drainage System
- 5 The Himalayan Drainage
- 6 The Peninsular Drainage
- 7 Comparison Between Himalayan and Peninsular Rivers
- 8 River Regimes and Usability
- 9 Important Definitions in NCERT Notes Class 11 Geography India Physical Environment Chapter 3: Drainage System
- 10 FAQs
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Introduction
The term ‘drainage’ describes the river system of an area. The drainage pattern is the outcome of the geological time period, the nature and structure of rocks, topography, slope, amount of water flowing, and periodicity of flow. An area drained by a river and its tributaries is called a drainage basin, while the boundary separating one basin from another is the watershed. There are major river basins with catchment areas over 20,000 sq km, including the Ganga, Brahmaputra, Krishna, Godavari, Narmada, Tapi, Mahi, Pennar, Sabarmati, and Barak.
Drainage Patterns
Rivers form different shapes or patterns based on the slope of the land, the structure of rocks, and past geological events. Here are the main types:
- Dendritic pattern: This looks like the branches of a tree. It develops where the rocks are uniform and flat-lying. You can see this pattern in the rivers of the Ganga plains.
- Trellis pattern: Here, the smaller rivers join the main river at almost right angles, forming a rectangular shape. This happens in areas with folded mountains. Examples include rivers in the upper Himalayas and parts of Singhbhum in Jharkhand and Odisha.
- Radial pattern: Rivers flow outwards in all directions from a high central point, like a hill or dome. This is common around the Amarkantak hills.
- Centripetal pattern: Rivers flow towards a central low area, such as a lake or swamp.
Classification of Drainage Systems
Indian rivers can be grouped in two main ways. First, based on where they finally empty their water, about 77% of India’s area drains into the Bay of Bengal, while 23% drains into the Arabian Sea. The dividing lines are features like the Delhi Ridge, Aravali hills, and Western Ghats (Sahyadris).
The second way is based on their origin and nature: Himalayan rivers and Peninsular rivers.
Evolution of the Drainage System
Today’s Indian rivers took their present shape because of changes in the land over millions of years. Himalayan rivers existed even before the Himalayas rose up, so they are called antecedent rivers. Peninsular rivers are much older. Most of them flow eastwards because the Peninsular plateau slopes gently from west to east. In ancient times, there was one large river called the Indo-Brahma. Geological changes during the Pleistocene period broke it into the present Indus, Ganga, and Brahmaputra systems.
The Himalayan Drainage
Rivers born in the Himalayas flow throughout the year because they get water from melting snow as well as rain. In the mountains, they cut deep gorges and V-shaped valleys. In the plains, they deposit sediment and form flat land. The three major Himalayan river systems are the Indus, Ganga, and Brahmaputra.
- The Indus System: This river starts near Lake Mansarovar in Tibet. It enters India through Ladakh. Its main tributaries inside India are the Jhelum, Chenab, Ravi, Beas, and Satluj. These five tributaries join to form the Panchnad, which then meets the Indus. The river finally flows into the Arabian Sea. Its basin is very large, but only a small part lies in India.
- The Ganga System: The Ganga begins as the Bhagirathi from the Gangotri glacier. It joins the Alaknanda at Devaprayag to become the Ganga. Important left-bank tributaries are the Ghaghara, Gandak, and Kosi. Right-bank tributaries include the Yamuna and Son. Some tributaries like the Chambal, Betwa, and Son start from the Peninsular plateau. The Ganga and Brahmaputra together form a huge delta called the Sundarbans. The Ganga is the longest river in India.
- The Brahmaputra System: In Tibet, it is called the Tsangpo. It enters India in Arunachal Pradesh as the Dihang. The river often has many channels and islands because of heavy sediment. Major tributaries are the Dibang, Lohit, Subansiri, Kameng, and Manas. It joins the Ganga in Bangladesh. This river often causes floods.
The Peninsular Drainage
Peninsular rivers are older than the Himalayan ones. Most of them depend only on rain, so they flow strongly only during the monsoon and become weak in dry seasons. Their valleys are wide and shallow. Many are superimposed or rejuvenated, meaning their courses were fixed long ago. East-flowing rivers reach the Bay of Bengal and form deltas. West-flowing rivers reach the Arabian Sea and form estuaries.
Major east-flowing rivers are the Mahanadi, Godavari, Krishna, and Kaveri. Major west-flowing rivers are the Narmada and Tapi.
- Evolution: The Peninsular plateau tilted slightly towards the east. Some areas sank, creating rift valleys where the Narmada and Tapi flow westwards along faults.
- Mahanadi: It starts in Chhattisgarh and flows eastwards into Odisha, where it forms a delta.
- Godavari: This is the largest Peninsular river. It begins near Nashik in Maharashtra. Tributaries include Pravara, Purna, Manjra, Penganga, Wainganga, Indravati, and Sabari. Its basin covers a very large area.
- Krishna: It rises near Mahabaleshwar in the Western Ghats. Main tributaries are Tungabhadra, Koyna, Ghataprabha, Malaprabha, and Bhima. The basin lies in Maharashtra, Karnataka, Telangana, and Andhra Pradesh.
- Kaveri: It starts in the Brahmagiri range of the Western Ghats. Tributaries include Hemavati, Shimsha, and Arkavati. It forms a delta in Tamil Nadu. Most of its water is used for irrigation.
- Narmada: It begins at Amarkantak in Madhya Pradesh and flows west through a rift valley. Tributaries are the Hiran and the Orsang. It forms an estuary, not a delta.
- Tapi: It starts near Multai in Madhya Pradesh and flows west parallel to the Narmada, but it is shorter. It also forms an estuary.
- Other west-flowing rivers: These include the Sabarmati, Mahi, and many small coastal rivers.
Comparison Between Himalayan and Peninsular Rivers
Himalayan rivers flow all year round, have long courses, cover large basins, erode deeply in mountains, and deposit a lot in plains. They are antecedent, meaning they existed before the mountains rose.
Peninsular rivers are mostly seasonal, shorter, have fixed courses, erode and deposit less, and are consequent, meaning they follow the natural slope of the land.
River Regimes and Usability
A river regime means how the water flow changes throughout the year. Northern (Himalayan) rivers have a steady flow because of snowmelt in summer and rain. Southern (Peninsular) rivers rise quickly in the monsoon and fall in the dry seasons. Rivers are useful for irrigation, drinking water, electricity generation, and transport, but problems like pollution, overuse, and disputes between states affect their proper use.
Role of Rivers in the Economy
Rivers are very important for India’s economy. They provide water for farming, drinking, inland navigation, and hydroelectric power. They support fishing, tourism, and many livelihoods. However, floods cause damage, so proper management is needed.
River Pollution
Pollution is increasing in Indian rivers because of untreated sewage, factory waste, and chemicals from farms. This makes water unsafe for drinking and harms aquatic life.
Important Definitions in NCERT Notes Class 11 Geography India Physical Environment Chapter 3: Drainage System
Here we have explained the key concepts and terms of this chapter to make it easy for you to understand.
- Drainage: The network of rivers and streams that carry water in a region.
- Drainage Basin: The entire area from which a river and its tributaries collect water.
- Watershed: The ridge or high ground that divides one drainage basin from another.
- Dendritic Pattern: A drainage pattern that looks like the branching of a tree.
- Antecedent River: A river that was flowing before the mountains in its path rose up.
- Perennial River: A river that has water flowing throughout the year.
- Consequent River: A river that flows in the direction of the natural slope of the land.
- Estuary: The wide, tidal mouth of a river where it meets the sea without forming a delta.
- Delta: The triangular deposit of sediment formed at the mouth of a river entering a sea or lake.
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FAQs
The two main types are Himalayan rivers, which flow all year and have large basins, and Peninsular rivers, which are mostly seasonal and have smaller basins.
The Godavari has the largest basin among the Peninsular rivers.
This happens because the Peninsular plateau slopes gently from west to east.
The Narmada and Tapi rivers flow westwards through rift valleys.
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