CBSE Class 9 Geography Chapter 3 Notes Understanding the Lesson
1. The term ‘Drainage’ describes the river system of an area. The area drained by a single river system is called a drainage basin.
2. Any mountain or an upland separating two drainage basins is called a water divide.
3. The Indian rivers are divided into two major groups
- the Himalayan rivers and
- The peninsular rivers.
4. Some of the features of the Himalayan rivers are-they are perennial, they have long courses from heir source to the sea, they perform intensive erosional activity in their upper courses and carry huge loads of silt and sand.
5. Some of the features of the Peninsular rivers are-they are seasonal, they have shorter and shallower courses as compared to the Himalayan rivers, most of them originate in the Western Ghats and flow towards the Bay of Bengal.
6. The streams within a drainage basin form certain patterns, depending on the slope of land, underlying rock structure as well as the climatic conditions of the area.
7. Types of drainage patterns are-dendrite, trellis, rectangular and radial patterns.
8. The major Himalayan rivers are-the Indus, the Ganga and the Brahmaputra. The river Indus rises in Tibet, near Lake Mansarovar. It flows through Baltistan and Gilgit and emerges from the mountains at Attock. The Indus plain has a very gentle slope. The Indus is one of the longest rivers of the world.
9. The Ganga emerges from the mountains on to the plains at Haridwar. The river is joined by tributaries such as the Yamuna, the Ghaghara, the Gandak and the Kosi. The length of the Ganga is over 2500 km.
10. The Brahmaputra is slightly longer than the Indus and most of its course lies outside India. The river rises in Tibet east of Mansarovar lake. It flows eastwards parallel to the Himalayas. Every year during the rainy season, the river overflows its banks, causing widespread devastation due to floods in Assam and Bangladesh.
11. Major rivers of the Peninsula such as the Mahanadi, the Godavari, the Krishna and the Kaveri flow eastwards and drain into the Bay of Bengal. These rivers make deltas at their mouths. The Narmada and the Tapi flow west and make estuaries.
12. The Narmada rises in the Amarkantak hills in the Madhya Pradesh. On its way to the sea, it creates many picturesque sites. The Narmada basin covers parts of Madhya Pradesh and Gujarat.
13. The Tapi rises in the Satpura ranges, in the Betul district of Madhya Pradesh. Its basin covers parts of Madhya Pradesh, Gujarat and Maharashtra.
14. The Godavari, the largest Peninsular river, rises in the Nasik district of Maharashtra. Its basin covers parts of Maharashtra, Madhya Pradesh, Odisha and Andhra Pradesh.
15. The Mahanadi rises in the highlands of Chhattisgarh. Its drainage basin is shared by Maharashtra, Chhattisgarh, Jharkhand and Odisha.
16. The Krishna rises from a spring near Mahabaleshwar. It drains into the Bay of Bengal. Its drainage basin is shared by Maharashtra, Karnataka and Andhra Pradesh.
17. The Kaveri rises in the Brahmagri range of the Western Ghats and it reaches the Bay of Bengal in south of Cuddalore, in Tamil Nadu. Its basin drains parts of Karnataka, Kerala and Tamil Nadu.
18. India has many lakes which differ from each other in size, and other characteristics. Most lakes are permanent while some contain water only during the rainy season.
19. Some of the lakes have come into existence as the result of the action of glaciers and ice sheets while the others have been formed by wind, river action and human activities.
20. Most of the fresh-water lakes are in the Himalayan region. The Wular lake in Jammu and Kashmir is the largest freshwater lake in India. Some lakes such as Guru Gobind Sagar have been artificially created by damming of rivers for power generation.
21. Rivers play an important role in country’s economy. Their water is used for irrigation, navigation, hydro-power generation, etc.
22. Excess use of river water has affected its quality. Untreated sewage and industrial effluents are emptied into the rivers as a result of which their self-cleansing capacity is lost.
23. Increasing urbanization and industrialization are also major reasons of river pollution. It is high time to think over it and do accordingly.
Drainage Class 9 CBSE Notes Important Terms
Drainage: The river system of an area.
Drainage basin: The area drained by a single river system.
Water divide: Any mountain or an upland that separates two drainage basins is called a water divide.
Perennial rivers: Rivers having water throughout the year.
River system: A river along with its tributaries.
Seasonal rivers: Rivers having water only during rainy season.
Floodplain: An area of low-lying ground adjacent to a river, formed mainly of river sediments and subject to flooding.
River delta: A landform that forms from deposition of sediment carried by a river as the flow leaves its mouth and enters slower-moving or standing water.
Gorges: Deep, narrow valleys with a stream or river running along their bottom.
Bhagirathi: The headwaters of the Ganga.
Tributary: A river or stream flowing into a larger river or lake.
Glacier: A slowly moving mass or river of ice formed by the accumulation and compaction of snow on mountains or near the poles.
Distributary: A branch of a river that does not return to the mainstream after leaving it as in a delta.
Meander: A winding curve or bend in a river.
Rift valley: A linear-shaped lowland between several highlands or mountain ranges created by the action of a geologic rift or fault.
Lake: A large area of water surrounded by land.
Sea: A lake of large extent.
Trough: A narrow depression as in the earth or between ocean waves or in the ocean bed. A narrow channel, gutter or gulley.