Quick Revision Notes & Formula Sheet

Class: 9th
Subject: Social Science (Geography)
Chapter: Drainage (अपवाह)

Drainage System: The term 'drainage' describes the river system of an area.
Drainage Basin: The area drained by a single river system is called a drainage basin.
Water Divide (जल विभाजक): Any elevated area, such as a mountain or an upland, that separates two drainage basins is known as a water divide. Example: Amarkantak hills.

Tributary (सहायक नदी): A river or stream which contributes its water to a main river by joining it from either side.
Distributary (वितरिका): A river that branches off and flows away from a main stream, usually found in a delta.
Meander (विसर्प): Large bends or loops formed by rivers as they twist and turn through broad plains.
Ox-bow Lake (गोखुर झील): A cut-off meander that forms a lake separate from the main river channel.
Estuary (ज्वारनदमुख): A tidal mouth of a large river, where the tide meets the stream (rivers flowing into the Arabian Sea form estuaries, e.g., Narmada, Tapi).
Delta (डेल्टा): A triangular deposit of sediment at the mouth of a river, where it enters an ocean or sea (rivers flowing into the Bay of Bengal form deltas, e.g., Ganga, Brahmaputra).

Indian rivers are divided into two major groups based on their origin:

Himalayan Rivers (हिमालयी नदियाँ):
- Nature: Perennial (flow throughout the year) as they receive water from rain as well as melted snow from mountains.
- Key Examples: Indus, Ganga, and Brahmaputra.
Peninsular Rivers (प्रायद्वीपीय नदियाँ):
- Nature: Seasonal (non-perennial) as their flow depends entirely on rainfall.
- Key Examples: Mahanadi, Godavari, Krishna, Kaveri, Narmada, and Tapi.

Origin: Tibet, near Lake Mansarovar.
Flow: Enters India in Ladakh, flows southwards down to Pakistan, and finally meets the Arabian Sea.
Major Tributaries: Zaskar, Nubra, Shyok, Hunza, and the Panjnad (Satluj, Beas, Ravi, Chenab, and Jhelum).
Indus Water Treaty (1960): India can use only 20% of the total water carried by the Indus river system.

Origin: Headwaters called Bhagirathi are fed by the Gangotri Glacier and joined by the Alaknanda at Devprayag in Uttarakhand.
Flow: Flows south and east, enters Bangladesh (as Padma), meets Brahmaputra (as Meghna), and drains into the Bay of Bengal, forming the world's largest delta—Sundarban Delta.
Major Tributaries: Yamuna, Ghaghra, Gandak, Kosi (Left Bank/Himalayan); Chambal, Betwa, Son (Right Bank/Peninsular).
Length: Over 2,500 km.

Origin: Tibet, east of Mansarovar Lake (known as Tsangpo).
Flow: Enters India in Arunachal Pradesh (called Dihang), where it is joined by Dibang, Lohit, and other tributaries to form the Brahmaputra in Assam.
Characteristics: Carries huge amounts of silt in Tibet; causes severe floods in Assam due to heavy rainfall.

Godavari Basin: Largest Peninsular river system (also known as Dakshin Ganga). Originates from the slopes of Western Ghats in Nashik (Maharashtra) and drains into the Bay of Bengal.
Mahanadi Basin: Rises in the highlands of Chhattisgarh and flows to the Bay of Bengal.
Krishna Basin: Rises from a spring near Mahabaleshwar and flows into the Bay of Bengal.
Kaveri Basin: Rises in the Brahmagri range of the Western Ghats and reaches the Bay of Bengal in south Cuddalore, Tamil Nadu.
Narmada Basin: Rises in the Amarkantak hills, flows westwards through a rift valley, and forms an estuary before entering the Arabian Sea.
Tapi Basin: Originates in the Satpura ranges (Betul district of MP) and flows westwards parallel to the Narmada.

Types of Lakes: Freshwater lakes, saltwater lakes, glacial lakes, and artificial lakes (created by dams).
Wular Lake (Jammu & Kashmir): The largest freshwater lake in India (results from tectonic activity).
Other Important Lakes: Dal Lake, Bhimtal, Nainital, Loktak, Barapani, Chilika Lake (largest saltwater lake), Sambhar Lake (saltwater lake used for producing salt).
Economic Importance of Lakes: Helps in regulating river flow, prevents flooding, develops tourism, provides freshwater, and supports fisheries (hydroelectric power generation).

Economic Importance:
- Water is basic for human survival, agriculture, and industries.
- Navigation and generation of hydroelectric power.
River Pollution (नदी प्रदूषण):
- Domestic sewage, industrial effluents, and agricultural runoff are heavily polluting rivers.
- National River Conservation Plan (NRCP): Initiated to clean rivers. Programs like Namami Ganga Programme have been launched for the conservation and rejuvenation of the Ganga river.

Drainage