Quick Revision Notes & Formula Sheet

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

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### Concept 1: What is Drainage? (अपवाह क्या है?)

• 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.

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### Key Terms & Definitions (मुख्य शब्दावली)

• 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).

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### Concept 2: Drainage Systems in India (भारत के अपवाह तंत्र)

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

1. 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.
2. Peninsular Rivers (प्रायद्वीपीय नदियाँ):
   • Nature: Seasonal (non-perennial) as their flow depends entirely on rainfall.
   • Key Examples: Mahanadi, Godavari, Krishna, Kaveri, Narmada, and Tapi.

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### Key River Systems (प्रमुख नदी प्रणालियाँ)

1. The Indus River System (सिंधु नदी तंत्र)

• 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.

2. The Ganga River System (गंगा नदी तंत्र)

• 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.

3. The Brahmaputra River System (ब्रह्मपुत्र नदी तंत्र)

• 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.

4. Major Peninsular Rivers (प्रमुख प्रायद्वीपीय नदियाँ)

• 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.

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### Concept 3: Lakes in India (भारत की झीलें)

• 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).

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### Concept 4: Role of Rivers in the Economy & Pollution (नदियाँ और अर्थव्यवस्था व प्रदूषण)

• 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.