Drainage refers to the flow of water through streams and rivers in a particular area. The area drained by a single river system is called its drainage basin or watershed. India has two main drainage systems — the Himalayan rivers and the Peninsular rivers — each with distinct characteristics.
Drainage Patterns
- Rivers develop different patterns depending on the slope and rock structure:
- Dendritic: Tree-like branching pattern (common in uniform rock, e.g., Ganga plains).
- Trellis: Rivers at right angles to each other (parallel ridges, e.g., Himalayan foothills).
- Rectangular: Rivers have 90-degree bends (fault lines, e.g., Vindhya region).
- Radial: Rivers flow outward from a central hill in all directions (e.g., Amarkantak Plateau).
Himalayan River Systems
Himalayan rivers are perennial (flow year-round — fed by snowmelt and glaciers in summer, monsoon rain in the rainy season). They are antecedent — they existed before the Himalayas rose and cut gorges through them.
Example 1: The Indus River System
The Indus rises near Lake Mansarovar in Tibet. It enters India through Ladakh, forming a spectacular gorge. Its tributaries include the Jhelum, Chenab, Ravi, Beas, and Sutlej — all five rivers of the Punjab ("land of five rivers"). Most of the Indus basin now lies in Pakistan after the Indus Waters Treaty (1960).
Example 2: The Ganga River System
The Ganga rises from the Gangotri Glacier as the Bhagirathi; it is joined by the Alaknanda at Devprayag to form the Ganga. Major right-bank tributaries: Yamuna, Son. Left-bank tributaries: Ghaghara, Gandak, Kosi (the "sorrow of Bihar" — prone to disastrous floods). The Ganga meets the Brahmaputra in Bangladesh and drains into the Bay of Bengal forming the Sundarbans delta — the world's largest delta.
Example 3: The Brahmaputra River System
The Brahmaputra rises in Tibet as the Tsangpo. It enters India in Arunachal Pradesh forming a deep gorge, then flows west through Assam. It carries enormous sediment loads and frequently floods. The Majuli Island in the Brahmaputra is one of the world's largest river islands.
Peninsular River Systems
Peninsular rivers are mainly seasonal (rain-fed, depend on monsoon) and flow in old, shallow valleys. They do not carry as much sediment as Himalayan rivers and are shorter.
Example 4: The Narmada Basin
The Narmada rises at Amarkantak in MP and flows west into the Arabian Sea through a rift valley (fault-formed valley between the Vindhya and Satpura ranges). It does not form a delta — it forms an estuary. The Sardar Sarovar Dam is built on the Narmada.
Example 5: The Tapi (Tapti) River
The Tapi also rises in MP and flows west into the Arabian Sea through a rift valley (parallel to Narmada). Like the Narmada, it forms an estuary rather than a delta.
Example 6: East-Flowing Peninsular Rivers
The Mahanadi, Godavari, Krishna, and Kaveri flow east into the Bay of Bengal, forming large deltas along the eastern coast. The Godavari (longest peninsular river, rising near Nashik) is sometimes called the Dakshin Ganga (Ganga of the south) due to its size and religious significance. The Kaveri waters the fertile rice-growing plains of Tamil Nadu and Karnataka.
- Example 7: Lakes — Natural and Artificial
- Important lakes include:
- Wular Lake (Jammu and Kashmir): One of India's largest freshwater lakes.
- Dal Lake (J&K): Famous for houseboats and tourism.
- Chilika Lake (Odisha): India's largest saltwater coastal lagoon — important for migratory birds.
- Sambhar Lake (Rajasthan): India's largest saltwater lake; major source of salt.
- Loktak Lake (Manipur): Contains the floating island (phumdis).
Key Concepts
- Watershed: The ridge separating two drainage basins.
- Perennial rivers: Flow throughout the year (Himalayan rivers).
- Ephemeral rivers: Flow only during rain (many Peninsular rivers in dry regions).
- Meander: A bend in a river, common in slow-flowing rivers on plains.
- Delta: Fan-shaped sediment deposit at a river's mouth.
Common mistakes
Students often think all east-flowing rivers form deltas — the Narmada and Tapi flow west through rift valleys and form estuaries, not deltas. Also, the Brahmaputra is called the Tsangpo in Tibet, the Siang/Dihang entering India, and Brahmaputra in Assam — it is the same river.
Summary
India's drainage divides into the Himalayan and Peninsular systems. Himalayan rivers are perennial, antecedent, and carry enormous sediment. Peninsular rivers are mostly seasonal, flow in harder rock valleys, and include the great east-flowing rivers (Godavari, Krishna, Kaveri) and the unique west-flowing rift valley rivers (Narmada, Tapi). Rivers and lakes are vital for agriculture, transport, and ecosystems.