Drainage Patterns, Watersheds, and River Basins of India

Drainage patterns and river basins are regularly tested in Kerala PSC geography sections. Understanding how rivers flow and how drainage systems form helps answer 2-3 questions per exam.

Key Terminology

Term	Meaning
Drainage	The river system of an area
Drainage pattern	The geometric arrangement of streams in a region
Drainage basin	Total area drained by a river and its tributaries (also called catchment area)
Watershed	The boundary line separating one drainage basin from another (also called water divide)
Tributary	A smaller stream that flows into a larger river
Distributary	A branch that flows away from the main river (common in deltas)
Confluence	Point where two rivers meet
Divide	Higher ground that separates two drainage basins

Types of Drainage Patterns

Pattern	Shape	Formed When	Example
Dendritic	Tree-branch like	Uniform rock; gentle slope; no structural control	Ganga and its tributaries in the Indo-Gangetic plain
Trellis	Rectangular grid; tributaries join at right angles	Folded mountains with alternating hard and soft rock	Streams in the Appalachian Mountains; parts of Singrauli coalfield
Radial	Streams flow outward from a central high point like spokes	Dome or volcanic cone	Rivers originating from Amarkantak (Narmada, Son, Mahanadi)
Rectangular	Right-angle bends in streams	Jointed/faulted rock with intersecting fractures	Streams in the Vindhyan region
Centripetal	Streams flow toward a central depression	Crater, caldera, or enclosed basin	Streams flowing into Loktak Lake (Manipur)
Annular	Ring-like pattern	Dome with alternating bands of hard and soft rock	Some tributaries around Pithoragarh (Uttarakhand)
Parallel	Streams flow nearly parallel to each other	Steep uniform slopes	Rivers of the Western Ghats flowing westward into the Arabian Sea
Deranged	Irregular, no clear pattern	Glaciated regions with disrupted drainage	Parts of Canadian Shield
Barbed	Tributaries flow in opposite direction to the main stream	River capture (piracy)	Some tributaries in the Himalayas

India’s Drainage Systems — Two Major Divisions

Feature	Himalayan Rivers	Peninsular Rivers
Origin	Glaciers in the Himalayas	Western Ghats, Central Highlands
Nature	Perennial (snow-fed + rain-fed)	Mostly seasonal (rain-fed)
Age	Young, still cutting their valleys	Old, reached maturity
Valleys	Deep, V-shaped gorges	Broad, shallow valleys
Meanders	Large meanders in plains	Smaller meanders
Deltas	Large deltas (Ganga, Brahmaputra)	Both deltas and estuaries
Drainage pattern	Mostly antecedent (older than the mountains)	Mostly consequent
Examples	Ganga, Yamuna, Brahmaputra	Godavari, Krishna, Kaveri, Narmada

Major Drainage Basins of India

India has 25 major river basins as classified by the Central Water Commission.

Largest River Basins by Area

Rank	River Basin	Area (sq km approx.)	Drains Into
1	Ganga	8,61,452	Bay of Bengal
2	Indus (in India)	3,21,289	Arabian Sea
3	Godavari	3,12,812	Bay of Bengal
4	Krishna	2,58,948	Bay of Bengal
5	Brahmaputra	1,94,413	Bay of Bengal
6	Mahanadi	1,41,589	Bay of Bengal
7	Narmada	98,796	Arabian Sea
8	Kaveri	81,155	Bay of Bengal
9	Tapi	65,145	Arabian Sea
10	Pennar	55,213	Bay of Bengal

Bay of Bengal vs Arabian Sea Drainage

Feature	Bay of Bengal	Arabian Sea
Percentage of total area	About 77% of India’s drainage	About 23%
Major rivers	Ganga, Brahmaputra, Godavari, Krishna, Kaveri, Mahanadi	Indus, Narmada, Tapi, Sabarmati, Mahi, Luni
Delta formation	Most rivers form deltas	Narmada and Tapi form estuaries (rift valley rivers)
Western Ghats role	Rivers originate from Western Ghats, flow east	Short, swift streams flow west

Water Divides of India

Water Divide	Separates
Western Ghats	Bay of Bengal rivers (east-flowing) from Arabian Sea rivers (west-flowing)
Ambala (Haryana)	Indus system from Ganga system
Aravalli Range	Indus system (Luni, western rivers) from Ganga system
Vindhya-Satpura	Northern rivers from southern Peninsular rivers
Maikala Range	Narmada basin from Son and Mahanadi basins

River Capture (Stream Piracy)

Concept	Explanation
Definition	When a more actively eroding stream captures the headwaters of another stream
Mechanism	Headward erosion of one river breaches the divide and diverts flow
Indian example	Some Himalayan rivers (like Brahmaputra tributaries) show evidence of river capture
Effect on pattern	Creates barbed drainage patterns

Watershed Management

Aspect	Details
Definition	Scientific management of land, water, and vegetation in a watershed for sustainable use
Objectives	Soil conservation, water harvesting, reducing runoff, preventing erosion
Key programs in India	Watershed Development Programme (WDP), Integrated Watershed Management Programme (IWMP), merged into Pradhan Mantri Krishi Sinchayee Yojana (PMKSY)
Techniques	Contour bunding, terracing, check dams, percolation tanks, afforestation
Niti Aayog	Watershed management is key to achieving water security in rainfed areas

Drainage Patterns of Specific Indian Regions

Region	Drainage Pattern	Reason
Indo-Gangetic Plain	Dendritic	Uniform alluvial deposits, gentle slope
Amarkantak Plateau	Radial	Dome-shaped uplift; Narmada, Son, Johilla originate here
Western Ghats (west-flowing)	Parallel	Steep western slope, short distance to sea
Shillong Plateau	Radial	Dome-shaped plateau
Deccan Plateau (eastern slope)	Dendritic to sub-dendritic	Relatively uniform basaltic rock

PSC Quick Recall

Question	Answer
Tree-branch drainage pattern	Dendritic
Rivers flowing outward from a central peak	Radial pattern
Largest river basin in India	Ganga basin
Narmada and Tapi form __ not deltas	Estuaries
Western Ghats act as a	Water divide between Bay of Bengal and Arabian Sea rivers
Percentage of India draining into Bay of Bengal	About 77%
Streams joining main river at right angles	Trellis pattern
Amarkantak shows which drainage pattern?	Radial
What is a watershed?	Boundary line between two drainage basins
Peninsular rivers are mostly	Seasonal (rain-fed)