India — Drainage system (Himalayan & Peninsular rivers)

India's drainage is best read as a map of relief, slope, monsoon rain, rock structure and human use, not as a list of rivers.

• Drainage system: the network of a main river, its tributaries, distributaries, wetlands, floodplains and mouth through which surface water leaves a region.
• Drainage basin: the land area drained by one river system; the Ganga basin is India's largest river basin in terms of area within the country.
• Watershed or water divide: the ridge or upland separating two basins; the Western Ghats separate short west-flowing coastal streams from long east-flowing Peninsular rivers.
• Tributary versus distributary: a tributary joins a main river upstream; a distributary leaves the main channel near a delta, as in the lower Ganga-Brahmaputra system.
• Drainage pattern: dendritic develops over relatively uniform rock, trellis follows alternate hard-soft rocks, radial flows outward from a dome or highland, and centripetal drains into an inland depression.
• Antecedent drainage: a river keeps its older course while mountains rise around it; Indus, Satluj and Brahmaputra are standard Himalayan examples.
• Superimposed drainage: a river inherits a course from an older cover and cuts through underlying structure; the Chambal-Banas sector is often used to explain such structural mismatch.
• Perennial versus seasonal: Himalayan rivers are fed by snow, glacier melt and rainfall, whereas many Peninsular rivers depend more directly on monsoon rainfall and stored base flow.
• UPSC trap: a river's present political basin is not the same as its geological age, source region, mouth type or water-dispute jurisdiction.
• Map discipline: locate source, direction, first major bend, major tributaries, dam/barrage, basin state and mouth before memorising length figures.