Drainage System
This chapter anchors all Prelims questions on river basins, drainage patterns, left/right bank tributaries, and the hydrographic divide of India.
Concept of Drainage and Drainage Patterns
UPSC frequently tests the precise classification of drainage patterns like dendritic (Plains of India), radial (Amarkantak, Girnar), trellis (older folded mountains), and centripetal (Loktak Lake). Focus on the distinct structural controls of these patterns. Skip overly generic introductory sentences on water flow, but pay extreme attention to the terms: catchment area, drainage basin, and watershed. The key trap is confusing a watershed (smaller area, micro-level) with a river basin (macro-level, large rivers like Ganga/Indus).
The Himalayan Drainage System
This is a super high-yield section. You must memorize the exact origins, left/right bank tributaries, and geographic features of the Indus, Ganga, and Brahmaputra systems. For Indus, memorize the North-to-South sequence of its five main tributaries (Jhelum, Chenab, Ravi, Beas, Sutlej) and minor Himalayan tributaries like Shyok, Gilgit, and Hunza. For Ganga, identify the confluence points of Alaknanda (Devprayag, Rudraprayag, Karanprayag) and the source glaciers of tributaries like Yamuna (Yamunotri), Ghaghara (Mapchachungo), Gandak, and Kosi. For Brahmaputra, track its name changes (Tsangpo, Dihang, Jamuna) and key tributaries (Lohit, Dibang, Subansiri, Manas, Teesta).
The Peninsular Drainage System
UPSC tests the major east-flowing (Mahanadi, Godavari, Krishna, Kaveri) and west-flowing (Narmada, Tapi, Mahi, Sabarmati) rivers. Learn the precise origins: Mahabaleshwar (Krishna), Talakaveri (Kaveri), Trimbakeshwar (Godavari), and Amarkantak (Narmada). Note the minor west-flowing rivers of Gujarat, Maharashtra, Karnataka, and Kerala (e.g., Vaitarna, Kalinadi, Bedti, Sharavati, Bharatapuzha, Periyar, Pamba) and east-flowing ones (Subarnarekha, Baitarani, Brahmani, Pennar, Palar, Vaigai). The classic trap is confusing the tributaries of Krishna (e.g., Bhima, Tungabhadra) with those of Kaveri (e.g., Kabini, Bhavani, Noyyal, Amaravati) or Godavari (e.g., Penganga, Indravati, Pranhita).
Comparison of Himalayan and Peninsular Rivers & River Regimes
Focus on the evolutionary history and structural differences. Understand the Indo-Brahma (or Siwalik) river hypothesis and how the Potwar plateau uplift disrupted it during the Miocene-Pleistocene era. Contrast the youthful nature of Himalayan rivers (gorges, V-shaped valleys, rapid headward erosion) with the graded, mature, and stable course of Peninsular rivers. River regimes (seasonal variations in discharge) of Himalayan rivers are perennial (fed by both glaciers and rain) compared to the strictly seasonal, rain-fed regimes of Peninsular rivers, except Kaveri which gets water from both Southwest and Northeast monsoons.