Drainage System — Class 11 Geography

Drainage is the flow of water through well-defined channels, and the network of such channels is a drainage system. An area drained by a river and its tributaries is a drainage basin, separated from another by a watershed. Indian drainage is grouped by orientation into Bay of Bengal drainage (about 77 per cent, including the Ganga, Brahmaputra, Mahanadi and Krishna) and Arabian Sea drainage (about 23 per cent, including the Indus, Narmada, Tapi and Mahi), separated by the Delhi ridge, the Aravalis and the Sahyadris. By origin, Indian drainage is classified into the Himalayan drainage and the Peninsular drainage. Himalayan rivers are perennial, fed by snow-melt and rainfall, forming gorges, V-shaped valleys, meanders, ox-bow lakes and deltas; the three major systems are the Indus (with the Jhelum, Chenab, Ravi, Beas and Satluj), the Ganga (with the Yamuna, Ghaghara, Gandak, Kosi and Son) and the Brahmaputra (the Tsangpo in Tibet, well-known for floods and channel shifting). The older Peninsular drainage has broad, graded, mature valleys with fixed courses and largely non-perennial flow; the major east-flowing rivers (Mahanadi, Godavari, Krishna, Kaveri) drain to the Bay of Bengal, while the Narmada and Tapi flow westward through rift valleys to the Arabian Sea. The Godavari is the largest Peninsular river. (Refer to the map in the NCERT textbook.)