The two great river systems of India, classified by source and behaviour: the snow-fed, perennial Himalayan rivers and the rain-fed, mostly seasonal Peninsular rivers.
- Himalayan rivers (Indus, Ganga, Brahmaputra systems) are perennial, fed by both monsoon rain and Himalayan snow and glaciers, so they flow all year.
- They are antecedent in parts (older than the mountains, cutting deep gorges as the Himalayas rose), have large catchments, and carry heavy silt, building wide flood plains and deltas.
- Himalayan rivers are youthful in the mountains (V-shaped valleys, gorges, rapids) and mature in the plains (meanders, ox-bow lakes, braided channels).
- Peninsular rivers (Godavari, Krishna, Kaveri, Mahanadi, Narmada, Tapi) are mostly rain-fed, hence seasonal, with smaller catchments and fixed, mature courses with little erosional power.
- Most Peninsular rivers drain east into the Bay of Bengal and form deltas; the Narmada and Tapi are exceptions that flow west through rift valleys into the Arabian Sea and form estuaries, not deltas.
The perennial-versus-seasonal contrast, the antecedent drainage of the Himalayan rivers, and the west-flowing Narmada-Tapi exception are recurring drainage facts and assertion-reason items.
Himalayan rivers are perennial (snow plus rain) and youthful in the hills; Peninsular rivers are seasonal (rain only) and have reached old age. Narmada and Tapi flow west in rifts and form estuaries, not deltas.
Himalayan rivers: snow-fed, perennial, antecedent, deltas; Peninsular rivers: rain-fed, seasonal, mature, mostly east-flowing (Narmada-Tapi the west-flowing exceptions).