The Gandak river is a tributary of which river?

Correct — C. The Gandak is a left-bank tributary of the Ganga. It rises in the Nepal Himalaya, is called the Narayani in Nepal, and meets the Ganga in Bihar at Hajipur, opposite Patna.

That puts it in the Ganga's northern, Himalaya-fed group alongside the Ghaghara and the Kosi — rivers that come down through Nepal and join the main stream from the left.

Option (c) is the river the Gandak feeds.

Why the others are wrong

• (a)
  Brahmaputra river — The Brahmaputra drains the north-east and takes the Subansiri and the Manas. The Gandak flows through Bihar, far outside that basin, and none of its water reaches it.
• (b)
  Yamuna river — The Yamuna is itself a tributary of the Ganga and runs well to the west, joining at Prayagraj. The Gandak enters the Ganga much further downstream, in Bihar.
• (d)
  Kaveri river — The Kaveri is a peninsular river of Karnataka and Tamil Nadu draining east to the Bay of Bengal. No Himalayan river feeds it.

The Ganga's tributaries fall into two families that behave differently, and knowing which family a river belongs to answers most questions about it.

The left-bank Himalayan rivers — Ghaghara, Gandak, Kosi — are snow- and monsoon-fed, carry heavy silt down from Nepal and spread over the north Bihar plain.

The right-bank peninsular rivers, the Son chief among them, rise on old plateau rock and are far more seasonal.

The Gandak belongs to the first family, which is why it turns up in flood and drainage questions alike.

Key facts

• The Gandak joins the Ganga at Hajipur in Bihar, opposite Patna.
• The Gandak is known as the Narayani in Nepal.
• The Ghaghara, Gandak and Kosi are left-bank tributaries of the Ganga that rise in Nepal.
• The Yamuna is the longest tributary of the Ganga and joins it at Prayagraj.

Common traps

• Picking the Brahmaputra because the Gandak is also Himalayan in origin — the source is Himalayan, the destination is the Ganga.
• Treating the Yamuna as a separate river system when it is itself a Ganga tributary.

No directly related past PYQ was found.