Which one of the following river basins is the largest in respect to area ?

Question

UnlockIAS · Accepted Answer

Correct — D, Mahanadi. Of the four rivers offered, the Mahanadi drains by far the largest basin, and the order of the four is Mahanadi, then Narmada, then Cauvery, then Tapti. One honest caution about the number itself: standard sources do not agree on the Mahanadi basin's exact area. It is given as about 1,32,100 square kilometres in one widely used figure and as about 1,41,589 square kilometres in the Central Water Commission and India-WRIS series, which count the whole basin including its minor coastal drainage. Nothing in this question turns on the discrepancy, because the Mahanadi comes first under either figure — the Narmada, its nearest rival here, is about 98,796 square kilometres, well below both. The Mahanadi rises near Sihawa in Dhamtari district, Chhattisgarh, and flows east across Chhattisgarh and Odisha to the Bay of Bengal, spreading over the broad saucer-shaped Chhattisgarh plain that gives it its width.

Why the other options are wrong — (a) Second of the four, with a basin of about 98,796 square kilometres shared between Madhya Pradesh (roughly 82 per cent), Gujarat, Maharashtra and Chhattisgarh. It is the tempting answer because the Narmada is the LONGER river — about 1,312 km from Amarkantak to the Gulf of Khambhat, against the Mahanadi's roughly 850 to 900 km — but length and basin area are different things. The Narmada runs west in a narrow rift valley penned between the Vindhya and Satpura ranges, so it gathers few large tributaries and its basin stays long and thin.  (b) Third of the four, with a basin usually given as roughly 81,155 square kilometres — an approximate standard figure — spread across Karnataka, Tamil Nadu, Kerala and Puducherry. Large and economically vital, but well short of the Mahanadi's.  (c) The smallest of the four, with a basin usually given as roughly 65,145 square kilometres. Like the Narmada it is a west-flowing river confined to a rift valley, which is exactly why the two westward rivers on this list have narrower basins than the eastward Mahanadi despite their length.

Concept: A river basin is the whole area of land whose runoff drains into a single river system, so its size is set by how widely the river's tributaries spread, not by how far the main channel runs. That distinction explains this question. The Mahanadi and the Cauvery flow east across the open peninsular slope and fan out into wide tributary networks; the Narmada and the Tapti flow west through structural troughs — rift valleys between the Vindhya, Satpura and Ajanta ranges — which physically confine them and leave them long, straight rivers with narrow catchments. It also explains the coastal difference examiners often pair with this: the east-flowing peninsular rivers build large deltas, while the Narmada and Tapti empty into estuaries.

State PCS 2022 Q79 — Geography PYQ with Answer

State PCS 2022 Q79 — Geography PYQ with Answer