Indian Physical Geography : Drainage Systems

Q 1 / 49

UPSC CSE Prelims 2026

Consider the following assertion:
In the Pleistocene period either the Yamuna once flowed into the Indus, or the Sutlej flowed into the Yamuna and one major tributary of either had shifted from the Ganga to the Indus or vice versa.
Which of the following is/are the basis of the above assertion?
  1. The Nadi-Sukta of the Rigveda
  2. The explorations of the Sutlej and the Yamuna by Robert Bruce Foote
  3. The presence of the same species of dolphins in both the Indus and the Ganga river systems
Select the answer using the code given below:

EXPLANATION

Correct Option

The correct option is 3.

[as per provisional answerkey]

Explanation

The assertion concerns the paleochannels and hydrographic shifts between the Indus and Ganga river systems during the Pleistocene period. Geomorphological evidence suggests that the Indo-Gangetic divide is a relatively recent feature, and these two major river systems were once interconnected or shared common drainage basins.

3. Statement-wise Analysis

  • Statement 1 is Incorrect: The Nadi-Sukta hymn of the Rigveda provides a geographical listing of rivers known to the Vedic people, including the Ganga, Yamuna, Sarasvati, and the tributaries of the Indus. While it confirms the historical existence and sequence of these rivers, it does not provide scientific or geological evidence for the Pleistocene-era hydrographic shifts or the specific inter-basin migration of tributaries.
  • Statement 2 is Incorrect: Robert Bruce Foote is primarily known as the "Father of Indian Prehistory" for his discovery of Paleolithic stone tools (such as the Pallavaram hand-axe). His work focused on prehistoric archaeology and geology in Southern India and parts of Gujarat, rather than the specific fluvial geomorphology of the Sutlej-Yamuna divide in the context of this assertion.
  • Statement 3 is Correct: The presence of the same species of freshwater dolphins (Platanista gangetica) in both the Indus and the Ganga-Brahmaputra river systems is a significant biological indicator. Since these dolphins are strictly freshwater mammals and cannot survive in seawater, their presence in two distinct drainage basins suggests that the Indus and Ganga systems were once connected. This biological evidence supports the geological theory that a common drainage system existed or that a major tributary (like the Yamuna or Sutlej) shifted from one system to the other during the Pleistocene period.

Key Takeaway:

The distribution of closely related freshwater species, such as the Platanista dolphins, serves as biological evidence for past geological connections between now-isolated river basins like the Indus and the Ganga.

SOURCEUpsc Cse Prelims Gs Paper I 2026