UPSC Prelims 2026 Q25: Antecedent Himalayan Rivers — Explained

Identify the river of the Indian sub-continent on the basis of the following information:

1. It has an antecedent drainage system.

2. It flows through three countries.

3. It originates in the Tibetan Plateau and is an important river for irrigation.

4. It does not form distributaries.

  1. Brahmaputra
  2. Indus
  3. Sutlej
  4. Teesta

Answer: (c) Sutlej

Statement-wise explanation

  • 1: correct — The Sutlej is an antecedent river. It is older than the Himalaya, and it kept its course by cutting down through the ranges as they rose. It enters India through a deep gorge near Shipki La in Himachal Pradesh and comes out of the hills at Rupnagar (Ropar). The Indus and the Brahmaputra are also antecedent, so this clue rules out only the Teesta.
  • 2: correct — The Sutlej flows through China (Tibet), India and Pakistan. In Pakistan it joins the Chenab, and their combined stream, the Panjnad, flows into the Indus. The Indus (China, India, Pakistan) and the Brahmaputra (China, India, Bangladesh) also cross three countries. The Teesta crosses only two, India and Bangladesh.
  • 3: correct — The Sutlej rises at Rakas Tal (Langa Tso), close to Mansarovar in western Tibet. Under the 1960 Indus Waters Treaty it is one of the three Eastern Rivers given to India for unrestricted use, along with the Ravi and the Beas. It feeds the Bhakra-Nangal canals, and through Harike Barrage it feeds the Indira Gandhi Canal, which irrigates the Rajasthan desert. The Teesta fails this clue because it rises in Sikkim, inside India.
  • 4: correct — The Sutlej ends as a tributary. It merges into the Chenab and then the Indus, so it never builds a delta of its own, and distributaries form mainly on deltas. The Indus splits into distributaries in its delta in Sindh before reaching the Arabian Sea. The Brahmaputra (called the Jamuna in Bangladesh) joins the Ganga to form the Ganga-Brahmaputra delta, which is full of distributaries. This is the clue that separates the Sutlej from the Indus and the Brahmaputra.

How to eliminate

Work through the clues one by one, removing rivers as you go.

  • Clue 3 (origin in Tibet) removes the Teesta. It rises from glaciers in north Sikkim, inside India. It also crosses only two countries, so clue 2 removes it as well.
  • Clues 1–3 fit the Indus, the Brahmaputra and the Sutlej equally well. All three are antecedent, all three rise in Tibet and all three cross three countries. These clues cannot settle the answer.
  • Clue 4 settles it. Ask how each river ends. A river that reaches the sea through its own delta splits into distributaries. A river that ends by joining another river usually does not. The Indus has a delta in Sindh. The Brahmaputra shares the Ganga-Brahmaputra delta, the largest in the world. Only the Sutlej ends inside another river system, by joining the Chenab and then the Indus.
  • The Brahmaputra is also better known for floods and navigation than for irrigation, which makes it a weaker fit for clue 3.

Fact to remember: the Sutlej is an antecedent tributary of the Indus system that crosses China, India and Pakistan. Tributaries do not build deltas, so they do not form distributaries.

Know more

Antecedent rivers are older than the mountains they cross. As the Himalaya rose, rivers like the Indus, the Sutlej and the Brahmaputra kept cutting down through the rising rock, carving deep gorges. Examples are the Indus gorge near Nanga Parbat, the Sutlej gorge at Shipki La and the Brahmaputra (Dihang) gorge around Namcha Barwa. Consequent rivers follow the slope of the land as it already is. Most Peninsular rivers are consequent.

Distributaries branch away from a main channel and do not rejoin it. They form mainly where a river approaches the sea and deposits sediment, building a delta. A tributary that ends by joining a larger river, as the Sutlej joins the Chenab and the Panjnad joins the Indus, usually has no reason to split.

River Source Countries Antecedent How it ends
Indus Near Mansarovar, Tibet (Kailash range) China, India, Pakistan Yes Delta in Sindh, Arabian Sea
Sutlej Rakas Tal, Tibet China, India, Pakistan Yes Joins the Chenab, then the Indus via the Panjnad
Brahmaputra Chemayungdung glacier, Tibet China, India, Bangladesh Yes Joins the Ganga in the Ganga-Brahmaputra delta
Teesta Glaciers of north Sikkim India, Bangladesh No (rises south of the main range) Joins the Brahmaputra (Jamuna) in Bangladesh

Sutlej facts to remember:

  • It is called Langchen Khambab in Tibet.
  • It runs roughly parallel to the Indus for about 400 km before entering India.
  • Bhakra Dam (Gobind Sagar) and Nangal Dam stand on it.
  • At Harike it meets the Beas, and Harike Barrage feeds the Indira Gandhi Canal.
  • It is the easternmost of the five Punjab rivers.
  • Under the Indus Waters Treaty, 1960, it is one of the three Eastern Rivers (with the Ravi and the Beas) allocated to India.

In the news

The Indus river system was in the news before the 2026 Prelims. India has kept the Indus Waters Treaty in abeyance since April 2025, and in March 2026 the Sutlej was declared National Waterway-98 from Sunni to Harike. The question itself tests static drainage geography.

NCERT Concepts to Revise

  • Antecedent river: Clue 1 depends on what an antecedent river is: one older than the Himalaya that cut gorges through the ranges as they rose.
  • Satluj river: Every clue tests Satluj facts: its Rakas Tal source in Tibet, its course through three countries, its canal irrigation, and how it ends by joining the Chenab.
  • Indus river: The Indus also rises in Tibet, is antecedent and crosses three countries, so clue 4 about distributaries in its Sindh delta is what tells it apart.
  • Indus Waters Treaty: Clue 3 links to the 1960 treaty, which gives India the Eastern Rivers, including the Satluj, for unrestricted use such as irrigation.
  • Ropar: Ropar (Rupnagar) is where the Satluj leaves its Himalayan gorges for the plains, a landmark of the antecedent course in clue 1.

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