UPSC Prelims 2024 Q6: Ganga Left-Bank Tributaries West to East

With reference to the Himalayan rivers joining the Ganga downstream of Prayagraj from West to East, which one of the following sequences is correct?

  1. Ghaghara – Gomati – Gandak – Kosi
  2. Gomati – Ghaghara – Gandak – Kosi
  3. Ghaghara – Gomati – Kosi – Gandak
  4. Gomati – Ghaghara – Kosi – Gandak

Answer: (b) Gomati – Ghaghara – Gandak – Kosi

Statement-wise explanation

  • a: incorrect — This sequence puts the Ghaghara west of the Gomati. The Gomati is the first of the four to meet the Ganga below Prayagraj, at Kaithi in Ghazipur district of Uttar Pradesh, downstream of Varanasi. The Ghaghara meets the Ganga much further east, near Chhapra in Bihar. The first two rivers are therefore swapped.
  • b: correct — The four confluences, from west to east, are: Gomati at Kaithi (Ghazipur, UP); Ghaghara near Chhapra (Saran, Bihar); Gandak at Sonepur, opposite Patna; and Kosi near Kursela (Katihar, Bihar). That is Gomati, then Ghaghara, then Gandak, then Kosi. This is the official answer.
  • c: incorrect — This sequence gets both pairs wrong. The Gomati joins west of the Ghaghara, not east of it. The Kosi is the easternmost of the four: it joins near Kursela, well east of the Gandak's confluence at Sonepur near Patna.
  • d: incorrect — The first two rivers are in the right order, but the last two are swapped. The Gandak meets the Ganga at Sonepur, opposite Patna, in central Bihar. The Kosi meets it near Kursela in Katihar district, close to the eastern end of Bihar. So the Kosi must come last.

How to eliminate

The options are two choices put together: is it Ghaghara–Gomati or Gomati–Ghaghara at the western end, and is it Gandak–Kosi or Kosi–Gandak at the eastern end? Settle each half on its own.

Eastern half: the Kosi is famous as the 'Sorrow of Bihar'. It drains eastern Nepal (the Everest–Kanchenjunga region) and joins the Ganga in north-east Bihar near Kursela. The Gandak comes out of central Nepal and joins at Patna. So the Kosi comes last. This removes the two options that end '…Kosi – Gandak'.

Western half: the Gomati flows past Lucknow and Jaunpur and joins the Ganga just below Varanasi, still inside Uttar Pradesh. The Ghaghara flows past Ayodhya (as the Saryu) and joins the Ganga in Bihar, near Chhapra. So the Gomati comes first.

Fact to remember: going downstream from Prayagraj, the left-bank joins are Gomati (Ghazipur, UP), Ghaghara (Chhapra), Gandak (Patna/Sonepur), Kosi (Kursela). Two traps to note. First, the Gomati actually rises in the plains near Pilibhit, not in the Himalayas, though the question calls it Himalayan. Second, a river's source being further west does not decide where it joins. The Ghaghara rises far west of the Gomati's source, yet it meets the Ganga further east.

Know more

Left-bank (Himalayan side) tributaries of the Ganga

After Prayagraj, where the Yamuna joins from the right, the Ganga turns east across the plain. A series of large left-bank rivers flowing down from the north join it one after another. Most of them rise in the Himalayas of Uttarakhand, Nepal or Tibet. Their joining points, from west to east:

River Rises in Joins the Ganga near State
Ramganga Garhwal Himalaya Kannauj (above Prayagraj) UP
Gomati Plains near Pilibhit (groundwater-fed) Kaithi, Ghazipur UP
Ghaghara (Karnali/Saryu) Tibet, Mapchachungo glacier Chhapra Bihar
Gandak (Kali Gandaki/Narayani) Nepal Himalaya Sonepur, opposite Patna Bihar
Burhi Gandak Plains of north Bihar Near Khagaria/Munger Bihar
Kosi (Sapt Kosi/Arun) North of Mt Everest, Tibet Kursela, Katihar Bihar
Mahananda Darjeeling hills Last left-bank tributary, near the Bengal border WB

Points to fix

  • The Ghaghara is a large Ganga tributary by discharge. It takes in the Sarda (Kali), which forms part of the India–Nepal border.
  • The Kosi is an antecedent river that changes course often. It shifts westward and floods often, which is why it is called the 'Sorrow of Bihar'.
  • The Son is a right-bank, Peninsular river. It joins near Patna, so do not mix it into a left-bank sequence.
  • The Gomati is plains-fed. It is often counted with the 'Himalayan' group because it lies on the northern (left) side.

Exam habit: For any 'west to east' or 'north to south' order question, place each river's confluence on a mental map using a nearby city (Varanasi, Chhapra, Patna, Katihar). Do not go by its source.

NCERT Concepts to Revise

  • Kosi river: The Kosi is one of the four rivers to order; knowing where it drains from helps place its confluence.
  • Himalayan drainage system: The question is framed around Himalayan rivers, so it helps to know which rivers count as Himalayan drainage.
  • Ganga river: The whole sequence is set along the Ganga's course downstream of Prayagraj, so the main river's path is the reference line.

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