RAS question
The Ghaghara (Ghagra/Karnali) River is the largest tributary of the Ganges by:
Correct answer: (B) Volume of water.
The Ghaghara, also known upstream as the Karnali, is the largest tributary of the Ganges by volume of water.
Explanation
Discharge, not length or basin spread, determines the Ghaghara's rank in this comparison. The Oryx article, published by Cambridge University Press, identifies the Ghaghara as the largest tributary of the Ganga and notes that it contributes about 21% of the river's total volume. The river rises as the Karnali in the Tibet-Nepal region, enters India in Uttar Pradesh, and meets the Ganges near Chhapra in Bihar. Its major tributaries include the Sarda or Mahakali, Rapti and Little Gandak. The key contrast is with the Yamuna: Yamuna is the longest tributary by length, while Ghaghara is the largest by volume of water.
Why the other options are wrong
- (A) Number of sub-tributaries is not the standard basis for ranking Ghaghara's primacy; volume of water is the relevant basis.
- (C) Length points to a different comparison, because the Yamuna is the longest tributary of the Ganges by length.
- (D) Basin area is a separate geographical measure, while Ghaghara is called the largest tributary of the Ganges on the basis of volume of water.
Concept
River length, discharge and basin area are distinct measures in the Ganga drainage system. Tributary rankings often change when the basis of comparison changes.