Ghaghara River, major left-bank tributary of the Ganges River. It rises as the Karnali River (Chinese: Kongque He) in the high Himalayas of southern Tibet Autonomous Region, China, and flows southeast through Nepal. Cutting southward across the Siwalik Range, it splits into two branches that rejoin south of the Indian border and form the Ghaghara proper. It flows southeast through Uttar Pradesh and Bihar states to enter the Ganges below Chapra after a 600-mile (970-km) course.
The major tributaries—the Kuwana, the Rapti, and the Little Gandak rivers—all flow into the Ghaghara from the mountains to the north. Together with the Ganges and its tributaries, it has helped form the vast alluvial plain of northern Uttar Pradesh. Along its lower course it is also called the Sarju River (the Sarabos of the 2nd-century-ce Greek geographer Ptolemy) and the Deoha.
The river’s hydrology is influenced by the South Asian monsoon and glacial melt in its source region in the Himalayas. Heavy rains occur during the summer monsoon (June to September), and the glaciers provide their greatest amount of water to the river during the same period. Vegetation varies from low-lying alpine plants at high elevations to tropical forest where the river crosses the Siwalik Range.