The river Ganges is a part of the composite Ganges-Brahmaputra-Meghna basin draining 1,086,005 square kilometres in Tibet, Nepal, India the Ganges-Brahmaputra divide. On the west the Ganges Basin borders the Indus basin and then the Aravalli ridge. Southern limits are the Vindhyas and Chota Nagpur Plateau. On the east the Ganges merges with the Brahmaputra through a complex system of common distributaries into the Bay of Bengal. Its catchment lies in the states of Uttar Pradesh (294,364 km²), Madhya Pradesh (198,966 km²), Bihar (143,961 km²), Rajasthan (112,490 km²), West Bengal (71,485 km²), Haryana (34,341 km²), Himachal Pradesh (4,317 km²) and Delhi (1,484 km²), the whole of Bangladesh, Nepal and Bhutan. Several tributaries rise inside Tibet before flowing south through Nepal. The basin has a population of more than 500 million, making it the most populated river basin in the world.
The basin comprises semi-arid valleys in the rain shadow north of the Himalaya, densely forested mountains south of the highest ranges, the scrubby Shiwalik foothills and the fertile Gangetic Plains. Central highlands south of the Gangetic Plain have plateaus, hills and mountains intersected by valleys and river plains. The important soil types found in the basin are sand, loam, clay and their combinations such as sandy loam, silty clay etc.
The annual surface water potential of the basin has been assessed as 525 km³ in India, out of which 250 km³ is utilisable water. There is about 580,000 km² of arable land; 29.5% of the cultivable area of India.
Water-related issues of the basin are due to both high and low flows. In India, the states of Uttar Pradesh, Bihar and West Bengal are affected by floods. Bangladesh -- at the confluence of Brahmaputra River and Ganges River -- suffers from severe floods almost every year. Northern Ganges tributaries such as Kosi, Gandak and Mahananda are the most flood-prone, but southern tributaries also contribute. Low flows are caused by scarcity of rainfall outside the summer Monsoon, and sometimes by failure of this monsoon to develop to its normal extent.
The basin is a high earthquake risk area and experts warn that as many as a million deaths could be expected on the Ganges plain, as the southern flank of the Himalayas has not been active enough over past centuries to release the energy accumulated by the millimetre per week upward movement of the Indian plate.
- Bibliography on Water Resources and International Law. Peace Palace Library
- S Asia's deadly Himalayan fault