The Son (length 780 km, basin: 54,000 sq km)

This is a large south bank tributary of the Ganga River. It originates from the Amarkantak Plateau not far from the source of Narmada. It leaves the plateau in a series of waterfalls and meets the Kaimur Range which turns its course towards the north-east and allows it to follow a strike valley. Below Garwa, it enters the Ganga Plain, where it widens upto about 5 kilometres, and finally flows into the Ganga at Bankipora near Aara to the west of Patna. During the rainy season, the river often flows in spate with an annual peak discharge of about 750,000 cusecs in the rainy season, while in the dry season it has little water.