The Karmanasa River is a tributary of the Ganges. It originates in Kaimur district of Bihar and flows through the Indian states of Uttar Pradesh and Bihar. Along the boundary between Uttar Pradesh and Bihar it has the districts of Sonbhadra, Chandauli, Varanasi and Ghazipur on its left (Uttar Pradesh side); and the districts of Kaimur and Buxar on its right (Bihar side).
The Karmanasa originates at a height of 350 metres (1,150 ft) on the northern face of Kaimur Range near Sarodag in Kaimur district of Bihar. It flows in a north-westerly direction through the plains of Mirzapur, then forms the boundary between Uttar Pradesh and Bihar, and finally joins the Ganges near Chausa. The length of the river is 192 kilometres (119 mi), out of which 116 kilometres (72 mi) lies in Uttar Pradesh and the rest 76 kilometres (47 mi) forms the boundary between Uttar Pradesh and Bihar. Total drainage area of the Karmnasa along with its tributaries is 11,709 square kilometres (4,521 sq mi).
Its tributaries are the Durgavati, the Chandraprabha, the Karunuti, the Nadi and the Khajuri.
The Karmanasa reaches the plains by a succession of leaps, including two falls known as the Devdari and the Chhanpathar, which, from their height and beauty, are deserving of special notice. Chhanpathar Falls is 100 feet (30 m) high. Devdari Falls, at an edge of the Rohtas Plateau, along the course of the Karmanasa is 58 metres (190 ft) high. However, Chandauli district administration mentions Devdari Fall as being on the Chandraprabha River.
There are two dams across the Karmanasa – the Latif Shah bund and the Nuagarh dam. There also is a dam across the Chandraprabha.
(Source : http://www.revolvy.com/main/index.php?s=Karmanasa%20River accessed on 10.06.2016)