The Punpun river is an important river bank tributary of the Ganga river in lower reaches. It originates from the Chottanagpur hills of Palamau district at an elevation of 300 m in Bihar and lies between east longitudes of 84°10' to 85°20' east and north latitudes of 24°11' to 25°25'. The river mostly flows in a northeast direction and finally joins the Ganga river at Fatawh, about 25 km downstream of Patna. The river is 200 km long and is mostly rainfed and carries little discharge during non-monsoon period. It meets a number of tributaries namely the Butane, the Madar and the Morhar while flowing through the Chottanagpur plateau. The Punpun often causes heavy flood damages on the eastern side of Patna city.
The shape of the Punpun basin is roughly trapezoidal. The catchment area of the Punpun catchment is about 8,530 sq. km. which is about 1% of the total area of the Ganga basin in the country. The agriculture area under the Punpun basin is about 5,000 sq. km. The average annual rainfall for the basin is 1,181 mm. The total gross recharge in the Punpun river system is 1.6 lakh ha-m. However, only 75% of the gross recharge can be utilised.