The geographical extent of the Gandak and others sub-basin lies between 83° 41' to 87° 44' east longitudes and 24° 0' to 27° 23' north latitudes of the country. The main river the Gandak and the Punpun, the Baya, the Mohana, the Dhadhar, the Sakri, the Harohar, the Kiul, the Badua, the Painiar, the Phalgu, the Dardhu, the Dardha, the Morhar form some of the major river flowing in this sub-basin. The Gandak and others sub-basin of Ganga basin has a total catchment area of 56260 Sq.km. It drains into the states of Bihar, Jharkhand and parts of Uttar Pradesh. The sub basin map is shown below: