The Burhi Gandak River is a tributary of the Ganges. It is also known as the Sikrahna river.^[2] The Burhi (“Old”) Gandak flows parallel to and east of the Gandak River in an old channel.^[3][4]

The Burhi Gandak originates from Chautarwa Chaur near Bisambharpur in the district of West Champaran in Bihar.^[1] It initially flows through the East Champaran district. After flowing for a distance of about 56 kilometres (35 mi), the river takes a southerly turn where two rivers - the Dubhara and the Tour – join it. Thereafter, the river flows in a south-easterly direction through the Muzaffarpur district for about 32 kilometres (20 mi). In this portion, the river spills over its banks and a number of spill channels take off and rejoin it later.^[3]

The Burhi Gandak runs a zig-zag course through the districts of Samastipur and Begusarai before covering a short distance in Khagaria district, running by the side of the town of Khagaria, and flows into the Ganges near Gogri and near Bairarpur in Munger . It forms the western boundary of the Khagaria town and a protection embankment built along the eastern side of this river, protects Khagaria town from the floods of Burhi Gandak.^[5][6][7]

The total length of the river is 320 kilometres (200 mi). The drainage area of the river is 10,150 square kilometres (3,920 sq mi).^[3]