river in south-central Nepal and northern Bihar state, northeastern India. It rises in several headstreams in the lowland area of Nepal and flows southward through the Siwalik (Shiwalik) Range (Siwalik Range), the southernmost range of the Himalayas. It continues across the plains of Tarai into Bihar and then flows southeastward to enter the Burhi (“Old”) Gandak River after a course of 225 miles (360 km).