The landscape of VTR encompasses foothill ranges of Himalayan Siwaliks with mosaic of the cliffs, ridges, gorges, hills, streams and valleys; dense forests, open woodlands, grasslands, swamps and riverine fringes. Situated in Gangetic plains bio-geographic zone of the Country, the forest has combination of bhabhar and terai tracts. Boulder and pebble deposits by the Himalayan rivers in foothills characterize the bhabhar tract while the finer sediments deposits feature terai lands.
Criss-crossing and meandering rivers, streams and rivulets, canals; swamps and grasslands features on these lands. River Gandak forms the western boundary of Valmiki wildlife sanctaury. It enters India at Valmikinagar, where two rivulets Sonha and Pachnad join it forming a holy confluence 'Triveni'. The river is called 'Narayani' in Nepal. Harha - Masan River system originates from the Valmiki Forests and forms Burhi Gandak River down south. River Pandai flows into Bihar (India) from Nepal in the eastern end of the Sanctuary and meets Masan. All these rivers with their precursor and tributaries namely Rohua, Kotrahia, Manor, Bhapsa, Koshil, Singha, Dhonghi, Ganguli, Dohram are full of youth and verve. Their cascades in wanton, and wayward playfulness while descending from hills, ridges and gorges are enchanting. Meeting the planes they slowly mature to serene grandeur.