The riverine flood plain of the reserve comprises hill wash and alluvial deposits. More than 33 percent of the reserve is covered by Sal (Shorea robusta) and other mixed forest. There are extensive grassland called phanta in Nepal. The biggest grassland is called Sukla Phanta. Several other extensive grasslands are separated by the patches of the forest. A small lake called Rani Tal (Lake) lies on the eastern side of the reserve and it is the most fascinating area for the water birds and migratory birds.
There are also several water-logged area known as the dhap or swampy ground covered by reed and tall grasses.