<p>In the Nepalese and Indian Terai Arc Landscape (TAL), protected nature areas are supported by groundwater systems that have remained largely understudied. This study schematizes the lithology of the Karnali fluvial fan located in the Bardia district (Nepal) as a basis for future hydrogeological investigations. Inversion results of 2D electrical resistivity tomography (ERT) profiles at 21 locations were interpreted by comparing with the local borehole lithology and regional geophysical studies. Multiple lithological cross-sections were prepared to develop a 3D lithological model spanning the fan, and the adjacent Bardia National Park up to the Babai River in the east. Sediment resistivities found were in the range of 8–6000 Ω m. Resistivity less than 40 Ω m was identified as clay, 40–80 Ω m represented silt and fine sand, 80–400 Ω m identified as fine to coarse sand and resistivities higher than 400 Ω m were interpreted as coarse sand, gravel and boulders. A coarse sand-gravelly layer is present at the fan apex and along the foot of the Himalayas in the north that functions as a recharge area and aquifer. The central part of the fan has sandy layers which transition to fine sand and silt layers in the distal south and southeast. Clay layers locally create confining conditions, within the sand and silt dominated areas. These findings on subsurface lithology provide valuable insights for the groundwater systems which sustain ecohydrological processes relevant to the protected ecosystem and fills a critical knowledge gap on regional hydrogeology of the TAL.</p>