Data-driven Groundwater Assessment in a Human–Wildlife shared Landscape of Nepal’s Terai

The Terai Arc Landscape of Nepal is increasingly affected by land use modification, water diversion upstream, settlement expansion and changes in seasonal rainfall.  These anthropogenic activities and climatic changes impact surface water availability and increases pressure on groundwater resources for supporting human consumption and ecological requirements. This study aims to quantify spatio-temporal changes in groundwater in and around a protected nature area of western Nepal, where wildlife such as tigers, leopards and rhinos and human beings share water resources. The study area encompasses part of the Bardia National Park, located south of the Siwalik hills and partly underlain by the Karnali fluvial fan. Three ephemeral rivers, the Kauriala, Gerua and Babai transcends north to south in the area. Lack of groundwater data and insufficient information on aquifer characteristics are some of the challenges which hinders sustainable groundwater management. A network on 18 groundwater monitoring wells were dug and installed with 18 pressure sensors and 2 barometers, within the framework of "Save the Tiger" project. Statistical methods and time series analysis were used to quantify groundwater heads changes in response to monsoon rainfall and river stage fluctuation, as a function of distance from the rivers. The monitored data established the hydraulic gradient from northeast to southwest, with average annual groundwater heads ranging between 187 – 143 m above sea level. An annual cycle with declining heads in the hot and dry pre-monsoon, a sharp rise in monsoon followed by gradual decline through winter was observed. Wells closer to the Gerua river along the western border of the National Park had rising heads at start of monsoon, reflecting strong hydraulic connectivity. While wells located further away showed slightly delayed rise of head indicating groundwater abstraction effects on recharge. In the agricultural areas of the Karnali fan between Kauriala and Gerua rivers, south of the National Park, a plateau effect was observed between monsoon rise and winter decline. This suggested a temporary buffering effect due to monsoon recharge against pumping. These insights improve understanding of recharge-discharge dynamics in the ecologically sensitive region. Further work includes developing a groundwater flow model for supporting groundwater management in the area.