COUPLING PHYSICAL AND ISOTOPE HYDROLOGY TO ESTIMATE SEASONAL GROUNDWATER RECHARGE: CASE OF NERI RIVER WATERSHED, ETHIOPIA

This study employs the WetSpass-M (Water and Energy Transfer between Soil, Plants, and Atmosphere under Steady-State Conditions) method to estimate seasonal groundwater recharge coupling with δ¹⁸O (Oxygen-18) mass balance seasonal groundwater recharge estimation method with a focus on the Neri River watershed in Ethiopia. The WetSpass model uses grid-based and database format (dbf) input parameters to estimate groundwater recharge. Conversely, the assessment of groundwater recharge based on the δ¹⁸O mass balance approach was conducted by examining groundwater and precipitation samples for stable oxygen and hydrogen isotopes. Seasonal variations in the leaf area index (LAI) and land use/cover (LULC) map of 2023 were used to estimate the recharge through the WetSpass-M model. The results of the physical hydrology approach revealed that 60.6% of the average groundwater recharge takes place from March through August, which is the rainy season, and the remaining 39.4% occurs from September through February, which is the dry season. In line with physical hydrology findings, the δ¹⁸O mass balance technique was also utilized to estimate groundwater recharge, revealing that 58.2% of recharge takes place during the rainy season and the remaining 41.8% during the dry season. The results of the study will assist local stakeholders and policymakers in creating a groundwater resource management strategy that is both sustainable and efficient for the watershed.