Assessing Groundwater Recharge Dynamics: A Comparative Study of Stable Isotope and Hydrological Modeling Approaches in the Omo Gibe River Basin, Ethiopia

Date of Award

5-1-2025

Degree Name

M.S. in Interdisciplinary Studies

Department

College of Arts and Sciences

Advisor/Chair

Zelalem Bedaso

Abstract

This study assesses groundwater recharge dynamics in the Gilgel Gibe, Gombora, and Neri watersheds of the Omo Gibe River Basin (OGRB), Ethiopia, using a comparative approach that integrates stable isotope mass balance and the WetSpass-M hydrological models. The research aims to analyze isotopic compositions of precipitation and groundwater, estimate seasonal and spatial groundwater recharge rates, and evaluate the performance of both models across diverse hydro-climatic zones. The stable isotope approach involved analyzing δ18O and δ2H compositions to establish Local Meteoric Water Lines (LMWLs), seasonal distribution of isotopes, and quantifying seasonal recharge contributions using the oxygen-18 mass balance method. Concurrently, using meteorological and physical data, the WetSpass-M model simulated monthly water balance components, including recharge, surface runoff, and evapotranspiration. Model calibration, validation, and sensitivity analysis were performed using observed streamflow data. Key findings indicate that groundwater recharge is primarily driven by wet-season precipitation, with minimal contributions from the dry season. An isotope analysis revealed that 88.1% and 83.7% of recharge in the Gilgel Gibe and Gombora watersheds, respectively, occur during the wet season. In contrast, the Neri watershed exhibits a more balanced distribution due to its bimodal rainfall pattern. The WetSpass-M model confirmed these results, showing peak recharge during the wettest months and emphasizing the influence of land cover, soil properties, and precipitation. Both methods agreed strongly on seasonal recharge patterns, with isotopes providing direct field-based estimates and WetSpass-M offering high-resolution spatial insights. The study concludes that combining stable isotope techniques with hydrological modeling improves the accuracy and reliability of recharge assessments. It highlights the critical role of wet-season precipitation in sustaining groundwater and underscores the need for tailored water resource management strategies, including land-use planning and climate adaptation measures. This research provides a methodological framework for sustainable groundwater management in the OGRB and similar regions, offering valuable insights for future hydrological studies.

Keywords

Geochemistry, Geographic Information Science, Hydrologic Sciences, Hydrology, Water Resource Management

Rights Statement

Copyright 2025, author.

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