Getnet Taye Bawoke

Surface water–groundwater interactions play a critical role in regulating hydrological fluxes and sustaining water availability, yet they remain poorly understood in hydrogeologically complex terrains. This study employed an integrated modeling approach combining SWAT+ and MODFLOW to quantify water balance components, groundwater flow dynamics, and river–aquifer exchanges in the Chemoga watershed, a representative headwater system of the Upper Blue Nile Basin characterized by strong environmental and geological contrasts. Model results revealed substantial spatial heterogeneity in hydrological partitioning, with annual groundwater recharge ranging from 105 to 711 mm (mean = 296 mm; 24% of annual rainfall). Simulated groundwater flow exhibited a pronounced topographic control, with hydraulic heads declining from highland recharge zones toward deeply incised lowland gorges. River–aquifer interactions showed marked spatial variability, with the Chemoga river predominantly acting as a gaining stream in the highland and nick-point gorge sections (up to 2867 m³ d⁻¹), while transitioning to a losing stream in the midland floodplains and lowland gorge areas, with leakage reaching up to 75.0 m³ d⁻¹. These findings highlight the value of integrated, process-based modeling for resolving complex hydrological interactions, advancing understanding of groundwater flow regimes and supporting sustainable groundwater management in the Ethiopian highlands and other similar regions worldwide.

This study aimed to evaluate the overall groundwater hydrogeochemical evolution and suitability for drinking in Andasa watershed (Northwestern Ethiopia). To achieve this, analyses of hydrogeochemical, multivariate (PCA, HCA), correlation matrix, and Water Quality Index (WQI) methodologies were employed. A total of 64 groundwater samples which had been collected during winter season (February–April, 2018) were assessed for ionic and composite variables (major physicochemical and composite parameters). The samples have been gathered from deep wells, shallow wells, hand dug wells and springs which are spatially distributed throughout the watershed. The study results revealed that major ions dominating are Ca>Mg>Na>K and HCO₃> Cl>SO₄> NO₃> PO₄ > F for cations and anions, respectively. Ca-HCO₃, Mg-Ca-HCO₃-Cl, Mg-Ca-Na-HCO₃-SO₄, Mg-HCO₃-SO₄, Mixed CaMgHCO₃, Mixed CaNaHCO₃ and Na-HCO₃ were recognized as water types where Ca-HCO₃ (59.69%) was identified as dominant. Ionic ratio plots are indications for groundwater enrichment by Na⁺, Ca²⁺ and Mg²⁺ cations (silicate minerals hydrolysis). Chloro-alkaline indices resulted for CAI-I (96.88%) and CAI-II (84.48%), showed Ca²⁺+Mg²⁺ exchange in groundwater with Na⁺+K⁺ in an aquifer, confirmed for cation exchanging. Four factor loadings (PCA analysis) explained for the existence of geogenic and anthropogenic pollutions. WQI values showed the majority of the samples comprised “good water” (57.81%), distributed in southern and western parts, followed by “excellent water” (20.31%). Additionally, WQI maps portrayed “Good” to “poor water” types in northern portions (waste disposal landfill, urban centers, irrigated areas), while “very poor” to “unsuitable” types are dispersed to northeastern tips. Generally, the study result is believed to give directions for groundwater management options.