CHARACTERIZING AQUIFERS AND ASSESSING GROUNDWATER PRODUCTIVITY IN THE LAKE HAWASSA WATERSHED USING REMOTE SENSING, GIS, AND HYDROGEOLOGICAL METHODS

Abstract

Groundwater is a vital resource for Ethiopia's rapidly growing population, particularly in waterscarce regions such as the Lake Hawassa watershed. However, sustainable management is hindered by the area’s complex hydrogeology, including fractured aquifers, competing agriculture, and urban and ecological demand, which increases the risk of depletion and contamination. A hydrogeological approach, remote sensing (RS), and a GIS-based analytic hierarchy process (AHP) are combined in this work to delineate aquifers and evaluate groundwater productivity in the tectonically active basin. Eight thematic layers land use/land cover, slope, soil type, rainfall, elevation, drainage density, lineament density, and topographic wetness index (TWI) were used as input factors for the AHP-GIS model to map groundwater potential zones. AHP was employed to assign weights based on each factor’s influence on groundwater occurrence. This spatial model was then correlated with field-based hydrogeological data, including borehole lithology, pumping test results, and calculated transmissivity, to interpret aquifer productivity. Four aquifer types were identified: very highproductive fractured basalts (1,000–6,580 m²/day), high-productive alluvial sediments (100– 1,000 m²/day), moderately productive sediments (10–100 m²/day), and low-productive fractured ignimbrites (<10 m²/day). These aquifer types are spatially variable, with central and northeastern highlands characterized by fractured basalts and western and southern regions featuring ignimbrite beds. Hydraulic conductivity and transmissivity values reflect this variability, correlating with lithological heterogeneity and tectonic features. Groundwater flow analysis confirmed recharge from the northern highlands to the southwest direction, towards Lake Hawassa. Flow paths are generally fault-controlled, with some faults functioning as conduits and others as barriers. The model identified 25.7% of the watershed with high potential, 44.7% with moderate, and 29.6% with low. Validation by 43 boreholes showed excellent correlation between potential zones and well yields. This study provides the first watershed-scale aquifer characterization within the Main Ethiopian Rift, offering a reproducible approach applicable to data-scarce regions. The findings provide valuable insights to inform strategic groundwater management in line with Ethiopia’s National Water Policy and advance sustainable water resource development in the Lake Hawassa watershed.