Telahun AzagegnWasihun Kibret2026-07-282026-07-282022-06https://etd.aau.edu.et/handle/123456789/8715The study area covers (big akaki) that situated in upper awash basins and it is part ofsubakaki river catchment, akaki catchment has massive drainage system mainly composed of Big and Small Akaki River. The two rivers meet at the man- made reservoir called Aba Samuel reservoir. The Akaki River gauged at Akaki Bridge and flows to Awash River. The study asses the Groundwater system of big akaki catchment using different approaches by estimating groundwater recharge, characterizing the groundwater system based on the hydraulic properties, ground water occurrence and hydro geochemical signature. The precipitation conditions of the area show bimodal rainfall type. The groundwater system and aquifer characterized based on hydraulic parameters and pump testing results (transmissivity, hydraulic properties, specific capacity, safe yield, water level, drawdown, depth variation and aquifer thickness to evaluate aquifer system of the investigation area. Hence, the transmissivity and hydraulic conductivity is maximum at akaki and legetafo well fields while lower or minimum at central western of the catchment. Additionally groundwater occurrence of the catchment classifying based on intergranular and fissured aquifer. Highly productive intergranular aquifer contains chefe donsa phyroclastic and alluvial sediments while fissured aquifer unit is mostly Addis Ababa basalt , Addis Ababa ignimbrite and entoto becho rhyolitic rock units. The aquifer system also classified based on productivity nature in which highly productive, moderate and low productive zones of the aquifer catchment identified. The hydrochemical signature of the catchment characterized based on spatial variations of anions and cations, hydrochemical facies, water type and chemical evolution entire catchment. Aquifer characterization described as the process of evaluating the transport characteristics and chemistry of aquifers. The study area is part of rift volcanic margin and covered by different geological sequence especially volcanic rocks like basalt, rhyolites, ignimbrite, tracky basalt and volcanic deposition. These above listed lithologies mainly occurred as on both the surface out crop and forming subsurface volcanic strata and used as ground water reservoir of subsurface aquifer. Dominantly the ground water system of the study area may transmitted through interconnected spaces that make the regional ground water flow, this is due to the highly porous and permeable formations and structures found (fault, joints, lineaments and fractures) .That the area is part of the rift system, which is tectonically active to produce different geological structure.en-USAquifer CharacterizationsBig- Akaki River CatchmentThesis