The groundwater potential in the Akaki catchment area is influenced by its geological formation, landscape attributes, and precipitation patterns ( Hailu et al., 2023; Kebede et al., 2023; Tefera et al., 2023; Demlie, 2015, Demlie et al., 2007). However, there has been a lack of comprehensive studies that systematically consider all the crucial factors contributing to groundwater potential. Therefore, this study aims to identify and characterize these parameters, develop an analytical hierarchy process, and validate the results.
In this study, lithology, rainfall, lineament, and drainage density hold significant importance. Similarly, research conducted in the Ethiopian Main Rift Valley found lithology (geology) and rainfall to be the most influential factors (Nigussie et al., 2019). In comparison, another study in the Western Escarpment of the Rift Valley System highlighted lithology as a primary factor while giving relatively less importance to rainfall (Abrar et al., 2021).
Furthermore, a study conducted in the northern part of Ethiopia aligns with the outcomes of this study (Berhanu and Hatiye, 2020). Although it considered lithology as a significant factor, it differed in its assessment of the importance of rainfall. This deviation in the significance of rainfall can be attributed to variations in rainfall patterns and differences in groundwater recharge mechanisms specific to each area (Fattah et al., 2024; Mengistu et al., 2021; Dey et al., 2020).
The Akaki catchment, located within the Main Ethiopian Rift, is characterized by prominent faults and lineaments trending NE-SW, E-W, N-S, and NW-SE (Tadesse et al., 2023; Bretzler et al., 2011; WEDSWS, 2008). This observation is reinforced by the fact that lineaments (faults) are associated with elevated permeability levels (Takorabt et al., 2018; Souissi et al., 2018). Studies in the Awash Basin further support the argument that lineaments are a critical factor for groundwater potential (Anteneh et al., 2022). Conversely, the significance of drainage cannot be overlooked due to the low drainage density within the catchment. This leads to enhanced recharge rates and increased groundwater potential, as lower drainage density is linked to higher water permeability (Hussein et al., 2017; Tolche, 2021).
On the other hand, slope, land use, soil texture, and elevation are also significant due to their respective roles. The upper catchment features steep slopes that contribute to high runoff, as steep gradients lead to a rapid downhill flow of precipitation, limiting the time available for infiltration and the replenishment of the saturated zone (Arulbalaji et al., 2019). This assertion is supported by the elevations within the catchment. Furthermore, unconfined aquifers are significantly influenced by topographical features (Tigabu et al., 2020).
Moreover, land use and land cover play a crucial role in groundwater occurrence and accessibility (Arabameri et al., 2019). Furthermore, alterations in land use impact the base flow within the catchment (Huang et al., 2016). Additionally, the infiltration of surface water into an aquifer system depends on soil type (Souissi et al., 2018). However, the relative importance of soil versus land use varies across locations and study environments (Arefaine et al., 2012; Berhanu & Hatiye, 2020).
Based on the results and justifications, the catchment is predominantly classified as having moderate to high groundwater potential. This finding is supported by the work of Abraha et al. (2022), who conducted a country-level assessment but did not provide a detailed classification at the micro-catchment level. In contrast, this study classifies the catchment into low, moderate, high, and very high groundwater potential zones. The low-potential area, predominantly covered by eucalyptus trees and located in the upstream region of the catchment, affects groundwater availability due to the selection and planting densities of the trees (Adane et al., 2018).
In the moderately groundwater-potential zones, the most common lithological structures are PNtbB, NcvTy, NadI, and NebRy (Demile, 2015; Kebede, 2013). These zones are characterized by moderate slopes, with prevalent clay and loam soils, and some areas of sandy loam and sandy clay loams in the central region. Additionally, they feature moderately elevated terrain and a diverse blend of land uses. Consequently, these factors, in conjunction with the broader environmental context, collectively influence groundwater potential (Ozdemir, 2011).
Previous studies support that Tarma Ber basalt (PNtbB) has moderate permeability and productivity (Hussein et al., 2017). This lithological unit is prevalent in the western and northern plateaus and is characterized by lenticular basalts and abundant scoriaceous lava flows (Abbate et al., 2021). In this basalt, an increase in well depth is associated with a decrease in aquifer productivity (Kebede, 2013). In the western part of the Akaki catchment, porphyritic trachytic lavas (NcvTy) are present, originating from the central volcanic areas of Wechecha, Furi, and Yerer (Kebede, 2013). On the other hand, the Addis Ababa Ignimbrite (NadI) consists of tall, poorly welded pyroclastic deposits found in the Addis Ababa and Legedadi plains and is characterized as a moderate potential zone (Yifru et al., 2022; Muleta & Abate, 2021). In contrast, Entoto Becho rhyolite (NebRy) is considered to have low groundwater potential and is characterized by obsidian-bearing rhyolite outcrops on the Entoto Mountain (Hailu et al., 2023; WEDSWS, 2008).
All lithological units, excluding NebRy, fall into the high groundwater potential category. This area includes the Addis Ababa basalt (NadB), which is characterized by high groundwater potential (Hailu et al., 2023; Mengistu et al., 2019). Addis Ababa basalt (NadB) is primarily composed of alkaline and olivine basalt lava flows that cover the central and southern regions of Addis Ababa (WEDSWS, 2008). In this zone, there are instances of both high and moderate rainfall and lineament density. The predominant characteristic of this area is low to moderate drainage density, which serves as an indicator of high groundwater potential (Hussein et al., 2017). In contrast, the central and southern sections of the catchment exhibit moderate to low slopes and elevations compared to the northwestern regions. Moreover, except for sandy loam and sandy clay loams in the central part, this zone is characterized predominantly by clay and loam soils with a mixed land use system.
A very high groundwater potential area is predominantly characterized by the presence of Akaki basalt formations, which are known for their significant groundwater productivity due to their geological properties (Shibeshi et al., 2019; Demile, 2015; Demlie et al., 2008). Akaki basalt (NakB) is distinguished by scoria and scattered cones along with associated basaltic lava flows extending in a northeast-southeast direction (Lulu et al., 2005; Muleta & Abate, 2021). Although the rainfall in this specific area is comparatively lower than in other parts of the Akaki catchment, it remains sufficient due to the overall high rainfall conditions across the region. The combination of high lineament density with low drainage density, gentle slopes, and low elevation levels provides a distinct advantage that contributes to the very high groundwater potential in this region. Additionally, these areas are primarily composed of clay and loam soils amidst diverse land use patterns.