Identifying recharge areas for the upstream portion aquifers of Awash Basin, Ethiopia

Study area

The western and eastern flanks of Ethiopia's Awash and Abay Basins, respectively.

Study focus

Identifying recharge zones of the main aquifers in the Upper Awash Basin, which are water resources targeted for long-term sustainable use. In this work, lithohydrostratigraphic concepts with fracture density, hydrogeochemical and stable isotopic insights were applied using information from 94 water-supply wells, 188 geoelectrical resistivity, 124 hydrochemistry, and 81 stable isotopic data sets.

New hydrogeological insights of the area

The results illustrate that recharge of superficial deposits and Rift basalt aquifers is from modern precipitation and from nearby streams/rivers through fractures, which is exemplified by mixed CaHCO₃ or CaMgHCO₃ water types of low TDS (<200 mg/l), high Ca/Na ratio (>5), low RA (<2.0), enriched isotopic signature, and high deuterium excess (13.3). Seepage from the overlying aquifers, as well as direct precipitation in locations where the unit is exposed, form the mechanisms of recharge for fractured ignimbrite aquifer. The highland and transition areas are dominantly the recharge areas for the regional scoriaceous basalt aquifer. These areas have high fracture density (0.96<FD<3.0 km/km²), mineralized NaHCO₃ water type, high TDS (>468 mg/l), low Ca/Na ratio (<1), high RA (>2.0), highly depleted isotopic signals, and low deuterium excess (<11) relative to the Local Meteoric Water Line. The results also reveal groundwater flux from the adjacent eastern flank of Abay Basin.