Hydrogeological Assessment on Upper Mille River Catchment
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Date
2020-09-09
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Addis Ababa University
Abstract
The study aims to elaborate and give some detailed picture of the Hydrogeological features of the study area. Mainly by characterization the aquifer, recharge mechanism, groundwater flow conditions and hydrochemistry of the groundwater. The basin is part of the western escarpment of Afar rift and measures about 1367 km². The mean annual precipitation as calculated by Thiession polygon method is found to be 1157. 6mm. The amount of recharge that is contributed to the subsurface as calculated by using Base flow separation, chloride mass balance and SWAT modelling gives a value of 135.9 mm, 115.66 mm and 140.48 mm (after calibration) and 138.5 (after validation) respectively. To describe the aquifer system of the area pumping test data, well completion reports, well logs and geology of the area were analysed. The study area is characterized by deep groundwater systems on average 214 m (depth of the wells) and groundwater reserve of the graben is estimated 3670.24 MCM. Hydraulic characteristics are spatially variable, in the area transmissivity of the valley ranges from 2.4–1580 m²/d.Its hydraulic conductivity ranges from 0.06 –18.1m/d. The Quaternary unconsolidated sediments are the main aquifer units in the area. The general trend for groundwater flow from pieziometric heads is generally from west to east. Piper plots were used to classify the water chemistry of the area. Groundwater type of the area generally evolved from Ca-Mg-HCO3 or Mg-Ca-HCO3 water type in the area closer to western escarpment to Na-Ca-HCO3 water type in the eastern part of the area. The water is also suitable for drinking purpose based on the standards.
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Groundwater, Resource, Recharges Estimation, Hydrochemistry, and Aquifer Characterization