Browsing by Author "Ayele, Gebeyaw"

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    Spatial and Temporal Hydro Chemical Variation of the Upper Awash Sub-Basin Central Ethiopia
    (Addis Ababa University, 2021-09-18) Ayele, Gebeyaw; Nedaw, Dessie (PhD)
    In countries like Ethiopia, regular hydrochemical variation follow-up is not common. The Upper Awash Sub-Basin is found in a region with high population density, high water demand, and is a highly vulnerable water resource that requires regular hydrochemical follow-up. This study was aimed to assess the spatial and temporal hydrochemical variation in the Upper Awash Sub-Basin conducted by combining previous hydrochemical data from various sources, and the present two year’s data analyzed in 2019 and 2021. The major cation variation is mainly attributed to the rock-water interaction due to the availability of complex geology in the area comprising highly weathered, olivine, pyroxene, and feldspar bearing basaltic rocks and acidic volcanic rocks that can alter the composition of water making the concentrations of calcium, magnesium, sodium, and potassium ions variable both spatially and temporally with minor effects from anthropogenic sources taken under consideration. The temporal variation of major cations in groundwater is due to the residence time of groundwater in the area, and the circulation of groundwater along the regional and local fault lines. Bicarbonate is the most abundant and varying anion in the area resulting from a high rate of carbon dioxide outgassing from thermal aquifers like Filwuha and from the reaction between dissolved carbon dioxide with the rocks to produce bicarbonate and clay or mica. Sulfate, chloride, and nitrate concentrations in both groundwater and surface water are increasing through time mainly due to anthropogenic factors from nitrate and sulfate fertilizers. In addition to the anthropogenic factors, chloride concentration is also related to the stagnation of water at compacted clay along fault zones. Despite their concentration below the acceptable standards, the concentration of toxic heavy metals like lead, zinc, and manganese show both spatial and temporal variation. The hydrochemical variation analysis depicted that groundwater is more stable with relatively lower hydrochemical variation than the lakes and Rivers as it is a hidden resource. On the other hand, Lakes and Rivers in the area show temporal hydrochemical variation due to their proximity to the controlling factors. Water-supply reservoirs in the Addis Ababa area have relatively stable hydrochemical parameters whereas Debrezeit Lakes and the Rivers have relatively higher spatial and temporal variation. Groundwater in most areas of Upper Awash is suitable for drinking and agricultural activities. Regarding water quality for irrigation, Mojo and Holeta Rivers, Lake Hora, and Lake Hora Hoda are highly saline that may affect soil fertility and crop yield.