Browsing by Author "Azagegn, Tilahun"

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    Groundwater Dynamics in the Left Bank Catchments of the Middle Blue Nile and the Upper Awash River Basins, Central Ethiopia
    (Addis Ababa Universty, 2014-12) Azagegn, Tilahun; Ayenew, Tenalem (Professor)
    Integrated geological, geophysical, hydrodynamic, hydrogeochemical and environmental isotopic studies together with simple regional groundwater flow model help conceptualize aquifer distribution, groundwater dynamics and relationship between aquifer systems of the Middle Blue Nile and the Upper Awash basins. A distinctive aquifer geometry reconstructed from regional stratigraphy, regional fault systems and geophysical evidences controls the size of recharge area for aquifer systems and aquifer distributions in the groundwater sub-basins. The NW-SE trending horsts beneath thick volcanic layers and ridges control aquifer distribution in the Middle Blue Nile basin into Guder, Muger and Jema groundwater sub-basins.The E-Wtrending impermeable mudstone capped horst underlying the volcanic aquifers controls aquifer distribution and constitutes a groundwater divide between the Blue Nile and the Upper Awash basins, channeling recharged water in the former to the latter. Among various recharge estimation methods employed, results from base flow separation that utilizes records from adequate river gauges better represent recharge distribution in the area. The overlay analysis made between base flow amount, lineament density and geological materials indicated that rock units exposed along the Yerer Tulu Wolel Volcanic Lineament zone and the Main Ethiopian Rift marginpromote more recharge than the rock units exposed away from these zones.Groundwater contours generally follow surface topography for flows considered at a catchment or sub-basin level. However, unique groundwater flow pattern that indicates interbasin groundwater flow from the Blue Nile to the Upper Awash basin has been obtained at a regional scale, which is attributed to the interplay between regional faults. δ18O and δD-depleted waters with high TDS, NaHCO3water types, positive residual alkalinity and low 14C activityobserved along the water divide between the Blue Nile and the Upper Awash together with horizontal annual groundwater inflow of 152Mm3to the Upper Awash groundwater basin obtained from the regional groundwater flow model, substantiate the interbasin groundwater flow conceptualized from litho-structural and hydrodynamic characterization. Keywords: Blue Nile, Upper Awash, Interbasin, sub-basins, groundwater dynamics