Browsing by Author "Kebede, Seifu"

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    Groundwater & Surface Water Interaction in Lake Tana sub-basin using Isotope and Geochemical Approach
    (Addis Ababa Universty, 2010-06) Admasu, Girum; Kebede, Seifu
    This investigation was made to figure out the interaction between the surface water and groundwater bodies in Lake Tana sub-basin using isotope and geochemical approach. The main objectives of this investigation were: 􀂙 To map the spatial and vertical distribution of water geochemical composition in the area. 􀂙 To identify the origin & evolution of the isotopic and geochemical characteristics of the water in the Lake Tana sub-basin. 􀂙 To investigate the interaction between surface water and groundwater. Isotope and Geochemical method has indicated that two major evolution processes of the salinity operate in Lake Tana sub basin. These are evapotranspiration on the the flat plain and Deep circulation associated with silicic dykes. Evapotranspiration is the main cause of Pockets of highly saline areas in the permanent and seasonal parts of the wetlands. It causes water to be transported by a plant through capillary action of vessels from the soil to the air by leaving dissolved matter with no net isotope fractionation causing salinity.It is mostly observed at the Dembia and Fogera plain close to the wetlands and trees. It is not distributed uniformly but random and is moderately depleted isotopically. The saline water associated with deep circulation is found close to silicic dykes. Fluid movement under pressure change due to the occurrence of the dyke and osmotic processes has often residual components because of the long relaxation time of the pressure gradient and thus salinity occurs. The shallow pocket salinities observed in this study may be exacerbated if other additional processes contribute to salinity of the area. Therefore, a comprehensive groundwater investigation is a priority to implementing large schemes such as irrigated agricultural development in the flat wetlands. This can be done by implementing a micro geo-morphological investigation in combination with diurnal water quality monitoring.
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    Hydrochemical and Isotopic Characteristics of the Groundwater System of Alleydege Plain
    (Addis Ababa Universty, 2011-06) Bekele, Bizuneh; Kebede, Seifu
    On the bases of geomorphology which is controlled by en echelon normal faults, the area is classified into two parts; the Alleydege plain, and Awash River valley. The groundwater dynamics of the area with emphasis given to surface water and groundwater interaction, origin of recharge; groundwater flow direction, groundwater evolutionary trend and direction, causes and origin of salinity and general groundwater quality issues relative to temporal variation are studied in this research using hydrochemical and isotopic data. Ultimately conceptual hydrochemical groundwater model of the area is constructed. XLSTAT _Pro version 7.5.2; for agglomerative cluster analysis, Aquachem 4.0 software package; for graphical plots and representation of hydrochemical data, PHREEQC built in aquachem 4.0 version; for inverse geochemical modeling, ArcGIS _9.3 software version; for Analysis of areal distribution and variation of hydrochemical and isotopic data and for production of different maps and Autocad-2007 version; for production of longitudinal geologic and hydrogeologic profiles, are employed in this study. Hydrochemical and isotopic studies reveal that there is interaction of Awash River with the groundwater of the alluvial aquifer of the Awash River valley and the Alleydege plain that lie within few kilometer distances from the Awash River during rainy season; during dry season such interaction is not observed. Recent meteoric water contribution to the groundwater reserve of the Alleydege plain is very limited. As a result subsurface inflow or percolation along the slope from southern, southeastern, and eastern highlands are found to be the major recharge mechanism for the Alleydege plain. Towards the rift, from the recharge areas of southern, southeastern, and eastern highlands; the ionic concentration, salinity and isotopic enrichment (δ2H and δ18O) increase following the groundwater flow paths. In general the groundwater flow and evolutionary trend direction follows the surface topography flowing from the south, southeastern and eastern elevated areas to the Alleydege plain and finally to the rift floor converging to the Awash River in the northern direction. The recharge area is characterized by Ca-HCO3, Ca-Mg-HCO3 or Ca-Na-HCO3 water type, where as the Alleydege plain and the marginal areas are characterized by a Na-Ca-HCO3-Cl water types. Na-HCO3-Cl and Na-HCO3 are the dominant water types in the Awash River valley and rift floor. K-mica, olivine, pyroxene, plagioclase and illite are the primary minerals of the Alleydege plain groundwater system.
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    Hydrology and Hydrochemistry of Bishoftu Crater Lakes (Ethiopia)
    (Addis Ababa Universty, 1999-06) Kebede, Seifu; Umer, Mohammed (PhD)
    The Bishoftu Crater Lakes, located on the western shoulder of the main Ethiopian Rift can provide a sedimentary record, which has registered the changes in the balance between precipitation input and evaporative water loss. However, groundwater fluxes may reduce sensitivity of the lakes to a change climate. In order to test the possibility to use the lakes as paleohydrometers, the modem balance between precipitation, evaporation and groundwater flux has been determined. In the Bishoftu area where hardrock form the terrain geochemical and isotope mass balance has been found suitable to be used to constrain the water budget. Although stable isotopes of oxygen and deuterium as aid in quantifYing water balance of the lakes have limitations due to the lack of measurement of environmental parameters such as h, s, As ; the same approach has been found appropriate for this study. The varying hydrology of the Bishoftu crater lakes has provided a suitable base for determining water budget using stable isotope method without reve11ing to the measurement of envirorunental parameters. Accordingly the lakes have been found suitable for quantitative isotope hydrology and quantitative reconstLUction of paleoclimate from lake carbonate records. Of the existing five crater lakes, lake Hora, lake Arenguade and lake Kilole are least affected by groundwater outflow while lake Babogaya and lake Bishoftu are more influenced by groundwater outflow. The hydrology of lake Kilole is recently influenced by the diversion of the Mojo river into the lake. Geochemical mass balance results show that lake Arenguade might be affected by geothermal water flux. Of all crater lakes, lake Hora is therefore selected as the most suitable for paleoclimate studies.
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    Hydrology and Hydrochemistry of Bishoftu Crater Lakes (Ethiopia) Hydrological, Hydrochemical and oxygen isotope modeling
    (Addis Ababa University, 1990-06) Kebede, Seifu; Leng, Melani(PhD)
    The Bishoftu Crater Lakes, located on the western shoulder of the main Ethiopian Rift can provide a sedimentary record, which has regis!ered the changes in the balance between precipitation input and evaporative water loss. However, groundwater fluxes may reduce sensitivity of the lakes to a change climate. In order to test the possibility to use the lakes as paleohydrometers, the modem balance between precipitation, evaporation and groundwater flux has been determined. In the Bishoftu area where hardrock form the terrain geochemical and isotope mass balance has been found suitable to be used to constrain the water budget. Although stable isotopes of oxygen and deuterium as aid in quantifying water balance of the lakes have limitations due to the lack of measurement of environmental parameters such as h, E, I1E ; the same approach has been found appropriate for this study. The varying hydrology of the Bishoftu crater lakes has provided a suitable base for determining water budget using stable isotope method without reverting to the measurement of environmental parameters. Accordingly the lakes have been found suitable for quantitative isotope hydrology and quantitative reconstruction of paleoclimate from lake carbonate records. Of the existing five crater lakes, lake Hora, lake Arenguade and lake Kilole are least affected by groundwater outflow while lake Babogaya and lake Bishoftu are more influenced by groundwater outflow. The hydrology of lake Kilole is recently influenced by the diversion of the Mojo river into the lake. Geochemical mass balance results show that lake Arenguade might be affected by geothermal water flux . Of all crater lakes, lake Hora is therefore selected as the most suitable for paleoclimate studies.