Browsing by Author "Chande, Chaka"

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    Lake-Groundwater Interaction and Isotope Mass Balance of Lake Ziway Integrated Approach
    (Addis Ababa University, 2020-09-09) Chande, Chaka; Azagegn, Tilahun (PhD)
    An integrated approaches based on the application of stable isotope of water (2H and 18O), radiogenic-isotope of Radon (222Rn) and piezometric evidences are employed in this research to determine the interaction between the lake water and the adjacent groundwater and to evaluate the water balance of the lake Ziway particularly for estimating the groundwater inflows and outflows of the lake. The result based on δ18O-isotope mass balance of the lake shows groundwater inflow accounts for about 4% of total inflow and groundwater outflow accounts for about 8% of total outflow. With respect to the lake and groundwater interaction, the analysis of isotopic compositions of groundwaters shows groundwaters located in the south and southwest of Lake Ziway have similar isotopic composition to that of the lake. This demonstrates the lake and groundwater interaction in that sector of the lake. In contrast groundwater located in the highlands and escarpments displays isotopic composition similar to the precipitation, portraying no hydrologic link between the lake and the subsurface waters in these sectors. Radon-222 concentrations in the lake varied spatially from less than 35.2 – 96.6 Bq/m3. Results from 222Rn measurements shows high concentration values of 96.6 Bq/m3 and 78.5 Bq/m3 at the northeast and southeast shores of the lake respectively demonstrating lacustrine groundwater discharges into the lake in that regions from local flow systems. The piezometric evidence is also in support of this observation. In the region between northeast and southeast groundwater level lies above the lake surface level and this indicates the groundwater flow to the lake. In the western and southern sectors of the lake the groundwater level lies below lake level and thus demonstrates groundwater flow direction to the south and southwest. Evidences from various methods clearly proved the presence of lake and groundwater hydraulic link in the south and southwest sectors indicating the lake recharges the groundwater. This work in particular demonstrates the importance of stable isotope of water in defining separately the groundwater flux components of the hydrologic budget of the lake and in determining the lake-groundwater interaction.