Surface Water-Ground Water Interaction in Hawassa Lake Catchment Using Geochemical and Isotopic Techniques
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Date
2015-02-02
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Addis Ababa University
Abstract
Hawassa lake catchment, which is located in the Main Ethiopian Rift, has different ideas about the direction in which the lake and the groundwater interact. Oxygen (δ18O), Hydrogen (δ2H) isotopes and hydrochemical method used to reveal Lake water-groundwater interaction and for determination of a lake water budget. Tritium also revealed the residence time of groundwater in the study area.
Stable isotope study result illustrates that, there is interaction between lake water and groundwater in the Northern and southwestern direction. To support the stable isotope result and to show the general groundwater flow water level measurements used and it show groundwater flow from all around the caldera rim to Lake Hawassa except from the northern side where the ground water flows away from the catchment to Lake Shalla and there is local groundwater flow away from the lake. Along the groundwater flow direction ionic concentration and isotopic enrichment (δ2Handδ18O) increases.
Hydrochemical study result reveals that the area is characterized by three major water types in the area. Main water types in the study area are Na-HCO3 which is the characteristics of the flow of the caldera followed by Na-Ca-HCO3 which is the characteristics of the highlands and Ca-Na-HCO3 which is rare.
Stable isotopes (oxygen-18 and deuterium) exist in water naturally used to quantify the groundwater inflow into the lake and the outflow from the lake. It was found that the average groundwater inflow to Hawassa Lake is 24% out of total inflow to the lake while the average groundwater outflow is 3% out of total outflow from the lake using oxygen-18 and deuterium.
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Surface Water-Ground, Water Interaction, Hawassa Lake Catchment, Using Geochemical, Isotopic Techniques