Groundwater Circulation and Hydrochemistry of the Corridor (Upper Gidabo River and Lake Awassa Catchments), Sidama Zone, Snnprs

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Date

2007-07

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Addis Ababa Universty

Abstract

The study corridor is found in Sidama zone, SNNPRS. It is situated in the Central sector of the MER system. The study area with 1582 km2, comprises parts of the two adjacent catchments namely Lake Awassa and upper Gidabo River, which is delineated arbitrarily so as to determine whether there is groundwater circulation between them or not and quantifying the amounts. Recently, the Awassa lake level is continuously rising since some times and evacuate so many residences from the lake shore and damage properties. This rising of the lake level causes a major threat for the Awassa town and surrounding rural communities. Integrated methodologies are used to find out the groundwater flow system and hydrochemistry of the corridor along with employing the appropriate software like Global Mapper, Surfer, ArcGIS, ArcView, and Aquachem that facilitate for analyses and interpretations of the data in order to get the output. The secondary date are collected from the concerning offices and some primary date are obtained during field work. Accordingly, groundwater flow system is considered as shallow and deep aquifer cases and the outputs indicate that there is the same flow trend within the two flow systems. Groundwater flows take place from south east towards north west and to the west; and there are also flows from central west (Yirba area) to the north (Lake Awassa) in the study corridor. The total groundwater flowing amount that outflow from upper Gidabo river catchmetnt is quantified to be 5.81MCM. On the other hand, hydrochemical data analysis part also reveals: evolution of major ions, water types, potablity of water for human consumption, spatial distribution of some major ions including fluoride and direction of groundwater flow. For example, the water sample from hot spring and Lake Awassa is Na-HCO3 type, which indicates the presence of evolution. Whereas cold springs mostly from highlands and the eastern rift escarpment has the water type of Na-Ca-HCO3, shows minor evolution. The increasing trends of the phisico-chemical analyses indicate that there is groundwater outflow towards the lake region

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Upper Gidabo River

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