Kebede, SeifuAdmasu, Girum2018-07-052023-11-092018-07-052023-11-092010-06http://10.90.10.223:4000/handle/123456789/6650This 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.enTana sub-basinThesis