On the bases of geomorphology which is controlled by en echelon normal faults, the area isrnclassified into two parts; the Alleydege plain, and Awash River valley. The groundwaterrndynamics of the area with emphasis given to surface water and groundwater interaction,rnorigin of recharge; groundwater flow direction, groundwater evolutionary trend and direction,rncauses and origin of salinity and general groundwater quality issues relative to temporalrnvariation are studied in this research using hydrochemical and isotopic data. Ultimatelyrnconceptual hydrochemical groundwater model of the area is constructed.rnXLSTAT _Pro version 7.5.2; for agglomerative cluster analysis, Aquachem 4.0 softwarernpackage; for graphical plots and representation of hydrochemical data, PHREEQC built inrnaquachem 4.0 version; for inverse geochemical modeling, ArcGIS _9.3 software version; forrnAnalysis of areal distribution and variation of hydrochemical and isotopic data and forrnproduction of different maps and Autocad-2007 version; for production of longitudinalrngeologic and hydrogeologic profiles, are employed in this study.rnHydrochemical and isotopic studies reveal that there is interaction of Awash River with therngroundwater of the alluvial aquifer of the Awash River valley and the Alleydege plain that liernwithin few kilometer distances from the Awash River during rainy season; during dry seasonrnsuch interaction is not observed. Recent meteoric water contribution to the groundwaterrnreserve of the Alleydege plain is very limited. As a result subsurface inflow or percolationrnalong the slope from southern, southeastern, and eastern highlands are found to be the majorrnrecharge mechanism for the Alleydege plain. Towards the rift, from the recharge areas ofrnsouthern, southeastern, and eastern highlands; the ionic concentration, salinity and isotopicrnenrichment (Î´2H and Î´18O) increase following the groundwater flow paths. In general therngroundwater flow and evolutionary trend direction follows the surface topography flowingrnfrom the south, southeastern and eastern elevated areas to the Alleydege plain and finally tornthe rift floor converging to the Awash River in the northern direction. The recharge area isrncharacterized by Ca-HCO3, Ca-Mg-HCO3 or Ca-Na-HCO3 water type, where as thernAlleydege plain and the marginal areas are characterized by a Na-Ca-HCO3-Cl water types.rnNa-HCO3-Cl and Na-HCO3 are the dominant water types in the Awash River valley and riftrnfloor. K-mica, olivine, pyroxene, plagioclase and illite are the primary minerals of thernAlleydege plain groundwater system.