Beles River Basin is part of northwestern lowlands and its adjacent highlands. It is found inrnthe southwestern direction of Lake Tana, It has the total areal coverage of 14,200 sq. Km andrnelevation varies from 500 to 2,700masl. The Basin has all climatic zones, except alpine. Thernobjective of the thesis work was characterizing the hydrgeology and hydrogeochemistry of thernbasin using integrated methodology and approaches. Secondary data has been collected fromrnthe respective institutes and organizations and primary data of water samples for waterrnchemistry was analyzed in the laboratory.rnThe rainfall pattern of the Basin is unimodal. It has an aerial depth of precipitation ofrn1352.9mm/yr that was computed using isohyetal cotour map method. The precipitationrncondition has high orographic effect. The hydrograph of the two main rivers reflects thernunimodality of the rainfall. The variation of these rivers discharge is very high from dry tornrainy season that shows the infiltration of the Basin is low.rnThe Basin has geology of Precambrian basement complex, undifferentiated formations,rntertiary and quaternary volcanic and quaternary sediments. It has lithological units of gneissrnand associated high-grade metamorphic rocks, low-grade supra-crustal metamorphic rocks,rnsyn- and post-tectonic intrusive of acidic to intermediate composition, Cenozoic volcanicrnrocks, and quaternary sediments. The most important tectonic settings are dominantly alignedrnN-S and NE-SW direction.rnHydrogeological map of the Basin was produced based on previous reports and maps andrnfield observations of geology, topography and water point inventory, weathering andrnfracturing condition of the formations. Accordingly the hydrogeological characterization ofrnthe area revealed; porous aquifers (alluvium, colluviums), fissured and karst aquifersrn(marble), fissured aquifers (sandstone and volcanic rock), fissured aquifers of low potentialrn(some non-carbonate metamorphic and intrusive rocks) and aquitards (some non-carbonaternmetamorphic and intrusive rocks). Accordingly the aquifer of the basin was classified in tornvery low, low, intermediate, intermediate to high and high productive formations.rnThe regional recharge zones are the highlands of the Basin Such as; Wombera, Balay, Dangurrnand Kar mountains and highlands areas of Dangila and Achefer. The discharge areas arernintimately linked with groundwater flow lines and the regional groundwater flow direction isrnto the southwest following the topographic gradient.rnHydrochemical data shows that evolution of major ions, water types, and direction ofrngroundwater flow. It shows a general trends increasing total ion concentration along flowrndirection.rnGraphical presentations of the physical and chemical parameters of the water samples providerna good deal of information on the characteristics of ground water flow systems, recharge andrndischarge zones, and evolution of major ions in the basin. The general natural water type ofrnthe basin is Ca dominated cation and HCO3 dominated anion (Figure6.9) and has low (freshrnviirnwater range) TDS values. The TDS can be relatively grouped in to three groups (figure 6.9)rnlow medium and high. But there are a very few samples with Na dominated cations and Clrndominated anions. In general the dominancy of bicarbonate ions shows the groundwater of thernarea is shallow.