The studied area is located 335 Km. southwest of AddisrnAbaba in the southwestern Ethiopian plateau . Over half of thernmap-area is underlain by thick basalt flows inter layered withrntuffs and volcanoclastic sediments . The Jimma Volcanics, whichrnis mainly composed of massive rhyolite in thick flowsrnalternating wjth trachytes, tuffs, ignimbrites and subordinaternbasalts, underlain small area in the eastern and northeasternrnpart of the basin.rnBased on the hydrometeorologic data collected for the lastrn38 years an attempt has been made to calculate the hydrologicalrnparameters l i ke precipitation, evapotranspiration, and runoff.rnThe ann ual mean rainfall in the basin is 1476.89 mm . Thernvalues of the annual potential evaportanspirtion and actualrnevapotranspiration are 837.51 mm and 822.29 mm respectively.rnThe only runoff that leaves the studied area comes through Boyernriver and is 90 .77 million cubic meter of water. The amount ofrnwater which is actually available to recharge the groundwaterrncirculation within the hydrogeological basin is 51.14 millionrncubic meter .rnThe hydrogeological character of the outcroppingrnlithotypes was discussed with particular reference torninfiltration and their water bearing capacity.rnThe hydr ogeology of the area varies in different parts ofrnthe basin. There is a great potential of groundwater in thernvalleys which is partly filled with alluvial sediments while aless significant ameunt exist within the velcanic recks fermingrnthe uplifted berders ef the valleys.rnDeterminatien ef the hydraulic parameters likerntransmissivity and permeability have been carried eut. Due to.rnthe absence ef ebservatien well nearby a discharging wells itrnwas impessible to. calculate the ceeff icient ef sterage, arnsignificant earameter which measures the velume ef water thernaquifer releases er take into. sterage. Fer basaltic aquifersrna transmissivity value ef 18.39 m2/day and a permeability valuernef 3.31 x 10-1 cm/ sec. have been calculated. A transmissivityrnvalue ef 1.89 m2 /day . and a permeability value ef 1.62 x 10-5rncm / sec. have been co.mputed fer beth alluvial and rhyeliticrnaquifers.rnBecause ef the lack ef bere wells in the seuthwest, seuth,rnand seutheast lewer mest part ef the basin a thereugh study efrnthe actual variatien ef greundwater level was net pessible.rnFer the ether part ef the basin, apprepriate greundwater levelrncenteur lines was censtructed on the basis of the availablernstatic level data.rnPreper chemical analysis ef beth the greundwaters andrnsurfaces water carried eut in the basin shew lew tetalrndisselved selids. All of the samples have less than 1000 mg / lrndisselved selids. The analysed samples also. cempared with thernacceptable standard for human, agr icul tural, and industr ialrnuse.