Akaki River Catchment is a sub catchment of Awash drainage basin with an approximaternsurface area of around 1462km2, boundary length of 216km and it lies at the eastern edgernof the Western Ethiopian plateau that descends to the Main Ethiopian Rift. The capital city,rnAddis Ababa and other smaller towns are found in this catchment. The catchment is totallyrncovered with volcanic rocks of various ages that correspond to different stratigraphic units.rnThe rocks were subjected to rift tectonics that is manifested by a number of fault systemsrnhaving a general trend of the rift system (NE â€“ SW).rnAs numerical groundwater flow models represent the simplification of complex naturalrnsystems, different parameters were assembled into conceptual model to represent therncomplex natural system in a simplified form. The conceptual model was input into thernnumeric model to examine system response.rnNumerical groundwater simulation was carried out using MODFLOW, 1996 (McDonald andrnHarabaugh, 1988). Two dimensional profile model was developed considering the systemrnto be under steady state condition and assuming flow system view point. Three scenariosrnof increased withdrawals and one scenario of decreased recharge were simulated to studyrnsystem response. Model calibration was carried out by trial and error calibration methodrnusing groundwater contours constructed from heads collected in 122 observation points.rnThe calibration showed that about 81% of simulated heads were within the calibrationrntarget and the overall root mean square error for simulated hydraulic heads is aboutrn10.42m. The poor fit at some points was due to numerous limitations associated with thernmodel.rnModel sensitivity analysis was conducted by taking recharge and hydraulic conductivity asrnthe model is most sensitive to them. A change in recharge by 20%, 40%, 60%, -20%, -rn40%, and -55% resulted in RMS head changes from the calibrated value by 17%,rn58%,106%, 26%, 86% and 147%, respectively. Equal changes in hydraulic conductivity (inrnthe order mentioned for recharge) resulted in RMS head changes from calibrated value by 12%, 33%, 55%, 19%, 90% and 193%, respectively. In addition, the effect of varying theserntwo parameters on stream leakage was tested. Accordingly, changes in steady staternestimated recharge by 15%, 30%, 45%, -15%, -30%, and -45% resulted in change inrnstream leakage from calibrated value by 12%, 24%, 36%, -20%, -24% and -28%,rnrespectively. The same changes in hydraulic conductivity (in the order mentioned forrnrecharge) resulted in stream leakage changes from calibrated value by 1.9%, 3.7%, 5.5%,rn-2.1%, -4.2% and -6.9%.rnThe results of the numerical simulations showed that increased well withdrawals by 15%,rn25% and 45% resulted in RMS (Root Mean Square) head changes of 0.7m, 1.3m, and 2m,rnrespectively. The same change in well withdrawal resulted in 1.4%, 2.4% and 3.7%rnrespective changes in river leakages compared to the steady state simulated value.rnSimilarly, these increased withdrawals resulted in reduction of the calibrated subsurfacernoutflow by 3.4%, 6.4%, 9.1%, respectively.rnOn one hand 20% decrease in steady state simulated recharge resulted in reductions ofrngroundwater level by 5.6m, stream leakages by 15.8% and subsurface outflows by 5%.