Traditionally, design engineers tend to be conservative in calculating pump stationrndecision variables by focusing on peak demands that occur about1% of the time. Onrnthe other hand, optimal design and operation of pumping stations are mathematicallyrnlarge-scale non-linear problems. Consequently, there is a possibility of using anrnoptimum operation schedule on a set of non-optimum pump combinations that arernselected narrowly based on peak discharge of system demand. Thus, optimizationrnmodel is developed in this thesis work to tackle optimization problems in pumprnstations.rnOptimal design and operation of irrigation pump station system is carried out with arnhelp of a computer model developed in a General Algebraic Modeling Systemsrn(GAMS). The model makes use of the latest advances in optimization techniques thatrnutilize in-built solvers in GAMS to solve optimization problems with lots of decisionrnvariables and constraints. It is based upon one major objective function to findrnoptimized solutions of equations. Automatically generated model outputs includernselected pump type, capacity, number of pumps and optimum schedule of pumprnoperation for problems involving design phase. For existing pump stations, it simplyrngenerates a preliminary optimum operation schedule.rnThe developed optimization model was tested on previously optimized problem byrndifferent researchers and then implemented on a case study, Fentale-Qawa PumprnStation, to optimize the annualized investment cost of the pumping station and itsrnannual operating cost. GAMS results were presented and compared with five otherrnwell-known optimization techniques. The results were unique and stood second tornLagrange multipliers (LM) method in minimizing Annual Total Cost (ATC) of thernsample problem.rnImplementation of the model would have saved 35% of Initial Investment Cost inrnpumps had it been used during design phase. The savings occurred in the annualrnoperation cost is 11% compared to the optimized operation cost of the existing pumprnstation. It is clear that the developed optimization model provides the designer and thernoperator with optimized combination of design variables and operation parameters.rn(Key words: GAMS, Optimum design variables, Optimum operation schedule, Pump)