The purpose of this thesis was to setup a three-dimensional numerical model on SSIIM 2for the peaking pond of the Paso Ancho Hydropower Project. Not limited to numericalmodel, failure reasons for the desander is also studied. The main aim of the numericalmodel is to obtain the distribution of bed sediment in the pond and compare with thedata from the field.The peaking pond has severe sediment problem due to the poor efficiency of thedesander located at the headworks. All the sediments entering through the intake passesthrough the desander and enter in to the pond. This has led to loss of capacity of thepond and extra financial cost for implementation of different sediment removal methods.At present, 200mm dredge installed by SediCon is removing the sediments from thepond. It was installed in August 2018 and by January 2018 had removed around14458m3 volume of sediments. The total capacity of pond is 70000m3.A survey was done by Acoustic Doppler Current Profiler (ADCP) to obtain the bathymetryand velocity profile of the peaking pond. Sediment samples from the bed of the pond wasanalyzed in the lab to obtain the grain size distribution of the samples. The discharge inriver was measured to obtain the inflow in the pond. These field data are compared withthe results from the SSIIM model.A three-dimensional numerical model has been setup to perform hydraulic and sedimenttransport simulation. A first model is setup with the measured discharge and surveyedgeodata to perform a water flow simulation. The obtained velocity magnitude iscompared with the surveyed velocity profile data. The hindrance most encountered wasin shaping the inflow structure for the peaking pond to imitate the same flow pattern asactual in the site. The model showing similar pattern of flow is chosen and two additionalcases of water flow simulation are performed which later is used for sediment transportsimulation. Second model is run with the higher discharge corresponding to the dischargeof wet season at which the pond receives high sediment inflow. And third model is runagain on the higher discharge but the geodata of original geometry of the pond is used,which has no sediment deposition. The second and third cases of water flow simulationare used to the run the sediment transport simulation. From the sediment simulation, thebed grain size distribution is obtained and compared with the sediment samples takenfrom the pond.Number of changes to the geometry and location of the inflow were done and differentalgorithms and parameters were used simultaneously to produce a likely result. Theresult showed similar flow patterns but different bed sediment distribution whencomparing with the field data. There are still uncertainties concerning the input data,geometry of inflow and outflow. The sediment deposition and distribution pattern inpond is affected by the daily fluctuation of water level in the pond. There is a dailylowering down of water level to the lowest possible operation level since this is a dailypeaking type project and has different inflow and outflow discharge. The numerical modelis run in the scenario assumed that in the wet season, when discharge is high in theriver, the level of water at the pond is maintained at constant normal water levelthroughout the day and has an equal inflow and outflow discharge.To conclude, the model requires more calibration and validation from the field data andfurther work on the geometry of model is also recommended to use the model for theprediction of sediment distribution.