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The increasing sedimentation of Mrica reservoir shows that the sedimentation control has not been effective. The sedimentation control have been made include the disposal of sediments that settle in the reservoir by dredging or flushing. However, the results are not optimal. This is caused by the large volume of sediment entering the reservoir each year. Controlling volume of sediment that goes into the reservoir have also been carried out by conducting a watershed conservation program and building checkdam in the upstream Mrica reservoir. However, the existing checkdam is still less effective in controlling sediments, especially suspended load sediments, that are transported in the river. Therefore this study was carried out by adopting the sediment trap concept to deposit sediments that escaped from checkdam. This study simulated changes in the width of the downstream channel of checkdam by three variations using HEC-RAS. There were width of 20%, 40% and 60% wider than initial width. The results showed the effect of changing the channel width on sediment concentration and volume sediment deposited. Based on the results of the study, the change in width to wider than the initial width could increase volume sediment deposited and decrease sediment concentration.