Abstarct: One of the most basic issues in the study of hydraulic structures is the issue of sediment and how to manage it.The shallow reservoir is one of the structures that are used to trap and remove suspended sediments before the flow enters the hydraulic facilities. Therefore, creating a suitable solution to increase the trapping efficiency in the shallow reservoir is considered as a major challenge for the designers of these structures. In this research, as an innovation, through numerical simulation by Flow-3D software version 2.11, the effect of submerged vanes on the trapping efficiency of shallow reservoir was investigated. The VOF method was used to predict the free surface profile and the k-ω turbulence model was used to calculate the Reynolds stress and also the GMRES method was used for the pressure solver. This research includes three main parts; In the first part, in order to validation, the numerical model was simulated with flow conditions without suspended sediment with the same conditions as the laboratory sample, and a good match was observed in the flow pattern with the laboratory model. In the second part, the model was compared with the laboratory model by the stream containing the suspended sediment. In order to increase the modeling verification, the parameters related to sediment in the software were adjusted by trial and error in such a way that the difference of the sediment accumulation profile compared to the laboratory model reached the lowest possible value. In the third part, submerged vanes were evaluated in two general groups, vanes without deviation in relation to the flow direction and vanes with deviation in relation to the flow direction. Five transverse narrowing ratios of 0.13, 0.19, 0.38, 0.88, 1 in four ratios of the distance from the entrance 0.03, 0.08, 0.17, 0.5, with a fixed ratio of height to depth of 75 0/ were installed in the tank, and the best efficiency of each group was controlled with the height to depth ratio of 0.6 and 0.9. After 5400 seconds of sediment entering the reservoir, the greatest increase in trapping was 37.4% in the form of three vanes with an angle of 60 degrees with a height ratio of 0.75, a narrowness ratio of 0.88 and a distance ratio from input 0.03, 0.08. 0.3 was obtained.