|ediment bypass tunnels are a countermeasure for reservoir sedimentation. However, it is known thatabrasion damage occurs on the tunnel bottom invert because the sediment flows with high velocitycondition. In this paper, we focused on process of abrasion damage at Koshibu dam sediment bypass tunnel,which has been operated since 2016. In order to analyze the abrasion volume, DEM images were createdusing 3D point cloud data obtained by MMS. As a result, it was clarified that the damage progress is notuniform in the longitudinal direction. Furthermore, by defining the local gradient and calculating the loadvariation before and after the abrasion, the mechanism of local abrasion damage was satisfactorilyexplained.