Erosion wear is a major problem for hydraulic turbines operating on rivers from the Himalaya Mountains. The runner is the most important energy conversion component but it suffers heavy damage due to direct contact with the sediment-laden water. In this research, the runner's physical erosion wear mechanism is revealed using numerical simulations and the results are compared with damaged runners from Francis turbines in the Jhimruk Hydroelectric Center (JHC). Simulations show that high erosive wear occurs near the blade outlet on the suction side, which is consistent with site observations. Because of the high relative velocity at the runner outlet, the high accretion rate appears to be directly responsible for the heavy erosion rate. The adjustment of the guide vanes is the main action available in real situation to change the operation condition of turbine and flow separation can easily occur under off-design conditions, causing interblade vortex production. The vortex guides particles to one location where they gather, producing high accretion rates and aggravating erosion wear. This implies that the interblade vortex is the main factor that induces severe erosive wear at the blade outlet. When the angle of the guide vanes is adjusted to provide the highest efficiency, the erosion rate can be greatly reduced.