The technical capacity to predict the erosion process is instrumental for the optimization of the runner designs and operation strategies of hydroelectric plants. A multiscale model of erosion recently formulated by the authors and validated on a laboratory-scale jet impingement case is used to study the erosion of a prototype-scale Pelton runner. The model is shown to provide physically-sound descriptions of the sediment impact condition distributions on the bucket surface; furthermore, the erosion distribution obtained is explained in terms of these underlying impact condition distributions. The model predictions for the erosion depth distribution on the bucket surface are validated with the corresponding experimental data, resulting in an average error of 35% for eight point-wise comparisons, 14% for line-averaged values along four transversal sections, and 4% for the surface-averaged erosion depth, directly linked to the total eroded mass. A careful error propagation analysis of the comparison between simulation and field data yields an uncertainty of ±22%. Based on these considerations, the modeling error is estimated to be 26±22%. The results obtained, namely quantitative predictions of the erosion of industrial-scale hydraulic machines, have no precedent in the literature; they demonstrate the accuracy and transferability of the multiscale model of erosion and suggest an improvement over the state-of-the-art computational fluid dynamics models based on empirical erosion correlations.