*3.3. Model Validation*

The model was applied to five catchments (Ribera Salada, Isabena, Hopland, Guerneville, and Meuse) where data for validation were available. For model validation, it was assumed that there were no observed suspended sediment data during the validation period. Thus, Cb(t) was substituted for C(t) as model input for phases 1 and 3. The number of flood events in the five catchments ranged from 10 to 101 during the validation period. The proportion of the cumulative mass of fine sediments released from the sediment bed during a flood event to total suspended load ranged from 44% to 66%. The mass was not compared in Hopland, where C data were not continuous during the validation period [32]. The validation results for each catchment are summarized in Table 3. The average RSR and R of the five catchments were 0.65 and 1.11, respectively. The model estimated the cumulative released mass of fine sediments well, with only 2% bias, for the Ribera Salada catchment (Figure 5a). The largest RSR of 1.04 was observed in the Isabena catchment, where R was 1.61 (Figure 5b). For the Meuse River, the model showed a good fit with the observations for the 10-year validation period with 20% bias (Figure 5c). Overall, the model bias in the five catchments ranged from 2% to 61% (Table 3).
