Calibration and model performance decay in prediction of the effect of human intervention in river systems

River managers intervene in the natural system to increase flood safety, inland shipping or biodiversity by dredging, sediment nourishments or other river engineering works. Complex hydraulic numerical models often form the basis of such decision making. Experience has shown that parameters of these complex models require calibration to increase performance to acceptable levels. However, we hypothesize that implementation of interventions will generally lead to decay in model performance. We used an experimental set-up to quantify this decline in performance due to modelling of levee relocation. Results show performance decay for all calibrated parametersets and an increasing uncertainty as to the predicted effect of the intervention. In closing, we argue that continued model testing and a better understanding of the relationship between reference and modified models might lead to improved model use for river management. Such sustainable model management might be a necessity in sustainable river management.