Uncertainty in water level predictions due to various calibrations

The modelling of river processes involves numerous uncertainties, resulting in uncertain model results. Knowledge of the type and magnitude of uncertainties is crucial for a meaningful interpretation of the model results and the usefulness of results in decision making processes. This case study comprises an uncertainty analysis of the effect of the discharge data used for calibration on the water levels. The roughness value of the main channel is calibrated on eight different water levels to assess the influence of the data used for calibration on the uncertainty in the model predictions. Comparison of the data used for calibration with verification model results gives insight in the effects of extrapolation of the calibration parameter. It is concluded that the uncertainties in the roughness coefficient of the main channel results in a total uncertainty up to 20 cm in predicted water levels similar to water level used for calibration. This indicates that extrapolation of the roughness coefficient introduces significant uncertainty in design water level calculations. 2 J.J. Warmink, M.J. Booij, H. van der Klis, S.J.M.H. Hulscher