Uncertainty quantification and sensitivity analysis applied to the wind wave model SWAN

We report on measuring uncertainty in the computational results of the wind wave model SWAN (Simulating WAves Nearshore) on an unstructured mesh and exploring the sources of this uncertainty. We considered an area in the vicinity of the Saint Petersburg Flood Prevention Facility Complex and treat the results as risks on using the model results for the Facility gate operation. We found that model response uncertainty is significant for small waves (H_s < 0.3 m), and the results variability is moderate (≈ 10 %) for the extreme values of the model prediction. Thus the risk on the use of model results to predict flood threats is low together with visible uncertainty about the prediction of flood start time. Uncertainty in wind velocity has a substantial influence on the model response. In addition, uncertainty in the bathymetry, water level, and breaker index affects model output. Therefore, result uncertainty can be decreased obtaining more certain values of these model inputs.