Managers of flood defences perform safety assessments of to check whether their flood defences satisfies the safety norm. They use the DUROS+ model for the dune safety assessments; this model uses hydraulic conditions and grain size as input variables and accounts for uncertainties induration and accuracy. These hydraulic conditions are calculated to execute the safety assessment without required knowledge about probabilistic calculations, and are based on probabilistic calculations. 
 
The impact of Non-Water-Retaining objects (NWO) on dune safety is currently not included in the Duros+ model (model for dune safety assessments). This study aims to include the impact of NWO's on dune safety in the probabilistic calculations for the determination of the input parameters in the Duros+ model. The impact of NWO's on dune safety in this study is based on calculation rules developed by Deltares and Arcadis.