Research program on 2DH processes for complex dune flood defences : calibration and validation datasets for application of XBeach in complex dune defences (background report)

A large part of the Netherlands is protected against coastal flooding by dunes, which function as completely sandy flood defences. Flood defence managers in the Netherlands are legally required to assess the failure risk of the dune flood defences under their management. Within the current basic toolkit of the BOI (Assessment and Design Toolkit) programme, a one-dimensional assessment method is available for the assessment, design and management of simple dune flood defences. These are dune flood defences consisting of a single row of dunes located along long, uniform coastlines. This method has not yet been developed or validated for application to complex dune flood defences, which include multiple dune rows or dunes located along non-uniform (e.g. curved) coasts. The “Knowledge for Flood Defences” research programme develops knowledge on the relevant physical processes for determining the flood risk of primary flood defences. This report describes laboratory experiments and field measurements that may be used in future research to calibrate and validate two-dimensional XBeach models for the safety assessment of complex dune flood defences. In line with the Roadmap for Sandy Flood Defences (Rijkswaterstaat, 2023), attention is given to three sub-archetypes of complex dune flood defences: curved coasts, multiple dune rows, and horizontal connections between dunes and hard flood defences. In addition, the report describes several datasets of elementary dune flood defences that can be used to investigate the differences between one-dimensional and two-dimensional processes along alongshore-uniform dune coasts. The report proposes a provisional separation of datasets for calibration and validation purposes, which will need to be confirmed following the future development of detailed calibration and validation plans.