Assessing the dune system for coastal safety utilizing morphological models

 Assessing the dune system for coastal safety utilizing morphological models

Emmy Sukchaiwan¹, Glenn Strypsteen², and Caroline Hallin³

¹SWECO, Malmö
²Hydraulics and Geotechnics, Department of Civil Engineering, Bruges Campus, KU Leuven, Bruges, Belgium (glenn.strypsteen@kuleuven.be)
³Faculty of Engineering, Lund University, John Ericssonsv 1, 221 00, Lund, Sweden

The Falsterbo Peninsula in Skåne, Sweden, is a low-lying area that provides a home to 7,000 residents. To protect the densely populated area, a dike and the natural dune system are used as safety barriers against storm surges. Despite being part of the protection strategy, the dune system’s capacity to protect the hinterland from storm impacts remains unexplored and requires comprehensive assessment. This study aims to provide a numerical representation of the severity of dune erosion due to historical storm conditions spanning from the period 1959 to 2022. The 1872 storm is the largest storm surge in the study area. Suggesting its potential recurrence, the 1872 storm was included in the analysis.

To increase the confidence of the prediction of dune erosion, two different morphological models were utilized: the process based XBeach model (Roelvink et al., 2010) and the analytical storm impact model (Larson et al., 2004). Although both models are capable in estimating dune erosion during storm conditions, they differ in their approach and level of complexity. The XBeach model is selected for its comprehensive representation of hydrodynamic and morphodynamic processes, while the storm impact model is chosen for its simplicity. This simplicity makes the storm impact model easier to use, unlike the XBeach model, which can be more computationally intensive.  Due to the lack of observational dune erosion data in the study area, model calibrations from other studies were used.

The eroded volume is expressed as a fraction of the available dune volume in that specific transect. The maximum dune erosion under storm conditions in the period 1959 to 2022, estimated by the XBeach and the storm impact model are 7.7% and 32.9%, respectively. These numerical results suggest that the dune system is capable to withstand storm conditions that had occurred during this 63-year timeframe. However, this conclusion is not valid when considering the estimated dune erosion resulting from the 1872 storm. For this event, the XBeach model estimated 67.9% erosion, whereas the storm impact model predicts a dune breach.

A comparative analysis revealed that large difference in the model results can be found in extreme conditions with long storm duration. This divergence is primarily attributed to the incorporation of the negative feedback mechanism in the XBeach model, which is absent in the simplified solution of the storm impact model.  The study’s findings highlight the critical role of negative feedback mechanisms in model outcomes.

 

 

 

Roelvink, D., Reniers, A. J. H. M., Van Dongeren, A. P., Van Thiel de Vries, J., Lescinski, J., & McCall, R. (2010). XBeach model description and manual. Unesco-IHE Institute for Water Education, Deltares and Delft University of Tecnhology. Report June, 21, 2010.

Larson, M., Erikson, L., & Hanson, H. (2004). An analytical model to predict dune erosion due to wave impact. Coastal Engineering, 51(8-9), 675-696.