Einfluss benachbarter Küstensysteme auf die Erosion von Dünen Systemen (MoDECS)
Physik, Chemie und Biologie des Meeres
Zusammenfassung der Projektergebnisse
Storm events have a prominent role in the assessment of coastal stability at beach and dune systems. Any assessment necessarily involves two steps. First, the occurrence of storm events needs to be accurately identified, which involves a storm classification. Second, the erosion risk needs to be analysed using a reliable method. Using statistical methods and process-based numerical modelling, a novel twostep framework was developed to investigate the storm impacted beach and dune erosion. Work was carried out with the collaborators from Leibniz University Hannover, NLWKN-Norderney, National Oceanographic Centre (Liverpool, UK), University of Brest (Brest, France) and CEREMA (Paris, France). A morphodynamically relevance storm classification was formulated considering the sequencing of wave height (Hs) and water level (TA: total water level-Astronomical tide). Approach used measured data from 2005 to 2018 at the Sefton coast (macro-tidal), and analysed by the properties of the probabilistic distributions. So far, storm classifications used a single environmental parameter (Hs, TA, Wind speed etc.). The proposed descriptor captured a wide range of severity events, which showed increased storm occurrence per year representing global change of extreme events, and more than 35% of events compared to single parameter classifications (e.g. Hs). Within the 3-month of XBeach simulation, the erosion volume of the proposed classification was higher by 12% than the existing Hs classification. The developed method was verified applying at the Norderney meso-tidal beach and dune system. For the simulation of storm erosion within a 1.5-month period, there were 3 events. However, the existing classifications using TA and wind speed alone captured only 15% of the last event. Simulated erosion of the proposed classification agreed well with the measured erosion volume (BSS=0.69, RMSE=0.32 m), while the maximum deviation was found using the wind speed alone (BSS=0.14, RMSE=0.53 m). Based on the Sylt meso-tidal coast, the effect of short wave groups on long waves (‘roller dynamics’) on the beach and dune erosion was investigated using two process-based models Delft3D and XBeach. Simulated waves in Delft3D had the highest agreement with the measured waves (R 2 = 0.91 and RMSE = 0.14 m). Both models predicted a similar storm erosion pattern along the coast, albeit high magnitudes in XBeach. Delft3D cannot produce comparable storm erosion to XBeach, when the roller dynamics and dune avalanching are considered. Delft3D is less sensitive to the roller dynamics than XBeach. Including roller dynamics in Delft3D increased storm erosion up to 31% and in XBeach decreased the erosion down to 58% in the nearshore area, while the erosion in the dune area increased up to 13% in Deflt3D and up to 97% in XBeach, indicating the suitability of XBeach for dune erosion modelling. Climate change impacts (sea level rise and future wave climate) on the nearshore wave dynamics at the Vougot macro-tidal coast were investigated using statistical approaches and numerical modelling. A measured 6-week wave time series was projected to future using three globally averaged sea level rise (SLR) scenarios for 2100, and combined SLR and wave climate scenarios for A1B, A2, and B1 emissions paths of IPCC. The B1 wave climate predicted the highest increase of storm occurrence. Simulated waves in all scenarios showed larger relative changes at the beach than in the nearshore area. The maximum increase of wave energy for the combined SLR and wave scenarios was 95%, while only 50% for the SLR-only scenarios. The effective bed shear stress from waves and currents increased up to 190% (combined) and 35% (SLR-only): the changes in waves and currents will likely have significant impacts on the nearshore sediment transport. Therefore, combined SLR and future wave climate scenarios need to be used to evaluate future changes in local hydrodynamics and their impacts. The proposed two-step framework is universally applicable to identify storm occurrence and to investigate the storm driven erosion on beach and dune systems. Simulating the morphological changes between the available surveys can provide high resolution spatiotemporal information for a comprehensive understanding of the storm erosion, which supports to select suitable coastal management strategies (e.g. estimating beach nourishment). For the simulation of a storm period with intermittent calm periods, it is suggested that applying a time-varying parameter setting for wave dynamics and sediment transport to capture storm erosion and post-storm beach recovery processes could improve results. Further studies are necessary to investigate the climate change impacts on local hydrodynamics and storm erosion considering ensemble approaches of future scenarios. An ongoing-work investigates beach and dune erosion at the Vougot coast as a part of a collaborative project with University of Brest, France.
Projektbezogene Publikationen (Auswahl)
- Role of water level in storm impacts of a hyper tidal coast, Proc. Coastal Sediment conference, Florida, USA, 2019
Dissanayake, P., J. Brown, P. Sibbertsen and C. Winter
(Siehe online unter https://doi.org/10.1142/9789811204487_0109) - Storm classification and the investigation of impacts on beach/dune, Proc. Coastal Structures conference, Hannover, Germany, 2019
Dissanayake, P., A. Wurpts and C. Winter
(Siehe online unter https://doi.org/10.18451/978-3-939230-64-9_063) - Modelling the effect of coastline orientation on storm erosion at the Sylt island, North Sea, Proc. International Conference on Coastal Engineering (vICCE), Sydney, Australia, 2020
Dissanayake, P. and C. Winter
(Siehe online unter https://doi.org/10.9753/icce.v36v.papers.50) - Climate Change impacts on coastal wave dynamics at Vougot Beach, France, Journal of Marine Science and Engineering, 9 (9), 1009, 2021
Dissanayake, P., M.L. Yates, S. Suanez, F. Floc’h and K. Krämer
(Siehe online unter https://doi.org/10.3390/jmse9091009) - Modelling Short- and Long-Term Dependencies of Clustered High-Threshold Exceedances in Significant Wave Heights, Journal of Mathematics, 9 (21), 2817, 2021
Dissanayake, P., T. Flock, J. Meier and P. Sibbertsen
(Siehe online unter https://doi.org/10.3390/math9212817) - Using a two-step framework for the investigation of storm impacted beach/dune erosion, Coastal Engineering, 168 (103939), 2021
Dissanayake, P., J. Brown, P. Sibbertsen, C. Winter
(Siehe online unter https://doi.org/10.1016/j.coastaleng.2021.103939) - Modelling the effect of ‘roller dynamics’ on storm erosion: Sylt, North Sea, Journal of Marine Science and Engineering, 10 (3), 305, 2022
Dissanayake, P. and J. Brown
(Siehe online unter https://doi.org/10.3390/jmse10030305)
