7. Modelling of Medium-Term (Decadal) Coastal Foredune Morphodynamics- Historical Hindcast and Future Scenarios of the Świna Gate Barrier Coast (Southern Baltic Sea)

Coastal foredunes are developed as a result of interplay among multi-scale land-sea processes. Natural foredune ridges along the Świna Gate barrier coast (southern Baltic Sea) developed since 6000 cal. year BP provide an excellent laboratory to study the land-sea interaction under a medium- to long-term climatic control. In this paper we investigate several basic driving mechanisms of coastal foredune morphodynamics as well as natural environmental factors involved in shaping the foredune geometry by a numerical model. The model couples a process-based module for subaqueous sediment transport and a probabilistic-type module for subaerial aeolian sand transport and vegetation growth. After an evaluation of the model performance for a 61-year (1951–2012 AD) historical hindcast of the foredune development along a 1 km-long section of the Świna Gate barrier coast, the model is applied for a future projection of the same area to 2050 AD based on three different climate change scenarios. The climate change scenarios represent three different impact levels with regard to their capacity to shape the coastal morphology. Simulation results demonstrate a remarkable variability in foredune development even along a small (1 km) coast section, implying that the medium-term land-sea interaction and foredune morphodynamics is quite sensitive to boundary conditions and various processes acting on multi-temporal and spatial scales. Foredune morphodynamics such as migration, bifurcation, destruction and separation are determined by different combinations of storm frequency, onshore sediment supply rate and relative sea-level change. In contrast to a low rate of relative sea-level rise during the last few decades, an accelerated sea level-rise over the twenty-first century predicted by existing literature, would result in a dramatic and non-linear response from the foredune development according to our simulations.