The Falsterbo Peninsula is a low-lying area that provides a home to 7,000 residents, as well as various bird and vegetation species. To protect this densely populated area, the municipality was granted a permit to build flood protections. As part of the strategy, the dune system in the study area will be used as natural barriers against storm surges. Despite being part of the protection strategy, the strength of the dune system in safeguarding the hinterland has not been assessed. This had led to the objective of this thesis, which aims to evaluate the strength of the current dune system. To achieve this objective, the following research question were formulated: To what extent does the dune system on the Falsterbo Peninsula contribute to safeguarding the hinterland against the impact of historical storm conditions? To seek answers to this question, the research was didvided into three parts. The first part of the methodology involves collecting the environmental data such as the wind, water level and wave data. Additionally, the data on the dune's morphology was collected during the field work. The second step of the methodology involves identification of extreme conditions within the time series spanning from 1959 to 2022. Considering the complex interaction between the waves and water levels, the extreme conditions were identified based on the combined effect of the two variables, which was represented in the total water level (TWL). The sampling method was based on the peak over threshold method applied to the time series of TWL. The choice of the threshold value was based on the scenarios of potential coastal flooding in the study area. The largest storm surge, the 1872 storm, was included in the analysis to evaluate its impact on the present dune system. The dune erosion due to the selected extreme conditions was determined in the last part of the methodology. Two morphological models, the XBeach model and the storm impact model were employed to estimate the dune erosion in four transects withing the dune system. The obtained dune erosion was expressed as a fraction of the available dune volume. The maximum dune erosion was found in the transect situated at the far-right end of the dune system when facing north. The maximum dune erosion under extreme conditions in the period 1959 to 2022, estimated by the XBeach and the storm impact model are 7.67% and 32.89%, respectively. Based on these results, it can be concluded that the present dune system is strong enough to provide protection to the hinterland against the impact of extreme condtions. For the 1872 storm, the XBeach model estimated erosion percentage of 67.89%, whereas the storm impact model estimated more than 100%. This indicates that in the event of recurrence of the 1872 storm, a dune breach could be expected. While the 1872 storm may not be the design storm condition for the dune system, the storm impact model result highlights the need of reevaluation of the formulation of potential plans to reinforce the dune system. For future studies, it is strongly recommended to establish a long-term monitoring program for the dune system on the Falsterbo Peninsula. The obtained dune erosion data can be used to calibrate the morphological models to enhance its accuracy in the predictions. Additionally, dune recovery data can aid in the understanding of the dune system as a whole.

Coastal aeolian sediment transport is influenced by supply-limiting factors such as sediment sorting by grain size. Sorting processes can cause a coarsening of the bed surface and influence the formation of aeolian ripples. However, it is not fully understood what influence sorting processes have on the magnitude of this transport. In this study, sorting processes of different grain sizes when interacting with wind and their influence on the magnitude of aeolian transport are investigated by performing a tracer study and developing a conceptual model. Sand grains were painted in different colors according to particle size and placed on Noordwijk beach, Netherlands. Several experiments were conducted with varying wind speeds. Surface sampling and cameras tracked the sand color movement on the bed surface, and wind speed and direction were measured. The tracer experiments show that for moderate wind conditions, ripples developed. Once the ripples have formed, the supply of finer tracer grains in downwind direction decreased over time, while the supply of coarser grains remained constant. A strong linear relationship between ripple speed and wind speed was found. For higher wind velocities, no ripples or differences in transport of grain size fractions were observed. Alternating phases of erosion and deposition of upwind sand were observed which could not be related to local variations in wind speed. Based on these results and literature, a conceptual model for an Active Bed Surface Layer (ABSL) with two regimes corresponding to moderate (I), and high (II) wind speeds was developed. The concept enables to estimate the magnitude of aeolian sediment transport as a function of wind speed, bed characteristics, and upwind sediment supply. For Regime I, a linear relationship between sediment transport and wind speed is suggested and for Regime II a third power relationship in combination with a process-based model accounting for supply limitations is suggested.

The Netherlands is a country with a history of human activity along the coast to ensure water safety. In the 1990's a new approach to coastal management was adopted that allowed for more experimentation in the Dutch dunes. Since then a slew of different types of projects have been undertaken, one of which is the construction of foredune blowouts. Foredune blowouts are gaps or indentations in the dunes from which bare sand can erode due to the wind. The motivation for the creation of constructed foredune blowouts can range from wanting to reintroduce gradients back into the landscape to ecological restoration, or water safety. Over the years different construction methods and designs have been created, however the evaluation of these projects has been difficult in the past due to broadly defined goals and limited monitoring data. The aim of this research is to investigate the potential of constructed foredune blowouts have in achieving water safety and preserving natural values in the Netherlands by modeling constructed foredune blowouts and evaluating the effect of various design aspects. Insight into the effects of different designs of foredune blowouts is gained through the use of a modeling study that is set up in AeoLiS, a supply-limited aeolian sediment transport model. Different combinations of width, orientation and number of foredune blowouts are simulated in a stretched profile of a section of the Dutch Coast, leading to thirty two simulations. Additionally three alternate methods of implementing foredune blowouts as well as a scenario without a foredune blowout are simulated. Model results show a pattern of erosion in the intertidal range and deposition along the dunefoot with limited sediment traveling from the beach through the foredune blowout. There is a clear pattern of erosion and deposition along the erosional walls of the foredune blowout and a limited development of a depositional lobe behind the blowout. Simulation of a foredune blowout induced through the removal of top soil and vegetation exhibits similarities with observations in the field. Constructed foredune blowouts offer a method of creating areas of bare sand which can create space for ecological succession in the vicinity of the blowout. The sand that is removed may also be used to reinforce weaker areas of the dune row. They can offer a diverse looking landscape if that is desirable. However model results do not indicate that constructed foredune blowouts facilitate additional growth of the dunes. The changes in bed level in the model are primarily a redistribution of sediment already situated within the primary dune row.

In future decades, coasts will be exposed to increasing risks because of climate change and sea level rise, which poses an increased threat of coastal inundation, erosion and ecosystem loss. The natural variability of coasts can make it difficult to identify these impacts. Most beaches worldwide show evidence of recent erosion. Sea level rise is currently not necessarily the primary driver, but will become very relevant in the future. Understanding both the short-term and long-term development of a coast is considered essential for coastal managers, in order to maintain safety in the future. For a generic evaluation of the state of the coastal zone, it is also important that not only the coastline changes are examined, but also the behavior of the dunes. The interactions between transport mechanisms should be investigated in order to make a good prediction of the large-scale and long-term development of the coastal zone. Therefore, the adaptation of the dunes and the coastline to interacting cross-shore and longshore sediment transport processes must be studied. To get a comprehensive view on those interactions, a new coupled surfzone-dune model is developed and validated. This coupled model consists of a combination of coastline model ''Unibest-CL+'' and coastal profile model ''the CS-model''. The coupled model has the capability to simulate beach and dune evolution at decadal to centennial timescales including the relevant sediment transport processes that impact the beach and dune evolution: dune erosion and overwash, aeolian dune build-up, beach erosion and accretion due to gradients in longshore sediment transport, adaptation to sea level rise and response to nourishments. The model is tested quantitatively based on the sediment balance, in a very simple and a more complicated academic case focused on the individual effects of all transport mechanisms included in the coupled model. All test cases in the simple case -- which consist of the smallest scale situation the coupled model is able to simulate -- demonstrate sediment conservation and therewith confirm that the implementation of the different transport equations and their interaction in the coupled model is correct. In the complicated test cases – covering a varying number of cross-shore profiles along a larger stretch of coastline – the accuracy of the predicted sediment fluxes and the subsequent coastline and dune volume changes have been determined. The accuracy of every individual transport mechanism included in the coupled model is found to be sufficient and the different sediment fluxes within the coupled model are balanced. After model testing, the model is used to hindcast the 22-year long coastal evolution near IJmuiden. The dune evolution in this highly dynamic case is simulated reasonably. Furthermore, the coastline evolution is predicted in accordance with the data. Overall, the coupled model is found to quantitatively and qualitatively perform satisfactory. The model is capable of quantifying the long-term beach and dune evolution with interacting longshore and cross-shore processes. Though coupling the models and therewith simulating the longshore sediment transport gradients instead of deriving them from data induces model uncertainties, the application of the model on the IJmuiden case shows that it is possible to simulate the longshore sediment transport gradients using a schematized wave climate to predict the dune volume evolution sufficiently. Furthermore, the interaction between the cross-shore and longshore sediment transport processes enables the simulation of the redistribution of nourishments, improving the predictive ability of both model components with regard to the coastline evolution as well as the evolution of the dune volume. For future research it is recommended to use the coupled model to look into nourishment strategies and their effectiveness on the long-term, climate change scenarios and their effect on decadal to centennial scale dune and beach evolution and the relative importance of different transport mechanisms on the long-term beach and dune evolution.

Coastal dune systems provide valuable functions that are threatened by human activity and climate change. Preserving and strengthening coastal dunes through coastal management and the implementation of interventions require accurate predictions of coastal dune development. The development of coastal dunes is driven by complex interactions between aeolian and marine processes. The aim of this thesis is to determine how marine and aeolian processes influence coastal dune development on yearly to decadal scale. Specifically, the effect of sea level rise and aeolian processes related to grain size were investigated.@en