In 1990 the Dutch government passed legislation that dictates the South West Texel coast must be maintained with regard to the 1990 coastline. The coast is currently maintained by applying shoreface and beach nourishments with an interval of approximately 3 years, because it experiences erosion. The problems with this approach are that the mobilization of the dredging vessels is expensive, dredging vessels cause nuisance in the ecological system and moreover, the dredging vessels emit carbon dioxide and therefore contribute to climate change. The first goal of this study was to to investigate if an alternative coastal protection strategy is able to mitigate the drawbacks of the current scheme. Consequently, the application of a mega nourishment was chosen over a cross-shore dam or an outer delta nourishment. To optimally design a mega nourishment, a morphological analysis was executed that focused on elements in the sediment balance of the system. Using Vaklodingen and JARKUS data, volume changes of each transect were identified for 4 parts of the transect: the dune, the beach, the shallow part of the foreshore and the Molengat channel. It was found that dunes started growing from the moment that the nourishments were structurally applied. When nourishments are aborted, it is expected that the shrinking of the dunes will resume, just like the pre-1990 situation. The Molengat in the transects was found to be moving towards shore before the nourishment program started, and its landward movement was not influenced by the implementation of the nourishment program. The Molengat filling rate was projected into the future, leading to a fill date in transects 880-930 by 2035, and in transects 930-1013 by 2055. In transects 1013-1108 and 1108-1210 the Molengat has already been filled. The late projection filling date of transects 930-1013 is a reason to put the mega nourishment at that location, combined with the largest natural erosion occurring at the same location. The application of a mega nourishment is done by putting 20 years worth of sediment at transect range 945-1053 in one construction project. Simultaneously, the mega nourishment aims to diffuse sediment alongshore in the shallow part of the transects, providing sediment to adjacent transects. The sediment supply to other transects could be able to limit the shrinking of the adjacent dunes, or even let them grow. However, this requires further investigation. Delft3D Model results showed that sediment transport in this area is mainly caused by waves on the NUN-shoal, and by the current in the Molengat ebb-tidal channel. The model resolution was not fine enough to accurately describe the accretion and erosion patterns alongshore. Yet, by the use of results of morphological updates it could be determined that the mega nourishment will likely cause accretion south of the nourishment area. This research can be used as a stepping stone for future design steps of a mega nourishment, and also for acquiring knowledge about future behaviour of different parts of the bottom profiles in the South West Texel area.

A significant part of the Netherlands lies below sea level. The Dutch have protected their land against seawater since the 10th century. Nowadays, the Netherlands is protected by 3800 km of primary flood defences. Since the Flood Defences Act was included in the Dutch law in 1996, all flood defences are tested against the national safety standards every twelve years. In the latest assessment round, a 47 kilometres long stretch of a Wadden Sea dike in the northern part of the Netherlands dike section, from Koehool to Lauwersmeer, did not meet the requirements. It is rejected to multiple foreshore influenced failure mechanisms. The dike area of Koehool-Lauwersmeer consists of cultural heritage in means of historical dikes and historical land reclamation structures. The (embanked) salt marshes that are present at the foreshores of the dike section, are of great value for both ecology and water safety in the area. The length of the dike section and the unique project location, provide an opportunity to explore alternative solutions for the dike strengthening project. Innovative dike strengthening solutions can potentially minimize the anthropogenic influence of the reinforcement projects, increase the systems adaptability potential to sea level rise and contribute to the ecological values of the area. In this research, an explorative study is conducted to find an alternative dike strengthening design and to assess the morphological developments and ecological opportunities of such a design. Based on the criteria to contribute to both flood safety and ecological value, a slufter alternative is chosen to be studied further. The slufter alternative engages an inland area between two dikes into the Wadden Sea by an artificial dike breach. The area is regularly inundated, creating opportunities for ecosystems to evolve. A depth-averaged (2DH) Delft3D model is used to explore the morphological developments of the slufter area and the potential to add to the ecological value of the area. The project area is characterized by a sediment-rich environment and a flood dominant tide. Higher flood than ebb velocities are present, causing an import of sediment into the slufter area. Model results indicate that the net sediment import of the slufter area mainly depends on the suspended sediment concentration, the critical shear stress and the tidal prism of the slufter area. A geometry that causes an increase in the flow velocity shows higher suspended sediment concentrations that lead to higher amounts of sediment import. Under the influence of a sea level rise (SLR) of +1m, the sediment transport increases with a factor of 2 to 3, depending on the initial geometry. SLR enhances the sediment trapping of the area. The slufter area can potentially keep up with SLR. Assuming an equal distribution of sediment over the slufter area, the average growth rate of the bed level is between 0.22 (minimum sediment import, maximum SLR) and 21.12 (maximum sediment import, minimum SLR) times SLR. Applying the slufter intervention adds 60 ha to the intertidal area of the Wadden Sea. Depending on the applied geometry this results in 30-50ha between MLW and MHW (lower marsh) and 10-30ha above MHW (middle and upper marsh). The slufter alternative creates opportunities for new ecosystems and contributes to the Natura2000 goals to create more gradual transition areas between the Wadden Sea and the surrounding land by creating an area with a gradual wet-dry transition. These potentially add to the biodiversity of the area as they create opportunities for specific plant species and waders. It is concluded that creating a slufter area at the Koehool-Lauwersmeer dike, provides opportunities for sediment trapping due to the flood dominance of the system and the high sediment concentrations. The amount of sediment trapping is influenced by the critical shear stress, the area’s tidal prism, and the suspended sediment concentrations. SLR increases the amount of sediment trapping. Depending on the applied geometry, the bed level growth rate is larger than SLR. Creating a slufter area creates an opportunity to improve both the flood safety and the ecological value in one design.