Implementation of nature-based solutions (NBS) in flood defenses is hindered by a lack of probabilistic tools and design guidelines that can be used to assess spatial and temporal variability in these biophysical systems. It is well established that nature-based elements, such as vegetation, attenuate waves, capture sediment, strengthen the subsoil and invoke numerous ecological benefits. This thesis proposes a conceptual framework to design and assess hybrid flood defense (HFD) systems within the context of current Dutch design guidelines: `wettelijk beoordelings instrumentarium' (WBI). The framework builds a dynamic probabilistic tool (DPT) to assess the effect of temporal variability of NBS elements on wave loading. The framework was applied in a case study at Hellegatpolder to investigate temporal effects of nature-based elements on nearshore wave heights during storm conditions. Data was collected specifically for the idealized HFD system at Hellegatpolder. Vegetation and nearshore wave height data was unavailable and therefore, an autocorrelation function was developed to sample temporal vegetation data. A numerical XBeach model was constructed to model nearshore wave heights for a bare and vegetated foreshore, resulting in a uniform database. Development of a static and dynamic Bayesian network allowed dynamic probabilistic modelling of nearshore wave heights. Application-specific model settings combine normative hydraulic storm data with the database and probabilistic models. The developed DPT was applied to model nearshore wave heights for a bare and vegetated transect for each vegetative season.Numerical modelling using XBeach was applied to model 7 years of data with a temporal resolution of 30 minutes for both bare and vegetated foreshore scenarios. The numerical results conclude that vegetation at Hellegatpolder attenuates waves with an average of 54%, where wave attenuation was 1.7 times greater in July compared to December. The effect of bathymetry morphology on nearshore wave height was found insignificant for short time scales.A static Bayesian network (SBN) was built to model nearshore wave heights in a fixed point in time. The validated SBN was able to model nearshore wave heights with 90% accuracy. A dynamic Bayesian network (DBN), was created to model offshore hydraulic parameters time series. DBN achieved an accuracy of >85% for short time scales (<25 hours). Utilizing the DBN for long term modelling resulted in progression towards the mean value of the marginal distributions. Statistical validation of both models rejected the representation of the dependence structure using only a Gaussian copula.Application settings were defined in MATLAB to manipulate the database, probabilistic models and normative hydraulic storm conditions. The configured DPT was run to model nearshore wave heights for a bare and vegetated foreshore specifically at Hellegatpolder. During storm conditions average wave attenuation due to vegetation was 45%. Average wave attenuation results were thus lower than those available in the numerical dataset (54%). Moreover, wave attenuation was 3 times greater in summer compared to winter months. Furthermore, the DPT resulted in dynamic wave loading (i.e. varying through time) compared to the static WBI loading conditions. Resulting DPT wave heights were 82% lower during winter months than the normative loading defined by the WBI.These results show the effect of variability on wave attenuation. The percentages and factors are expected to differ for other locations. Nevertheless, the obtained results clearly illustrate the significance of temporal modelling of HFD systems. The method presents a novel conceptual framework to include the effects of NBS elements in the design and assessment of flood defenses. The conceptual framework, numerical and probabilistic models can be applied for other HFD systems, enabling engineers to assess flood defenses more realistically - a critical step in the implementation of NBS in design guidelines.

The World Heritage Site Kinderdijk consists of a landscape of preserved 18th-century windmills and is a popular touristic location. The number of visitors is continuously growing for the World Heritage Site at Kinderdijk. Visitors arriving via the water network have to cross a busy road to reach the heritage site. This is an unsafe and unfavourable situation. A new water entrance at Kinderdijk is the solution to this problem. The plan is to add the function of a pedestrian passage to the existing discharge sluice at Kinderdijk named the Elshoutsluice. The discharge sluice is part of a flood defence and must keep its original function. The objective of this thesis is to provide a conceptual structural design for the multi-functional use of the discharge sluice at Kinderdijk including the functions for water discharge, flood defence, passage for (motorised) vehicles and pedestrians, which fulfils standards for flood safety and buildings in the Netherlands. This thesis shows how to approach a design case for adjustments of an existing hydraulic structure as a part of a flood defence. A conceptual design was made for the adaptation of the Elshoutsluice. For this study a design method according to Roozenburg and Eekels (1995) and Voorendt (2020) was used. The Elshoutsluice was divided into different subsystems and elements. The concepts for the location of the new pedestrian tunnel, the floor configuration, the roof and gates were developed. After the functional verification and evaluation, a selection was made from the best remaining alternatives for the elements and subsystems. The selected alternative is a pedestrian tunnel above culvert number 2. As a result, the existing gates of culvert 2 will be replaced with new gates to provide flood protection in case of high water. A flap gate and a vertical unfolding gate are selected. The existing technical area expands above culvert number 3. A multi-functional space is included above culvert number 3. Culverts 1 and 4 remain unchanged. Additional soil will be placed on top of the structure to provide a slope for the connection of the heightened road on top of the sluice to the road at the adjacent levee. The conceptual design and construction phase was checked for the flood safety based on the WBI 2017 and OI 2014 and fulfils the requirements. Stability checks were performed for governing load situations of the Elshoutsluice for the construction phase and use phase. The difference in loading on the structure for the initial design and the new situation was analysed. Additional checks are needed for the lateral walls in all the culverts and the top slab of culvert 1 and 4 due to the increase in shear force and bending moments. The conclusion is the resulting conceptual design.

The combination of continuous sea level rise, and more frequent extreme river discharges will become a rapidly developing problem for the Rhine-Meuse delta over the course of the next century. The current Dutch delta management policy mostly revolves around the consistent improvement of the existing dikes to account for the increasing water levels in the region. An alternative solution to this problem is the Delta21 project. The Delta21 project proposes the construction of a large scale storage lake, and a high capacity pumping station at the Dutch coast. The project is meant to allow for the simultaneous closure of the storm-surge barriers on the Dutch coast, while actively discharging river water that would normally be pilling up behind the closed barriers. The Delta21 project foresees it will be able to save up to 5billion euros by the end of the century in dike reinforcement costs. In order to enable the flood safety operation of the Delta21 project, the project also requires the construction of a new storm-surge barrier in the Haringvliet ebb-tidal delta, roughly 10km away from the current Haringvlietsluices. The objective of this thesis is the conceptual design of the new Delta21 storm surge barrier, the New Haringvliet barrier. The aim of this design process is to identify critical design components, and requirements that could potentially be hurdles in the development of the New Haringvliet barrier, as well as the overall Delta21 project. For the hydrodynamic design of the barrier, a schematized 1D hydrodynamic model was used to get a first insight into the impact the new barrier will have on the on the tidal range in the tidal delta. As well as how much it could potentially impact the reintroduction of the tide to the Haringvliet. The reopening of the Haringvliet would be a part of Delta21's effort to restore some of the local ecological value to the region as a compensation measure for the project. Additionally, the model was also used to determine the effects of the construction of the barrier on the capability for the system to handle high river discharge rates. The findings of the assessment show that the selection of a small tidal opening in the New Haringvliet barrier will significantly negatively impact the capability for the system to discharge high river water, as well as limit the amount of tidal range that will be available in the system. It was determined that constructing the barrier with a tidal opening with an effective cross-section of 10000m2 will provide the best balance between hydrodynamic performance of the system, and barrier construction costs. An analysis of the possible Delta21 construction sequences was used to determine the preferred construction method for the barrier. In this analysis, an economic construction sequence alternative, and an environmental construction sequence alternative were developed, and consecutively evaluated using a multi-criteria analysis. This MCA revealed that the construction of the New Haringvliet barrier using prefab construction elements and techniques was the desired construction method for the project. The results of hydrodynamic and construction sequence assessment, were used as the basis for the barrier's spatial design. The structure was designed with a total of 20 vertical lift gates, each spanning 80m. This would bring the total tidal opening to 10400m2. Vertical lift gates were chosen for the design due to their great reliability and overall cost effectiveness, which are both important considerations for a barrier of this magnitude. On the southern side of the barrier a shipping lock will be the barrier's primary navigational opening. The final phase of the conceptual design focuses on the design of the gated barrier section, and includes the validation of the transport stability of the caisson, the design of the vertical lift gates, and the design of the scour protection and it's filter layers.