Including vegetation in flood defense systems has the potential to be a more cost-effective solution than conventional dike reinforcement measures, as vegetation contains wave damping properties. However, more insight is required on the complex physical processes due to wave-vegetation interaction in order to predict the amount of wave damping. Past research found that these processes are dependent on both flow conditions and vegetation characteristics. Therefore, reliable quantification of these vegetation characteristics is of importance to understand these processes and thus to improve predictions for wave dissipation due to vegetation. This study aims to gain insight on practical methods for quantifying relevant vegetation characteristics for wave damping. Data is used from full scale physical experiments conducted in the Delta Flume at Deltares, with 40 meters of willow forest. The vegetation characteristics are quantified in this study both by manual measurements on the willow trees and by executing Terrestrial 3D laser scans (TLS) of the whole forest. The frontal area of vegetation is found in literature to be a relevant parameter for determining the wave attenuation, therefore the focus in this study lies on schematizing this parameter over the vertical, which is seen as representations of the average willow tree. This schematization is referred to in this report as “tree model”. In this study, four tree models are obtained. The four tree models include: tree model 1a (manual measurements on the primary branches, excluding side branches), tree model 1b (branching method based on Strahlers ordering scheme, including side branches), tree model 1c (adjusted branching method) and tree model 2 (from terrestrial laser scanner). The reconstructed area from the TLS point cloud is determined by using Matlab built-in alpha shape function. The tree models are compared in terms of frontal area distribution over the vertical and of their effect on the corresponding wave attenuation. The latter comparison is achieved by using the numerical wave model SWAN and confronting the results with the measured wave attenuation from the physical experiments. With regards to the manual measuring methods, the frontal area of the average tree from tree model 1a serves as a lower limit, while tree model 1b gives the upper limit. The TLS outcome (tree model 2) underestimates the frontal area as computed by the other tree models. In particular, the underestimation is 70% when compared with tree model 1b, and 30 % when compared to tree model 1a. Adjustments on tree model 1b leads to tree model 1c. This tree model accounts for the tapering form of the branches and results in a total frontal area in between tree model 1a and tree model 1b. In this study, the representative area for the willow trees can be best captured with tree model 1c. This tree model results in a drag coefficient (CD) of 1.15 averaged over the tests with leafless willows and showed a negative correlation with the Keulegan-Carpenter number (KC). However, the capabilities of the TLS should be analyzed further and this study encourages to use a larger data set of trees in order to find a relation between the laser penetration and corresponding mismatch. Gathering of vegetation parameters by hand is in fact not economically attractive forwoody riparian vegetation, as these trees are characterized by complex canopy structures and high elevations. The TLS can serve as a practical tool for obtaining these relevant vegetation parameters for applying willows in hybrid solutions.

Mangroves are productive ecosystems. Degradation of mangroves has been observed since the 1970s, due to a variety of reasons. Successful rehabilitation focuses on restoring conditions suitable for mangroves. Sediment availability has been shown to positively impact mangrove growth. Therefore, it can likely play a role in mangrove rehabilitation. This research aims to explore if the rehabilitation of coastal mangroves is possible using a sediment nourishment. A process analysis is performed, to identify the processes driving sedimentation on a mangrove coast. This analysis uses a schematised, cross-shore, one-dimensional model, based on global data of mangrove coasts. Convex, linear and concave bottom profiles are used. The forcing on the coasts consists of three different wave heights, tidal ranges, and sea level rise rates. A homogeneous mangrove forest is present above mean sea level. Sedimentation within the mangrove forest is caused by a combination of processes. Waves pick up the sediment, which is transported by the tide. Tidal asymmetry then drives the actual sedimentation in the forest. An increase in asymmetry results in increased sedimentation. Mangroves increase the flood dominance of slack water asymmetry, but also cause an ebb dominant peak flow velocity and duration asymmetry. Dependent on the tidal range, the influence of mangroves on net sedimentation can either be null, negative or positive. Sea level rise increases sedimentation within the mangrove, by enhancing slack water asymmetry. The main tipping point identified is the gradient of the bed slope in cross-shore direction. If the slope becomes milder towards the shore, i.e. a convex coast, this value is negative. If the slope becomes steeper, which is the case for concave coasts, it is positive. The tipping point is when the slope does not change towards the shore. The gradient of the slope then is zero. The net sedimentation is considerably less for concave coasts than for convex coasts. Sediment nourishments can increase sedimentation in the mangrove forest. Four nourishment designs were simulated, using the same model as for the process analysis. The designs varied in location and achieved depth across the coast. Three design considerations for a successful sediment nourishment have been identified, which are firstly the obtained bed level by the nourishment, secondly the slope of the original bed, and thirdly the location of the nourishment. First, the obtained bed level by the nourishment influences the quantity of sediment pick-up. Higher bed levels increase the sedimentation within the mangrove, by increasing sediment mobilisation rates. Second, the slope of the original bed largely influences the feasibility of a nourishment. Due to mild bed slopes, the construction of a nourishment is difficult and large volumes for a nourishment are required. Finally, the location of the suppletion should be close to the mangrove. If the nourishment is located far offshore, the sediment is not transported towards the mangrove. Rather, it then is transported away from the coast. This thesis has shown the rehabilitation of mangroves using a sediment nourishment is possible.

Mangrove is a coastal vegetation type primarily located in the tropical regions between 5 North and 5 South. This coastal vegetation is capable of reducing the force of incoming waves. This is a result of the obstruction created by the roots, stems and canopies against waves to propagate through. Because of this capability, mangrove vegetation offers coastal protection against extreme annual flood events for 15 million people. Recent studies identified that in 2050, the present-day 100-year extreme sea level will occur annually in a large part of the tropical region. The increase of these extreme events is primarily driven by the projected sea level rise. The hypothesis is that before this chronic flooding is observed, storm-induced flooding might already be observed. The expected increase in the probability of these extreme events is defined as non-stationarity of extreme events. The hypothesis therefore is that the non-stationarity of extreme events could already be observed in historical data. This study examined non-stationary extreme events between 1987 and 2018 for a total of 5809 hydrodynamic environments distributed around the global mangrove coastline. These mangrove environments defined the hydrodynamic wave characteristics and water levels. The results showed that 87.5% of the mangrove environments have a positive trend in the location parameter of the Generalized Pareto Distribution for the extreme events. The shift of the location parameter indicates an increase of the impact of the extreme events. These extreme events were defined as multivariate extreme events consisting of the significant wave height, the mean wave period and the skew-storm surge, respectively the parameters Hs, Tm and S. This combination is based on the fact that the coastal protection offered by mangroves is depending on the water level and the energy within the long-period waves. The methodology proposed is capable to perform a non-stationary multivariate extreme value analysis and observe the evolution of the extreme events in these three dimensions between 1987 and 2018. The study showed that the average of the extreme events has been increasing at 70.6%, 72.6% and 64.6% of the mangrove environments in the discussed three dimensions. The average multivariate extreme event in mangrove environments increased by 0.06 m, 0.16 s, and 0.7 cm in three dimensions respectively Hs, Tm, and S. Furthermore, the number of extreme events increased, on average, between the first and second half of the time period, from 4.16 to 4.32 extreme events per year. The global impact assessment of the non-stationarity of these multivariate extreme events was translated to the 27440 mangrove locations along the global coastlines. Statistical upscaling methods allowed the application of a numerical expensive hydrodynamic model to propagate the offshore conditions to onshore. The impact of the non-stationarity of extreme events was applied to a theoretical framework, introducing the possibility of defining the vegetation width as an optimization parameter. To meet the same safety standard for the 1/40 year design condition in 2018 concerning 1987, the vegetation width of the theoretical framework had to increase on average by 16.8 m. After post-processing the hydrodynamic runs, the results showed that the coastal safety offered by mangrove vegetation is depending on the combined impact of these three parameters, emphasizing the importance of expanding the mangrove vegetation to withstand the non-stationary multivariate extreme event. The main recommendations from this study are based on the results. First, the study showed that the required vegetation width to ensure coastal safety has increased. It is therefore highly questionable if a stationary extreme value analysis is still valid in these environments, especially when the currently neglecting sea level rise is taken into account. Second, the observed increase in multivariate extreme events and the number of extreme events may reduce the persistence of mangroves and therewith their ability as coastal protection. It is therefore recommended to monitor the condition of the global mangrove forests more closely and to take action when mangrove vegetation is decreasing.

The aim of the Building with Nature (BwN) design philosophy is to improve on a traditional approach for infrastructural projects by utilising natural processes to create benefits for society and nature. In a fast-changing world where climate action is becoming increasingly important, there is need for an innovative approach in large infrastructural projects where nature is not considered as an obstacle, but stimulated and used in a sustainable way. The BwN design philosophy offers the opportunity to realize this improvement. This research first aimed to create an evaluation framework of (international) standards and goals to identify opportunities for improvement of a port masterplan and to get a better understanding of the need for sustainable port development. Included in this evaluation framework are, amongst others, the Port Vision2030, the Corporate Social Responsibility statement and the international strategy of the Port of Rotterdam (PoR). On the basis of these visions and standards, the corporate governance of the PoR was tested by conducting an informal opinion poll amongst twenty colleagues at the PoR (International, Environmental Management and Port Development). A practical example of a traditional port development project that can be improved by applying BwN is the Kuala Tanjung (KT) Port-Industrial complex at Sumatra, in Indonesia. This port development project is still in its initiation phase where a first master plan is proposed. Since the goal of the Indonesian government is to build a world-class port, international and sustainable standards apply. This project was used as a case to identify opportunities to improve a traditional master plan by applying a BwN approach. The evaluation framework was applied to the current master plan of KT to check whether this project meets the requirements for international port development, in particular from a nature/social point of view. It is concluded that the current design mainly focuses on the functional requirements of the port, proposing mitigation and compensation measures against the negative social and environmental impact of the port development. The BwN philosophy, on the other hand, prescribes a thorough understanding of the natural system emphasizing on the positive effects of the project for stakeholders and nature, to create a win-win solution. After applying the general evaluation framework, it became clear what aspects in the current master plan should be improved. A literature study of applied BwN solutions resulted in an onshore and offshore alternative for the port development including several BwN solutions. Together with experts involved in the KT project, it is concluded that the onshore alternative is more realistic (from a functional point of view), while still offering opportunities for applying the BwN philosophy. In the current natural system of KT the mangroves offer various important ecosystem services. In addition, it is concluded that the breakwaters proposed by the current master plan form a large part of the CAPEX. Consequently, a solution is proposed where mangroves are integrated in the design to attenuate waves and enhance nature at the same time. To test whether this BwN solution is realistic, a preliminary feasibility study has been executed. The results of a mangrove coastal protection program at Demak (Java, Indonesia) and various scientific articles (Ecoshape BwN Guidelines, 2018) about rehabilitation programs for mangroves have been used to set up a general checklist with habitat requirements for mangroves. These requirements were compared with the local conditions at KT and recommendations for creating these conditions at the breakwater location were given. According to the checklist, the site at KT appeared to be suitable for mangrove establishment. This resulted in preliminary mangrove breakwater designs for various depths. In addition, the effect of the BwN solution on the phasing of the adapted master plan was determined, rough cost estimates were made and the implementation risks were identified. According to these conditions, the mangrove-based breakwater appeared to be technically feasible for the first 2000 m of the shallow part of the south-eastern breakwater at KT. Finally, the evaluation framework was applied again to check if the current master plan of KT has been improved (read: less dilemmas occurring from deviating standards in Indonesia) and a general advice is given on the applicability of the selected BwN solution to other ports in Indonesia and (sub)tropical zones of the Asia Pacific region.

To estimate wave attenuation by mangrove forests, trees are often schematized as uniform cylinders (over the height) representing a tree’s stem. However, trees have more complex geometrical features that influence the interaction between waves and tree structures. Recent studies have shown that the frontal surface area distribution over the height Av(z) is a crucial parameter for estimating wave attenuation by vegetation (Kalloe et al., 2022; van Wesenbeeck et al., 2022) because it can account for complex geometrical features. This study aims to model the complex geometry of the Avicennia marina mangrove species. The research question then becomes: How to construct geometrical tree models of Avicennia marina vegetation and how to obtain the projected frontal surface area distribution over the height, Av(z)? In this study, manual measurements were performed to obtain tree structure parameters. Both canopy and root measurements were conducted for Avicennia marina vegetation with varying characteristics (age and density). Two saplings (approximately 1.5 years old) with variable canopy densities and two young trees (around five years old) with varying canopy densities were measured. We stored canopy measurements in a so-called tree data structure consisting of nodes (representing the branches) that contain information about the individual branches, such as branch orders, -lengths and -diameters and edges, which are links that establish direct relations from one branch to another. After that, we developed a search tree algorithm to loop through all tree data, compute parameters of interest and store the results in assigned data arrays. Parameters of interest to obtain after the data analysis were branch dimensions and diameter ratios of branches (between various branch classes). This information was necessary to create a blueprint for constructing geometrical tree models. Tree modelling started with the construction of a root (pneumatophore) model. Additionally, the frontal surface area of these roots was computed and displayed as a function of the height. In addition to the root model, we constructed two canopy models. The first model is based on relations between branches and can be called deterministic or dependent (canopy model 1). The second canopy model (canopy model 2) generates branch dimensions based on the normal distribution of branch diameters and is, therefore, more probabilistic with branches independent of each other. Both canopy models construct branches based on information travelling from preceding branches. The models account for the proper placement of branches within 3D space by rotations and translations. The algorithm computes and outputs the projected frontal surface area over the height of a system of branches for a given direction (XZ-plane projection or YZ-plane projection). We validated the two canopy/tree models against validation measurements. Three trees were divided into seven vegetation layers, and branches were registered that intersected with the layers. As a result, estimation could be made on the frontal surface area per layer. This study found that the frontal surface areas due to roots and canopies are significant and are well represented by the parameter Av(z). The contribution of the roots and canopy cannot be neglected in modelling wave dissipation by vegetation. The contribution of smaller branches to the total Av is significant, proving that considering only the tree stem is an underestimation. Moreover, the research shows that it is possible to develop a geometrical tree model based on a set of measurements and design rules that follow from observations, at least for the considered tree species. We could extrapolate and interpolate our results to generate tree models for a wide range of tree ages. Additionally, it is possible to create a forest by generating multiple trees. Both tree models (1 and 2) showed little differences in Av(z) during the model validation process. Moreover, the validation measurements led, in general, to an overestimation of the total frontal surface area. Consequently, model validation was inconclusive regarding both tree models. However, we found that constructing tree models according to tree/canopy model 1 is preferred because it resembles an L-system more and is more practically applicable in computer models. We can improve future tree models by collecting more measurements regarding branch structures and root distribution as a function of tree age. This will result in increased model reliability.