The increasing frequency and intensity of extreme events due to global warming and climate change is increasing flood risk. To act, rather than react, nature-based solutions (NBS) involving vegetation and wetlands are being explored on top of conventional solutions like dikes. WHY? There was a dire need for global study quantifying the potential of vegetation in reducing flood risk and eventually make a decision support tool which enables quick assessments about flood risk reduction in a vegetated hydrodynamic system. WHAT? The developed tool can predict flood risk anywhere in the world without rigorous modeling through user defined conditionalization of in-situ hydrodynamic or vegetation characteristics. HOW? Multivariate dependence among parameters of schematized system can exhibit characteristics of vegetated hydrodynamics. To ensure global representation of vegetated hydrodynamics a copula-based multivariate stochastic model has been developed which caters global ranges of each parameter, their probability distributions and the inter-parameter dependencies through ranked correlations. Numerical modeling has been carried out through XBeach non-hydrostatic model by resolving full spectrum of high and low frequency waves. A non-parametric Bayesian network-based flood risk prediction tool has been developed from the synthetic dataset developed from the simulations. SO? Bulk results conclude that saltmarshes attenuates waves by 87% and mangroves by 94% as a mean value. Wave attenuation, flood risk reduction and wave run-up manifests maximum dependence on offshore wave height, water depth, drag coefficient, vegetation height, frontal width, and forest length and least on offshore slope and vegetation density. NOW? The flood risk prediction tool would help decision makers in implementing NBS, in making better informed decisions about early warnings and policy making related to flood risk reduction and climate change adaptation by incorporating vegetation. NOVELTY? To the author's knowledge no such study exists which captures natural variability of hydrodynamics and vegetation together in a probabilistic model over global scales. Additionally, no such study exist which applies non-parametric Bayesian networks to predict flood risk. The dependence modeling of global vegetated hydrodynamic environments is also unique which skims out the most critical parameters.

During construction of breakwaters, adverse weather conditions can result in damage, in the form of reshaping and loss of material to the open work fronts of the structure. Based on literature research, analysis of work methods, analysis of damage to older breakwater projects and interviews, it was deduced that during construction, the open work fronts of the submerged core section, emerged core section and underlayer section are in particular prone to the following damage mechanisms: - Reshaping of the submerged core due to head-on and oblique wave attack - Reshaping of the emerged core due to head-on and oblique wave attack - Reshaping of the underlayer due to head-on and oblique wave attack. - Mixing of rock material of different sections. - Overwash of dislocated material. When a damage event occurs, construction is delayed as repair works are needed. This delay increases the probability of encountering unfavourable conditions in the remaining construction time. Such positive feedback complicates any quantitative risk assessment. The main objective of this thesis was to investigate the feasibility of a computational model with which risks related to the construction phase of rubble mound breakwaters in sea-state conditions can be assessed. By simulating the construction process in time with a fully probabilistic process-based model, the financial risk due to storm-induced damage during construction can be assessed. Due to the stochastic behaviour of the parameters used in the building process simulation, the simulation outcome itself is characterized by a stochastic behaviour. To calculate the financial risk, the simulation is run multiple times like a Monte Carlo simulation. Quantitative damage calculations in the model were performed using methods reported in the relevant literature. However, currently available literature did not cover all damage mechanisms or the full extent of it. For these damage mechanisms, some newly developed methods were introduced. The damage profiles predicted by these methods turned out to be in excellent agreement with data from an older breakwater project. This older breakwater project was used as a reference case to test the model and analyses its performance. Furthermore, a sensitivity analysis on the breakwater parameters showed that the nominal diameter of the core and underlayer material and the start date of construction works have the strongest sensitivity on the financial risk.

On the 29th of December 2016 a large Rhine ship loaded with 2000 ton benzene sailed through the weir at Grave, located in the river Meuse in the Netherlands. The accident created a large gap in the weir and within 12 hours the upstream water level decreased by a maximum of 3 meters. Due to this decreased water level shipping was limited, houseboats were skewed and there was a risk of instability of the river banks and upstream weirs.

Several alternative measures were considered to close the damaged part of the weir in order to reinstate the upstream water level, and make it possible to repair the weir. Finally it was decided to build a rock-fill dam behind the damaged part of the weir which closed nearly 55% of the weir. Due to this closure, all the discharge had to pass the weir through the remaining 50 meters-wide southern opening. As a result of this upstream water levels were set-up faster than during normal operations. High upstream water levels, relatively high discharges and a low downstream water level caused extreme flow situations with even supercritical flow (hydraulic jump) over the bed protection. At weir Grave the existing bed protection was injected with colloidal concrete and an additional ballasting sill, made of 3-6t carefully placed stones and 4t rock nets was constructed, to prevent additional damage to the bed protection.

In this study the stability of the measures which were used to prevent additional damage to the bed protection are analyzed. This study focusses on the 3-6t carefully placed stones, rock net sill and the bed protection behind it. The 4t rock nets were not able to withstand discharges up to 450m3/s and flow velocities up to 7.0m/s due to the internal instability of the small rock material inside the nets. The 3-6t stones were able to withstand discharges up to 850m3/s and flow velocities up to 6.7m/s. Due to the fact that the stones were carefully placed, the stability increased. A stability correction factor (Φsc) up to 0.73 can be used instead of 1.5 as prescribed by Pilarczyk for stones on the edge of a bed protection. The 40-200kg bed protection with colloidal concrete has withstood extreme flow velocities up to 7.2m/s whereby only small damages occurred. The 40-200kg quarry stones without colloidal concrete also showed limited damages after the 850m3/s flood wave and depth averaged flow velocities up to 5.2m/s. The conclusions of the analysis are projected to the other six weirs in the Meuse and to the possible calamities which could occur here.

In order to perform the stability analysis of the bed protection measures at weir Grave, the Meuse and the seven weirs in the Meuse were analyzed. The Meuse is a controlled river in the Netherlands and is kept navigable by a seven weir system. These weirs differ in dimension, head loss and operating system. Based on the characteristics of these weirs one simplified fictive weir is chosen and tested on the consequences of various calamities. Besides, also the long-term maintenance strategy is considered in this study. Both have the similar result that part of the weir is non-operational for a longer period, discharge capacity is limited and all highly variability in occurring discharges is possible.

In this study the consequences to the water management of the fictive weir are considered. To guarantee an upstream water level to a certain target level, panels and slides are removed from a weir for increasing discharge. If part of the weir is not available due to a closure, panels and slides have to be removed earlier than in a normal situation. Therefore, the limit discharge, the discharge for which the weir is completely open, is reached earlier for the different closure situations. If the limit discharge is reached, the upstream water level starts to increase. In this thesis the discharge, according to an upstream water level equal to the flood plain level, is the maximum considered discharge. For further increasing discharge, and water levels, the flood plains start to discharge water and the flow velocities downstream of the weir will no further increase.

The flow velocities for three closure situations and three discharge situations are considered in this study. It turned out that the flow velocities which are calculated in this thesis are always lower than the flow velocities which occurred during the Grave weir calamity. Therefore it is concluded that the measures used during the Grave calamity, are all applicable to the other weirs in the Meuse. But lastly is must be concluded that due to a relative large closure of a weir (>50%), severe flow circumstances like supercritical flow, can occur. In case of a future calamity or long-term closure, it is advised to minimize the closure width as much as possible.

In recent years, the use of Xbloc units has increased exponentially. However, the placement of this unit is not always done as randomly as it should be and consequently, the stability of the armor is affected. In order to overcome this problem, Delta Marine Consultants is developing a new armor unit called Xbloc+ that has a regular placement. In this research, the hydraulic performance of version 1 and 2 of this block are analyzed. Small scale tests were performed in a 2D wave flume in order to analyze the damage, rocking and the (partially and fully) displacement of units. In total, 1 series of tests were performed with Xbloc+v1 and 6 series with Xbloc+v2. To analyze the influence of the wave steepness and the slope angle, three wave steepness were tested (Sop = 2%, 4% and 6%) and tests were conducted in two different slope angles (1:2 and 3:4). Each series is formed by several sub tests conducted with increasing wave heights (and wave period in order to maintain a constant wave steepness). Tests were carried out until the failure of the armor slope was reached in order to completely define the failure mechanism. Furthermore, tests after failure where also executed to further investigate the stability of the armor after the damage has started.
Results obtained from the laboratory tests provided an overall understanding of how the Xbloc+ performs under certain conditions. It was perceived that the permeability of the armor layer is low as it happens often with single layer units. Thus, the pressure gradient between the underlayer and armor layer is significantly high creating an uplift pressure that leads to a revetment-like failure mechanism.
Although the failure mechanism can be related to both slopes used during the laboratory tests, (3:4 and 1:2), the behavior of the armor layer differed completely between slopes. On a steeper slope, the armor layer remained undamaged for wave heights significantly higher than the design wave. However, once one unit was fully displaced, the damage was quite destructive.
In contrast, on a milder slope, failure occurred much faster but the damage was not as aggressive. Moreover, after the failure was reached, the structure gained a new level of stability in which remained to provide shelter without reflecting significant damage.
Furthermore, the wave height variation did not have much influence as the wave steepness. There was a noticeable difference between the performance of the structure during swell and wind waves. During swell waves, it could be seen that not only failure was achieved faster but it caused much more damage to the structure, while during wind waves the structure had a higher stability.