The current flood risk assessment framework in the Netherlands aims at ensuring a nation-wide protection level with a long-term vision. It assumes that future river bed level changes will not pose negative effects on flood safety and it adopts a fixed-bed assumption. However, the river bed level shows a strong spatial and temporal variability, where bed aggradation trends could lead to higher water levels in the future. Recent measurements in the Dutch Rhine have shown both bed degradation and aggradation in different river sections along the lower river domain. This raises questions to what implications does future river bed level changes have on flood safety in the Netherlands and whether the current fixed-bed assumption has adverse connotations to it.

The objective of this MSc thesis is to study the impact of river bed level changes on flood safety in the Netherlands. To achieve this, a framework for incorporating large-scale bed level changes into flood risk assessments is developed and applied under the current Dutch context. The implications on the long-term and short-term flood safety are analyzed separately, as fundamentally different approaches and uncertainties relate to the flood safety standards derivation and for the periodic safety assessment in the Netherlands.

In the long-term, I propose to incorporate morphodynamic modelling scenarios into the flood safety standards derivation process to account for future bed level changes and their long-term uncertainties. Modelling scenarios should include future river discharge, sea level rise, river maintenance and the evolution of river bifurcations, as they represent main drivers in the long-term river bed response in the Netherlands. Based on existing long-term morphodynamic modelling studies of the Rhine River, it is estimated that the extreme water levels decrease over the upper Waal, but increase over the lower Waal by 0.15 m and 0.30 m in 2050 and 2100, respectively. These scenarios consider that river dredging is not maintained after 2025.

In the short term, I propose to incorporate the analysis of the recent river bed level behaviour into the safety assessment process to account for its uncertainty in the near future. Based on yearly bed level measurements in the Waal from 2005 to 2020, decreasing and increasing water level trends have been identified in the upper and lower Waal, respectively, with increments in the order of 0.05 m. This is small in absolute terms, but significant compared to the accuracy level of the hydraulic loads used in the safety assessment process. As a consequence, these increments can have important economical implications on dike reinforcement programs.

In summary, this thesis provides a framework incorporating large-scale river bed level changes into the current flood risk assessment framework in the Netherlands. Furthermore, it quantifies the impacts of bed level variability on flood safety in the Waal River. In general, the fixed-bed assumption in the current flood safety framework is a conservative, or safe, assumption for the hydraulic loads’ calculation in the upper Waal. However, it may underestimate the future hydraulic loads in the lower Waal and impose adverse conditions on flood safety. ... Read more

It is observed that the bed level development of the Pannerden Canal (PC) and the Waal changed since the peak flows of 1993, 1995 and 1998. The erosion rate of the Pannerden Canal decreased greatly just downstream of the bifurcation while the erosion rate of the Waal stayed more or less constant. This leads to an increasing depth of the Waal relative to the Pannerden Canal and therefore the Waal attracts more discharge. The model results from this study confirm that without anthropogenic interventions in the future, the Waal discharge fraction keeps increasing. The shift in discharge partitioning towards the Waal is an undesired development of the system as it causes problems for navigability, ecology, freshwater distribution and flood safety. Currently there is a lack of knowledge on how interventions can be used to mitigate the gradual change in discharge partitioning at the Pannerdense Kop (PK). This study aims at filling the knowledge gap by considering several interventions studying their effect on the discharge partitioning at the PK and on the Rhine branches surrounding the PK.

Firstly, an inventory of interventions which could possibly increase the Waal discharge fraction is made. The resulting selection of interventions is: A) a side channel from the Boven-Rijn towards the PC, B) fully opening the weirs in the NR-Lek, C) widening on the IJssel, D) directly steering the sediment partitioning at the PK and E) dredging in the PC and dumping in the Waal. These interventions are implemented in a 1D-morphological model of the Dutch Rhine branches.

It is found that the side channel from the Boven-Rijn to the PC (A) is not capable of significantly influencing the discharge partitioning at the PK. The backwater effects due to the water addition counteract the added discharge to the PC.

Furthermore, it is found that for the low Lobith discharges opening the weirs in the NR-Lek (B) can reduce the Waal discharge fraction below the initial value from the reference case for the whole simulated period of 60 years. The opening of the weirs does however lead to significant relative decrease in the IJssel discharge fraction which is unwanted regarding the freshwater supply of the IJsselmeer. For low Lobith discharges the widening on the IJssel (C) initially leads to a significant reduction in Waal discharge fraction of 2.4%. The effectivity reduces throughout the simulation because of aggradation along the widened reach. For high flows the opening of the weirs and the IJssel widening are less effective. The final relative Waal discharge fraction decrease is respectively 1.1% and 0.7%.

The results of the directly steering the sediment partitioning (D) are similar for high and low flows. The water level is not changed initially and therefore initially the discharge partitioning is not affected. Throughout the simulation the slope of the Waal adjusts to the increased sediment supply and the slope of the PC adjusts to the decreased sediment supply. For both flows the final relative decrease in Waal discharge fraction is 1.8%.

Dredging and dumping (E) shows similar effects on the bed level and discharge partitioning as steering the sediment partitioning at the PK. Dredging and dumping also does not alter the water level and the discharge partitioning initially. The relative bed level increase of the Waal is somewhat higher for the dredging and dumping simulation than for the simulation in which the sediment partitioning at the PK is steered. Therefore also the relative decrease in Waal discharge fraction is higher with 2.4% for the low Lobith flows and 2.2% for the high Lobith flows.

Currently the IRM program aims at stopping further skewing of the discharge partitioning of the PK. None of the interventions from this study is capable of realising this on its own. Therefore multiple river interventions will have to be combined to be able to reach the ambitions of IRM. The knowledge on the effect of the interventions on the discharge partitioning at the PK and the bed levels of the Dutch Rhine branches can be used as a basis for further study towards to combined effects of river interventions on the bed level development of the Dutch Rhine branches and the discharge partitioning at the PK.
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Radar technology has evolved into a versatile and robust tool for critical air traffic control, meteorology, surveillance, and defence applications. In surveillance radar, the need for continuous monitoring of large areas, often cluttered by ground or sea reflections, presents significant challenges for multitarget detection. This clutter can obscure true targets, complicating detection in environments where standard radar noise assumptions fall short.

This thesis introduces a novel implementation based on the relevance vector machine (RVM) to address the complexities of multitarget detection in cluttered environments. Unlike conventional approaches that assume white Gaussian noise, the proposed method jointly estimates a clutter covariance matrix, allowing it to adapt to the estimated clutter model over subsequent iterations. Performance evaluations using simulated data in one-dimensional (range or angle) and two-dimensional (range-angle) settings demonstrate that the framework achieves accurate AR parameter estimation. Results indicate a marked improvement in reducing false and missed detections compared to the white-noise-based model. Notably, the framework performs multitarget detection without prior knowledge of target locations and the need for guard cells, underscoring its adaptability to real-world scenarios. ... Read more

Climate change is adding more and more pressure to the water systems. The area which is protected by the storm surge barrier of Ramspol have high probability of flooding for climate projections in 2050 and 2100.
Nowadays, the development of the technology is providing with numerous tools and analytical models for the engineers. However, in the early stages of assessment is important to have in hand a decision making method capable to fast and reliably highlight the most promising solutions.
In this thesis an assessment method of multiple flood protection improvements have been developed in order to highlight the most promising ones. The assessment method is based on three decision making parameters, the decrease of water level maximum, the cost and the ecological impact. To handle the first aspect, the wind set-up formula, a lake level formula, the normal flow depth formula and the probabilistic model Hydra-NL have been used for the water level calculations. The implementation cost has been calculated using rough dimensioning and characteristic unit values. To qualitatively assess the aspect of the ecological impact, the concept of the ecological sign has been developed. The qualified improvements can be then handled from a second detailed assessment. In this thesis the second assessment stage is only a recomendation and have not been applied.
The method which developed have been applied for the case of Ramspol Barrier. From the 20 designed improvements, 5 have been qualified as the most promising and those are the construction of a breakwater in IJssel Lake, the construction of an outflow channel at Ketelbrug, the sizing-up of Zwarte Lake, the raising of the height of the dikes and the construction of flood plains.
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Cities worldwide are facing increasing impacts from climate hazards such as heavy precipitation, heat stress, flooding, and drought, exacerbated by climate change. This study focuses on unembanked areas (NL: buitendijkse gebieden), vulnerable to flooding due to factors like sea-level rise, river peak discharges, and land subsidence. However, there are many plans for (re)development in Dutch unembanked areas for the coming years. To address these challenges and avoid passing on consequences of what we build now to future generations, effective adaptation measures are crucial. The study investigates the decision-making process for local flood risk measures in unembanked areas, examining appropriate evaluation methods and stakeholders' needs. Qualitative research methods, including expert interactions, a literature review, case studies, and interviews, were employed. Although there are not evaluation methods, the Dutch multi-level safety approach and resilience-based planning methods like adaptative pathway and adaptative tipping point were found applicable to guide the decision-making process in unembanked area development.
For evaluation methods, multi-criteria analysis (MCA) emerged as a suitable tool for decision-making in unembanked area development, considering social values and intangible criteria. Combining MCA with cost-effectiveness analysis (CEA) or a form of cost-benefit analysis (CBA) proved effective in balancing quantitative and qualitative criteria, facilitating inclusive decision-making. The research emphasizes the extensive involvement of various stakeholders and identifies barriers related to legal aspects, risk awareness, and communication. Stakeholders call for well-defined guidelines, legal regulations, and collaboration between private and public entities. The study recommends establishing principles for unembanked area development and translating them into MCA criteria, addressing both social values and local characteristics. Further research is suggested to address legal assurance for climate-adaptive construction, increase awareness, enhance flood risk assessment methods and communication, and strengthen collaboration between private and public stakeholders in flood risk management and spatial planning. ... Read more

The Netherlands is prone to flooding as more than a quarter of the country lies under sea level. To combat flooding and ensure that the country remains dry structures such are levees and dikes have been installed. However, older water retaining structures are more than ever failing the stringent safety standard assessments. These older conventional reinforcement measures, including berm constructions, are not only costly but require an expanse of ground to ensure performability.

Backward erosion piping is an internal erosion mechanism during which shallow pipes are formed in the direction opposite to the flow underneath water-retain structures as a result of the gradual removal of low cohesive material by the action of water. This mechanism is an important failure mechanism in both levees and dams where a cohesive layer covers a sand layer. Although failure resulting from backward erosion piping is not common, several levee failures in the United States, China and the Netherlands have been attributed to this mechanism.

There are mitigation measures known to stop the backward erosion mechanism. One such measure is the placement of a seepage wall, to create a physical barrier directly in the flow path trying to reach the lowest region of the hydraulic head. A review of the literature showed that current design rules only consider groundwater flow calculations when determining the likelihood of hydraulic heave, one of the failure modes within the backward erosion process. Hydraulic heave in the backward erosion piping context is closely linked to the quicksand condition, essentially stating that once the effective stress is zero, the sand particles become suspended, liquifying a solid layer. The absence of an assessment of the effective stresses during the design process in conjunction with hydraulic heave has contributed to the main research question addressed by this thesis; How does a restricted exit for groundwater flow affect hydraulic heave compared to Terzaghi’s free exit situation?.
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This study examines the validity of constant failure rates in the reliability assessment of storm surge barriers, with a focus on the Stormvloedkering Oosterschelde (SVKO). Analysing a dataset of 1,501 malfunctions, including 87 critical incidents over six years, we employ Exponential and Weibull statistical models to assess failure rates. The research question—whether the assumption of constant failure rates over time is valid—is addressed with a nuanced perspective. The findings in this study reveal that neither model conclusively fits all failure scenarios, with some data supporting constant rates and other data indicating variability. The Weibull model better describes certain scenarios, suggesting variable failure rates, while in other instances, both models show comparable performance. The p-values from hypothesis testing and visual inspection of component data provide inconclusive evidence, leading to the suggestion that both constant and variable failure rates may exist in storm surge barrier components. The research contributes to the field by challenging the prevailing assumption of constant failure rates, developing a statistical framework, and by suggesting the need for a flexible, scenario-specific approach to modeling failure rates for improved reliability assessments. ... Read more

Sea level rise will increase the risk of flooding in coastal areas. This poses a risk to the coastal protection as well as rivers and lakes close to the coast. Solutions are needed to cope with this threat. The past decade, nature based solutions have gained significant interest. One of these solutions could be sandy foreshores. Due to the use of natural materials, sandy foreshores are a ‘nature-based solution’ opposed to a more traditional approach of dike reinforcement. For sandy foreshores to be a viable alternative to regular dike reinforcements, the order of magnitude of construction and maintenance costs need to be known. For this reason, it is necessary to be able to calculate a failure probability of a dike with sandy foreshore, to predict the required maintenance and to optimize the design based on life-cycle costs.

To improve the calculation method, a step-wise calculation of the failure probability for wave overtopping of a hybrid structure was developed. The calculation included an iterative process. The calculation methods consists out of calculating the failure probability for wave overtopping in Riskeer and a dune erosion calculation in Xbeach. In this research, overtopping was considered as the dominant failuremechanism. For the assessment, the dike was seen as an impermeable hard layer and the foreshore as a beach. Therefore, dune erosion could not erode the main structure and is considered a sub-mechanism of overtopping.

Next, a calculation was performed to predict the longshore transport along the beach in Almere Duin. The occurrence of different wind directions, together with a Delft3D model of the Markermeer, was combined to find the longshore transport. The LST was calculated with transport formula calibrated for coastal areas. The life cycle costs (LCC), including design and maintenance costs, were calculated for different strategies. The calculated alongshore transport together with cost estimates were used to calculate the LCC. Subsequently, the net present value of the maintenance costs was calculated to determine the LCC for each maintenance strategy. At the end the uncertainty and sensitivity of each strategy were analysed.

The time-varying protection level can be optimized by calculating the failure probability due to wave overtopping, with Riskeer and calculating the erosion of the foreshore, with Xbeach. To use this method, Riskeer and Xbeach should have the same design point and if the design point shifts, an extra iteration is necessary. For a 1/10 profile, only a 0.25 m lowering of the foreshore height was found and one extra iterative step was required to carry out the calculation. A maintenance strategy with a 100 year maintenance interval period was found to be optimal in this thesis and a Monte Carlo simulation, which included uncertainties, led to similar results. However, the total LCC were 21% to 34% higher, when uncertainties were included in the calculation. These findings suggest that it is not necessary, to carry out a probabilistic calculation, to find the optimal maintenance strategy. However, the models used, aswell as the local boundary conditions, such as the longshore transport and the cost of sand, were found to influence the life cycle costs significantly. For this reason, it is concluded that a location specific analysis is important to optimize the maintenance strategy.
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The production and consumption of electricity need to be balanced at all times. Due to the ever-growing shift towards renewable energy generation, this poses an increasingly difficult challenge. Currently, supply is regulated to maintain balance. However, there is potential to improve reliability and save costs by shifting the balancing to the demand side, known as demand response. The flexibility of water systems can play a role in this, thereby benefiting from cheaper price fluctuations and reducing operating costs.

This research investigates the IJmuiden pumping station, which drains water from the Noordzeekanaal-Amsterdam-Rijnkanaal system into The North Sea. The primary focus of the control of this system is ensuring safe water levels as it runs through areas of high economic value. The flexibility of the range of safe water levels allows costs to be minimized by selecting favourable moments to consume electricity. This simultaneously contributes to the stability of the electrical grid. This research explores the potential for a Reinforcement Learning controller for such an optimization problem, as there are some drawbacks to the Model Predictive Control methods that are currently widely used. The research objective is formulated as follows:

To optimize the control of the IJmuiden pumping station using Reinforcement Learning while complying with local water level restrictions and compare it to the state-of-the-art Model Predictive Control methods in terms of constraint violation, energy costs, and computational speed.

The Reinforcement Learning controller will use a deep Q-learning algorithm that chooses the most cost efficient control in IJmuiden while respecting the water level restrictions. To do so, the model makes decisions based on electricity prices and details about the state of the water system for the current time step as well as a forecast of 48 hours ahead. This data is provided as an input to the model.

The inputs of the model consist of historical data, meaning that the associated uncertainties are not included. The water system that the model can interact with is represented by a linear reservoir model. Therefore, the water system is influenced dynamically by the actions taken by the model. The possible actions are determined by the state of the water system.

The trained model was tested on 2 years of unseen data (data that was not used during training). Using the same test data, control plans were generated using Model Predictive Control. The Reinforcement Learning model was very successful in ensuring safe water levels. However, this did result in approximately 50\% higher energy costs. The use of the gate was close to optimal but the pumping was not clearly correlated with favourable prices and power consumption. The trained model was robust, with consistently accurate results with regards to respecting the water level constraints.

The most significant difference with the Model Predictive Control was the computation time. The Reinforcement Learning model was able to create a control plan approximately 300 times faster. This opens doors for further development of the model and increased complexity. A more accurate model of the water system can be used to take into account temporal and spatial effects and individually representing the six pumps in IJmuiden.

There are still many steps before such a model can be used for operational control, but the method has potential for such an application. Many aspects of the model can be improved as well as making adjustments to increase the usability for control operators. ... Read more

Weather generators (WGs) based on temporal resampling algorithms are not able to generate new extremes with the same or a higher temporal resolution as the historical data series of the thus far
observed precipitation. This is problematic for catchments with a time of concentration shorter than the resolution of the used data and conflicts with the increasing occurrence of more local, short duration extremes not yet observed.

In this thesis, it was researched if spatial permutation of precipitation could provide a solution to these problems by introducing historical events from related locations into the area of interest. The generated precipitation series were expected to have a larger variety of precipitation events compared to the historical data, thereby representing the current changing weather patterns better and being more suitable for small basins. This is beneficial for insurance companies, governments and aid organizations which rely on long term precipitation series to generate event catalogues and risk predictions.

To develop, improve and widen the knowledge about the effects of spatial permutation, four different questions were formulated for a case study on spatial permutation in the Rhine basin. A literature study showed that precipitation regimes in Europe can be defined based on spatial and temporal variability, precipitation amounts and the influence of controlling factors like atmospheric circulations, topography and climate change. This information was used to built three permutation models. The first model shifted historical precipitation fields over fixed distances and directions. In the second model this fixed approach was replaced by semi-random vectors including spatial and temporal correlation. The last
model used a vector approach with vectors conditioned with historical wind data. The effect of each model on the Generalized Extreme Value (GEV) distributions, the cumulative distribution functions (cdfs) and the main characteristics of precipitation for different basins and aggregation times was determined. The July 2021 Meuse flood was used as example to show the working method of each model visually and to better understand the effect of each permutation model on individual extreme events.

The results showed that spatial permutation did influence precipitation patterns, characteristics and statistics. Strongest changes in extreme precipitation events were seen for small basins and short aggregation times. The permutation direction and distance were important determinants for the outcome of each model. Precipitation permutation with semi-random vector fields was shown to be a promising method which allowed for the inclusion of both spatial and temporal correlation. However, the model had a high sensitivity to the initial and boundary conditions. Wind based vector fields were able to replicate the most important historical precipitation characteristics while at the same time generating new extremes. Yet, a clear trade off was visible between similarity of the historically observed and modelled precipitation characteristics and the number of new extremes introduced.

With the knowledge obtained, it can be concluded that spatial permutation is a promising method to generate more divers precipitation time series for the Rhine basin. Both semi-random and wind-based vector permutations can already be used to generate new precipitation series as long as the initial and boundary conditions are chosen carefully. To improve the results, a fusion of spatial and temporal relations and a physically wind-based vector generation method is advised. In addition, possibilities are seen in a combination of the currently used temporal resampling algorithms and a spatial permutation approach. The outcomes of these suggestions are not known yet. Nevertheless, it is expected that a better understanding of spatial permutation, on top of the results presented in this thesis, can advance the current methodologies used to generate long term precipitation series. Therefore, it is hoped that this research provides the incentives to explore spatial permutation of precipitation patterns in more detail and in such, contributes to a more accurate risk profile for the livelihoods of people worldwide. ... Read more

Flood simulations can give insight into the consequences of flood scenario's and can help to create hazard- and risk maps to support decision-making in flood risk management and in crisis management. 2D hydrodynamic simulations give accurate descriptions of the propagation of a flood and rely on advanced numerical methods to solve a set of physics-based mathematical equations. A drawback of these models is that they can be computationally expensive with run times in the order of hours or days depending on the time and spatial resolutions. In this study we explore the use of deep learning techniques in a surrogate model for 2D flood simulation. We propose and test a deep learning-based surrogate modelling framework that can be used to train a deep learning-based surrogate model. Once trained, the surrogate model can be used as a substitute for the hydrodynamic model with the advantage of being much more efficient in terms of run time and can be of great value in for example crisis situations. For training, a data set of expensive 2D hydrodynamic simulations was created using the SOBEK software program. Such simulations require a lot of input data, such as input parameter maps specifying the terrain over the computational grid and boundary conditions. To make training data-efficient, a sampling strategy was used for the input of the flood simulations. Three deep learning architectures were trained and tested. The first two architectures are feed-forward networks and the third architecture is of recurrent network type. These networks contain convolutional neural network (CNN) architectures with an encoder-decoder structure to make patch-level predictions of the flood characteristics in time. These patches contain a small section of the flood prone area and an encoder network is used to extracts coarse feature maps from this data that is then refined by a decoder network to create a prediction of the flood propagation. Using patches has the advantage of making a surrogate model able to create flood simulations over prone areas without restrictions on size or shape by tiling the output patches with flow predictions. Also it allows the surrogate to focus only on regions where the flood has reached and not on the regions where no water has arrived. It was found that with the recurrent architecture, the surrogate model was most capable of emulating the ground truth flood simulations in the test simulation. This trained network architecture was used in a case study where the surrogate was applied to create flood simulations in a small dike ring in the Netherlands. This shows that the surrogate modelling framework can be used to train a deep learning-based surrogate and, once trained, can be used to create flood simulations similar to hydrodynamic simulations. However, two main challenges were identified in using such data-driven deep learning-based surrogates. Firstly, keeping the predictions of the flood characteristics accurate enough to avoid large error propagation. Secondly, accurately generating large amounts of data from relatively little information present in the boundary condition and terrain. ... Read more

Since 2017, Dutch flood defences are assessed according to new safety standards. These standards are based on flooding probabilities and rely on several assumptions and approximations. There are concerns that the combination of these assumptions leads to conservative results. Recently computed probabilities of failure are often much higher than expected by dike managers and the outcomes of former assessment methods. This conservative bias results in a large and expensive reinforcement task in the coming years which can be reduced by improving the current assessment procedure.  One of the reasons for the current conservatism is the assumption of mutual independence of dike sections and failure mechanisms. Currently, the different elements are assessed independently, while failure mechanisms and failure at different dike sections are likely to occur during the same extreme load event. Furthermore, correlations in space and between different parameters are present within the subsoil characteristics. Neglecting these correlations results in rather high estimations of the failure probabilities.  The aim of this thesis is to investigate how correlations affect the reliability assessment of a dike trajectory. To achieve this, an integral, full probabilistic model is developed that enables simultaneous assessment of dike sections and failure mechanisms while accounting for uncertainties and (spatial) correlations within the model input. The model is based on Monte Carlo simulation. The failure probability of a dike trajectory is computed by counting failure if one or more limit state function 푍푗,푘 for failure mechanism 푗 of dike section 푘 returns a negative realisation. Correlations between the model input parameters are provided by means of a Gaussian copula. A particular aspect of the model is the implementation of metamodeling for the assessment of macrostability. This failure mechanism cannot be described by an analytical limit state function that is easily implemented in the Monte Carlo framework. Therefore, metamodels are created by means of Gaussian process regression. This method makes it possible to assess macrostability within an integral, full-probabilistic framework that is able to include interdependencies between e.g. macrostability and piping, within acceptable computation costs. The model is applied to a case study of dike trajectory 43-4, which is located along the Waal between Sprok and Sterreschans, in the east of the Netherlands.  The effects of different plausible correlations have been studied. This research shows that including certain correlations can significantly reduce the assessed failure probabilities, by a factor ten or more in some situations. However, the impact of correlation strongly depends on the situation. The most significant reduction can be achieved for cases in which (1) parameters that play a dominant role in failure of the corresponding mechanism are correlated; (2) the failure probabilities of the different elements are similar, i.e. for a flood defence where failure is not dominated by one dike section or one failure mechanism; and (3) the failure probabilities of the corresponding elements are smaller than approximately 10−3. The model forms a solid, flexible basis that can easily be adapted or extended to improve the understanding about interactions between failure mechanisms, even though some aspects are simplified or neglected. All in all, the conservatism in current safety assessments can be partly solved by considering the interdependencies between mechanisms and dike sections and by approaching a dike trajectory as an integral system. ... Read more

The construction of a dike improvement often causes a decrease in reliability during construction. Raising a dike may give rise to excess pore water pressures in the subsoil, resulting in a temporal strength decrease. Observing the survival of such a loading condition might provide information on the strength of a dike. Therefore, this research investigates the effect of incorporating construction survival in estimating the slope reliability of dikes. Assessing slope reliability can be done by means of simulation. However, due to the high reliability of dikes, many realizations and thus model evaluations may be needed to achieve sufficient accuracy, leading to infeasible computation times. In this research, a method is developed for reliability updating using metamodelling, providing reasonable computation times while not losing accuracy. The effect of incorporating construction survival is explored by updating the inward slope reliability of a case study dike improvement. The case study shows that the current semi-probabilistic approach to assessing construction stability in practice leads to situations not effective for reliability updating. Though adjusting the construction phasing may lead to a significant update. It is shown that adapting the dike improvement design after survival of the critical construction step results in a 75% reduction of the dimensions of the berm to be constructed, while achieving the same reliability as prior to the update. The main finding of this research is that incorporating construction survival in the reliability assessment can be very effective in terms of reliability, and in making dike improvements more efficient and less space consuming. ... Read more

The Kampereiland is an island located at the south eastern part of the IJsselmeer in the middle of the Netherlands. This island serves a purpose to lower water levels in the IJssel- and Vechtdelta during high water, by being inundated. This inundation is meant to result in lower water levels in the IJssel near Kampen. However, the flooding of the Kampereiland is a complex case. There are numerous stochastic variables that are used to determine the water levels, as well as breaching possibilities and a compartment structure which is present on the Kampereiland. All these aspects have influence on inundation of the island. In this thesis research, the flooding of the island is analysed, during multiple different types of high water scenarios, as well as with a variation of breaches or no breaching. This is all done while taking the compartment structure on
the Kampereiland into account.

To analyse how the Kampereiland floods, three main types of highwater scenarios have been analysed. These types are stormdominated scenarios, which are defined by high wind speeds and low discharges. The second type of high water is the discharge dominant scenario. The high water levels in these scenarios are reached by high discharges from the Vecht and the IJssel rivers, in combination with low wind speeds. Lastly, a number of extreme events have been analysed, to give a worst case perspective of the flooding of the Kampereiland. In these scenarios, high wind speeds coincide with high discharges from the two rivers, resulting in extreme water levels in the Ketelmeer, ZwarteMeer and in the Ganzendiep.

Each of the analysed scenarios have outside water levels exceeding the crest height of the flood defenses surrounding the Kampereiland. The scenarios have been analysed for multiple breaching cases. Three different breach locations have been determined. The locations have varying crest heights, type of flood defense (overflow resistant or non overflow resistant), type of high water (storm dominated or discharge dominated) and different hinterland compartments. Each scenarios has then been used to run the model to determine water levels in each compartment. This is done for situations without a breach, a single breach or two breaches at one location. The determination of the water levels is calculated by the use of spillway formulas.

The results show that the Kampereiland mainly floods from west to east. Storm dominated scenarios lead to high water levels in the Ketelmeer, leading to overflow from here. In scenarios up to 32 m/s wind speeds without breaches, the flooding is contained to the compartments to the west of the N50. The entire island floods once water levels increase due to wind speeds of 37 m/s and higher. Adding breaching into the storm dominated scenarios, the results are shifted. Now the evaluated scenarios with 32 m/s also lead to flooding
of the entire island. This case still leads to less high water levels on the Kampereiland than the scenarios of 37m/s without breaching, but every compartment is inundated.

The discharge dominated events are contained in the Willem Meyer- and Stikkenpolder. This is due to the presence of the old flood defense, which contains the flooding in cases with and without breaches.

Finally, the extreme events flood the majority of the Kampereiland, similarly to the stormdominated scenarios. The water levels that occur in the Zwarte Meer and Ganzendiep are higher during the extreme events. They also last longer than in the storm dominated scenarios. This results in a small inflow from the north
and southeast, while the western side of the Kampereiland rapidly fills up. Breaching during these extreme events leads to higher water levels when the breach occurs in the overflow resistant part of flood defense 225. The rising velocities in the west are also the highest in this case. Eastern compartments have higher rising velocities in case of breaching in flood defense 101 (along the northern boundary). ... Read more

The water levels along the dike of Kampen are affected by the magnitude of the discharge on the IJssel and the water level set-up caused by the wind characteristics on the IJsselmeer. The Kampereiland has been assigned as a retention area to reduce the water levels near Kampen during a storm. This area should store excess water during a storm at the IJsselmeer of a magnitude corresponding to an annual exceedance probability of 1/500, to prevent this water from flowing in the direction of Kampen. The Kampereiland is protected by dike trajectory 225 and a part of this trajectory has been made resistant to the overflow of water. According to new insights, the crest of this dike section seems too high and the Kampereiland inundates less frequently. Furthermore, not sure is whether the water level at Kampen benefits from the inundation of the Kampereiland and what the consequences are for surrounding dikes. The Kamperzeedijk is one of these surrounding dikes and protects the city IJsselmuiden, along with the polder behind. The influence of the crest height of this overflow resistant part on the water levels at Kampen and at IJsselmuiden is investigated. The most important assumptions are that dikes do not breach and that the water level at Kampen remains constant after water flows into the Kampereiland. The influence on the water levels at Kampen and at the Kamperzeedijk is evaluated for multiple crest heights of the overflow resistant dike section. Eventually, these water levels are processed with a statistical model to compute multiple water level exceedance frequency lines for each location and for various chosen crest heights of trajectory 225. The results show that higher crest heights of trajectory 225 lead to increased maximum water levels at the Kamperzeedijk and to lower maximum water levels at Kampen, and vice versa. The water levels in front of the overflow resistant dike section remain unaffected. The return periods for overflow at Kampen and IJsselmuiden are derived by comparing the water level exceedance frequency lines to their individual crest heights. Concluded is that the inundation of the Kampereiland does not immediately lead to a load increase in front of the Kamperzeedijk. A delay is observed as a result of the storage capacity of the Kampereiland. As soon as water from the Kampereiland flows into the Ganzendiep, the loads rapidly increase. Furthermore, concluded is that the Kampereiland is capable of reducing the water levels at Kampen. Based on the results from this research, a crest height of 2.7m +NAP leads to equal return periods for overflow at trajectories 10-2 and 11-2. The reduction of the crest height by ten centimeters increases the return period for overflow at Kampen from 30,000 years to 45,000 years. At the Kamperzeedijk, the return period is reduced from 80,000 years to 45,000 years. In reality, these return periods are also affected by other failure mechanisms. A full dike assessment has to elaborate on this. Furthermore, trajectory 225 is assessed whether it meets its safety standard. It would be more legitimate to assess trajectory 225 by explicitly quantifying its consequences on trajectories 10-2 and 11-2 ... Read more

Rivers have long since exceeded their natural purpose of discharging excess water, by becoming subject to many practical applications demanded by present day society [61]. In order to comply withthis variety of needs and demands, the necessity for proper water management arises, which in turn requires data and knowledge of hydrological parameters like water levels, water quality and river dis-charge [50]. This research focuses on the hydrological data demand and specifically on the measurement of riverdischarge. Discharge is generally estimated with intrusive measurement methods [64], this means that the measurement device is in physical contact with the water which can be difficult in strong current or high discharges and even dangerous during floods . Furthermore, in remote and low-resource settings, collecting discharge data is compromised by accessibility problems and difficulties maintaining and acquiring monitoring equipment. When numerous measurements are performed, it is common practice to establish a stage-discharge relationship [66] to facilitate discharge determination, i.e. by shifting to stage measurements. However, due to the empirical character of the method and the sporadic occurrence of high discharges, the relationship can contain considerable uncertainties for these higher discharges [67]. The aim of this research is to provide a sustainable and low-cost data collection and processing method in order to establish a rating curve based on a three dimensional hydraulic modelling approach. One of the main processing methods is Large-Scale Particle Image Velocimetry (LSPIV). LSPIV is a computer based technique that computes flow velocities at the river surface based on video images. Hence, with the development of such a model a more physically based stage-discharge relationship can be determined based on non-intrusive measurements, meaning that measurements can be taken during safe (low flow) conditions in a restricted amount of time. Furthermore, due to the sole use of relatively simple methods and the limited amount of observations needed, this method is particularly suitable for remote and low resource settings. The study is based on data collected during a two month field trip at the Luangwa river in Zambia. The dataset consists of point clouds collected with the aid of photogrammetry, sonar and RTK GPS which are used to create a bathymetric chart, videos recorded with a drone for the computation of the surface flow velocities, surface flow velocities measured with a current meter for LSPIV validation and discharges measured with an ADCP. The bathymetric chart is used as bed level for the three dimensional discharge model created with Delf3D D-Flow FM which is calibrated with the surface flowvelocities (LSPIV) and ADCP discharge measurements. The discharge model represents approximately 9.2 kilometres of the Luangwa river in length and can reach a maximum width of about 390 metres. The model is calibrated at a discharge of 191 m3/s by minimising the difference between measured and simulated values of ten surface flow velocities and five water levels. This resulted eventually in a Manning friction coefficient of푛= 0.014 s/m1/3. The calibrated model resembles the actual river in location, depth, width and surface flow velocity. The LSPIV velocities are approached to a mean average deviation of 0.07 m/s (1.1 m/s average) and the water level deviates 0.06 m at the research area (1.3 m average). The model is used to establish a stage-discharge relationship which is subsequently compared to two existing relationships, one based on a similar approach using a 1D model and one based on stage-discharge data measured at a conventional gauging station. The three stage-discharge relationships are in the same order of magnitude although the geometry of the river at all sites is likely to be different. Since a stage-discharge relationship is heavily dependent on the geometry [66] this comparison is only a rough indication of the accuracy. Ideally, the discharge, water level, and surface flow velocity should be measured for different discharges and compared (using the model) to the established relationship. The stage-discharge relationship could, if needed, be adjusted based on the new measurements. ... Read more

To develop warning systems for flood events, create precipitation-runoff relationships, validate runoff models, or to understand the behaviour of rivers, understanding of the amount of water flowing through rivers is needed. The low-cost and novel gauging method using Large-Scale Particle Image Velocimetry (LSPIV) could complement discharge measurements at locations and stages where the possibilities of using traditional gauging methods are limited. This report investigates the feasibility of using LSPIV to quantify river discharges in an equatorial urban stream with fast response time.

LSPIV uses videos to extract surface flow velocities by tracing movements of seeds on the water's surface. Combined with the local bathymetry and water level, an estimation of the river's discharge can be made. This study consists of two sets of experiments. The first set of experiments were performed at the Dommel regarding processing software, image preparation, seeding densities, and point of views and discussed by assessing their accuracy relative to benchmark measurements -- using the mean error and root mean squared error -- and the method's precision – using the relative standard deviation.

The second set of experiments were performed along the Chuo Kikuu, Dar es Salaam, Tanzania. A flood wave was monitored through the capture of 73 5 second videos. These videos were turned into separate frames and corrected for lens distortion and perspective distortion. Thereafter the frames were gray scaled and gamma correction was applied. After the LSPIV process additional filtering removed unrealistic low flow velocities, and through substitution missing velocities were replaced with flow velocities based on the vertical logarithmic progression relationship between the surface flow velocities and water depth. The surface flow velocities found using this method match optical observations. Discharges were estimated using the empirical depth-average coefficient and local bathymetry. Results showed that the post-processing reduces the uncertainty bandwidth with 37% and increases the mean flow velocities with 96%.

The found discharges were compared with precipitation measurements observed at a nearby TAHMO meteorological station. The total volumetric precipitation was determined by estimating the contributing catchment using a digital elevation map and the locations of man-made drainage systems. When comparing the volumetric precipitation with the flood wave, a runoff coefficient of 53% [35-68] is found. This coefficient falls within the ranges found in literature, but is probably an underestimation of the true runoff due to an overestimation of the catchment area and underestimation of the discharges.

This study shows that the LSPIV method is feasible for continuously monitoring flood waves in an urban environment. Especially during peak flows LSPIV proves to be valuable, as observations using conventional gauging methods are labour intensive, unsafe, or not executable. Because of the possibility to monitor streams from a distance -- which ensures access to power and safety against vandalism -- there is a possibility to observe complete flood waves at regular intervals without the need for direct contact with the water. For Dar es Salaam, this method opens doors for continuous and secure stream monitoring, at low costs and with local devices. ... Read more

In this master thesis the current Dutch method of combining failure probabilities at different spatial scales is researched. This method is used in the Dutch flood risk analysis of earthen dikes to assess the probability of flooding. Currently, probabilities of flooding for geotechnical failure mechanisms are obtained which are not considered to be realistic. To obtain more realistic results the following steps are researched; the assessment of cross-sections, scaling to dike sections and combining sections to a dike trajectory. The increase of failure probability over increasing length, known as the length-effect, is of importance in the current Dutch method of combining failure probabilities. This research shows the conservatism of the assessment of cross-sectional failure probabilities and offers possibilities to reduce the length-effect within and between dike sections to obtain more realistic results. ... Read more

Sediment nourishments have become an increasingly attractive alternative to deal with continuous bed degradation problems in the river system. When supplied to the river, sediment nourishments induce a sediment wave that propagates through the system causing changes in bed level and bed surface texture. In the present study we use a one-dimensional numerical model to analyse how the propagation of these sediment waves varies under different conditions. We find that the propagation of the sediment wave tends to be predominantly dispersive for large spatial variations of the flow, which is the dominant case when the height of the wave is large in comparison to the flow depth, or when the sediment is dispersed over a large enough reach to lead to a backwater effect. In artificial sediment nourishments the height of the sediment wave is usually limited to prevent creating an additional obstacle to navigation, and it is then that the temporal variations in the flow, due to high discharge events for example, determine the propagation of the wave. We study the morphodynamic response in a mixed-size sediment river system to a sediment nourishment, and identify the physical mechanisms that impact the propagation of mixed-sized sediment waves. In order to prevent it from being easily flushed downstream, the grain size distribution of the nourished sediment is typically selected to be coarser than the river bed. This reduces sediment mobility and enhances sediment deposition over the nourished reach, which in turn causes a deficit in sediment supply to the downstream reach and leads to the formation of a degradational wave. The propagation celerity of the degradational wave is found to be significantly faster than that of the sediment wave, which means that the effects of the nourishments in a river system can be observed significantly further downstream than from where the front of the sediment wave is found. We find that the celerities of both the sediment wave and the degradational wave are predominantly affected by the adjustments in surface grain size in the system. These adjustments migrate in the river system as a fining wave, which both accelerates the sediment wave, and decelerates the degradational wave. We learn that higher content of the finer fractions in the nourished sediment accelerate the evolution of the wave and lead to a predominantly translational behaviour. It also affects the magnitude of the incision depth, the closer the composition of the nourished sediment is to that of the bed surface, the less severe the scour. And even though it does not affect the propagation celerity of the degradational wave, it does impact how far downstream the wave travels, affecting a larger river reach the coarser the grain size composition of the sediment wave is. Finally, we analyse the results from a nourishment pilot project carried out in the Bovenrijn from 2016-2019. We find that the propagation of the sediment wave associated with the nourishment is only observed during high discharge events. The wave is predominantly dispersive, and only during a prolonged extreme discharge event did the wave show slight translational behaviour. We observe that lateral sorting mechanisms caused the tracer sediment to have a different trajectory from the sediment wave, which highlights the limitations of using a one-dimensional model. We also observe that the changes in bed level are related to the changes in surface grain size, with sediment deposition over the nourished reach and bed degradation just downstream. ... Read more

Hurricanes impose great threats on coastal communities in terms of hazard and impact. Recent hurricanes like Harvey (Texas, 2017) and Idai (Mozambique, 2019) emphasize the global character of this threat. In the U.S., Hurricane Harvey tied with 2005's Hurricane Katrina as the costliest tropical cyclone on record, inflicting $125 billion in damage. Harvey hovered above the state of Texas for six days in 2017, making it the longest landfalling storm in Texas history. During this time, over 600 millimeters of rain had fallen in most of the Houston area, with extreme observations showing 1500 millimeters of rain. This, in combination with surge and river discharges, caused inundation for over one-third of Houston. Current generation coastal flood early warning systems are often not designed to take into account the compound effects of pluvial, fluvial and marine flooding (e.g. the ADCIRC + SWAN model deployed by the Coastal Emergency Risks Assessment group ignores pluvial flooding). Moreover, the advanced models applied in these systems are computationally demanding and can therefore not be used in probabilistic real-time forecasting applications in order to include uncertainty in meteorological conditions. Furthermore, despite the importance of tropical cyclone rainfall, this field is not completely understood. Tropical cyclone rainfall distributions are dependent on best track data parameters (e.g. storm motion velocity), but also on environmental elements (e.g. topography). Current modelling approaches are either computational inefficient (e.g. large-scale climate models), are location-specific or are dependent on parameters not always available in archives. Therefore, there is need for a simple generic parametric rainfall model. Main focus of this research was the derivation of a methodology for assessing the joint probability of fluvial, pluvial and marine flooding. For this study, a case study is carried out for Houston, Texas. The TCWiSE tool is used to generate a set of synthetic hurricane tracks based on historical data and a Monte Carlo sampling method. A derived parametrization of tropical cyclone rainfall is used to generate a spatial tropical cyclone rainfall field. Furthermore, a Delft3D-FM model is used to generate offshore water level time-series for the synthetic hurricanes. A combination of SFINCS and Delft-FIAT is used to make an assessment based on both hydrodynamics and exposure for every single generated hurricane. The model train is capable of carrying out a flood risk assessment, derive flood maps for given return periods (e.g. 1 in 100-year flood) and make an exposure assessment for the joint occurrence of pluvial, fluvial and marine flooding. This framework can potentially be a useful tool for future policy- and decision making. ... Read more