On large dams, spillways are used to evacuate excess inflow discharges from the upstream reservoir to the downstream tailwater. When passing over the spillway the high potential energy of the water is transformed into kinetic energy and must be dissipated, which generally happens in stilling basins or plunge pools. Failing to dissipate sufficient energy can lead to erosion or scour in these structures. If this process is left uncontrolled, the structural safety of the foundation might be endangered and therefore the stability of the whole dam. During construction of the Calderwood Dam in the USA, a scour hole of 15 meter occurred because the weir controlling the water level in the pool was still under construction. At the Kariba Dam, the rock in the plunge pool has eroded to a depth of 70 meters below the original riverbed. Various spillways with different dissipation structures exist, the focus of this thesis is on the free-falling nappe initiated on a sharp crested weir in combination with a man-made plunge pool. When not all energy is dissipated before reaching the pool bottom, the remaining nappe exerts dynamic pressure on it, potentially causing scour to develop. Being able to predict the characteristics of these pressures is crucial for designing structures that can withstand them. In practice this is often done by performing pressure measurements on scale models and extrapolating the results to prototype scale. This is done by using appropriate scale factors or by making the measurements dimensionless. However, due to
the inability of achieving full similitude between scale and prototype models, scale effects influence these measurements. The objective of this study was to quantify the influence of these scale effects on pressure measurements performed downstream of the free-falling nappe. To fulfil this, 2 scale models of the same prototype but of different scale were constructed in the Hydraulics Lab of the University of Liège. On both models pressure measurements were performed and their results compared. Due to scale effects the properties of the dimensionless pressures are different across the models. In absence of a water cushion, the mean in the centre is overestimated on the small model and the
fluctuations around this mean underestimated. Additionally, when comparing the empirical density histograms, on the large model two peaks are observed. One close to the fall height and one close to 0, while on the small scale model only the peak close to the fall height appears. Furthermore, the impact location of this centre is further downstream on the large model than on the small one. With increasing water cushion height in the plunge pool, two phases affecting impact pressures related to effective and non-effective cushions can be observed on the small model. For the non-effective cushion, the cushion does not reduce impact pressures compared to the absence of a cushion. In contrast, during the effective phase, a reduction in impact pressures occurs, and this reduction increases with increasing cushion height. This distinction is absent on the large model, where any cushion height
reduces impact pressures. This reduction continues as the cushion height increases.
To increase the understanding of these scale effects, future research should focus on several aspects. If results from other scale models are published, scaling relationships could be developed to better predict pressures across different model sizes. Additionally, conducting measurements on existing prototypes, where controlled test conditions can be replicated, could be an option. Further investigation is needed to understand the cause of the peak observed near zero in the density histograms of the large model. Since air concentration in the flow has been identified as a potential primary cause of these scale
effects, qualitative research is necessary.

In July 2021, an extraordinary precipitation led to severe flooding across Europe, particularly affecting South Limburg in the Netherlands, causing significant damage. In response, the Dutch government is seeking methods and new ways to mitigate the effects of future flash floods. Consequently, Waterschap Limburg (Limburg Water Board) initiated a physical experiment in Roermond in May 2023 to assess the effectiveness of movable flood protection barriers under various conditions. TU Delft, Flood Proof Holland, and AccessHub B.V. were involved in establishing a monitoring system that evaluated the stability and performance of these temporary flood barriers.

Although the experiment yielded success and Waterschap Limburg profitably selected appropriate temporary flood barriers to address flooding for the 2023-2024 festive season from Storm Pia, there remain knowledge gaps concerning these barriers. Limited documentation has left some aspects unclear, such as the fundamental physical processes and mechanisms of failure detection. This study aims to provide a thorough understanding of how to monitor physical changes through image processing and identify failure mechanisms by applying the horizontal stability equation.

In Dutch polders, numerous structures like bridges, weirs, culverts, and pumping stations have
been constructed over centuries to manage water levels. These structures play a crucial role in
maintaining water levels within predefined targets. The flat topography of the Dutch landscape
combined with the collective impact of head losses, induced by these structures may result in
flooding of polders during high runoff scenarios. Over time, culverts and bridges may
underperform due to alterations in the water system, increased pressure from climate change,
evolved design rules, insufficient maintenance, and shifts in land use.
A challenge is the potential hydraulic underperformance of structures and the need for their
premature replacement, which is costly. Waiting until the end of their technical lifespan may
contribute to floods. Therefore this thesis focuses on improving existing structures to mitigate
the need for replacement, specifically by streamlining inlet and outlet openings to reduce
energy losses. This leads to the research question of this thesis: “How can the head loss over
existing (too tight) culverts be minimised by adding an inlet or outlet profile and does this lead
to a substantial enhancement in the performance of these culverts, providing a practical option
to postpone the replacement of underperforming culverts?”
To answer this question, the problem is explored by looking into the fundamentals of energy
losses, including entrance losses, friction losses, and exit losses. This gives an understanding of
the conditions under which these losses manifest. However, these basic calculations have
inherent limitations due to their reliance on predefined coefficients. This renders them
inadequate for evaluating the effects of introducing new profiles onto an existing structure.
To overcome this, a flume experiment has been performed to verify whether it is possible to
measure water level differences for various profiles at the culvert entrance and exit. With a 3D
Computational Fluid Dynamics (CFD) model (OpenFOAM), flows around different culverts
are simulated. The results of the CFD model are compared to the flume experiment, after
which the CFD model is used to simulate a variety of scenarios, with different profiles, culvert
dimensions, velocities, and water depths.
As such, this thesis addresses challenges and uncertainties in quantifying head losses in culvert
structures through experimental methods and CFD modelling. Experimental setups struggle
with controlling all flow-influencing parameters, while CFD modelling offers flexibility but
requires careful consideration of uncertainties and limitations. The discussion emphasizes the
complexities of comparing experimental and model results, highlighting trade-offs and
uncertainties in each approach.
The conclusion answers the central research question, confirming that specific profiles added to
culverts can significantly reduce entrance losses up to 65%, thereby lowering headwaters for a
constant discharge.
The recommendations section outlines possibilities for further research, including optimizing
profile dimensions and conducting sensitivity analyses of influential parameters. Practical
recommendations involve aligning large-diameter concrete culverts with the socket end in the
flow direction and integrating groove or rounded profiles during construction for cost-effective
inlet loss reduction.

Dam failures are rare but highly catastrophic events which can be devastating for both infrastructure and the population living downstream. The recent failures of Abu Mansour dam in Libya (September 2023) and Kakhovka dam in Ukraine (June 2023) have shown that large number of fatalities are associated to these events. It is therefore important to understand the hydrodynamic behaviour of dam break waves to ultimately identify the risk they pose, especially for dams which do not have detailed data information for modelling studies. The objective of the present study is to determine the hydraulic characteristics of the waves and to predict the potential loss of life in case of a dam failure event using a simplified screening method which can be applied to a larger dam dataset. The approach of the research was to utilise the original theory of Ritter (1892) who presented an idealised solution to the Saint-Venant equations. These equations were modified by incorporating the effect of friction which eventually had a reducing effect on the idealized dam break wave celerity. Using this simplified hydraulic model the dam break wave depths and velocities were able to be determined from the required input of dam height. From additional past dam failures, the proposed limits of fatality rates in the curves of Reclamation Consequence Estimation Methodology (RCEM 2014) were validated. To determine the Population at Risk (PAR) the study utilised Geographic Information System (GIS) tools and buffer methods were tested. For a smaller dataset of 22 dams, selected based on range of dam heights from the Global Reservoir and Dam (GRanD) database, the results showed that a buffer with downstream distances determined by one hour travel time and a 1000 m width gave the most consistent estimates of the exposed population when compared to the method incorporating Digital Elevation Models (DEM). When the analysis was extended to the complete dataset of GRanD, a new buffer method was proposed because of the limitation of GIS analysis tool. This buffer method with downstream distance of 25 km was tested against three different inundation widths. Results showed that using a buffer with fixed downstream distance of 25 km and an inundation width of 1000 m gave the most closest estimates when compared with the DEM method. The study was able to highlight the total population at risk on a global scale and also zoomed into the region of Europe. Comparison between the dams allowed identification of high risk dams in terms of the exposed population. Specifically, the total potential fatalities were determined for the top ten PAR dams of Europe. Furthermore, to demonstrate the usability of the risk screening method the analysis was extended to two developing countries, Pakistan and Madagascar, where Multi Hazard Early Warning Systems (MHEWS) do not tend to exist. The results showed the difference in PAR and fatalities for each dam and provides valuable insights to develop preliminary risk management and evacuation plans both at local and national level. Despite its limitations, the study provides a quick risk screening method which can serve as an alternate to the resource intensive numerical modelling approach. Future research might be needed to reduce uncertainties and achieve more accurate estimates.

Hydropeaking is a widely applied management practice in the generation of hydropower. When the demand in electricity is high, the operator of a hydropower plant rapidly increases released discharges to meet this demand. Vice versa, when the demand is low, no or less water is released. However, while river regulation practices offer valuable resources, they can also inflict adverse environmental consequences on downstream river segments. More specifically, hydropeaking introduces high sub-daily variance in downstream reaches of the hydropower plant. This large sub-daily variance is harmful to the river regime and ecosystems. In Finland, hydropeaking has the highest negative environmental impact of all river regulation practices. The most prominent, known negative impacts due to high flow variations are a direct impact on aquatic biota, such as trout, and a compromised recreational use of the river corridor. The main objective of the thesis research is to investigate the impact of hydropeaking on rapids in a complex riverine system. More precisely, a system that includes multiple subsequent weirs, vegetation, large riverine boulders, a rather flat topography and a small-scale anabranch. Additionally, related to the modelling approach, two state-of-the-art calibration methods and their benefits and limitations are discussed. The formulation of operational and morphological mitigation measures to counter impacts is the secondary objective. A case study for the downstream region of Hamari Hydropower Plant at Ylivieska (Finland), the site Juurikoski, provides insight on the different aspects related to these queries. During a series of simulation runs, including the original situation and three hypothetical mitigation scenarios, the impact of hydropeaking is quantified and studied. Results include post-processed water level, velocity and shear stress data. Furthermore, conclusions and a discussion are given regarding the potential of calibration and validation for a 2D hydrodynamical model by state-of-the-art methods. These methods refer to a hot spot analysis comparison based on LSPIV-data and velocity profile comparisons based on ADCP-data. On a local scale, mitigation recommendations are suggested or excluded from a practical point of view. From a more global perspective, the report provides a modelling approach to tailor mitigation measures according to riverine lay-out, despite limited bathymetry data and increased riverine complexity.

Due to the rising sea level in combination with land subsidence there is a need to reinforce the dikes. The use of a crest element to increase the height of the dike is an effective and relatively cheap way to reinforce the dikes (Hogeveen, 2021). When a crest element is used, the jet generated by wave breaking on the dike slope impacts on the crest element, leading to an upward spraying motion of the water. This upward sprayed water can potentially be transported by the wind over the crest element and therefore contribute to the wave overtopping discharge. Small scale physical model tests were performed on a smooth dike slope of 1:6 to gain more knowledge about this influence of the wind on wave overtopping. Studying the influence of the height of the crest element, a promenade in front of the crest element and the slope of the dike was part of the research.

Following significant physical and economic damage associated with large tsunami disasters, this research assessed the efficacy of both nature-based and man-made tsunami mitigation measures. With an expected increase of the population living in tsunami-prone areas, it is critical to develop a better understanding of tsunami engineering.

To achieve this, a series of large-scale tsunami modelling experiments was carried out at HR Wallingford. The experiments utilized the Tsunami Simulator and involved generating a set of 20 trough- and crest-led waves with periods ranging from 20 to 240 seconds in a divided flume with a length of 100 meters.

The effectiveness of nature-based mitigation techniques was assessed through the implementation of land cover roughness onto a sloping bathymetry. The man-made measures included the in-situ construction of a scaled-down offshore breakwater similar to the Kamaishi breakwater. The study involved a comprehensive assessment of multiple factors, including run-up height, delay of inundation, pressures exerted on the breakwater, and a stability analysis of the breakwater.

In addition to determining the effect of roughness on tsunami-like wave run-up, the results were compared to available predictor equations. The empirical relation defined by McGovern et al. (2018) is found to be suitable for the prediction of waves with a period of 50 seconds or less. On the other hand, the predictive equation proposed by Wronna et al. (2021) displayed a similar trend but significantly overestimated the dimensionless run-up parameter.

The results demonstrate that nature-based run-up mitigation strategies are most effective for waves with laboratory periods less than 60 seconds. However, nature-based mitigation measures provide more promising results in terms of inundation delay. The offshore breakwater was found to be the most effective measure against tsunami run-up, significantly reducing the dimensionless run-up parameter.

Man-made mitigation measures are found to be the most effective solution for tsunami mitigation. However, not all coastal communities possess the financial resources to construct an offshore breakwater. In such cases, a combination of nature-based and man-made measures with robust early warning systems and evacuation strategies should be considered. This balanced approach maximizes coastal resilience given financial constraints and geographical circumstances.

Water is essential for life on earth and is vital for numerous sectors of our society. Pressures arising from climate change, growing populations, and the shift towards clean energy accentuate the importance of effective water management. To make decisions about water resource allocation, hydraulic modeling studies have been undertaken on large African rivers. These studies employ global terrain models, utilize remotely sensed water surface elevation data, and often involve estimating river channel bathymetry. Typically, these models also require an estimation of the river channel bathymetry. However, observed bathymetry data is seldom available and crucial for the hydraulic model performance. It has resulted in a key challenge of modelling large rivers in this data-sparse context.
This research aims to model a medium to large sized river with wide floodplains in three dimensions by integrating discharge data and a highly accurate bathymetry. The primary objective is to quantify the friction coefficient and establish a reliable rating-curve for the river system. By utilizing these key components, the study seeks to provide a comprehensive understanding of the hydraulic behavior of the river, contributing to improved water flow predictions and management strategies. The bathymetry data is acquired through two different methods. The dry bathymetry is obtained using an UAV (DJI Phantom 4) and photogrammetry (WebODM). The wet bathymetry data is collected using both, sonar with the Deeper Chirp+ and spatial referencing with the RTK-GNSS from ArduSimple. These methods are cost-effective and require minimal manpower, making them practical options for acquiring accurate bathymetric information. The discharge data is acquired using the open-source software, OpenRiverCam. OpenRiverCam uses Large Scale Particle Image Velocimetry (LSPIV) to determine the surface velocities and combines the results with the bathymetry data to calculate discharges, providing an efficient solution for assessing river flow characteristics. LSPIV has the advantage that it is a non-intrusive method of measuring the flow velocity and does not require physical probes or instruments in the water. The bathymetry data and discharge data are integrated into the Delft3D FM Suite to assess the accuracy of the measurements and estimate the friction coefficient in both the river and the floodplain. This modeling approach enables a comprehensive analysis of the hydraulic characteristics of a medium to large sized river and supports the evaluation of flow resistance in the study area.
The data acquisition took place at three study sites close to the Bui Dam, in the Black Volta Region, Ghana. The Bui Dam is the second largest hydro-power dam in Ghana managed by the Bui Power Authority (BPA). The Bui Bridge and Bamboi Bridge study sites are positioned downstream of the Bui Dam, allowing for accurate quantification of the discharge and the bathymetry measurements. The third study site, Chache, is positioned upstream of the dam, where daily water level measurements are taken. BPA has observed that the rating curve at this location is outdated. Therefore, efforts are made to update the rating curve and quantify the friction coefficient at this site in both the river and the floodplain.
This research has made significant progress in developing a three-dimensional discharge model and rating curve for medium to large rivers using advanced data collection methods and integration techniques. The study successfully combined photogrammetry and sonar measurements to effectively determine the bathymetry of the river, overcoming challenges related to high water velocities and dense vegetation. The LSPIV technique and OpenRiverCam were utilized to integrate surface velocities and discharge measurements, leading to a more comprehensive understanding of river dynamics. However, limitations were encountered in assessing the accuracy of the model at the Bamboi Bridge site due to the LSPIV results. This highlights the importance of obtaining more comprehensive data and observations to enhance the model’s accuracy. The comparison of rating curves at the Chache site resulted in positive results. Although, further verification during the wet period is required through velocity and discharge measurements to determine the accuracy. Overall, this research contributes to a better understanding of river behavior and provides valuable insights for water flow prediction in an efficient, cost-effective manner with minimal intensive manpower, ensuring a non-intrusive approach.

Due to an extraordinary precipitation event in July 2021, the Dutch government want to utilise the temporary flood barriers to reduce the impact caused by a flash flood event in the future. As a result, Water Board Limburg, Flood Proof Holland and Delft University of Technology made an agreement to conduct a physical experiment in Roermond on May 2023 to test the functionality of the temporary flood barriers in different spatial conditions.

This report aims to provide a comprehensive understanding of the temporary flood barriers and their performance in spatial variability before the experiment. To achieve this, available information on various barriers has been summarised to make a valid argument for the comparison of different barriers.

The first part of this report provides an overview of worldwide available barriers with their corresponding physical concepts explained, while more detailed information is given on those tested in Flood Proof Holland. The report then presents a theoretical hypothesis based on the calculation of the resisting force of the barriers. The findings reveal that most of the tested barriers can withstand a water level of 50 cm on asphalt, concrete, sand, and grass. However, BoxBarrier and BoxWall(Waterschot) show exceptions when subpressure is taken into account.

The report also includes a comprehensive outline of a physical experiment that will be conducted in May 2023, which provides a detailed description of the experiment, as well as preliminary assessment criteria. These criteria include logistics, failure mechanisms, spatial conditions, and additional requirements from the water board, and will be used to assess the performance of the temporary flood barriers. Additionally, an ideal monitoring plan utilising video camera, tracer fluid, and RBR-Diver has been proposed for the experiment.

Lastly, the report features a discussion of a preliminary test conducted on February 15th 2023 in Flood Proof Holland, to evaluate the effectiveness of the designed monitoring approach. The test proved that the proposed monitoring plan was successful and emphasised the significance of proper equipment inspection, anchoring, and quality control of materials for the temporary flood barriers.

Between July 12 and 15, 2021, extreme rainfall in Luxembourg, Belgium, Germany, and the Netherlands caused severe flooding. The total damage in the Netherlands is estimated to be between € 350 and € 600 million, with Valkenburg aan de Geul suffering the most damage. The economic and tourist heart of this city is located in the lowest part of the valley, therefore developing a flood reduction measure is challenging due to the limited space and restrictions in this location to protect the culture and nature.

In previous studies, different solutions were proposed for reducing the flood risk such as flood walls in Valkenburg; however, due to the locational difficulties, many options are difficult to implement except for the option of a flood bypass tunnel. A flood bypass tunnel has never been applied in the Netherlands, however; it is applied in mountainous countries. A flood bypass tunnel rapidly conveys floodwaters through densely populated areas. For Valkenburg, a flood bypass tunnel will reduce the flood risk locally while taking up little space and keeping the historic district intact.

Recent research did not look further into the opportunity of a flood bypass tunnel as a flood measure assuming it would be too expensive (Asselman & van Heeringen, 2023). However, different studies concluded that a flood bypass tunnel is a viable option (Van Dijk, 2022; Kallen et al., 2022; Leijser & Nijhof, 2022). Nonetheless, a flood bypass tunnel has never been applied in the Netherlands, and there is no prior research detailing the hydraulic and operational applicability of a flood bypass tunnel for Valkenburg aan de Geul. The main objective of this thesis is therefore to develop a hydraulic flood bypass tunnel design for Valkenburg aan de Geul which should operate to reduce the flood risk.

The objective is reached by combining the design approach for hydraulic structures with a Systems Engineering approach. First, the river system and its environment are analysed. Secondly, the basis of the design is determined. Thirdly, two alternative designs are developed from the two different types of reference projects: a passive and an active flood bypass tunnel.

The first design alternative is based on a passive flood bypass tunnel. It consists of a 2.4-meter-tall and 24.5-meter-wide Ogee weir, two tunnel tubes of 3.5 m diameter, and allows for a maximum discharge capacity of 55 m³/s. Once the tunnel is filled, the flow is pressurised. After a flood, the remaining water will be pumped out. A co-current channel is designed to prevent water from refilling the tunnel from the outlet side in a non-flooding situation.

The second design alternative is based on an active flood bypass tunnel. It consists of four vertical moving flat gates at the inlets and outlets, two tubes of 3.5 m diameter, and allows for a maximum discharge capacity of 58 m³/s. The water level will be controlled by the flat gates using a system for early automatic detection of flood hazards. The tunnel is always filled, thus pressurised. After a flood, the gates at the in- and outlets will close off the tunnel from its environment. The gates are tested twice a year, during which the system is flushed and refreshed.

The two design alternatives were evaluated according to six weighted criteria and ranked using a multi-criteria analysis in discussion with the municipality (gemeente Valkenburg aan de Geul) and the waterboard (waterschap Limburg), and a cost analysis was conducted. The first design alternative with the passive flood bypass tunnel was selected due to its high reliability and serviceability, which were highly valued, and low maintenance costs, compared to the second design alternative

The flood bypass tunnel reduces the flood risk based on discharge reduction from an estimated once every 19 years to once every 250 years in the current climate. This accounts for uncertainty due to climate change and ensures flood risk reduction in the future. The flood bypass is only active when a flood is impending; hence the water remains to flow through the Geul and does not interfere with the cultural heritage and tourism of Valkenburg aan de Geul. Due to the cost-efficient pipe jacking method, the total construction cost is approximately €40 million with an estimated yearly maintenance cost of €100 k.

With combined efforts from water management, architectural and hydraulic engineering students, an interdisciplinary and resilient design is set up for the Paraná Delta. The design relates to all the current environmental, architectural and flood risk challenges - among others, as well as the potential issues in the future since the Paraná Delta is a highly dynamic environment.

In the area of Bunde in the south of Limburg, the Netherlands, the Geul river flows beneath the Juliana Canal through an inverted siphon before reaching the Meuse. During July 2021 a large scale flood event occurred, showing an insufficient capacity of the inverted siphon when both the Geul and Meuse had high water levels.

Such inefficiency can be explained by the significant head losses at the entrance due to a sub-optimal geometry that also favours the accumulation of debris, as proved during the recent flood. Therefore, the purpose of this study is to investigate the hydraulic behaviour of the Geul inverted siphon, focusing on potential implementation measures. Additionally, this study investigates the possibility of replacing the current inverted siphon with a Minimum Energy Loss (MEL) culvert.

Accumulations of floating debris at culverts and inverted siphons cause partial blockage of the hydraulic structure’s inlet, leading to an increase in head loss that is also referred to as backwater rise. This effect is of high importance in flood management, because backwater rise associated with floating debris accumulations can cause or intensify flooding in the area upstream of the hydraulic structure, yet it is often not adequately addressed in practice or in design guidelines due to a lack of fundamental understanding. A prime example of this was observed at the Geul inverted siphon located near the village of Bunde in the south of Limburg, the Netherlands. During the 2021 floods the inverted siphon experienced a reduction in conveyance capacity due to accumulation of large wood at its inlet, intensifying flooding of nearby villages.

This thesis studied the development of floating debris accumulations at fully submerged and outlet-controlled culverts and inverted siphons, and analysed the effect that floating debris accumulations have on backwater rise. Experiments were performed in a flume under varying conditions of Froude number and submergence rate, achieved by adjusting the upstream flow depth compared to the culvert’s height. The scale model was representative of inverted siphons typical of the Limburg province. Upstream and downstream water levels were measured after addition of fixed batches of debris to the flume. The debris mixture consisted of six size classes of natural wood and was based on logs observed at the Geul inverted siphon. A grate was placed at the culvert’s inlet to prevent logs from passing through. In addition, flow velocities were measured at various locations using Laser Doppler Anemometry.

Based on visual observations and a feasibility study three mechanisms were proposed that describe the development of floating debris accumulations, and the feasibility of these mechanisms was confirmed in preliminary analyses. Furthermore, the experimental results were analysed to determine the influence on backwater rise of canopy drag due to skin friction within and below the accumulation, as well as form drag due to partial blockage of the inlet. It was found that in all cases inlet blockage was the dominant cause of head loss. Using this knowledge a theoretical framework based on a momentum balance equation was derived that relates the inlet blockage ratio to backwater rise, separating the contributions of the grate and debris. A regression analysis was then performed to obtain a design equation for the inlet blockage ratio caused by debris. In conclusion, this thesis provides improved understanding of the development of floating debris accumulations and their influence on backwater rise at submerged culverts and inverted siphons. The results enable more accurate predictions of water levels that can occur during floods and thus offer a solid foundation for flood management strategies.

The report tackles Galveston's flooding challenges, which are currently in development with the US Army Corps of Engineers (USACE) ring barrier. However, the current design, predominantly addressing coastal flooding, falls short in dealing with pluvial flooding, relying heavily on pumps. This top-down approach neglects environmental and stakeholder considerations, resulting in a decoupled response to compound flooding, lacking adaptability, and overlooking the impact of chronic flooding on local businesses. The central research question revolves around reshaping the Galveston ring barrier in The Strand area for enhanced functionality against both coastal and pluvial flooding, sustainable management of catastrophic and chronic flooding, and improved public space value. The methodology consist of a literature review, fieldwork in 'The Strand,' stakeholder engagement in Texas, the design of multiple alternatives that deal with the issue at hand and evaluation through a Multi-Criteria Analysis. Two alternative designs, sensitive to identified issues, are presented for the Strand area. The outcome emphasizes an interdisciplinary approach incorporating the knowledge of the different academic backgrounds of the team, with designs adaptable for broader implementation in Galveston.
The design alternatives centres on measures to counteract flooding, specifically cloudburst roads, retention areas, and a promenade. Caution is advised in interpreting results, emphasizing the need for further investigation into hydraulic conditions. Climate change effects are underscored, considering sea level rise, precipitation rates, and increased hurricanes. The project area, focusing on a 1 km stretch, offers local adaptation measures, with potential extension to larger areas to explore system behaviour on a larger scale. The study notes the uncommon implementation of sustainable drainage systems in the United States,
highlighting the importance of addressing common failure causes such as incomplete knowledge and poor communication. While two measures for pluvial flooding are examined, the report suggests a more detailed design should consider additional factors like green roofs and their impact on runoff speed and drainage capacity.

In the last few years, the climate crisis has been accelerating at a dizzying pace and poses an emergency threat to our planet. Rainfalls have transformed into intense downpours, and flash flooding, combined with the sea level rise, leads to a higher risk of inundation of densely populated coastal cities. Moreover, the melting of the permafrost can lead to significant landslides, triggering the generation of mega-tsunami waves. The latter can have a catastrophic impact, not only on the infrastructure but also on human life. Man-induced climate change is responsible for the increase in frequency and intensity of extreme natural events, such as tsunamis, floods, and storm surges. Recent research indicates that almost one-fourth of the world population lives at high-risk locations to at least 0.15m of inundation depths with a return period of 1 in 100 years. Therefore,
the urge of implementing protection measures against unsteady flows is imperative.

Undoubtedly, the involvement of engineers can play a pivotal role in order to analyze these flows in the built environment and provide sufficient coastal and building plans to ensure safety and reduce reconstruction
costs. The behavior of the unsteady flow around a structure is not a well-understood topic and results in a lack of accuracy and reliability. More insights are required into the fluid-structure interactions to come up
with a safe building design.

In the present study, unsteady flows are generated using the dam-break technique in line with previous research. The Thesis aims to model, validate, and implement a simplified approach to analyze the complexity of the hydrodynamic behavior of unsteady flows around impervious buildings, with different orientations
and blockage ratios. To do so, the research introduces a numerical simulation method of a dam-break wave, using the two-dimensional, and non-rotational shallow water equations. The Galerkin finite-element model is applied for the discretization of the solution on a limited domain.

Initially, the flow of the dam-break wave was validated in the absence of the structure, using a dam-break experimental work for comparison. Then, in order to insert a structure in the domain, a second experiment with a structure is used, which generates tsunami-like waves using the vertical release technique. The gate, which represents the dam, is located at x=0 and opens instantaneously at t=0s. Behind the gate, the reservoir maintains an amount of water that flows, after the opening of the gate, into the channel generating the shock
wave. At the channel downstream of the gate, initial water levels are considered and the behavior of a bore propagation is simulated. The building is located on the downstream side and different impervious building configurations were studied in terms of orientation and shape to investigate the impact of the unsteady flow.
To analyze the complex hydrodynamic processes of flooding, four fixed points around the structure are set to measure the action of the bore on different impervious building configurations. The water elevations and the averaged velocity profiles in time were derived at each point. Moreover, the horizontal forces in the x and y directions are calculated by the model, integrating the stresses over the wet surface of the buildings.

The general behavior of the fluid-structure interactions is captured well, especially upstream of the building, and insights are gained regarding the behavior of the fluid around the structure and the parameters of
influence. Results showed that orientation changes completely the impact on the building configurations. The separation of the flow and the blockage ratio are the main parameters that are influenced by the angle of rotation and change the behavior of the loading process at the initial impulsive phase, when the wave arrives at the structure, and at the hydrodynamic phase, where the flow has a quasi-steady behavior. Overall, a good agreement is achieved with the experimental data, although the numerical model overestimates the loads
acting on the different building configurations. Results proved that the orientation of the building with respect
to the flow facilitates the flow around the structure and contributes to lower water levels, and to a better distribution of the horizontal loads on the surface. The best results were achieved for an angle of rotation of 45°, where symmetrical separation of the flow is also playing an important role.

A dam-break wave can result in considerable damages and casualties. Events that can lead to such waves include dike and dam breaches, storm surges and impulse waves. Dutch history is familiar with a number of coastal dike breaches but also river dike breaches have occurred, resulting in dam-break waves reaching far inland. Beyond the Netherlands, propagating walls of water could occur when dams of water reservoirs collapse. More specific knowledge of the hydrodynamic behaviour of dam-break waves is necessary in the battle against water.
The impact of a dam-break wave can be reduced through a better understanding of the currently poorly understood link between bed roughness and wave hydrodynamic properties. The objective of the present study is therefore to study experimentally the effect of bed roughness on the hydrodynamic properties of dam-break waves, on both dry and wet beds. The approach was to generate dam-break waves through a lift-gate and a reservoir with a depth d0 = 0.4 m and to measure the water levels over time in the downstream channel. 7 different bed roughness configurations were made (range of ks = 0.6 to 48 mm) in addition to smooth bed reference test. Dry bed tests were performed, 5 wet bed tests with an initially still water level (h0) (range of h0/d0 = 0 to 0.125) were performed. The analysis focused on wavefront celerity, inundation depths and roller length which are used to characterise the hydrodynamic properties.
Visual observations showed substantial differences in wavefront behaviour between surges and bores as well as between smooth and rough beds. Validation of the generated waves was done by successfully comparing the reconstructed water levels over the flume length with a new approach.
Results showed that an increase in bed roughness resulted in a decrease in wavefront celerity for surges and that the initially still water level can work as a lubricant for bores. The initial still water level is dominant over the bed roughness when h0 >0.5ks.
The maximum water level increased with increasing bed roughness for surges, while bores showed an opposite behaviour. Increasing the initially still water level reduced the relative maximum water level for rough bed configurations.
In the present study, only some test configurations revealed the presence of a plateau height. If there was one, an increase in bed roughness showed a decrease in plateau height for bores with h0/d0 = 0.125. Three sections in the h0/d0 range with different plateau height behaviours were noticed.
The roller lengths were determined with the wavefront celerity and the plateau height. No trivial relations were found for the influence of bed roughness or initial still water level.
Overall, this project revealed some interesting behaviours that need to be further investigated in the future. It is recommended to conduct a full quantitative analysis once precise values of the bed roughness configurations are determined. Nevertheless, these results present some preliminary, yet interesting, findings that will contribute to a better understanding of the behaviour of dam-break waves over rough bed.

Weirs are constructed inside rivers to manage the water level. On the one hand they need to be designed sufficiently strong to prevent failure or destruction, while on the other hand they need to be economically feasible. If a structure is designed too strong, unnecessary costs are made and the structure becomes too expensive.

One of the potential failure mechanisms for weirs is erosion of the soil downstream of the weir. Bed protections consisting of rock and concrete are placed to prevent this erosion. Numerical modelling can give additional insight in the design of such a bed protection. This thesis aims to improve the design of bed protections downstream of underflow weirs through numerical modelling. This is done through two research objectives, being 1) proposing a numerical modelling strategy to create a design method for riprap bed protections downstream of underflow weirs, and 2) preserving a small computation time compared to full scale 3D models, as this is ideal for a future application in engineering.

A new approach is formulated by using the stability parameter of Steenstra (2014), ψRS, as basis. This parameter is based on multiple flow situations, except the underflow gate. For this reason the underflow gate is investigated in the current research. The output of the created OpenFOAM models can be applied to this parameter, leading to ψ-curves that can be compared with measured damage.

The first research objective is obtained by the application of three different turbulence mixing length approaches, of which two approaches created interesting results. The first approach is the Bakhmetev approach, leading to a conservative design outcome with a gradual decreasing stability pattern. The second is the Shear Stress Relation (SSR), leading to a promising result with better defined instability regions that compare with measured bed damage. From the desire to work conservatively, the results reveal that in the design phase of a bed protection downstream of a weir, the application of the Bakhmetev approach for the mixing length is recommended over the SSR approach.

Extended physical testing containing three aspects is needed to strengthen the promising findings of the SSR. These aspects are 1) a damage stone count including a sieve distribution, 2) a setup with varying gate heights and stone dimensions, and 3) varying water levels and discharges per different gate height and stone size. In addition a preliminary 2D numerical model study is advised, which allows to investigate the areas of interest for PIV flow measurements.

The second research objective is achieved by the application of a 2D RANS model and the simplification of the water level through a rigid lid. This simplification still leads to workable results, with computation time that are in the range of two to eight hours, operating on ten cores in one computer. This makes the approach attractive for engineering applications and for future applications in renovation tasks for weirs in the Meuse.

The geographical features in the Southern part of Limburg forces precipitation from upstream located areas to flow through a bottleneck, which is exactly located at the city centre of Valkenburg. This makes increasing the safety level more complicated than in other areas. The safety level of Valkenburg has a lower standard in comparison to the rest of the country, namely 1 in 25 years. The combination of those two characteristics is not desirable. Official documents
state that this lower standard is based on detailed (societal) Cost-Benefit Analyses. In reality however, the safety standard is based on simple back of the envelope calculations. The Limburg Waterboard has indeed developed a Cost-Benefit tool which they could use to find out whether the implementation of safety measures are cost effective, however they have not been able to
implement it until now. Additional safety measures to increase the safety level are assumed too costly based on the same brief calculations. It is doubtful whether individual risk laws are met, since the Limburg Waterboard assumes no casualties in the Geul area. The 2021 flood however showed that this might be false for future floods which get more severe over time due to climate change.

The citizens and entrepreneurs in Valkenburg were not completely aware of the risks they were exposed to and their sense of safety related to flooding decreased after the flood. Most of the people questioned in a survey demanded a higher safety level than the current standard. They would even be open for an increase in tax to realise this improvement. Raising the quay walls would be a cost-effective solution according to some of the citizens. However, the entrepreneurs who rely on tourist based income, do not prefer this option due to loss in aesthetic value.

Hydraulic, structural, and non-technical solutions which are investigated in this report, have the aim to increase the safety level or make the safety level more acceptable for citizens. The hydraulic, and structural solutions focus on four main aspects. The first aspect is related to the redesign of bridges in the city centre. This is mainly done by applying a flat bridges design, which is further elaborated with a case study for the collapsed Emmalaan bridge, and a liftable bridge design. The second aspect is related to closing the gaps in the quay walls, and increasing the height of the quay walls. The third aspect is related to the implementation of water tunnel concepts with six different design concepts. The fourth aspect is related to implementing parts of Meerssen’s 4-step approach. The first three aspects of the hydraulic and structural solutions are focused on increasing the discharge capacity of the Geul, while the latter aspect focuses on retaining, delaying, and storing the precipitation. Non- technical solution are also proposed
that focus on making people more aware of the risk they are exposed to. This could eventually lead to more acceptance and thus more pleased citizens.

The first order estimations for investment costs and safety level for the hydraulic, and structural solutions are graphically displayed in order to provide an overview of possible interventions to the municipality of Valkenburg and the Limburg waterboard. Although preliminary, and based on limited available data, these results should encourage both stakeholders, and other relevant parties, to reconsider safety standards and search for measures that could increase the safety level of Valkenburg when desired.

Global economic losses due to flooding have increased over the last 50 years, with damages estimated in the billions of dollar each year. Governmental institutions face great challenges to reduce flood risk under the influence of population increase, urbanization and climate change. Interdisciplinary urban planning becomes more important to mitigate flood risk with a multidisciplinary approach and insights in conceptual designs is important to support interdisciplinary cooperation. An example of a country facing great challenges is Albania, where on average 23 flooding events occur each year and at least 54% of the regions have been affected. In addition, the country faces challenges in the disciplines of urban planning, transport and water quality. The capital city Tirana and surroundings were highly affected by flooding events in 2017. The city is prone to flash floods and, especially in the winter months, river flooding. It is crucial to identify areas susceptible to flooding and to quantify the impact on flood risk reduction of potential measures. Data availability imposes a major constraint to quantify flood risk in urban areas with currently available assessment methods. Therefore a flood risk assessment method needs to be identified that is applicable in areas with poor or scarce data. Once the method is identified it can be applied in the Tirana region to identify flood risk and to quantify the impact of measures. Potential measures were developed in an interdisciplinary workshop with students from the TU Delft and Tirana and focussed on the Tirana region, including the Lana river area. The proposed measures for the Lana river are quantified in the risk assessment in this thesis. The identified method defines flood risk as the product of hazard, exposure and vulnerability expressed in Expected Annual Damage (EAD) in Euro. European depth-damage functions for four land use classes are used, in combination with maximum damage values, to express the exposure and vulnerability component. The hazard is described by inundation maps and the development forms the core of this thesis. With the use of a Digital Elevation Model (DEM) a Height Above Nearest Drainage (HAND) map is developed. A Synthetic Rating Curve (SRC) was constructed based on the application of the Manning equation with reach-averaged geometries derived from the HAND map. With a time series analysis of measured discharges, inundation maps could be constructed linked to a return period. The identified method was applicable in the Tirana region. Major benefits are the low computational requirements, easy applicable GIS operations and low data requirements, which make the method easily transferable to other regions. Constraints were found in the use of the coarse DEM with 25 meter resolution, which did not cover river geometries and local measures with high enough accuracy. This was solved by the manual inclusion of river geometries and verification of the developed inundation maps. The Lana catchment is identified as the area most susceptible to flooding with an EAD of approximately one million Euro. One of the proposed measures, a multifunctional cross-section, proved to be most effective with a reduction of 65%. An urbanization scenario, in which the risk increased with 84%, demonstrated the need of the measures. Finally, the assessment revealed potential adverse effects of upstream measures on other areas and proved to add beneficial insights.

What long ago started as a small fishing village, seeking refuge from the Romans, slowly evolved into the city of Venice that we know today. With its unique location came unique problems, most of which were related to the interplay between Venice and its lagoon. By severe measures in the past it has continued to withstand the test of time.
In the decades to come, Venice, once again, has found itself in a difficult situation. Like has been done in the past, drastic measures are required to deal with the current and upcoming difficulties threatening the survival of Venice. These difficulties range from over-tourism to sea-level rise and the subsiding of the city. Acting like the Magistrato alle Acque acted in the past, extreme visions where laid out as possible solutions to these threats.
A workshop week with focus on interdisciplinary design formed the basis for two extreme visions which are laid out in this report. With the aim of answering the main research question: How do flood defense systems influence the spatial aspects of the territory in the context of a high dynamic landscape in the Anthropocene?
The plan for the Perfect Lagoon is one of these, which has focuses on tackling all of the current and upcoming problems were the emphasis lies on preserving and perfecting the lagoon using the building with nature philosophy, while also saving the city from drowning. Preservation is done by solving the sediment budget problems. Due to the constantly eroding system, salt marshes and land is slowly disappearing.
In this plan, drastic actions will be taken to counteract the constant erosion as well as the effect that sea level rise will have on this unique estuary. Drastic measures like redirecting rivers and re-purposing the MOSE contribute towards this goal.
After preservation comes restoration as one of the goals is to restore and increase ecological value, restoration of salt marshes and removal of negative influences like pollution.
As a second vision, the plan of the Symbiotic System deals with the same problems but here the emphasis lies on interconnectedness of Veneto. More attention is paid to mass tourism. The plan aims to turn Venice into a modern interconnected metropolitan area. The city and the lagoon will be treated as two separated system where the focus lies completely on the city of Venice. The lagoon will be left to its own devices in order to find a new, still unknown, equilibrium.
These visions are then further worked out and explained, and for both visions, technical design are made to, step-by-step, bring these visions closer to reality. From these visions along with their technical design we can conclude that flood defence systems have a major influence in the spacial aspects of the territory. Not only in its primary function, but more importantly in the secondary functions. Both primary and secondary functions can be used to create a paradigm shift for the territory. Using the multidisciplinary approach, an integral design can be made for the flood defence, in which the opportunities in a territory can be maximized.