A changing climate means that the combination of storm surge and river flood waves is becoming increasingly likely. The turbinepumping station of the Delta21 concept, is designed just for that. The energy storage lake and the pumps capable of up to 10,000 m3/s mean that even the highest river discharges can be sluiced to the North Sea in the event of closure of the storm surge barrier. When the pumps are not being operated to combat flood waves, the pumpturbines can be used for the purpose of storage of intermittent renewable energies. The required capacity of the pumping station means that the total width of the structure is in the order of kilometers. Past studies into the conceptual design have shown that if the pumping station and flood barrier are integral then this results in a massive structure. AnsorenaRuiz (2020) showed that such a massive structure performs very poorly in a life cycle analysis. For this reason, the goal of the thesis research is to develop an improved design for the turbinepumping station in which the structure can be separated into two parts resulting in a less monolithic form. The design is separated into two main parts: the hydraulic design and the structural design. The hydraulic design ensures that the turbinepumping station can operate at the required functionality. A pump characteristic as well as a turbine characteristic was received from equipment manufacturer Pentair and was adjusted to the requirements of the Delta21 turbinepumping station. A simulation showed that the total efficiency of the turbinepumping system is around 67%. Using timeseries of storm surges and predicted flood waves with various return periods, a simulation was also done of the response of the energy storage lake and pumping station. It showed that for flood waves of very low annual exceedance probability the required capacity of the turbinepumping station should be larger than 10,000 m3/s, but however the storage function of the energy storage lake does contribute to the sluicing of the superfluous discharge. Various alternatives for the hydraulic design were conceived, and it was concluded that the draft tube shape of the intake is the optimal solution. For the structural design the elements of the turbinepumping installation were integrated into a sea dike. The dike acts as a flood defense, keeping the North Sea out of the energy storage lake, while the elements of the pumping station ensure control of the water level inside the lake. This separation of functions allows for a less imposing structure to be achieved, without compromising on the performance. In this study, sea level rise and energy transition go hand in hand. On the one hand, pumping technology is used to protect delta areas from flooding, while on the other hand the technology of hydropumped storage is used to increase the productivity of renewable energies to offset further climate change. On top of this, the gridbalancing capabilities of the system make it financially attractive for potential investors. Hydropumped storage is already an upcoming technology in mountainous areas, but its potential in deltas and coastal regions is even bigger. ... Read more

The floods of 1953, 1993, 1995, 2021 and the almost flood in Rivierenland show that floods have major consequences. Before a flood people can evacuate preventively or vertical and during a flood people can flee, being rescued or permanently stay behind. This research focuses on fleeing and being rescued to a safe region. The research question is: ‘How much time does it take to flee to a safe region during a flood, and what are the core factors that determine the success of a rescue operation by a lifeboat in the Netherlands?’. To indicate how much time it takes for people to flee to a safe region, an experiment took place at test facility Flood Proof Holland in Delft. During this experiment 25 persons walked or bicycled over a parcourse divided into five rounds with different water depths, namely 0.2, 0.4 and 0.6 meter. Additionally, there were other variations, such as walking with a floating object, bringing luggage, bringing a domestic animal, fleeing during darkness and the addition of debris in the water. Time measurements took place during the experiment. If people cannot flee, rescue is needed. To gain more insight into rescuing of people during floods, a questionnaire is spread among experts. Relations between time measurements are found with the use of the Pearson moment correlation coefficient, paired t-test and determining the line by using intersept free linear regression. The relations are combined into a flow chart. Further, the time needed during a rescue attempt is combined into a formula. The navigation speed deviates for different water depths and types of lifeboats. Further, it is estimated by the experts that it takes 7½, 30 and 1 minutes from the contact with a person located at respectively a higher floor or attic, collapsed building and out of the water until having this person into a lifeboat. There is no direct singular answer to the research question, because it depends on the area where the flood takes place and the extent of the flood. Larger water depths increase the fleeing time. If a person decides to flee, it is recommended to walk with a bicycle or bring an air mattress. A stick is useful to check where the road is located. Avoid areas with a lot of debris and do not flee during darkness, except if this is inevitable to survive. People can also wait for rescue at a higher (dry) floor. For the rescue crew, number one priority is safety. Try to avoid to navigate through areas with a lot of debris as this may damage the lifeboat. Search the area systematically and make notes of where people are located. ... Read more

Coastal communities across the globe are often protected by structures, such as seawalls, levees or dikes, which allow only a safe volume of water to pass over or “overtop” them due to wave action during storms. The area seaward of these structures is often characterised by shallow, gently sloping beds referred to as foreshores.
As storm waves propagate over the shallow foreshores, two notable processes occur. The first, is the attenuation of high-frequency waves that are collectively referred to as wind-sea and swell (SS), with periods less than 20 seconds. The limited water depth over the foreshore forces the SS waves to shoal and ultimately break. This shoaling and breaking, in turn, results in the second important process: the growth of infragravity (IG) waves, with periods in the order of minutes.
The methods used in current practice to estimate wave overtopping are able to accurately quantify the impact of SS waves. However, they tend to neglect the influence of IG waves, which are known to play a critical role in erosion and flooding along shallow coast lines. In light of this, this dissertation aimed to develop new methods to estimate the influence of IG waves on the safety of coastal defences with shallow foreshores against wave overtopping. This aim was ultimately achieved by using state-of-art numerical models, empirical methods and field measurements to develop a suite of tools, that together, provide a framework to accurately quantify the influence of IG waves on wave overtopping.
As data on shallow foreshores was limited, a numerical model (XBeach Non-hydrostatic) was first used to generate a large dataset of wave measurements at the toe of the structure for varying offshore, foreshore and structure slope conditions. The analysis, detailed in Chapter 2, revealed that the influence of IG waves increased for higher, directionally narrow-banded (long-crested) offshore waves; shallower foreshore water depths; milder foreshore slopes; and reduced vegetated cover. The combined effect of the different environmental parameters on the IG waves was then captured in an empirical model, which formed the base of the framework to follow.
For determining wave overtopping, the standard approach requires the use of a wave model (often a phase-averaged model like SWAN) to estimate wave parameters at the toe, which are then used as input to the well-known formulae of the EurOtop design manual. However, this approach largely neglects the impact of IG waves. In Chapter 3, this is rectified by augmenting the traditional approach with the empirical model developed in Chapter 2 to include the effects of the IG waves on the design parameters. Considering accuracy and computational demand, the modified approach proved superior when assessing wave overtopping at dikes with shallow foreshores. This approach formed the first sub-method to estimating wave overtopping in the overall framework.
Nevertheless, it is often difficult to obtain accurate estimates of wave parameters at the toe of structures with shallow foreshores. Chapter 4 offers a solution to this problem by proposing a new set of overtopping formulae that instead rely on deep-water wave parameters as input. This is done by revisiting the old but proven approach of Yoshimi Goda, now with additional data and new trend analysis techniques. The newly-derived formulae proved accurate and can be considered an alternative to the current standard (Chapter 3). Particularly, for dikes and seawalls with very and extremely shallow foreshores, where IG waves tend to dominate. This approach formed the second sub-method to estimating wave overtopping in the overall framework.
Finally, in order to estimate the impact of IG waves on safety, a probabilistic method (FORM) was introduced to the framework in Chapter 5. Using the first sub-method (Chapter 3), the probability of dike failure by wave overtopping with and without IG waves was determined for dikes along the shallow Dutch Wadden Sea coast. Including the IG waves resulted in 1.1 to 1.6 times higher failure probabilities for the Dutch Wadden Sea coast, suggesting that coastal safety may be overestimated when they are neglected. This was attributed to the influence of the IG waves on the wave period and, to a lesser extent, the wave height at the structure toe. Furthermore, the spatial variation in this effect observed for the Dutch Wadden Sea highlighted its dependence on local bathymetric and offshore forcing conditions—with IG waves having greater influence on the failure probability for cases with larger offshore waves and shallower water depths.
The general conclusion of the dissertation is that IG waves can have an important impact on safety. Moreover, findings indicate that the safety of existing coastal defences with shallow foreshores may be overestimated, since IG waves are largely neglected in the current practice for their design and assessment. For the case considered here (the Dutch Wadden Sea), the increase in required crest level due to the IG waves was around 2 dm with a cost in the order of M€1/per km. For shallower coastlines exposed to more energetic wave conditions, the influence of the IG waves and the corresponding safety costs are likely to be greater. This dissertation provides practitioners with a suite of tools to quantify to influence of IG waves on the safety of coastal defences with shallow foreshores against wave overtopping. Thereby, reducing the uncertainty in the overall impact of shallow foreshores and allowing dike managers to make more informed decisions when considering hazard mitigation strategies.
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According to the European Environment Agency (2016, pp. 137–140) annual mean river flow and the frequency of fluvial floods will have increased by 20% before the year 2100, in North-western Europe. It had been postulated in media in reports (De Ingenieur, 2014; „MIRT-verkenning Grevelingen”, 2012; Slootjes et al., 2010; Slootjes, 2013; Lammers, 2014) that because of this, large pumping stations are required in the Rhine-Meuse delta in the Netherlands. To investigate this postulation, a simulation model in Python was created that describes the Rhine- Meuse delta as four separate water basins with flow exchanges and boundary conditions (astronomical tides and river inflow). From this simulation model it was concluded that every 86–137 years, flood flow rates of the rivers are such, that the design maximum water level is compromised. The acceptable flooding risk is only once every 2.000 years, so this situation is unacceptable. Dutch engineer answered to the postulation and invented a high-capacity pump called the „Deltapump”, with a capacity ranging 170–200 m3s-1. Moreover, a conceptual design for a pumping station was created. After a conceptual design creation, verification calculations and a cost-to-merit evaluation, a pumping station with 28 Deltapumps in total, based on the conceptual design of Schut, was created. This pumping station is integrated within the Haringvlietdam and is covers an area of 420 × 190 m2. Its capacity, dependent on water levels in the Haringvliet, ranges 4.900 to 5.250 m3s-1, making it by an extremely large margin, the biggest pumping station in the world. Its costs, expressed as Net Present Value, are estimated at € 915 million by the year 2100, 70% of which covers the mechanical components of the pumping station and 30% the civil components. After the flood risk analysis and the pumping station design, it was posed that, whilst the pumping station itself has advantages—better capacity per unit width and less costs per unit capacity, it is not a cost-effective method to prevent flooding in the Rhine-Meuse delta. Calculations and the simulation show it only requires operation once every 92 years. It would therefore seem more cost-effective, and a permanent solution, to upgrade all dykes and dams along the Rhine-Meuse delta, so that more water can be stored. This should be investigated in future reports. ... Read more

The number of fatalities due to a potential flood event is traditionally determined utilizing 'mortality functions’. Data of recent large-scale flooding in the Netherlands are not available since the Netherlands was successful in flood prevention. Therefore, only data from the last coastal flood event in 1953 with 1795 direct fatalities are available. The mortality functions are empirical relationships to provide mortality as a function of three explicit flood characteristics, namely water depth, flow velocity, and water level rise rate. Many more factors are included implicitly since the functions were derived from 1953 data. These underlying factors are thus based on the circumstances of the coastal flooding in 1953 and might not be representative anymore for future flood events elsewhere in the Netherlands. The three flood characteristics in current flood risk assessments are determined by means of coarse flood simulations. Since modern software is becoming more advanced, more detailed flood simulations are becoming possible. Therefore, the applicability of the mortality functions needs to be studied if finer model resolutions are used. This report presents the case study of river area the Bommelerwaard in which the validity of the 1953-based functions, possibilities for alternative functions, and finer model resolutions in hydrodynamic models are tested and analyzed with regards to their impact on flood fatality risk. A hydrodynamic model is developed using the new software program D-Flow Flexible Mesh which is able to apply finer resolutions at locations that require more detail. The different model resolutions that are tested are 100m and 25m, and 5m for the area close to the breach. The flood simulations with these model resolutions resulted in similar outcomes for the number of estimated fatalities in this case study. Overall, the 100m model is preferred because it is sufficiently able to indicate the dangerous locations, provide the order of magnitude of the flood characteristics, while it demands short computation times and matches the level of detail of the data of 1953. However, it is recommended to model the area around the breach (‘breach zone’) with finer model resolutions because the resulting higher local peak velocities are relevant for potential building collapse. For the areas around obstacles and underpasses, it is also recommended to use finer resolutions or to make use of 1D objects or fixed weirs. This study concluded that finer model resolutions at dangerous locations have an impact on the individual risk value of the neighbourhood, and this can have consequences for the maximum individual risk value and thus the overall safety standard of a large dike ring. Furthermore, the case study illustrated that compartment dikes have a significant impact on the local mortality because of the high water level rise rates just upstream. It is recommended to look into possibilities to reduce this high local mortality rate and hence, individual risk, for example by optimizing the location and number of compartment dikes or exploring the effects of openings in the dikes. Moreover, this study identified the discussion points in the current Dutch loss of life approach by a literature study, knowledge of recent flood events abroad, and loss of life approaches internationally. Alternative mortality functions are proposed based on the literature and analyzed through sensitivity analyses in the case study. It is recommended to substantiate and take into account the factors water arrival time, improved building characteristics, and age in the loss of life approach. Preventive evacuation is already taken into account in this approach, but in addition, water arrival time can be included by means of fleeing. This study shows that water arrival time has a great effect on the number of fatalities because some areas have relatively large arrival times and this enables inhabitants to flee the area. Emergency response is thereby of crucial importance. Also in 1953 this factor proved to be relevant. The improved building characteristics compared to 1953 are shown to have a limited impact on the absolute number of fatalities in this case study but it reduced the maximum value of the individual risk and is thus of relevance, especially for dike ring areas with large water depths (>2.1m) and high rise rates (>0.5m/h). Moreover, this study underlines the vulnerability of the elderly during flood events. Since the age distribution has shifted since 1953 and significantly more elderly are present in society nowadays, it is relevant to take this explicitly into account. This case study shows that correcting for age can have a significant impact on the number of fatalities. The impact on the individual risk is limited, but this depends on the spatial distribution of the elderly and should be further analyzed. Finally, the individual risk is sensitive to the configuration of the neighbourhoods. It is therefore also recommended to look into more robust approaches to determine the individual risk. ... Read more

As a low-lying city, Shanghai faces threats from typhoon and spring tide under the condition of climate change and land subsidence. With high water level at the toe, the sea embankment is likely to be overtopped and breached, finally resulting in inundation inland.  The objective of this research is to study climate change and land subsidence effects on Shanghai inland inundation due to dike overtopping and breaching under extreme weather condition.  A hydrodynamic model and a wave model have been established by Delft3D-FM and Delft3D respectively. Through validations on historical events, the hydrodynamic model and wave model are proved to be valid. The water level and wave condition along the coast, which are concerned as the results of these two models, are also essential inputs for overtopping and breach discharge calculation. In overtopping and breach discharge calculation, the threshold of breaching is estimated as an overtopping rate of 0.1 m3/m/s. The resulting overtopping and breach discharge gives the boundary condition of the overland simulation. The inundation map over Shanghai area can then be achieved by the overland simulation. A sensitivity analysis of the breach widths is also done.   Ten hypothetical typhoon events are provided by the Met Office Hadley Center under past and future climate conditions. These cases are applied to the whole process to study the effects of climate change on coastal flooding in Shanghai. The relative sea level rise is also considered for both past and future climate conditions.   The results show that places with high water level and low sea dike elevation are more likely to get high overtopping that can finally result in breaching. For Shanghai city, such vulnerable places can be found along Hangzhou Bay, especially in Jinshan District and the south-east corner of Shanghai. Besides, the entrance of Shanghai Yangtze River Tunnel is also vulnerable due to land subsidence. For some extreme cases, the whole Shanghai coast is in danger.  For the past climate and land elevation around the year 2000 with the wind speed return period of 1.3 yr and the breach width assumed to be 300 m, it is simulated that the maximum inundation area in Shanghai can be 1,805 km2 (33.3% of the simulated area in Shanghai). In the future, given the challenge of climate change and land subsidence, the sea level is relatively rising. The intensity of typhoon will generally strengthen. For the future climate and land elevation around the year 2100 with the wind speed return period of 4.5 yr, it is simulated that the inundation area in Shanghai can be 3,388 km2 (62.4% of the simulated area in Shanghai), which is almost twice of the inundation area around the year 2000.  The breach width also affects the inundation situation. If the breach width becomes larger, the inundation situation will be worse. However, as the breach width grows, the increase of the inundation area decreases. ... Read more

Root zone storage capacity Sr is a significant variable for hydrology and climate studies, as it strongly influences the hydrological behaviour of a catchment. A climate-derived method (water-balance between precipitation and transpiration) was applied for estimating Sr values for 113 catchments in Australia. Various climate, hydrological and vegetation characteristics were compared with Sr, and the relations between them were analyzed. The eucalyptus forests ,evaporation and the seasonal pattern of climate were determined as more important variables. Principal Component Analysis and K-Means clustering method were applied for clustering these catchments, which indicating the co-evolutionary impacts of climate and vegetation on root zone storage capacity. ... Read more

Small Island Developing States, including many low-lying atoll islands, are among the most vulnerable countries to natural hazards and climate change disproportionately amplifies this vulnerability. Hence, there is a strong need for disaster risk reduction and risk management. Further development and implementation of methodologies for flood hazard assessment of atoll islands contributes to this. The methodology proposed in this thesis was applied to Majuro, an atoll island and capital of the Republic of the Marshall Islands. More specifically, the flood hazard related to different flood drivers, and including compound events (i.e. the combination of coastal flooding and precipitation) was assessed for the densely populated Delap, Uliga, and Djarrit region, in the east of Majuro Atoll. Main flood drivers are waves during typhoon events and distantly generated (swell) waves, but precipitation and high water levels (mainly tide) are important as well. To include all possible combinations of these flood drivers, and to include the spatial variation in events, 1000 years of synthetic events was generated based on data for historical events. Accurate simulation of inundation depths was computationally unfeasible for all synthetic events. Hence, a method was developed to reduce the number of model simulations, without losing information on the probability of occurrence of each event. The main steps of this method seem applicable to many other study areas where many scenarios are needed to include all (combinations of) drivers. Main steps are: (1) Selection of representative events – by Maximum Dissimilarity Algorithm, based on parameters that characterize the events. Hereby, the most extreme events are included as well. (2) Simulation of inundation depths for the representative events – by use of Delft3D, SWAN, and XBeach models. The XBeach model included a module for rainfall (first application). (3) Weighted interpolation to obtain the inundation depths for the synthetic events – based on the same parameters as in step 1. Based on the inundation depths for 1000 years of synthetic events, flood maps for different return periods and flood drivers were derived. These provide insight in the flood hazard for the DUD region due to the different flood drivers and for different return periods. The importance of different flood drivers varies significantly per area. Generally speaking, flooding related to (swell) waves in combination with high water levels is more frequent, while infrequent typhoons lead to the most severe flooding. Precipitation is an important flood driver as well, and exclusion would lead to underestimation of the flood hazard. Analysis of inundation depths suggests that for many areas these are limited to a maximum, where after excess water drains to the ocean – mainly into the lagoon. The derived flood maps could be used as a base for assessment of flood risk, climate change impacts, and closely related freshwater availability. In relation to the latter, more in-depth understanding of the contributions of precipitation and coastal flooding to the total flood hazard is needed, as on the long term infiltration of precipitation seems favourable, while that of oceanic water is not. ... Read more

The existing hydrodynamic models consider full physics approaches to calculate storm surge at coastal regions. However, due to the complexity of the equations that model these processes, the computational time and power required to run them can be large, compared to models that consider simplified equations. By contrast, simplified hydraulic models lack physical background, what leads to a minor accuracy in the surge estimations with respect to hydrodynamic models. In this project, a stochastic model has been developed with the objective to estimate surge at the coast of Mississippi (United States) at a reasonable accuracy and time, without solving equations that represent complex physical processes. The stochastic model needs to be trained by means of hurricane data, including surge levels. This information must be generated beforehand, by simulating a limited number of hurricanes with an hydrodynamic model. In this project, the hydrodynamic model Delft3D Flexible Mesh has been used for this purpose. The approach followed to build the stochastic model has been based on three main steps. The first step has been setting up and validating the hydrodynamic model in Delft3D FM. Hurricane Katrina (2005) has been simulated to calibrate the input parameters of the model, by comparing the maximum simulated water levels at 41 stations along the shoreline of Mississippi to the high water marks observed at the same locations during the event. Tide, surge and wave setup have been considered in the validation. The results of the validation show a line best fit slope from the origin of 0.912 and an R-squared of 0.996. At Gulfport, the absolute error of the surge estimation is 19 centimeters, equivalent to a relative error of 2.5%. The second step in the construction of the stochastic model has been the generation of a historical hurricane data base. The hurricane best tracks have been retrieved from the HURDAT2 data base. The variables considered have been the forward speed and the forward direction of the hurricane at landfall, the wind speed at landfall, the distance from landfall location to a reference point (Galveston Bay) and the maximum storm surge during the hurricane. In this case, only the hurricane forcing is considered as external action. The storm surge has been recorded at Gulfport Harbour (central coast of Mississippi). The values of the surge have been obtained by using the validated model to simulate the historical hurricanes making landfall in a rectangular domain of 600 kilometers, being Gulfport Harbour the center of the rectangle. Due to the scarce number of hurricanes making landfall in this region, the tracks of the hurricanes making landfall in the North of the Gulf of Mexico but outside the rectangular domain have been shifted inside the domain, in order to generate a sufficiently large data base to train the stochastic model. A data base with 140 hurricanes has been built, from which the 85% (119 hurricanes) have been used for the training of the stochastic model and the other 15% (21 hurricanes) have been used for the validation of the stochastic model. The third and last step has been the setup and validation of the stochastic model, by comparing the storm surge obtained from the stochastic model to the surge obtained from the hydrodynamic simulations. The stochastic model used to estimate storm surge has been a Bayesian Network that assumes normal copulas to represent the joint distribution between nodes of the network. The calculated slope of the best fit line for the mean surge values has been 0.861, with an R-squared of 0.885. Moreover, the average standard deviation of the estimations is 1.16 meters. These results indicate a reasonable estimation of the surge by means of the Bayesian Network. This estimation can be made in the order of seconds. ... Read more

The BAM Tidal Bridge is a proposed bifunctional concept of a bridge connection between two Indonesian islands, and the world’s largest tidal power plant. The wave forcing on the floating structure leads to an undesired dynamic response and a decreased operating reliability. The thesis objective is about designing an additional structure or a design modification to the Tidal Bridge that reduces the downtime to a maximum of five days per year. A model has been developed to analyse the dynamic response of the original Tidal Bridge design, and to test possible design optimisations. Three successive design loops lead to the resulting design of an innovative sway plate structure which fulfils the design objective well. ... Read more

Over the recent years, flood risks and losses have been increasing for coastal cities due to climate change, subsidence, population and economic growth. Hong Kong and Macau are two cities located in the Pearl River Delta that experience a significant flood risk due to storm surges. The increased losses and risks has sparked interest around the world for efficient and accurate flood forecasting. At the moment coastal flooding events are often simulated with difficult hydrodynamic models that reproduce the physical phenoms. Over the last decades there has been more interest in other methods to forecast storm surges, namely neural networks. Other than hydrodynamic models a neural network is capable is making predictions in seconds, while the model can take hours to finish simulation. fast and accurate storm surge forecasting is of importance for disaster and evacuations management strategies and will only become more important in the future. During this research the main goal is to develop a neural network capable of prediction maximum water levels due to storm surges in case of an approaching tropical cyclone. The neural network is trained with data that is obtained from hydrodynamic simulations. A synthetic storm database is used to provide the necessary data to conduct 1000 simulations of which the results are used in the neural network. The first focusses on developing a hydrodynamic model capable of accurately simulation tropical cyclone induced storm surges in Hong Kong and Macau. The model is calibrated in a way to reproduce the real world as close as possible. It accounts for the real life bathymetry, topography, astronomical tides and wind forcing. The storm surge model is validated extensively based on three historical tropical cyclones. The errors between the observed and simulated water level are below 20 cm, after calibrations of different physical parameters within the model. The second step of this research is to use the validated storm surge model to run synthetic storm simulations. Instead of using historical storms who only have been recorded for 40 years, a synthetic storm database is used containing 10000 years worth of data. From that storm data, 1000 synthetic tropical cyclones are selected that come close to Hong Kong and Macau. With the data obtained from the previous two steps, it is finally possible to training the neural network. In this network a total of seven input parameters (tropical cyclone track parameters) are used to estimate the maximum water level that will occur during the tropical cyclone. The input parameters considered are: latitude, longitude of TC eye, maximum wind speed, minimum eye pressure, radius of maximum winds, forward speed, forward propagation direction. During the development of the network, three different types of configurations are tested. Extensive validation and calibration shows that neural networks are capable of making maximum water level predictions for a large number of cases. However, variety in the quality of the prediction is observed. Improvements still can be made for more accurate predictions. ... Read more

Ships in rivers create waves and these can have a negative impact on fish habitats along the river banks. A modelling study is carried out to investigate how these ship-induced waves can be damped in groyne fields by making structural modifications to the groynes. For this purpose, different types of openings (notches) are applied to the groynes. Next, hydro-ecologic indicators are used to assess the impact of notching of groynes on fish habitat suitability. The results suggest that relatively simple modifications can significantly improve the ecological value of the groyne fields. ... Read more

The conventional evacuation modelling assumes that that family members are to be together in the face of tsunamis and evacuate as a household or each person evacuate individually. This assumption, however, can cause an inaccurate prediction when taking family gathering behaviour into account, which was reported to have occurred during the 2011 earthquake off the Pacific coast of Tohoku in Japan. This thesis first investigates the family gathering behvaiour during the event using the survey data of evacuation by the survivors of the 2011 Tohoku tsunami. It aims to identify statistically significant travel choices and parameters defining travelers who performed the family gathering during the evacuation. Using the result of this first part, this thesis also suggests a methodology to model that family gathering behvaiour and performs a simulation for a coastal city in Japan using a general activity-based transportation model. It was found as for the behavioral analysis that stay / leave choice, departure time choice, and mode choice shows significant differences between those who performed the family gathering and those who did not whereas concerning the parameters defining those who performed the family gathering initial location, gender, and age have been found significant. The choice frequencies of alternatives developed in the behavioral analysis have been applied into the model formulation taking these findings into account. Depending on whether they performed the family gathering or people's attributes, different choice frequencies have been applied. The simulation indicates that the characteristics of the family gathering trips in comparison with the evacuation trips are explained by the faster speed achieved by the earlier departure time and by the longer travel distance caused by the destination choice being fixed locations such as home and relative’s
home rather than nearby buildings. A scientific contribution has been made in terms of evacuation behaviour and evacuation modelling methodology for the family gathering during evacuation. Also, taking this particular behaviour into account for evacuation modelling leads to better prediction of evacuation trips, which in turn helps develop enhanced evacuation planning. ... Read more

Design criteria for the stability of rock filters on river beds (i.e. rock bed protection) are extensively researched and successfully applied in practice. The most common stability criteria are the Izbash and Shields criteria. These methods define a critical flow (Izbash) or parameter (Shields). Rijkswaterstaat (RWS) wants to explore a more sustainable bed protection by using logs. A pilot project is started where logs will be used as bed protection. It is yet unclear if the design and construction approaches for rock bed protections can be used for log bed protections. The most dominant aspect is that logs are cylindrical objects, while rocks are spherical. This means that the design criteria for rock filters might not be directly applicable to log filters. This research aims to verify if the Izbash and Shields criteria for rock can be used for logs to create functional and safe designs. To achieve this, two experiments are performed at the TU Delft faculty of Civil Engineering & Geosciences. The first experiment, done in a water filled tank, explores the settling behaviour of logs for multiple drop methods. Insight is gained in the settling velocities, horizontal spread and magnus effect (force exerted on a rotating object, e.g. the curve of a football spinning through the air) of logs settling in a water column. Results from these experiments are used in the second experiment. This experiment is done in a 14.3m long flow flume where a log filter is constructed. The log filter is constructed using the drop method that was preferred from the first experiment. The roughness, stability and porous flow of a log filter are investigated. The results are compared with what is known for rock filters. Tree branches were used as model logs. This was done to be able to correctly scale the results to prototype scale. Primary reason for this was the effect of bark on the roughness of a cylinder. This is difficult to replicate on model scale. Using branches of trees that will be used Saturating the model logs however was more time consuming than initially expected. Attempts were made to accelerate the process but they were futile. One method, using a diaphragm vacuum pump, could not be applied due to lack of resources. For any future research on the topic of tree branches as model logs it is highly recommended to use a vacuum pump to ensure that the maximum density is reached. From the first experiment it was concluded that large quantities of logs can still be used to create functional log filters. This is a positive result as this will reduce construction time on prototype scale. The method used was a funnel. This method was applied in the flume to create the log filters. By measuring the velocity profile for multiple discharges the roughness of a log filter was measured. This also resulted in an equation of the shear velocity as a function of the discharge. By increasing the discharge step by step, several mobility stages of a log filter were found. This resulted in a dataset that could be directly compared with the Izbash and Shields equations for rock. Higher critical Shields parameters were observed than for rock of the same diameter. The behaviour of a log filter differed from a rock filter in the transition from one stage to another (stable to mobile to transport to failure) did not occur slowly, but almost instantaneous. This behaviour is unwanted because it is difficult to monitor in what stage a log filter is if no changes can be observed between stages. Thus, although applying the equations for rock filters to log filters are conservative, the behaviour of log filters are more sudden and prone to escalation close to their critical thresholds. Final conclusion is that more research is required to better understand the significance of variables for the settling behaviour and stability. These are water depth, log diameter independent of density and vice versa, log orientation and log length to diameter ratio. This can be done by doing more experiments in a similar fashion where only one variable is changed at a time. For the application of the design criteria for rock to a log filter with regards to the pilot project, it is recommended to be conservative. Based on these experiments it is safe to assume that when the most unfavourable scenario is used (e.g. low log density, small log diameter, high flow velocities near the bed) a sufficient design is made, especially if the top layer(s) of the filter are placed parallel to the flow direction. Backfilling of the log filter did not increase the stability significantly in this research and is only be beneficial for scour protection. ... Read more

The goal of this research is to assess technical and economic feasibility of hydropower at the weir-complex of Driel. A local initiative opting to improve the environment gained interest in the idea and asked Arcadis NL for help. The weir complex at Driel lays in a key position in the Dutch river Delta and regulates the flow to the IJssel and Nederrijn, both important parts of the flood protection and important shipping routes. In the Nederrijn 2 other hydro-power plants have been built at weirs. Driel was considered as well, but at the time could not be made feasible due to the low head difference at Driel. Developments in low-head hydro-power have given new possibilities and reason for reassessment. First the location has been analysed, in particular the flow situation. Except for the low head difference, the location lends itself well for a hydroelectric plant. The crux of the research is therefore in making the most of the available head. 4 variants have been worked out: a copy of the downstream hydro-power plant of Maurik as a reference, several variations on low head Kaplan turbines and an Archimedes screw have been assessed. A special variation of the Kaplan is the Venturi enhanced Kaplan, which uses part of the discharge to increase the head difference over the turbine. To estimate the annual production, first a simple approach, assuming a turbine can create a certain head difference, and later a hydraulic model incorporating hydraulic losses and using turbomachinery theory, has been used for the Kaplan design variants. The result of the comparison is that the regular Kaplan variant number 4 with 5 turbines, a combined capacity of 3.160kW and a LCOE of 0,154 € per kWh (using interest rate of 3,3%), has the best economic performance and is therefore recommended for further development. A good second option with a lower initial investment (9,6 million euros versus 20,5 of variant nr. 4) is design variant number 1 with a set of 2 Kaplan turbines having a combined capacity of 1.475kW and a LCOE of 0,161 € per kWh. Despite the regular Kaplan performing better economically, the Venturi Enhanced Kaplan Turbine certainly has potential for low head run of river hydropower and is therefore recommended for further research as well. The increase in power and produced energy gives reason to believe that further optimisation and detailing will lead to a competitive design compared to the regular Kaplan turbines. ... Read more

Every year hundreds of thousands of people are affected by natural disasters that occur due to various physical phenomenon. They include earthquakes, tsunamis, volcanic eruptions, and hurricanes. In this research the focus is on hurricane events and the impact they have on a community. The ability for a community to bounce back is defined by their disaster resilience which, in turn, depends on their ability to identify vulnerabilities and prepare for the inevitable. Within this line of research, one of the main challenges is defining local risk due to hurricane events, especially when considering more than one hurricane-induced hazard. Furthermore, the challenge becomes even greater when analysing risk in locations around the world where data availability is scarce. This study aims to clarify and improve the existing methodology to define multi-hazard risk due to hurricanes. This methodology is verified by applying it to the case study of St. Martin, in order to delineate hurricane risk on the island. St. Martin was chosen to investigate, as it is a Small Island Developing State in the Caribbean that recently suffered immeasurable damages during Hurricane Irma (September 2017), and is still struggling to recover. The two hazards that were considered, in the application of the methodology, were hurricane-induced winds and hurricane-induced coastal flooding. In the case of St. Martin, hurricane-induced winds were found to contribute to 98% of damages due to Hurricane Irma, when compared to the coastal flood damages. Coastal flooding was found to be due to both increased storm surge levels and wave-induced flooding, showing that neither one is negligible for a reef island like St. Martin. Storm surge variation around the island was found to be minimal due to the scale of the island, and the fact that storm surge was predominantly pressure driven. Validation of the models to simulate hazards and impact on St. Martin proved to be challenging. An unconventional data source was used to validate the flooding model, which included analysis of Twitter data of images posted during Hurricane Irma. This is an example of a solution of how to deal with data scarcity in hazard modelling. The risk assessment of St. Martin involved simulating synthetic hurricane track scenarios and determining their respective wind and flood damages on the island. Combining the respective damages was done by including a damage threshold to ensure combined damages did not exceed 100%. The applied framework resulted in a hurricane risk map of St. Martin indicating Expected Annual Damages per community. The intention of the improved methodology is to apply it to a hurricane risk prone region, like St. Martin, and to use the outcome to delineate hurricane risk. This indicates hot-spots in the region of interest and improvements to disaster resilience can be discussed. The approach of Build Back Better is highlighted in this research to show how this risk map can be interpreted and what the results mean. Three branches are discussed, namely building back stronger, which involves ensuring infrastructure can resist more extreme events in the future. ... Read more

Small Island Developing States (SIDS) are increasingly under threat of coastal flooding, which challenges the safety of their societies and vulnerable economies. The emergency of this issue, exacerbated by climate change, has alarmed international organisations and national governments that have been demanding for robust risk assessments to guide the development of resilient adaptation strategies. In SIDS, the paucity of local data, required to perform such kind of coastal risk analyses, hinders the application of highly detailed models that therefore need to rely on inaccurate and publicly available data, thus introducing uncertainty in the assessment. This thesis aims to investigate the uncertainty in input data and its impact on coastal flood damage estimates. This study examines prominent uncertainty sources in the coastal flood risk modeling chain, namely: the stochastic variability of (i) significant wave height and (ii) storm surge water level, the quality of (iii) bathymetry data and (iv) digital elevation models and (v) the choice of depth-damage function. To account for risk temporal changes, two other inputs are included, specifically (vi) different sea level rise projections and (vii) socioeconomic developments. A methodology is developed to test the afore-mentioned inputs through global sensitivity analysis, using an ensemble of hydrodynamic models (XBeach and SFINCS) coupled with an impact model (Delft-FIAT). The impacts of these sources on the flood damage estimates are evaluated in a case study on the islands of São Tomé and Príncipe. Model results indicate, for the current time horizon, depth-damage functions and digital elevation models as the inputs with the most significant contribution to the overall damage estimation uncertainty, yielding a variation in the output prediction of a factor 16 and 10, respectively. As future climate and socioeconomic development uncertainties are introduced in the system, sea level rise projection becomes, followed by digital elevation models and depth-damage functions, the most relevant input for the year 2100. Neglecting economic growth in the risk analysis leads to an extremely high underestimation of damages. However, given the constrained intrinsic uncertainty for the projected societal trends, its sensitivity on the risk output is limited. The scarcity of accurate input data proves to have an enormous impact on risk assessments in Small Island Developing States, leading to considerable prediction error and affecting the model outcome uncertainty. New emerging data collection techniques, such as unmanned aerial vehicles, could augment the trustworthiness of risk assessments by providing more accurate datasets for bathymetry and topography. Furthermore, research efforts could be directed towards developing knowledge on the physics of damages and their implementation in a risk modeling scheme. The uncertainty framework presented could be applied in projects with the aim to support risk communication to stakeholders by portraying the implications of the various inputs used and assumptions made, but also to guide the allocation of limited economic resources towards the acquisition of the input data that matters the most in terms of reliability of damage estimates. ... Read more

Recent major tsunami events generated by earthquakes inundated coastal cities and caused extreme destruction and loss of human lives. The collapse of coastal bridges due to tsunami wave impact represents a huge obstacle for rescue works. The need to understand tsunami effects and develop tsunami-resilient bridges became apparent in the aftermath of extreme tsunami events in the Indian Ocean (2004), Chile (2010) and Japan (2011).

Different coastal topographies affect tsunami propagation near shore. Varying wave characteristics lead to various failure mechanisms of bridge decks. Together with the wave characteristics, the bridge properties and the settings around the bridge play a major role in this failure, think for example of shear keys, seawalls or inclination of the bridge.

To find out more about these failure mechanism and what role all these measures have in the failure, a laboratory experiment is executed and a numerical SPH model is set up to investigate the impacts of various wave characteristics, a seawall, shear key and inclination of the bridge deck. The numerical SPH model is validated with the help of wave gauge data and tracked bridge deck movement from the executed physical tests.

In this thesis the focus is on the movement of the bridge deck, what kind of effect do the different interventions have on the movement of the deck. Since the movement is highly dependent on the forcing on the bridge deck, the forces are analyzed thoroughly. From the force time series countermeasures are proposed and modeled in the SPH model.

Wave forces from different type of waves are simulated with the SPH model. The overall behavior of the hydrodynamics and the deck movement are validated and suited for qualitative analysis.
Some disadvantages of the model are the lack of bottom friction and air bubbles in turbulent regions.
The 3D model represented the movement on the deck in a very good way, runtimes and storage capacity formed an obstacle. A 2D model was used to do qualitative analysis of the changes of wave characteristics and the effects of the structural measures.
The limiting factor in the commercial use of SPH is the computation time. In future models this could be accelerated by the use of GPU processors instead of CPU processors which are able to solve many parallel processes at the same time.

Apart from wave heights and inundation heights, the wave phase appeared to be a major decisive factor in the failure method of the bridge deck. If the wave breaks near the shore and reaches the bridge structure as a propagating wave front, the hydrodynamic situation results in high horizontal forces and a sliding failure mode is apparent. When a wave is still in a surging phase and the fluid particles still have their rotational movement, the dominant forcing on the bridge is in vertical direction. Since the vertical force applied to the bridge deck moves from seaside to shore side, the sea side of the bridge deck has a higher vertical velocity which initiates rotation.
A seawall causes the water to confine underneath the bridge deck. Which will result in higher vertical forces, thus a rotational failure mode follows. Inclination of the bridge deck has significant effect on the vertical forcing. Positive inclination lead to a decrease of upward forcing and negative inclination lead to an increase of upward forces. The introduction of shear keys resulted in higher moments, since the point of rotation is set at the point the deck interacts with the shear key, which creates a larger distance around the point of rotation.

Possible countermeasures that are introduced are a sacrificial beam and a different geometry of the deck. A sacrificial beam was effective in lowering the total horizontal forces on the combined structures. The deck itself was not exposed to a high horizontal impact force. Different geometries are tested to see how the forces on the structure would chance. A wing shaped geometry has positive effects in mitigating the horizontal forces on the bridge deck. ... Read more

’De Watersnood van 1953’, the largest Dutch flood in recent history, caused the death of 1795 people in the Netherlands directly from the flood conditions, while in the UK, 315 were recorded. Most of them were among those whose residence collapsed due to high water depth, quick rise rate of the water or strong flow velocity. Based on historical data of floods with similar flood characteristics and comparable buildings, mortality functions were developed to estimate the number of fatalities. These functions are still used, but the correlation between the flood characteristics and the damage observation is not clear according to multiple studies. The current study contributes to improving these functions by investigating which flood conditions may lead to collapse of the residences in the current Dutch building stock. From the BAG-registration (in Dutch: Basisregistratie Adressen en Gebouwen) it is found that 50% of the Dutch live in terraced houses (in Dutch: rijtjeshuizen), which is similar in the areas which are most likely to be affected by flooding. Most of these residences are built in the period of the housing shortage between 1965 and 1975 and the energy crisis between 1975 and 1994, which are considered as ’the typical Dutch residence’. This residence type consists of cavity walls with a load-bearing leaf of concrete or unreinforced masonry (URM), which can be clay or calcium-silicate. This inner leaf is tied to the outer leaf of URM consisting of perforated clay units, wood-based materials, or concrete. Stability is provided by piers in the façades in case of the URM walls or rigid connections between the concrete floor and walls. To define the properties of the building materials, existing experimental research on the masonry is used.
Experiments with a physical model were conducted herein to measure the quasi-steady load in the form of pressures acting on different elements of the residence. This enables the comparison of the quasi-steady flood load and the lateral load due to wind on different elements of a building. Similar to FEMA (2011), it was found that the pressure coefficient decreases when the width-to-water depth ratio decreases. However, higher coefficients are found from the experiments than those provided by FEMA, resulting in higher hydrodynamic loads. Furthermore, the orientation of the residence compared to the flow direction changes the angle of attack. When the flow is perpendicular to the wall, the pressure coefficient is the largest. Decreasing the angle of attack causes a decrease of the pressure due to equal flood conditions. The pressure coefficients obtained from the experiments are used to define the hydrodynamic load due to flooding. The resistance of the load-bearing cavity walls, windows and piers were compared to the acting moment due to different depth-flow velocity combinations. The resistance of out-of-plane bending of the load-bearing wall is the critical failure mechanism for typical Dutch residences. Residences with calcium-silicate masonry walls and system floors have a higher resistance than residences with clay masonry walls and timber floors. Cracks start to develop at a small lateral load resulting in zero tension strength after cracking and an eccentricity of the normal force. This makes the influence of the dead weight carried by the wall, in combination with the compression strength and the thickness, more important than the flexural bending strength.
All types of residences, using design values, already collapse before the hv-product (water depth times flow velocity) of 7 m2/s is reached according to Clausen (1989). A water depth of ±1.2 meters for the older residences (1965-1975) and ±1.8 meters for the newer residences (1975-1994), already cause the design moment resistance of the wall without taking the velocity or wave action into account. If the flood water has a flow velocity of 2 m/s or waves are generated by a wind speed of 29.5 m/s over a fetch of 100 m, the critical water depth reduces to respectively ±0.9 and 1.5 meters. ... Read more

The objective of this master thesis is to gain knowledge regarding the dynamic behaviour of The Palmerah Tidal Bridge to hydraulic loads. The Palmerah Tidal Bridge, an enterprise of the construction company BAM, will become future's largest tidal power plant and a floating bridge between two islands in the Flores region, Indonesia. A combination of the two functions requires a dynamic design that allows movements and a design that is able to withstand severe loads. A pre-feasibility design is proposed, however the technical feasibility is not proven yet. Safety and stability are two key concepts to substantiate the technical feasibility. In addition, an estimation of the probable motions and accelerations may indicate whether traffic is able to cross the bridge safely. The aim of the project is to create insight in the rotations and accelerations of the coupled floating bridge structure. In addition, obtaining information regarding the most sensitive structural parameters of the system may suggest design changes that result in an increase in stability. First, data is acquired that is required to create a virtual bridge model. The project location and present bridge design are analysed with available data, literature and calculations. Serviceability limits are estimated that allow traffic safely across the bridge. Governing loads that act on the bridge are determined and the structural properties of the bridge are calculated. The natural frequencies and hydrostatic properties of a single freely floating floater are calculated. The hydrostatic stiffness is used to calculate a first estimation of the roll-rotation as a result of current-induced pressures. The software programs used for the data computations are Matlab, Matrixframe, MathCad and Excel. Secondly, the data is converted into a virtual bridge model in the software package Ansys Aqwa. Ansys Aqwa is globally used to indicate the dynamic response of offshore maritime structures to wave induced pressures. The software has limitations regarding the current velocity implementation. The drag force should be defined manually and acts at the centre of gravity of the structure. As a result, the force 'moves' with the structure and the application point of the drag force can be located above the waterline. The virtual bridge model seems realistic for waves and positive flow speeds. However, the response to negative flow speeds is unrealistic, indicating that the Ansys Aqwa model is inaccurate. The model can not be calibrated as knowledge about the likely motion of the bridge is unknown, but the roll-rotation during a positive current is of the same magnitude as the stability calculation. The dynamic response to governing wave and flow speed combinations is computed. With an iterative process, the sensitivity to certain parameters is found. The observations and results that are obtained during the process resulted in various alternative design proposals that may decrease the magnitude of rotation with 70%. However, even with the improved design suggestions, the estimated serviceability limits are still exceeded. The dynamic response is based upon two components, a gradual main rotation that originates by the drag force and a fluctuating line over that curve that represents wave induced motion. In the end, wave induced motion will result in sincere discomfort for traffic. ... Read more