Marine biofouling is a major concern in the operational performance of submerged floating tunnels (SFTs). The objective of this research is to investigate the effects of marine fouling (represented by surface roughness) on the hydrodynamic behavior of SFTs, including the hydrodynamic forces on the SFT subject to current-only, wave-only, and combined current-wave flow conditions. The effects of increased surface roughness induced by marine fouling on the dynamic response of an SFT are characterized by hydrodynamic force coefficients, including drag and inertia coefficients. At the Water Lab of Delft University of Technology (TU Delft), experiments have been performed in a wave-current flume to compare the SFTs’ behaviors as affected by different roughness characteristics. In addition, a parametric cross-section for an SFT is presented, and the hydrodynamic performance associated with surface roughness effects on the parametric shape and circular SFT cross-section shape are compared. The results show that the parametric shape can effectively reduce the drag coefficient (C_d) under current-only conditions and lower the inertia coefficient (C_m) when waves are present. As roughness height and coverage ratio increase, C_d generally increases while C_m decreases. However, small differences in C_d and C_m can be observed with regard to roughness parameters for wave-only conditions. The Morison coefficients adapted for a marine-fouled SFT measured in the experiments are compared to predictions from engineering standards and are recommended for engineering practice.

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Overtopping plumes from wave impact is relevant to coastal defence for overtopping analysis of sea walls, levees, and gates. Improved insight into this phenomenon will further enhance the prediction of wave overtopping and its induced hazard, e.g., erosion, saltwater ingress, and a hindrance to traffic. A series of small-scale experiments have been carried out in the WaterLab at TU Delft to characterize the droplets formed by wave impacts. Focused waves were generated by the piston-type wavemaker to control the wave breaking point on the wall, which allowed the creation of different types of wave impact. Impacts were investigated respectively: non-breaking, flip-through, and air pocket. After the wave impact, all the stages of the plume formation were filmed using a high-speed camera at a frame rate of 500fps. In this study, the spray sheet breakup and droplet formation are investigated. A simple approach to estimate the maximum spray height is proposed, which can be used for the splash type overtopping in the future.@en

Submerged floating tunnels are considered as feasible concepts for strait and estuary crossings where traditional tunnels and bridges face technical difficulties. An unknown factor is the environmental conditions that would allow safe, SFT construction and operation. This paper focuses on the effect of the environmental conditions like surface waves and ocean currents on the structural and dynamic behavior of the SFT. The effect of the hydrodynamics on the SFT has been covered by some studies in the literature. However, the increase of knowledge of especially the behavior of an SFT in a combined wave-current environment is of interest. In the research field of hydrodynamics around an SFT, there is a demand for more experimental studies. This study comprises of experiments on a rectangular cross section which was fixed with tethers, subjected to regular waves with varying wave heights and wave periods under different conditions of currents, submerged depth and inclined mooring line angle (IMA). The experiment results show that the SFT motion depends on the wave orbital motions mainly. When waves combined with the following currents, the currents will reduce the SFT motion by attenuation of the wave motion. The submerged depth and IMA are the two key parameters which are relevant to the SFT motion.@en

This paper describes a method of determining the reaction forces of a vertical structure with an overhang to impulsive wave impacts. The aim is to develop a method to design a hydraulic structure exposed to the impulsive wave impact. At present, there is a lack of guidelines on the designing and verification with such a purpose. The impulse of the impact is taken as the primary design variable to estimate the impulsive reaction force instead of peak impact forces. By using extreme value analysis (EVA), the characteristic impulse (e.g., I _im,0.1% ) can be determined. Then a simple structure model is used for obtaining reaction forces to the characteristic impact impulse. The sum of the impulsive reaction force and the quasi-steady wave force could represent the total reaction force, which can be used as a design load on the structure. The advantage of using the impact impulse could give an approach in which several aspects of the impulsive wave impact force can be incorporated better, like determining the exceedance probability of a certain load, incorporating the flexibility of the structure and correcting possible scale effects in small scale hydraulic models. The proposed method based on the characteristic value of the I _im,0.1% is applied to forces measured in a small scale model of the Afsluitdijk discharge sluice, and compared well to a full-time domain solution. The results indicate the initial assumption that using the impact impulse of the impact as the primary design variable, it is possible to estimate the dynamic response of the structure.

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Mass balance analysis of ice sheets is a key component to understand the effects of global warming. A significant component of ice sheet and shelf mass balance is iceberg calving, which can generate large tsunamis endangering human beings and coastal infrastructure. Such iceberg-tsunamis have reached amplitudes of 50 m and destroyed harbours. Calving icebergs interact with the surrounding water through different mechanisms and we investigate five; A: capsizing, B: gravity-dominated fall, C: buoyancy-dominated fall, D: gravity-dominated overturning and E: buoyancy-dominated overturning. Gravity-dominated icebergs essentially fall into the water body whereas buoyancy-dominated icebergs rise to the water surface. We find with unique large-scale laboratory experiments that iceberg-tsunami heights from gravity-dominated mechanisms (B and D) are roughly an order of magnitude larger than from A, C and E. A theoretical model for released iceberg energy supports this finding and the measured wave periods upscaled to Greenlandic outlet glaciers agree with field observations. Whilst existing empirical equations for landslide-tsunamis establish estimates of an upper envelope of the maximum iceberg-tsunami heights, they fail to capture the physics of most iceberg-tsunami mechanisms.@en

Overtopping bore impact forces on a dike mounted vertical wall were measured in similar large-scale (Froude length scale factor 1-to-4.3) and small-scale (Froude length scale factor 1-to-25) models. The differences due to scale effects were studied, by comparing the up-scaled force measurements from both models in prototype. It was noted that if a minimum layer thickness, velocity of the overtopping flow and water depth at the dike toe were maintained in the small-scale model, the resulting differences in impact force due to scale effects are within the range of differences due to non-repeatability and model effects.@en

During the last decades, the spectral wave period T_m-1,0 has become accepted as a characteristic wave period when describing the hydraulic attack on coastal structures, especially over shallow foreshores. In this study, we derive an empirical prediction formula for T_m-1,0 on shallow to extremely shallow foreshores with a mild slope. The formula was determined based on flume tests and numerical calculations, mainly for straight linear foreshore slopes. It is shown that the wave period increases drastically when the water depth decreases; up to eight times the offshore value. The bed slope angle influences the wave period slightly. For short-crested wave fields, the strong increase of T_m-1,0 starts closer to shore (at smaller water depths) than for long-crested wave fields.@en

Een onderzoeksprogramma van de TU Delft, Universiteit van Twente en Wageningen Universiteit heeft diverse ontwerpaspecten van zogenoemde multifunctionele waterkeringen onder de loep genomen. Dit artikel belicht het technisch en ruimtelijk ontwerpproces van dergelijke keringen, en het betrekken van stakeholders in dit proces.@en

Bij het ontwerp van multifunctionele waterkeringen spelen twee specifieke constructieve aspecten een rol: golfimpact en constructieve verificatie. Een onderzoeksprogramma van de TU Delft, Universiteit van Twente en Wageningen Universiteit heeft zich hierover gebogen.@en

The vulnerability of buildings on coastal dikes due to overtopping wave impacts is difficult to assess. A method is developed in this paper to quantify the vulnerability of masonry buildings on a coastal dike exposed to wave overtopping. Using previous studies, the accidental loads due to the extreme wave impacts are characterized. Using the approach from Eurocode 6, the strength of masonry buildings under these loads is assessed. Results from a case study in Belgium show that masonry buildings located 10–15 m away from the seafront would suffer from localized damage, such as windows being broken under a 1000 year storm. The building would collapse under a 10,000-year storm. The method can be used to assess the safety of existing buildings on coastal dikes and to design new buildings.@en

Overtopping wave loads on vertical structures on top of a dike have been investigated in several small scale experiments in the past. A large-scale validation for a mild foreshore situation is still missing. Hence the WALOWA experimental campaign was carried out to address this topic. In the present paper the objectives of the WALOWA project are outlined in detail, the model and measurement set-up described and the test program presented. Furthermore, preliminary results featuring a single 1000 irregular waves test of the test program are highlighted. This includes the study of the mild and sandy foreshore evolution by comparing profiles before and after the test execution. The profile measurements are obtained with a mechanical profiler. The wave parameters offshore and at the dike toe are numerically simulated using a SWASH model. The numerical results are validated against the measurements. Finally, the force and pressure time series of the waves impacting against the wall are processed and filtered. The load cell measurements and the time series of integrated pressures are compared to each other and for each impact event the maximum force is derived.@en

In low-lying countries like the Netherlands and Belgium, coastal areas are often highly urbanized, and buildings are often built on or close to the flood defenses (Figure 2 shows a typical Belgian seaside town). This is an example of multifunctional flood defense, where urban functions are integrated with flood defense structures. In this example, the wide crest of the coastal dike is used as a promenade with building frontage. However, policy makers as well as the users and owners of the properties may be unaware of possible overtopping effects, and they may lack records of wave overtopping and the potential direct damage it can cause. The goal of this research project was to develop a tool that can measure the risks and potential cost of wave overtopping events on buildings. @en

De organisatie voor Economische Samenwerking en Ontwikkeling schat dat in 2070 in grote havensteden wereldwijd 140 miljoen mensen en 30000 miljard euro aan economische waarde beschermd worden, Bescherming lijkt alleen mogelijk met multifunctionele waterkeringen.@en

On coastal dikes in Belgium, many residential buildings are found. Most of the old buildings are masonry structures with two to three floors (Figure 1). The ground floors are always elevated (Figure 2), and the entrances of the basements are closed by shutters (Figure 3). The most modern buildings are concrete reinforcement structures with concrete piles/columns as foundations. The walls are consisting of masonry or concrete. These buildings are 5 to 9 floors high. Some of the ground floors are elevated, and some are used as cafe, restaurant or store. The ground floors are equipped with large glass windows and doors. @en

Wave overtopping is one of the key parameters for designing coastal structures: the crest level is usually determined using admissible overtopping discharges. Several formulae already exist for wave overtopping assessment that predict the average overtopping discharge per meter width of the coastal defence, generally for deep or intermediate water depths at the toe of the dike. However, the process of wave overtopping on sea dikes with shallow and very shallow foreshore is not yet fully understood. Gentle foreshores in combination with (very) shallow water conditions lead to heavy wave breaking and a significant change of the wave spectra from offshore to the toe of the dike. The wave steepness is assumed as one of the main criteria to identify cases of severe wave breaking on shallow and very shallow foreshores. For these conditions, Van Gent's formula, generally used for wave overtopping with shallow foreshores, has been implemented and validated against experimental data. It is the purpose of this paper to show that Van Gent's formula overestimates the average overtopping discharge for cases of very shallow foreshores. Moreover the existing formula cannot be applied to cases with an emergent toe. The present work therefore introduces a new “equivalent slope” concept to obtain an estimation of average wave overtopping discharges on sea dikes with shallow and very shallow foreshores. This study uses data from CLASH database and experimental campaigns, specifically carried out at Flanders Hydraulics Research (Belgium), in order to validate this approach. Results indicate that this concept shows better performance compared to other empirical formulae, which suggests that the influence of the very shallow foreshore on the average wave overtopping discharge should be included.

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The impact force induced by waves overtopping a dike with a vertical wall on its crest, and with a shallow foreshore seaward of the dike, was studied. To this end, physical model tests were performed in a wave flume at a typical scale of 1:25. The goal of this study was to develop a method to estimate the maximum forces on the wall during a known storm peak. The time series of water depth at toe of the dike, flow thickness at seaward edge of the dike crest and impact forces were measured. An empirical Generalized Pareto distribution is verified as the best distribution for the extreme overtopping wave forces.@en

Due to climate change, sea level rise, increasing frequency and intensity of storms, and growing population in low-lying coastal regions, the risk of flooding is expected to increase. Owing to these developments, maintenance and adaption of the existing coastal flood defence is often required. To meet this dilemma, the concept of multifunctional flood defence (MFFDs) is promoted. It aims at integrating urban functions with flood defence structures. Considering the threat from possible wave overtopping to the buildings on the top of coastal dikes in the low-lying highly populated regions like Belgium, this thesis focuses on advancing the understanding of the hydraulic impact of wave overtopping and developing a practical approach to assess the vulnerability of coastal buildings on the dike. The results can be used for the design and assessment of coastalMFFDs. Two-dimensional physical model tests were used to study wave overtopping and overtopping wave impact for the situation of coastal dikes where a shallow foreshore affects the wave overtopping. @en