This paper presents the first field measurements with an innovative laser scanner system, during an actual severe winter storm with very oblique wave attack. The goal of this paper is to validate this innovative system for measuring wave run-up and wave overtopping parameters during storms with very oblique wave attack. The paper describes the analysis of the run-up and overtopping data obtained during storm Ciara (10 - 12 February 2020) and validates the results with data from overtopping tanks and video recordings. Storm Ciara was a highly unique and complex storm, with offshore-directed wind and alongshore-directed waves at the dike. This posed large challenges for measuring the front velocities. The wave run-up heights and the overtopping discharges could be measured accurately with the laser scanners. Reasonable results were achieved for the run-up depths. This has led to several new insights into the probability distribution of oblique wave run-up and the run-up depths of up-rushing oblique waves. Larger deviations were found for the 2D front velocities and wave angle of incidence, which could not be determined as well for storm Ciara. This arose from the highly complex conditions during Ciara with very oblique wave attack. The mobile system is now ready to be used at several different locations in the measurement campaign in this area over the coming years. ... Read more

This dissertation focuses on the Eems-Dollard estuary in the north of the Netherlands and contributes to the MVED (’Meerjarige Veldmetingen Eems-Dollard’) field measurement project in the area. The Eems-Dollard estuary is part of the Wadden Sea, a shallow shelf sea with barrier islands, deep tidal channels, shallow tidal flats and wetlands. The Eems-Dollard estuary is even more complex than theWadden Sea, because of the deep channels, which run close to the dikes, and the very shallow flats, as well as the funnel shape, which can lead to very high water levels during storms. A particular aspect for this area is that the dike design conditions consist of an offshore-directed wind and very obliquely incident waves, up to 80° relative to the dike normal. Almost no studies have been performed on the estuary and almost no measurements were available inside the estuary. This dissertation considers two main knowledge gaps, related to the modelling of wave propagation effects and measuring of (very) oblique wave run-up and overtopping, in a complex estuary. First, the performance of the SWAN wave model in predicting the wave conditions in a highly complex area, such as the Eems-Dollard estuary, has not been assessed before. Second, knowledge on and (field) measurements of the extra parameters (such as front velocities) necessary for the cumulative overload method are still scarce. This method considers the overtopping and erosion of the dike cover explicitly. Added to this, the few available (lab) investigations on wave run-up and overtopping during (very) oblique wave attack have not yet led to clear conclusions or guidelines. Therefore, the aim of this dissertation is to gain more insight into the uncertainties related to wave propagation processes and (very) oblique wave run-up and overtopping, which are important for the extreme wave loads on the dikes around the Eems-Dollard estuary. ... Read more

Wave overtopping is typically measured in the field using overtopping tanks. In this paper, an alternative system is developed that uses two laser scanners. The system also measures wave run-up, as well as run-up depths and velocities, both during perpendicular and oblique waves on a dike in the field. The paper considers the first calibration tests with the system in the field, with perpendicular and oblique waves generated by the wave run-up simulator on a grass dike slope. Furthermore, simulations are performed with the numerical wave model SWASH, to gain more insight in the potential performance of the system during actual oblique wave attack during a storm. The run-up is determined from the measured elevation and reflection intensity, which agrees well with the visually observed run-up. Run-up depths and front velocities can be determined accurately as well. The (virtual) wave overtopping discharge can be calculated from the data, which agrees well with the most commonly used overtopping equations for perpendicularly incident waves. Finally, from the simulated run-up data of obliquely incident waves, it is concluded that an estimate can be obtained of the incident wave period and wave angle of incidence at the toe of the structure. ... Read more

Practitioners often employ diverse, though not always thoroughly validated, numerical models to directly or indirectly estimate wave overtopping (q) at sloping structures. These models, broadly classified as either phase-resolving or phase-averaged, each have strengths and limitations owing to the physical schematization of processes within them. Models which resolve the vertical flow structure or the full wave spectrum (i.e. sea-swell (SS) and infragravity (IG) waves) are considered more accurate, but more computationally demanding than those with approximations. Here, we assess the speed-accuracy trade-off of six well-known models for estimating q, under shallow foreshore conditions. The results demonstrate that: i) q is underestimated by an order of magnitude when IG waves are neglected; ii) using more computationally-demanding models does not guarantee improved accuracy; and iii) with empirical corrections to incorporate IG waves, phase-averaged models like SWAN can perform on par, if not better than, phase-resolving models but with far less computational effort. ... Read more

Oosterlo et al. (2019) developed a system using two terrestrial laser scanners, which can measure run-up heights, depths and velocities of waves on a dike in field situations. The system has now been placed next to two overtopping tanks on a dike in the Eems-Dollard estuary in the Netherlands to measure during actual severe winter storms. The goal of the present paper is to further validate this innovative system with data obtained during storm Ciara (10 - 12 February 2020), a severe winter storm with very oblique wave attack. Furthermore, the data gathered during storm Ciara will be compared to the current knowledge on wave overtopping, to possibly gain new insights in the influence of very oblique wave attack on wave overtopping. ... Read more

Oosterlo et al. (2019) developed a system using two terrestrial laser scanners, which can measure run-up heights, depths and velocities of waves on a dike in field situations. The system has now been placed next to two overtopping tanks on a dike in the Eems-Dollard estuary in the Netherlands to measure during actual severe winter storms. The goal of the present paper is to further validate this innovative system with data obtained during storm Ciara (10 - 12 February 2020), a severe winter storm with very oblique wave attack. Furthermore, the data gathered during storm Ciara will be compared to the current knowledge on wave overtopping, to possibly gain new insights in the influence of very oblique wave attack on wave overtopping. ... Read more

Wave overtopping is commonly measured using overtopping tanks. In this paper, an alternative system is developed by using two laser scanners. It measures wave run-up, as well as layer thicknesses and front velocities, both during normally and obliquely incident waves on a dike in the field. The paper considers the first field validation tests with the system, with normal and oblique waves generated by the wave run-up simulator on a grass dike slope. Furthermore, a range of environmental conditions are simulated, to determine the robustness of the system. From the measured distance and reflection, the run-up is determined, which corresponds well to the observed run-up. From the data, the layer thickness and front velocity are determined as well. Layer thicknesses and front velocities are determined reliably with the laser scanners. Also, the (virtual) wave overtopping discharge can be calculated, which corresponds well with the most commonly used overtopping equations. ... Read more

Shallow foreshores in front of coastal dikes can reduce the probability of dike failure due to wave overtopping. A probabilistic model framework is presented, which is capable of including complex hydrodynamics like infragravity waves, and morphological changes of a sandy foreshore during severe storms in the calculations of the probability of dike failure due to wave overtopping. The method is applied to a test case based on the Westkapelle sea defence in The Netherlands, a hybrid defence consisting of a dike with a sandy foreshore. The model framework consists of the process-based hydrological and morphological model XBeach, probabilistic overtopping equations (EurOtop) and the level III fully probabilistic method ADIS. By using the fully probabilistic level III method ADIS, the number of simulations necessary is greatly reduced, which allows for the use of more advanced and detailed hydro- and morphodynamic models. The framework is able to compute the probability of failure with up to 15 stochastic variables and is able to describe feasible physical processes. Furthermore, the framework is completely modular, which means that any model or equation can be plugged into the framework, whenever updated models with improved representation of the physics or increases in computational power become available. The model framework as described in this paper, includes more physical processes and stochastic variables in the determination of the probability of dike failure due to wave overtopping, compared to the currently used methods in The Netherlands. For the here considered case, the complex hydrodynamics like infragravity waves and wave set-up need to be included in the calculations, because they appeared to have a large influence on the probability of failure. Morphological changes of the foreshore during a severe storm appeared to have less influence on the probability of failure for this case. It is recommended to apply the framework to other cases as well, to determine if the effects of complex hydrodynamics as infragravity waves and morphological changes on the probability of sea dike failure due to wave overtopping as found in this paper hold for other cases as well. Furthermore, it is recommended to investigate broader use of the method, e.g., for safety assessment, reliability analysis and design. ... Read more

This paper considers the Eems-Dollard estuary in the north of the Netherlands, which is part of the shallow shelf sea the Wadden Sea. This estuary is a highly complex area with tidal flats and deep channels and is characterised by an offshore directed wind, posing a challenge to wave prediction models. As little measurements are available, a measurement campaign is set up to provide field data for verifying and improving these wave models. The paper presents the locations that are most suited for wave measurements in the estuary, insight in the performance of the phase-averaged numerical wave model SWAN, and insight in the processes that play a role in the area around the corner of the Eemshaven. Furthermore, it presents insight into the reliability and applicability of SWAN in this highly complex area. An analysis of propagation effects is performed, as well as a comparison between the SWAN version as used for the Dutch dike safety assessment and the newest version, used for development, which includes the state of the art parameterisations of the physics. Furthermore, modelling is done for a schematised version of the area around the corner of the Eemshaven, considering several different model settings. Large differences occur in the results between the two SWAN versions. These differences are studied in more detail, and the causes of these differences are identified. ... Read more

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. ... Read more

De organisatie van de Waterbouwdag geeft dit jaar alle bezoekers een boek cadeau met alle ingediende projecten van de Agemaprijs 2015. ... Read more

The main goal of this study is to determine the relation between very oblique wave attack and overtopping, and to accordingly adjust the formulae for oblique wave attack. The required knowledge to be able to read and understand this report is of a Bachelor in civil engineering level. All around the world different types of structures are built to protect adjacent areas from river or coastal flooding during high water levels. Only limited research is available on the influence of oblique wave attack (for angles over 45 degrees) on wave overtopping. Hydralab is an EU-project, which gives researchers in the European Union the possibility to carry out research in large hydraulic facilities. Cornerdike is a part of the Hydralab IV program. The Cornerdike research project was performed at the shallow-water basin at DHI in Hørsholm, Denmark. To achieve the goal of this research, tests, data processing and analysis were done. ... Read more