When waves are required in a lab to study aspects like loads on hydraulic structures, wave dynamics, and sediment and pollutant transport, they are generated by wavemakers. The wavemaker’s motion is prescribed by a control signal. Most commonly, a position-controlled wavemaker is used, for which the control signal is the paddle position. This means that the paddle position is prescribed to the machine. An alternative approach is to prescribe the force measured directly in front of the wavemaker. In this case, the control signal is the demand force and it is called a force-controlled wavemaker. When active absorption is included, the force in front of the wavemaker is measured and compared to the demand force. If the measured force deviates from the demand force, the movement of the wavemaker is adjusted. Force-controlled wavemakers are already in use for over forty years but the theory behind calculating the demand force is still in development. In this thesis, the theory for the control signal of a new force-controlled piston wavemaker is studied.

A control signal can be calculated with different theories, of which two theories have been expanded to force-control wavemakers, referred to as the broad-band and the narrow-band theory. The broad-band theory makes no assumptions about the type of wave and the force equations specifically have been derived in Bayle et al. (2025); Spinneken & Swan (2009a). The broad-band theory has been implemented in a MATLAB code of Edinburgh Designs Ltd. The narrow-band theory assumes a narrow wave spectrum and it neglects the evanescent modes in the force equations, which results in a set of equations that is faster to compute. For a narrow wave spectrum, the narrow-band theory should give the same results as the broad-band theory. However, for a broader wave spectrum, inaccuracies will occur. The force equations of the narrow-band theory have been derived in Bayle et al. (2025). In this thesis it is studied if the force equations of both theories are correct and it is analysed under which conditions the narrow-band theory can be used to calculate the demand force instead
of the broad-band theory.

To reach these objectives, the force equations of the narrow-band theory are evaluated, they are connected to the broad-band theory, one of the missing force terms is derived and all equations are implemented in a MATLAB code. To be consistent with the force equations, the evanescent modes are neglected in all narrow-band equations. Subsequently, the intermediate steps to find the demand force are calculated with both the broad-band and narrow-band codes and the results of the two theories are compared. This analysis is performed for focussed wave groups of a Gaussian spectrum in shallow to deep water (kph = 0.28 to kph = 3.1) in which both the first and second order harmonics are included. In addition, it is verified that the control signal is processed correctly when it is provided directly to the wavemaker.

For a narrow spectrum (ν = 0.02, where ν is the spectral width) and a shallow water wave (kph = 0.28), the narrow-band and broad-band theory give similar results (< 0.8% relative difference for all components) and consequently the narrow-band theory can be used. For waves in intermediate and deep waters (kph = 0.58 to kph = 3.1), some of the intermediate calculation steps give a higher relative difference. This can be caused by the choice to neglect the evanescent modes for the narrow-band theory or by implementation errors and requires further research. A broad spectrum (ν = 0.10) results in a relative difference for the second order harmonics of up to 8% for the shallow water wave (kph = 0.28) and a larger difference of up to 100% for intermediate and deep waters. This suggests that the broad-band theory should be used for a broad spectrum if the second order harmonics play an important role in the studied process. The large relative difference requires research to explain. The results show that for all studied cases, the evanescent modes can be neglected for the shallow water wave (kph = 0.28) but they should be included in intermediate and deep waters (kph = 0.58 to kph = 3.1). Before any definitive conclusions can be drawn, the narrow-band theory should first be completed with respect to the force equations and an analysis of the final demand force calculated with both the broad-band and narrow-band theory is required.

Marine plastic debris has become an established concern as a threat to marine and coastal ecosystems. Despite progress in understanding plastic transport dynamics under deep-water conditions, the characterisation of these processes in the nearshore environment remains incomplete. This poses significant challenges in their parametrisation, essential for the accurate representation of coastal transport dynamics in predictive models.

In this study, experimental measurements of the plastic particles wave-induced transport in intermediate to shallow water depths are presented. The focus is put on the influence of wave steepness as a key parameter affecting the transport of marine plastic debris in the transition from deep water to the shoreline. Its potential as a predictive parameter is investigated through controlled laboratory experiments involving the generation of seven regular breaking wave conditions, characterised by varying offshore steepness, propagating in shallow water depth over a sloped bathymetry.

The results reveal a consistent increase in particle drift speed with increasing offshore wave steepness. While the exact functional nature of the observed positive relationship could not be definitively concluded, the trend appears more likely linear than quadratic, aligning with previous findings for particles deviating from perfect tracers undergoing deep water breaking conditions. Furthermore, wave breaking was observed to play an important role in enhancing particle drift speed. Finally, particle drift speeds were consistently underestimated by the Stokes drift and only partially captured by the wave crest speed estimates, progressively diverging from the former and approaching the latter as offshore steepness increased, though remaining consistently lower than crest speeds. This trend was most recognisable in the breaking zone across all the tested wave conditions.

Overall, the findings suggest offshore wave steepness as a robust predictor for marine plastic debris transport in the nearshore environment, proving its value as a classification parameter for future modelling efforts. By investigating how plastic particles respond to changing wave conditions in the nearshore environment, this study aims to contribute to a better understanding of their dynamics.

Floating marine plastic debris has emerged as a major global environmental threat in recent years due to its persistence, long-distance transport, and harmful impacts on marine ecosystems. Understanding the key processes affecting plastic beaching is essential for accurately modelling plastic transport and predicting accumulation zones in nearshore marine environments. So far, research on plastic transport in shallow, nearshore waters is limited compared to deep ocean studies, resulting in significant uncertainties about wave-driven transport in these zones. While it is established that the impact of plastic density on the movement of floating plastic debris varies across wave zones, the dynamics in shallow water remain poorly understood. This research investigates how the density of finite-sized plastic particles influences the beaching dynamics under controlled, regular wave conditions in a laboratory flume simulating a nearshore environment using a sloped bathymetry. The densities relative to water of idealized spherical particles were systematically varied ranging from 0.09 to 0.93. Particles were released in the shoaling zone and tracked through the wave flume until beaching, allowing drift speeds to be analysed across different wave zones. It is observed that prior to breaking, in the shoaling zone, particles travel onshore with a speed close to the locally estimated Stokes drift regardless of the particles' relative density. In the breaking zone, density significantly affects particle drift speed: low-density particles accelerate strongly, nearing crest and phase speeds, while higher-density particles show only modest acceleration. Extending these findings to real-world coastal environments indicates that low density plastics tend to beach quickly, while denser particles remain suspended longer and thus may be affected more by lateral currents. While further research is needed to fully understand the role of density in plastic transport near the shore, this study clearly demonstrates that density significantly influences beaching dynamics—underscoring its importance in accurately modelling plastic transport in the nearshore environment.

In this thesis I use a novel approach to estimate the economic impact of the 2021 Limburg flood using high-frequency transaction data from ABN AMRO bank. High- frequency bank transaction data have previously been proven valuable in accessing the economic impact of the COVID-19 pandemic (Neuteboom et al., 2021). To the best of my knowledge, this type of data has not been used to estimate the economic impacts of a natural catastrophe. I focus on a synthetic difference-in-differences methodology to estimate the impact. I find that the economic impact is 18,045 EUR on average of extra spending per inundated individual in Valkenburg aan de Geul, the most heavily hit area. This is very similar to the damage estimate of the ENW (2021) of 18,713 EUR on average per person for the inundated in Valkenburg aan de Geul. Further- more, the duration of the economic impact for the inundated is roughly 35 weeks on average. Finally, I did not find a measurable economic impact to uninundated and evacuated individuals. In summary, high-frequency bank transaction data paired with a synthetic difference-in-differences model is a reliable gauge of the economic impact of a flood and should be used to estimate the economic impact of future natural disasters. Additionally, it can be be the empirical foundation for calibrating existing damage models.

Accurately predicting the surface transport in the ocean is crucial for estimating the course of marine pollution, which is considered one of the most pressing environmental issues of the 21st century. In the ocean, floating marine pollution is transported by several mechanisms, including waves. Current models predicting the surface transport set the wave-induced transport component to be equal to the Stokes drift, which is defined as the net drift that a fluid parcel experiences in the direction of a propagating wave. However, Deike et al. (2017) and Pizzo et al. (2019) indicated that the transport induced by the Stokes drift is enhanced by breaking waves. Despite extensive study of the wave breaking phenomenon, it is still not possible to accurately predict the surface transport for breaking waves in deep water irregular seas. Thus, in this thesis, the contribution of the transport from breaking waves to the total wave-induced transport at the surface of a deep-water unidirectional irregular sea is estimated. To do this. a theoretical model is developed. The model computes the transport of individual breaking wave groups from surface elevation measurements of a deep-water unidirectional irregular sea. Thereafter, the contribution of the wave-induced transport from breaking to the total wave-induced transport is defined by an enhancement factor. This enhancement factor shows how much the total surface transport in a wave field without breaking waves is enhanced by the transport of breaking wave groups.

The model that is developed is an extension of the relationship from research by Sinnis et al. (2021). In their research, they defined a transport relationship for isolated breaking wave groups based on the spectral bandwidth and the linear slope of the wave groups. In the model, the transport relation from Sinnis et al. is applied to the breaking wave groups from surface elevation measurements of deep water irregular seas. In order to do this, the surface elevation spectrum was approximated by multiple Gaussian wave groups. From the Gaussian wave groups, the spectral bandwidth and the linear slope could be determined. The breaking waves were identified based on a steepness threshold for the wave groups. The wave-breaking-induced transport was calculated for all individual breaking wave groups.

Additionally, experiments were carried out to validate the theoretical model. The experiments were performed in the Atlantic Basin of Deltares. In this facility, unidirectional irregular waves were generated in deep water. During the experiments, an overhead camera filmed the behavior of quasi-Lagrangian particles floating on top of the waves. The particles were tracked using OpenCV and their trajectories were obtained. Because the particles in breaking waves travel faster than in non-breaking waves, a velocity threshold was used to identify the breaking waves in the trajectories. From the identified breaking waves the wave-breaking-induced transport was quantified.

Furthermore, the theoretical model was validated by comparing the number of breaking waves, the strength of the breaking events, and the enhancement factor with the experimental results. The results showed that all values were in the same order of magnitude and that the wave-breaking-induced transport enhanced the surface transport for non-breaking waves by a factor up to 1.5. Besides, a sensitivity analysis on the relevant parameters showed that the error margin remains within 10% from the mean. In conclusion, the theoretical model gave reasonable predictions of the contribution of the wave-breaking-induced transport in a unidirectional irregular sea. Hence, this framework can be fruitful grounds for further extension of the breaking induced drift in the ocean.