A possible way of generating a stable and predictable base load of renewable energy, supplementing the unpredictable wind and solar energy, is dynamic tidal power (DTP). DTP is generated with the use of large dam, which is built in the sea, under an angle with the propagating tidal wave. A dam of sufficient length can create a phase difference between the propagating tidal waves on either side of the dam, creating head differences over the dam, which can be used to generate renewable energy using large turbines in the dam. Previous studies considered a DTP dam built perpendicular to the coast and the direction of the propagating tidal wave. However, a structure of this size extending into the North Sea interferes with other functions of the area such as shipping. Instead of a perpendicular dam, an oblique dam off the Dutch delta coast has been proposed to reduce this interference. This design has the additional benefits that it could increase the coastal safety of the surrounding area and potentially increase the sediment budget of the Voordelta area in front of the coast. In this study, a first-order assessment of an oblique DTP dam has been carried out. This assessment focuses on three aspects: the expected energy yield and how this compares to the expected energy yield of a perpendicular dam under the same conditions; the impact this dam has on the coastal safety of the surrounding area. To this end, an analysis of the change in hydrodynamic and morphological processes in the Voordelta as a result of the construction of such a dam has been carried out. The propagation of the tidal wave around an oblique DTP dam in the North Sea has been modelled using the FINEL modeling software, applied as a two-dimensional flow model. The reference layout of the DTP dam has been determined beforehand based on several requirements concerning the location and length. Using a turbine module integrated into FINEL, the discharge through each turbine has been determined, base on which the energy output of the DTP dam has been calculated. A comparison was made of the energy output of the oblique dam and that of a perpendicular dam, as used in previous studies. To do this, the same model has been run with a dam positioned perpendicular to the Dutch coast. A DTP dam with a length of 62.5 km and a southwest orientation starting at the Maasvlakte 2 was found to have a maximum power output in the order of 8 * 10^2 MW and a yearly generated energy yield in the order of 2 TWh. Both of these values were approximately a factor five lower than the power output of the perpendicular dam with the same length also starting at Maasvlakte 2. This is because, in the case of the perpendicular dam, a phase difference in the tidal wave over the dam was created, creating a large head difference over the dam. In the case of the oblique dam, the phase difference was lower, significantly reducing the water head over the dam. As opposed to the perpendicular dam, the head difference was created as a result of amplification of the tidal wave within the estuary. Subsequently, a SWAN wave model has been coupled to the FINEL flow model. In this coupled model, a design storm with a return period of 10000 years has been simulated. Of this storm, the wave characteristics and water level in the area were compared between the scenarios with and without oblique dam. A large decrease in both significant wave height and peak period behind the dam was found across nearly the whole Voordelta area, with the largest decrease offshore immediately behind the dam. However, the significant wave height increased on the outside of the dam and near Westkapelle. The same result was found for scenarios where 25 cm and 80 cm mean sea level rise has been applied. This is because the incoming waves from a northwestern direction are blocked by the dam, resulting in locally wind-generated waves behind the dam becoming dominant in the area. On the offshore side of the dam, significant wave heights are increased as a result of reflection of incoming waves. The maximum water level during the storm decreases in the nearshore area. As the area behind the dam is transformed into an area resembling an estuary, the dominant hydrodynamic and, consequently, the morphodynamic processes are changed. The dam blocks all incoming waves from the west and northwest, which are the dominant wave directions in the area. Because of this, the wave energy within the area decreases significantly under storm conditions. At the same time, the tidal amplitude is expected to be amplified within the area. These changes cause the area to become more tide-dominated. As a result, a decrease in the onshore directed sediment transport into the area is expected. The entrance of the estuary is expected to become more flood-dominant, as a result of which more inflow of sediment into the created estuary is expected. Dominant sediment transport mechanisms with the estuary are also changed, but for a more accurate view of the extent to which this happens, a complete morphological model is necessary, which has not been applied in this study. In summary, a DTP dam oblique to the Dutch coast can provide a substantial amount of energy, although it is significantly less when compared to a perpendicular dam and to previous studies. A further advantage of this dam is that the area behind is sheltered against storm wave conditions and extreme water levels, thus increasing the coastal safety. It is foreseen that the area attracts more sediment by the creation of the dam, but this needs to be confirmed by a future morphological model assessment.

Shallow jet flows are often coupled to high flow velocities and complex flow patterns. To properly ensure the stability of the barrier between both water bodies surrounding the jet, a scour analysis is often a necessity. Such analyses are inevitably coupled to the hydrodynamic processes occurring in jet flows, either in the form of loads on potential bed protections or equilibrium scour hole depths. Numerical models could assist in the design of bed protections by supplying accurate hydrodynamic input parameters for the design formulae or by predicting the hydrodynamic processes at play. Due to the limited computational power available, simplifications must be made within the numerical model to ensure reasonable computational costs. One of these simplifications is to resolve the flow in depth-averaged sense to create a 2DH model. To allow this simplification to be made, the performance of a 2DH model compared to a fully 3D model needs to be researched. By comparing simulations of a controlled environment and of a prototype scenario, insight in the predictive capabilities of the numerical models for possible other projects can be gained. This work aims to research the performance of 2DH and 3D numerical models regarding the reproduction of the hydrodynamic processes in shallow jets. First, it was investigated which hydrodynamic processes thrive at a prototype shallow jet by analysing measurement data available at Waterdunen. Afterwards, we systematically determine the performance of both a 2DH and 3D numerical model by setting up FINEL models both for a laboratory experiment of a shallow jet and for the shallow jet at Waterdunen. Insight in the predictive capabilities of 2DH and 3D numerical models for shallow jets can contribute to future design problems surrounding shallow jets. Information regarding the shallow jet at the seaside of the culvert at Waterdunen was obtained by Svasek Hydraulics, commissioned by the public government Waterschap Scheldestromen and the province of Zeeland, during a measurement campaign split into six individual measurement scenarios. Immediately at outflow from the culvert, the jet is subject to a 1:6 slope in streamwise direction. The geometry of the seaside channel is asymmetric, with 1:4 lateral slopes at either side of the channel. Furthermore, morphological changes as a result of the jet flow introduce an asymmetric topography in the channel. Visual observations during the measurement campaign indicated the flow can be characterized by an horizontal contraction over the longitudinal slope and an asymmetric flow profile depending on which casings were active within the culvert. The analysis of the measurement data shows the jet concentrates on the eastern side of the channel during all six scenarios. As a result, the recirculation zones on either side of the jet can be characterized as a small, non-dominant recirculation zone on the east side of the jet and a large, dominant recirculation zone on the west side of the jet. The streamlines show a continuous horizontal contraction until the flow hits the eastern side of the channel. Over the longitudinal slope, the flow seems to remain attached to the bottom rather than separating. However, due to a relatively large clearance of the ADCP measurements with respect to the bottom, this cannot be proven directly. It was decided to simulate the shallow jet of experiment 2.4.1 of van de Zande (2018) to investigate the performance of a 2DH and 3D numerical model for a laboratory simulation. In this experiment, the behaviour of an asymmetric shallow jet over a longitudinal slope at the point of the horizontal expansion was investigated. It was shown that both the 2DH and 3D numerical model were capable of reproducing the most dominant hydrodynamic processes within the jet. However, the accuracy with which the processes were reproduced differed significantly. The 2DH model reproduced too much curvature of the flow towards the lower wall of the flume compared to both the 3D model and the measurement data. As a result, the high flow velocities in the jet center were located further down in the channel. The flow velocities in the jet center were modelled with a maximum error of 12.4% in the 2DH model and 3.02% in the 3D model. The lower accuracy of the 2DH model is caused by the comparison between depth-averaged velocities and surface PIV velocities. Due to the additional curvature the recirculating velocities in the non-dominant recirculation zone were modelled too high by the 2DH model, with an error of up to 56.6% relative to the jet center velocity. In the 3D model, this error decreased to 18.9%. However, it was remarked the recirculating flow velocities in the PIV data were subject to clumping of tracer particles. The horizontal streamline contraction was simulated in the 2DH model, but can only be directly related to the changes in water depth. In both the 3D model and the measurements, this horizontal streamline contraction was shown to continue further downstream of the slope. It was concluded the horizontal streamline contraction is directly related to the vertical velocity profile, which was observed to differ from the standard log-profile both on the slope and downstream thereof. The 3D model was capable of reproducing the vertical velocity profile with a maximum relative error of 10%. In the numerical simulations at Waterdunen, both the 2DH and 3D models were shown to behave similarly. Both the 2DH and 3D numerical models were capable of reproducing the eastern concentration of the flow. However, the curvature of the jet further downstream was modelled more accurate in the 3D model. The better reproduction of the flow curvature in the 2DH model compared to the laboratory simulations is the result of the asymmetric inflow boundary, which allows the 2DH model to more easily resolve the flow curvature. Both models underestimate the flow velocities throughout the entire DOI. It was concluded this was caused by errors in the model input. Similar to the laboratory simulations, the 2DH model reproduced the horizontal streamline contraction over the slope but failed to reproduce the contraction further downstream. The 3D model was capable of reproducing the continuing streamline contraction. Furthermore, the 3D model reproduced vertical flow attachment over the slope, which complies well with the measurement data. It was concluded that a 3D numerical model can better reproduce the flow curvature in case of asymmetrical flows. Furthermore, the recirculating flow is better reproduced by a 3D model compared to a 2DH model. Finally, a 3D model is capable of accurately reproducing the vertical velocity profile, which supplies additional information of accurate flow velocities at the bed. However, on a prototype scale the differences between a 2DH and 3D numerical model are small. In channels with symmetrical boundaries, it is suggested to use a 3D numerical model in case the flow is subject to the Coanda-like effect. However, if the inflow into the channel is already asymmetrical, a 2DH numerical model can be considered to save computational effort. Nevertheless, when employing a 2DH model one should be wary of geometric and topographic asymmetries, as the effect of both factors on the flow symmetry is still unclear.

As a result of growth in the offshore energy infrastructure, the connection between the offshore environment and the mainland is increasing in importance. This leads to an increased use of the seabed for cables and pipelines as part of our energy infrastructure. Cables or pipelines are placed in trenches and covered by sediment, to be protected from any damage from activity near the sea bed. During execution, the trenches will refill with sediment prior to the placement of the cable or pipeline, which is known as siltation. The siltation rates are increasing when entering the breaker zone near the shoreline. The predictability of the siltation rates are a crucial step in efficient and safe realisation of new connections between the offshore energy infrastructure and the mainland. Inclusion of nearshore processes is missing in existing quick-assessment siltation tools. Complex process-based models, like Delft3D or XBeach, are capable of predicting siltation volumes in the nearshore environment accurately. However, these models demand large computation capacities. This makes them unsuitable for probabilistic modelling, requiring large numbers of calculations. Probabilistic modelling however is a crucial step in identifying and quantifying uncertainties and related risks in the execution. This research presents a quick-assessment tool that includes nearshore processes. Ensuring low complexity makes quick-assessment tools suitable for probabilistic modelling of siltation predictions, reducing and quantifying uncertainties within nearshore trench siltation. This research presents an approach to include wave transformation and wave-driven currents into an existing siltation prediction tool (SedPit). The resulting SedPit Nearshore tool allows fast predictions of siltation volumes in the nearshore zone. The performance of the SedPit Nearshore tool is assessed by comparing it to data from a field case, and comparing the accuracy to the accuracy of the existing SedPit tool. The SedPit Nearshore tool gives accurate predictions on the total siltation volume, and gives good insights in the spatial distribution of siltation volumes. The potential of the SedPit Nearshore becomes most evident when comparing it to the existing SedPit tool. A great improvement compared to the existing SedPit tool is seen. For the test case, the SedPit Nearshore tool reduces the absolute error in redicting the total siltation volumes by 82% compared to the existing SedPit tool. The SedPit Nearshore tool predicts the total siltation volume with an error margin of 7%, while the existing SedPit has an error margin of 41%. The largest improvements compared to the existing Sedpit are seen in the most onshore regions, as this is the zone where most wave-driven currents are generated. The computational speed of the tool has proven its applicability for analyses on model sensitivity and uncertainty quantification. Computation times are reduced by factor 9,000 when comparing it to XBeach, a complex process-based model. Bottom roughness ks and wave roller steepness β were identified as most influential free variables in driving nearshore siltation volumes. Calibrating the model to obtain likely values for a range of free variables has helped to reduce the 95% confidence interval of peak siltation rates by 36%. The inclusion of wave-driven currents into existing siltation prediction tools has shown a great improvement in the accuracy of siltation predictions in the nearshore zone. Although the SedPit Nearshore tool is calibrated on one specific field case, the method and the workflow of the tool show potential to help as general prediction tool of nearshore trench siltation. The power of the SedPit Nearshore tool lays in its simplicity, making it a fast, efficient, and accurate tool, suited for probabilistic modelling.