Tidal stream turbines are becoming an affordable option for harvesting sustainable energy in coastal areas. They can be retrofitted in barrages, providing an integral solution for flood protection and emission-free power generation, within environmental constraints. To optimize the turbine-barrage configuration with respect to these objectives, simulation tools are needed to predict the efficiency of the turbines as well as their impact on the adjacent tidal system. These tools should be based on an accurate representation of the underlying flow processes, which cover a wide range of spatial scales — from meters at the barrage and turbines to tenths of kilometers in the tidal basin. This article presents the development of such a tool by linking an analytical model for turbine fences in barrage gates to a regional flow model. The turbine model is validated with experimental data, and data from a thoroughly monitored tidal energy pilot project. Simulations reveal how clustering the turbines in small arrays can increase their efficiency, owing to array blockage effects, with only little effect on the tidal exchange. We also demonstrate the potential of using turbine fences to manipulate the tidal jet, issued from the barrage, with benefits for coastal — and wildlife protection in the basin. The presented research helps understanding how turbine fences in barrages can be configured with high energy yield and calculated impact to the environment.

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A bifurcation in an engineered river system (i.e., fixed planform and width) has fewer degrees of freedom in its response to interventions and natural changes than a natural bifurcation system. Our objective is to provide insight into how a bifurcation in an engineered river responds to peak flows and human interventions. To this end, we analyze the change in hydraulics, bed level, and bed surface grain size in the region of two bifurcations in the upper Rhine delta in the Netherlands over the last century. We show that, over the last two decades, the water discharge in one bifurcate (the Waal branch) has steadily increased at the expense of the other. This gradual increase in the water discharge of the first branch is associated with its erosion rate being larger than the other branch. The quick succession of two or three peak flow events (1993, 1995, and 1998) caused rapid sediment deposition over the upstream part of the bifurcate that has gradually lost discharge, which seems to have triggered the slow change in flow partitioning.@en

The flow between bridge piers and through storm surge barriers and barrages is an untapped and promising source of water energy. This energy can be harvested with tidal or hydro turbines. In 2015, five turbines with a total capacity of 1.2 MW were retrofit in a flow opening of the Eastern Scheldt storm surge barrier (the Netherlands). These turbines form world's first commercial-scale tidal fence. However, there is still a major challenge to optimize the configuration of these turbines based on their energy yield and their possible environmental effects to the hinter-lying estuary. This thesis presents a model tool to optimize the energy yield and impact on the environment of installing turbines in flood defences by altering the turbine placing. Mapping out the effects of turbines on the flow is the central question. To answer this question, this research consists of three parts: (1) measuring the field situation, (2) testing a turbine in the laboratory and (3) setting up an analytical model that is coupled to a regional flow model. In the first part of this study (1), unique, high-resolution data of the flow through the Eastern Scheldt storm surge barrier and around the turbines were investigated. In particular, for the first time in the literature, commercial-scale turbines are used to determine the effect of tidal turbines on the water flow. The power output of the turbines is also quantified. The data is used to derive an analytical model of the flow around a turbine in a barrier. This model can calculate the power of tidal turbines and the resistance of the barrier and turbine for different forms of the installation and variable strength of the external flow. In the second part of this study (2), these insights were refined in laboratory tests, in which the configuration of the turbine and barrier was varied. This method is more representative of real turbines because it has a larger scale factor (1:9) than is usual in the literature. The tests show that the generated power strongly depends on the position of the turbine relative to the barrier. The data also show that the combined resistance of a barrier and turbine is lower than the sum of the individual resistances. These outcomes are used to successfully validate the previously developed analytical model. In the last part of this study (3), the developed analytical model was implemented in a larger-scale numerical flow model. In this larger-scale model, the small-scale flow around a barrier with turbines is linked in an efficient way to the large-scale water movement in a tidal basin. This makes it possible to optimize existing or new tidal power stations, both at the level of the entire barrier and at that of a single flow opening. The impact on the environment can therefore be determined with the model, even more accurately than was previously possible. The research in this thesis shows that the effect of the turbines on the flow at a larger distance is smaller than previously thought. This offers the possibility, for example, to install more turbines and harvest more energy without exceeding the acceptable environmental impact (e.g. ecological effects). This study has contributed to confidence in the technical and economic feasibility of turbine installations that can be built in hydraulic engineering works in the Dutch Delta. The developed calculation tool is freely available to investigate energy yield and environmental effects of tidal energy projects worldwide.@en

Sediment transport capacity and supply of sediment to a river channel increase significantly during peak flow events. Here we study how a river bifurcation system (partitioning water and sediment over its downstream branches) responds to peak flow events. We focus on the Pannerdense Kop bifurcation in the Dutch Rhine River, an engineered system where planform and channel width are fixed. We analyze water discharge and bed level data measured over the last century. We observe rapid aggradation in one of the branches (Pannerden Channel) following the peak flow events of 1993 and 1995, and little to no bed level change in the other branch (Waal). Prior to the event, both branches eroded, and the upstream part of the Pannerden Channel had a greater erosion rate than the Waal. After the 1993 and 1995 peak flow events, the erosion in the upstream part of the Pannerden Channel slowed significantly, whereas the upstream part of the Waal branch continued to erode (though at a smaller pace than before the peak flow events). This differential erosion has resulted in a gradual increase of water discharge toward the Waal branch. Interestingly, the bifurcation system does not appear to respond equally to all peak flow events. We hypothesize that the bifurcation response to the 1993 and 1995 peak flows differs from previous peak flows because of the sequence of the two events. Between the 1993 and 1995 events, the system may not have had sufficient time to disperse the sediment deposited at the upstream end of the Pannerden channel. Another reason for the response to the 1993 and 1995 peak flows to differ from previous events may be that the channel bed surface within the region of interest has coarsened significantly. This study illustrates the importance of peak flows regarding bifurcation dynamics, and further research is focused on the interaction between bifurcation dynamics and the dynamics of the larger-scale system.@en

The tidal flow between bridge pillars and through open barriers is a promising source of ocean energy which can be exploited using tidal stream turbines, as proven recently by operational demonstration plants. The aim of this study is to clarify the consequences for the power output of tidal turbines when placing them in a hydraulic structure. To this end, experimental measurements of turbine power and wakes are performed, using a down-scaled turbine mounted at a submerged weir. The results are compared to an analytical model, validating its range of application for optimising turbine-weir geometries. The experimental data show that the power coefficient of the turbine can be increased by optimising the blockage of the channel and the distance between the turbine and the structure, which is related to the wake configuration. In this way, the power coefficient increased by 40% when the turbine was re-positioned from the upstream to the downstream end of the structure. The theoretical model could reproduce the measured power within 10% accuracy, proving its value as a rapid assessment tool. As such, this work advances the knowledge needed to meet targets on the transition towards renewable energy.

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An economical way to harvest tidal energy is by integrating free stream turbines in coastal infrastructure. While numerous studies have investigated how turbines should be arranged in idealized geometries to optimize their performance, only a few have considered the influence of realistic bed features. This research investigates the influence of a hydraulic structure on the performance of a tidal turbine, using the combination of field monitoring of full scale turbines installed in a Dutch storm surge barrier - comprising a weir and pillars - and by developing a corresponding theoretical model. The observed production by the turbines was large compared to situations with an unconstrained flow for two reasons. Firstly, the flow contraction by the weir increased the mass flux through the rotor plane. Secondly, the turbine suppressed energy losses in the recirculation zone downstream of a weir. The proposed model provides a quantitative estimate of these effects and is validated against field data. The model can be used as a design tool or parametrization of turbines in a large scale shallow water model, providing performance estimates covering a range of turbine-weir configurations. The work contributes to efficiently exploiting tidal energy with turbines in coastal bridges or flood defenses.

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Coastal infrastructure, such as bridges and storm surge barriers with weirs, provides an attractive location for harvesting renewable energy using tidal turbines. Often stone layers are applied downstream of coastal infrastructure to protect the sea bed from erosion. However, little is known about the potential effect of tidal energy extraction on the stability of this granular bed protection. This paper describes a study of the flow conditions influencing the stability of the bed protection downstream of a weir-mounted tidal turbine, using hydrodynamic data of an experimental test. The analysis indicates that the flow recirculation zone downstream of a weir may become shorter and flatter due to the presence of a horizontal-axis turbine. As a result, energetic turbulence eddies can transport more horizontal momentum towards the bed - hence the reason a heavier bed protection may be required for granular beds downstream of weirs when a turbine is installed. This information is essential when designing safe bed protections for coastal infrastructure with tidal turbines.@en

In 2015 heeft Tocardo met een consortium van bedrijven in een van de zuidelijke doorstroomopeningen van de Oosterschelde-stormvloedkering (Roompot 8) een getijdencentrale gerealiseerd, die in december van dat jaar in gebruik is genomen. Het project Oosterschelde Tidal Power (OTP) waarvan hier verslag wordt gedaan, kent meerdere doelstellingen: de doorontwikkeling van de toegepaste technologie en het bereiken van een aanzienlijke kostenreductie. Een belangrijk onderdeel van het project is het monitoren van mogelijke omgevingseffecten op door de vergunningverlener relevant geachte natuurwaarden in de Oosterschelde en de aangrenzende Voordelta (zie Besluit vergunning Nb-wet 1998 van 16 december 2010; ref. DRZZ/2010-403). Het monitoringproject is zo opgezet dat daarmee niet alleen invulling wordt gegeven aan de vereisten vanuit de vergunning ex. de Wet natuurbescherming maar ook aan een breed vorm gegeven stakeholderproces. De aspecten die vanuit de vergunning moeten worden gemonitord zijn: effecten op de stroming en verandering in stroombeeld, vermindering getijdeamplitude en invloed op zandhonger (gevolg: afname intergetijdenareaal), aantalsontwikkeling van zeehonden en bruinvissen in het gebied, en mogelijkerwijs optredende directe effecten op individuele dieren zoals aanvaringen met turbines. In 2017 is additioneel een analyse van zeehonden-trackdata uitgevoerd, en in 2018 door Seamarco een academic position paper opgesteld, dat als Engelstalige bijlage aan deze rapportage is toegevoegd.@en

Coastal infrastructure, such as bridges and storm surge barriers with weirs, provides an attractive location for harvesting renewable energy using tidal turbines. Often stone layers are applied downstream of coastal infrastructure to protect the sea bed from erosion. However, little is known about the potential effect of tidal energy extraction on the stability of this granular bed protection. This paper describes a study of the flow conditions influencing the stability of the bed protection downstream of a weir-mounted tidal turbine, using hydrodynamic data of an experimental test. The analysis indicates that the flow recirculation zone downstream of a weir may become shorter and flatter due to the presence of a horizontal-axis turbine. As a result, energetic turbulence eddies can transport more horizontal momentum towards the bed – hence the reason a heavier bed protection may be required for granular beds downstream of weirs when a turbine is installed. This information is essential when designing safe bed protections for coastal infrastructure with tidal turbines.@en