To combat the emission of greenhouse gasses and the corresponding climate change, emission reduction goals have been established in the recent Paris Agreement. In order to meet these reduction goals and minimise the global average temperature increase, implementation of renewable energy sources is critical. Wind energy is one of the fastest growing renewable energy sources in the European Union, since Europe has the largest offshore wind energy capacity with its shallow shelf sea: the North Sea. Over the last twenty years, the wind energy capacity has increased significantly to become the current second highest power generation form of the European Union. The downside to offshore wind energy however, are the high costs that come with its generation. Cable losses of alternating currents between the wind turbines and the shore become increasingly high, as the distances towards the shore increment. For long distances, this inefficiency becomes unacceptable and conversion to a direct current is deemed necessary. A recently presented concept that aims to reduce the costs of offshore wind energy, is the concept of a large scale roll-out of interlinked offshore turbines, coordinated at an European level, including a so-called hub island. This artificial island facilitates converters, as well as a home base for engineers and large scale power storage. Technically, no big problems are expected with the construction of such artificial island. The major reason that could stop the hub island concept, is resistance from environmental organisations. To predict ecological repercussions of an artificial island, the impact on hydrodynamic parameters most important to the bottom of the marine food chain are explored. The primary producers represent this foundation of the food chain, and are most affected by the island through changes in water stratification and residual currents. These parameters highly influence the light and nutrient availability, thereby regulating the primary production dynamics of the ecosystem. By developing and applying the Three Dimensional Dutch Continental Shelf Flexible Mesh (3D DCSM-FM) model, the impact of an artificial island on the stratification and residual currents is explored for five case studies. Each case study comprises a 6km$^2$ cylindrical island, for different North Sea locations with distinct hydrodynamic properties. The implementation of an artificial island alters residual currents up to 10km from its position. The location determines the impact pattern, but influences remain local without any large scale North Sea impacts. Since changes in nutrient availability are only expected for large scale residual current impacts, no significant alterations in primary production dynamics are to be expected. The impact on stratification however, can have a significant influence on the dynamics of primary production. The originally well-mixed areas remain mostly unchanged, while islands in the more stratified regions can cause significant changes in absolute stratification up to 20km from the banks, and alterations in regimes or the seasonal onset timing up to 2.5km. The location and its hydrodynamic properties are paramount to the type of expected stratification impact, and proves to be an important design parameter for ecology around an offshore energy hub island in the North Sea.

Valdivia is a Chilean city located near an estuary system, 800 km south of Santiago. The navigation capacity of the Valdivia river mainly determines the present state and future possibilities for the welfare of the city. Since sedimentation problems arose in the river, the capacity for navigation became limited. The ministry of Valdivia therefore desires a solution for this problem in order to create possibilities for future growth. However, it is not known to what extent solutions for the sedimentation problem will actually contribute to an increase of welfare. By identifying the problem for the Ministry of Public Works of Chile, the boundaries and goal of the project could be set. In this research an attempt is made to answer the following research question: How can the surplus of sediment in the Valdivia river be remedied and to what extent will this contribute to the economic and social values of the city of Valdivia? In order to know how to remedy the surplus of sediment, a qualitative analysis of probable causes of the sedimentation was necessary. The main subjects which were researched by means of data and literature are tidal influence, river discharges, sediment composition and salt intrusion. With this knowledge it was concluded that the directions and magnitudes of flow lines in the river system can give good indications on what locations sedimentation can occur. The interaction between tidal currents and river discharges are the main drivers behind these flow characteristics. To verify the theoretical analysis, a basic Delft3D model was set up containing only tidal movement and river discharges. The pattern of the flow lines which was obtained from the Delft3D model supports the possibility that sedimentation occurs on the current identified sedimentation locations. Although other hydrological and morphological processes were found to possibly influence sedimentation rates in the river, qualitative data for studying these processes were missing. The current Delft3D model is therefore a good result regarding the available data and can be seen as a part of preliminary research in order to support further studies. Because the exact causes of the sedimentation were not identified in this research, it was not possible to come up with suitable solutions and to research how these solutions could affect the system. However, in order to gain insight in the effects of a river system without sedimentation problems, a fictitious scenario was studied by means of a social cost benefit analysis. The goal of the social costs and benefits analysis was to give insight in what factors should be taken into account when considering a project plan which solves the sedimentation problem. A dredging design was made in order to make the Valdivia river navigable for larger cargo vessels to increase the trading capacity of Valdivia. This dredging design comprises the deepening of the Valdivia river to a minimum water depth of 10 meters. Considering investment and maintenance costs of the dredging activities of this magnitude, it is concluded that the costs are not profitable compared to the social and economic effects of a higher traffic intensity on the river. With the social costs and benefits analysis all effects of solving the sedimentation problem are inventoried. When the Delft3D model can identify what the remedy of the sedimentation could be, the impact on the economic and social values of Valdivia can be determined. This research was not sufficient to answer the research question. Both the Delft3D model and the SCBA model were lacking accurate and reliable data. To expand this research, it is necessary to collect the data of which an overview has been made. Therefore, this research can serve as a preliminary study for further research. It is recommended that after data collection, solutions will be identified which can solve the sedimentation problem. These solutions need to be compared with a scenario analysis in order to decide on which is the most suitable solution for the sedimentation problem. Besides this, it is advised to research whether it is actually necessary to expand the river for transport when looking at all actors involved.