Abstract
The energy transition plays an important role in the work towards mitigating climate change and working towards a sustainable development. Wind energy is an energy source which holds a huge potential when it comes to providing energy from renewable energy sources. This can be applied to Sweden and neighbouring countries, as well as globally. There are two types of wind energy, onshore and offshore. On shore is based on land, while offshore is based in ocean areas. This report deals with offshore wind power.
Offshore wind turbines are installed in sea areas, and the foundations by currents standards are attached to the seabed. An important question to take into account when installing a new offshore wind farm is how the local marine wildlife might be affected. The currents cause the particles and sediment around the foundation to move, and these movements can create a hole-like structure in the sea bed against the foundation. This phenomenon of the sea bed close to the turbine moving, is called scouring. In order to prevent scouring, wind turbine foundations shall be installed together with a feasible scour protection. The foundation of the wind turbine as well as the scour protection has the ability to work as an artificial reef for the fish living in the area.
Svea Vind Offshore AB is currently developing offshore wind farms in the Baltic Sea, with the aim of contributing to sustainable development in as many parts of their projects as possible. At the request of Svea Vind offshore, the aim of this master’s thesis is to investigate how local marine wildlife interact with different designs of scour protections, with the purpose of finding the alternative that has the highest positive effect on local marine wildlife. The operation of wind turbines also emits low frequency underwater noise, which is taken into account in the study.
The study included three different experiments. The first one tested fish behaviour in an environment with noise and scour protection, in comparison to a quieter environment without scour protection. This experiment included testing three different designs of scour protections; one made out of small to medium-sized rocks, one made with concrete bricks, and one made with geotextile sand containers. Atlantic cod, shorthorn sculpin and black goby were selected as fish species for the experiments. The second experiment involved testing the scour protections against each other, without adding any turbine noise, and observing which one was the one preferred by Atlantic cod and shorthorn sculpin. The third experiment tested if the scour protection that was shown to be most preferred by the fish, was efficient in reducing scouring from currents. This was carried out by the use of a hydraulic flume machine that generated artificial currents. Based on the results, the rocks scour protection may offer the most preferable environment for the Atlantic cod and shorthorn sculpin. This could be due to the fact that the scour protection resembles their natural habitat and provides shelter. The black goby did not show any clear preference for any of the three scour protections, which can be due to its natural hiding behaviour.
The comparison experiment of the scour protections did not demonstrate a clear preference from any species for one particular scour protection design, which may be explained by the low number of replicates for this part of the study. Moreover, the experiment with currents successfully highlighted the importance of scour protections in the offshore wind power farms, since they effectively prevented the wind turbine foundation against scouring. In summary, the results of the conducted experiments indicate the potential benefits of rocks scour protection.