Despite the challenging conditions in the Gulf of Bothnia, the surveys were completed safely and successfully. The results are promising for the offshore wind farm project of Metsähallitus and Vattenfall.
Seabed surveys are a key phase of each offshore wind farm project.
“They are an important part of the technical planning of the offshore wind farm project,” says Mikkel Klahn, the project’s geophysical lead at Vattenfall. The over seven-month-long seabed surveys were thus a significant milestone for the Korsnäs Offshore Wind Farm project.
A project that is unique in many ways
Vattenfall has conducted numerous seabed surveys across Europe, but this project was unique in many ways. “Firstly, this was the first project where we had to factor in icy conditions and frost. The second challenge was the rocky soil for which no previous research data was available,” explains Klahn. The third unique feature was information security. Klahn points out that the survey was an extensive operation, in which several experts needed detailed information. The strict information security requirements of the Finnish authorities made the exchange of information challenging. Finnish expertise played a big role in the project. Vattenfall worked in cooperation with GEOxyz, which utilised, for example, Finnish Arctia Meritaito in the project.
Great cooperation with the Defence Forces
Despite the challenging conditions, the survey was completed safely and successfully. According to Klahn, the Finnish Defence Forces was quick to react and always helped resolve any ambiguities.
Three vessels were used in the seabed surveys. The surveys were mainly carried out using sonar, magnetic measurements and ultra-high-resolution seismic mapping. In addition, 30 seabed samples were taken to determine the composition of the sediments and the grain size of the stones. ”Efforts were made to disrupt the marine ecosystem, especially fish stocks, as little as possible,” Klahn points out.
The seabed is rockier than expected
The surveys were able to collect high-quality data. It indicates the composition of the seabed and the potential hazardous locations, such as cables and wreck residues. The results are a relief for the project: the surveys did not reveal any hazards or obstacles to construction. The seabed is suitable for the development of offshore wind farm.
However, the seabed of Korsnäs is harder and rockier than expected.
”We expected to find a lot of rocks, but not this much!” says Klahn.
Accurate information about the seabed and the location of stones helps to plan the locations of wind turbines safely and efficiently. “The results bring certainty and enable the next stages; the planning of the foundations of wind turbines and the assessment of environmental impacts. This is a good place to continue.”