Floating wind – with new territories come new geohazards
26 May 2023
Sophie van Zanten and Grant Lewis
Geohazards can present a significant threat and cause damage to floating wind farms and export cables. A tailored geohazard assessment can help wind farm developers to identify, evaluate and mitigate these risks at an early stage.
In recent years, the rapid growth of the offshore wind market has seen wind farm projects becoming ever larger. Many fixed-bottom turbines are in the shallower waters of the European continental shelf, for example in the North Sea and the Baltic. We see new developments are being planned further from shore, in more complex, deeper water regions where floating wind is the only feasible solution.
This requires designing floaters, anchors, mooring lines and dynamic cables. Floating wind will increase the areas available to harness wind energy, boosting the potential supply of renewable energy. But with new territories come new challenges.
From a geological perspective, developing floating wind farms can be much riskier than developing fixed-bottom offshore wind farms. But floating wind farms are more energy efficient and will enable us to reach net zero faster. There are geohazards at floating wind farm sites that have not been typically present in much of the fixed foundation offshore wind farm sites. The geohazards can add a lot more complexity to the site investigation and ultimately the design of turbines, the layout and cable routing compared to fixed-bottom offshore wind farms. That’s why understanding the geological conditions and potential geohazards at a floating wind farm development early on is crucial to reducing risk, keeping the infrastructure safe throughout its lifetime and delivering a more sustainable energy supply.
A booming market
80 % of the world’s potential offshore wind resource blows over waters deeper than 50 metres. Upcoming markets for floating wind include, but are not limited to, the UK, South Korea, the US, Italy, Norway, Japan, France, Spain and Portugal. Deep water sites, like those in the Mediterranean Sea and the Pacific Ocean, have great wind resource opportunity. However, they also present different hazards.
Floating wind farms are built in deeper water, which generally are on or beyond the continental slope, where geohazards such as slope stability, variable soil conditions, debris flows or earthquakes may present a risk to the development and longevity of floating wind farms and their cables. This is why geohazard assessments tailored to the site are critical to reduce risk for a well-planned floating wind farm development.
Why conduct a geohazard assessment?
To reduce uncertainty, every floating wind farm development must include a geohazard assessment at an early stage. And that’s not all. Where certain geohazards are considered a risk in the early stage assessment, the site investigations must extend up-slope of the wind farm borders, the lease area and the export cable corridor. Why? to assess the risk at your project site, you need to look beyond what’s on the surface and below the surface, but also consider any environmental changes over time. It’s the bigger picture.
The transition zone
There are many geohazards to consider. Unstable submarine slopes can have dramatic consequences to a floating wind farm development. When a submarine slope fails, significant volumes of sediment are mobilised and its energy may increase to such an extent that it could damage any seabed infrastructure in its path, including export cables and any systems designed to secure floating wind farms.
Our expert team of engineering geologists, seismologists, meteorologists and geotechnical engineers can model and integrate many different types of Geo-data to assess the distance over which the risk of slope failure may affect any infrastructure. We did exactly that for a project in the Mediterranean. The risk assessment involved:
1. Assessing slope stability
2. Working out the frequency and magnitude of these events in the past, where the material would go, its speed and its impact
3. Modelling the potential currents scattered with sediment or debris that flows downslope where it may damage the infrastructure
4. Determining the likelihood of these geohazards occurring (we factored in the site location, its regional context and geological history).
Our team of consultants advise on potential geohazards at your project site to reduce risk
A challenge we relish
Decades of experience have informed and improved our approach to geohazard assessments at offshore wind farm locations:
1. We combine publicly available data with our extensive local and global experience to research and describe the geological setting, predict the soil conditions and rank the potential geohazards
2. We rank the applicability of different foundations and their location, given the soil conditions and potential geohazards
3. Based on the most likely foundations, we advise and plan the optimal site investigation campaign.
The techniques for acquiring in situ Geo-data for geohazard assessment have many similarities with those used for regular site investigations, such as cone penetration tests, boreholes, piston cores and grab samples. We send the samples off to our global network of in-house geohazard core logging facilities to examine every millimetre of sediment; work out how the soil laminae arrived in the core.
By forensically analysing the core to age-date those millimetre layers of sediment, we’re able to record the frequency of turbidity current events during a specified period. We then model the events to assess whether the risk and frequency are applicable to the lifespan of the offshore wind farm.
Did you know?
In 2022, we completed 40 desktop studies for floating wind projects around the world