It’s all too easy to forget that without undersea cables, offshore wind developments are essentially functionless. And their placement can have a significant impact on the commercial success of a project.
We sat down with Adam Caton, Senior Geotechnical Engineer at Ternan Energy, to discuss the commercial imperative of cable burial risk assessment – and how it protects the profitability of offshore wind developments.
What is cable burial risk assessment?
In simple terms, a cable burial risk assessment (CBRA) is concerned with identifying hazards that could damage offshore wind cables. By assessing these hazards, it’s possible to make informed decisions on cable routing, cable burial depth and the use of cable protection to preserve cable integrity and longevity.
What value do offshore wind developers get from CBRA?
It can cost millions of pounds to repair damage to offshore wind cables. Such damage accounts for more than half of offshore wind insurance claims. Mitigating the risk of cable damage reduces the chance of downtime, inflated insurance premiums and capital expenditure further down the line.
CBRAs can also save significant sums during the development phase of a project. The more protection you give to a cable, the higher your expenses. By pinpointing the risks along a cable route, you can make sure you are not over-protecting your cables – and thus over-spending. When you consider that it costs upwards of £100,000 per day to commission a cable laying vessel, it’s easy to see how proper CBRA can optimise development costs.
What goes into a cable burial risk assessment?
Every CBRA is different based on the nuances of the development site, cable routes and client ambitions. But a thorough CBRA should examine anthropogenic, geophysical and geotechnical risks. Anthropogenic factors include assessing patterns of vessel activity – particularly fishing vessels – shipping lanes and so on to deduce the type and amount of shipping traffic passing over the cable, as well as the likelihood of these vessels dropping an anchor on or near the cable (risking damage from anchor strikes and anchor drag).
Geophysical factors include identifying the presence, type and depth of mobile sediment – and detecting the possibility of seabed creep: where a whole layer of seabed gets pulled away, which can stretch and snap cables or leave them exposed to anchor strikes. Finally, geotechnical considerations include analysing the composition of the seabed to determine how far different types of anchors could penetrate.
How is risk calculated?
CBRA isn’t about completely removing the risk of cable damage. It’s about giving a probabilistic impression of how likely damage is to occur – and reducing that likelihood down to a tolerance that the developer is happy with.
For instance, CBRA might conclude that if certain steps are taken regarding cable burial depth, then the probability of anchor strikes is one every 10,000 years. While it’s technically possible to reduce that probability, it costs a lot of money. So cable protection measures must always be balanced with the economic viability of development.
What’s the Ternan Energy approach?
Here at Ternan Energy we have an integrated team of geotechnical and geophysical specialists. That means we can conduct extremely thorough CBRAs to provide a comprehensive overview of cable route risks.
Our approach is to help the client understand the risks, the probability of cable damage and the cost of mitigation. It’s about providing the clear information they need to make confident commercial decisions.
One highly specialist service we offer is live trenching support. Let’s say that it was agreed that a cable should be buried at a depth of one metre. But during live trenching, the cable laying vessel is only achieving a burial depth of 0.8m. We can then calculate the new cable risk – and help you ascertain whether adding 0.2m of cable depth is worth retracing the cable laying route, which could add hundreds of thousands of pounds to development costs.
What are the risks of CBRA?
The main dangers of CBRA are ideological. Some developers see it as a box-ticking exercise and fail to get an appropriately detailed assessment of cable risk. Others pay only cursory attention to CBRA recommendations and lay cables at the depth they think will be the most cost-effective.
But detail is crucial. Just one example is scrutinising shipping data. During COVID-19, shipping activity was subject to wild fluctuations. If a CBRA is drawing conclusions from shipping data without scrutinising when the data was gathered, you could end up making decisions on data that is unrepresentative of post-pandemic vessel activity.
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To discuss your project, contact Adam via adam.caton@ternan-energy.com.