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Discover how a well-planned and good quality offshore site survey and ground investigation helps to make sure offshore wind developments are commercially viable and financially sustainable.

A marine site survey and intrusive ground investigation is about finding a detailed answer to one big question: what's below the waterline? It involves a range of integrated specialisms such as hydrography (subsea topography), geophysics (the study of the seabed and subsurface) and geotechnical engineering (understanding the physical, mechanical and chemical properties of soil and rock for the design of foundations and support structures).

Offshore wind development is increasingly – and necessarily – commercially focused. Margins matter. Not least following an economic environment of high interest, high inflation and supply chain shortage, which has increased development costs as well as the cost of accessing development capital. Developers must be able to accurately forecast potential profit margins to test the commercial viability of a site.

That requires data. Data that demystifies a development site and tells you everything you need to know about what the site looks like, what it's made from and where it's best to build. Here's a quick introduction to the ways a marine ground investigation can reduce development costs and protect profit margins.

1. Creating detailed project Scope of Works and Specifications

Once you have a good understanding of your site through an initial desk study, you can create clear project specifications and Scope of Works (SoW). And with clear specifications, you can get accurate costs from external suppliers. A poorly worded and/or poorly briefed Scope of Works will always hinder any site survey or intrusive ground investigation commercially and result in knock on affects that cause program delays. Ambiguity leads to data being missed, variation orders (VO) and additional work having to be requested, milestone dates missed, early warning notices issued or standards simply not being adhered to. This will ultimately have an impact on the financial viability of a project.

2. Understand the layout of the seabed

Bathymetry is the practice of mapping the ocean floor. Gathering data on water depth, the profile of the seabed and obstacles (such as boulders) can help to begin planning intrusive locations for the placement of wind turbine infrastructure and the best routes for connecting turbines to the grid.

Hydrographic and geophysical surveys can also identify geological faults and areas of seismic activity as well as the location of existing civil infrastructure such as electrical cables, telecommunication lines and gas pipelines. Picking the correct type of site survey during the reconnaissance stage of a project is crucial for reducing risk early on in a project – and lessens the possibility of issues rising to the surface later on.

>> The hazards that lie beneath

3. Understanding the subsurface and seabed geology

It's all very well knowing what the profile of the seabed looks like. But to plan foundations or anchor points for offshore wind turbines, you need to know what the seabed is made from – and the materials of the seafloor can be considerably less consistent than you might have expected.

During intrusive ground investigations you can use tools – such as gravity corers, vibrocores, rock coring and cone penetration testing (CPT) – to drill or poke into the seabed and study the sediment. These studies can be conducted mechanically from the ocean surface using purposely designed ships or floating offshore barges, without any need to send divers down to the seabed. Remotely operated underwater vehicles (ROV) that can recover seabed sediment are becoming more widely available for use in certain circumstances where you have extremely deep or very shallow water depths such as exposed sandbars.

This detailed information on the seabed and its geology is used to create a 3D ground model of the site. However, even if you have undertaken the best ground investigation and collected the best quality data possible, it's essential to implement this into your ground model correctly.

4. Identify unexploded ordnance

Unexploded ordnance (UXO) refers to explosive weapons – such as bombs, grenades and mines – that did not detonate when deployed. The vast majority are connected to WWI and WWII – remnants from combat, exercise drills and the offloading of munitions. The discovery of UXO can massively delay a project if it’s found too late. And delays cost money. So if UXO is part of a development site, it's best identified early. It's thought there are around 500,000 items (100,000 tonnes) of UXO in the water surrounding the UK.

5. Make accurate financial projections

When you have a clear idea of costs, you can forecast profit margins. This arms you with crucial knowledge before heading into allocation rounds or bidding for development sites, allowing you to submit bids based on solid financial projections – rather than risking bidding too low and committing to a project that isn't financially viable, let alone profitable.

For this reason more emphasis and importance should be placed onto the preliminary and reconnaissance site survey and ground investigation. This is becoming more common in the industry now that a focus is being placed on commercial viability. That makes it even more crucial to ensure the information you are gathering through your initial site survey and ground investigation is reliable and the subsurface geology is understood. This information can be used to accurately determine a FEED study based upon a foundation design. Determining foundation method through subsurface geology will help to understand installation method and risk, this gives a forecast of capital expenditure over the project lifecycle.

Offshore wind sites are becoming more complex

Many of the areas where it's easy to build offshore windfarms have now been allocated. Tomorrow's offshore opportunities will not only encompass increasingly larger and more efficient wind turbines but sites that are far more geologically, operationally and engineeringly complex. At Ternan Energy we have the expertise and capabilities to not only asses the feasibility of a site but design, supervise and manage all stages of a site survey and ground investigation to make sure you gather only the data you need – rather than paying for data that you don't.

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