Comparing environmental effects of offshore wind turbine foundations

We developed a white paper for Bureau of Ocean Energy Management (BOEM) on the environmental effects of offshore wind turbine foundations to provide material that can be incorporated into NEPA documents and used for stakeholder outreach.

BOEM’s stakeholders—commercial fishers, recreational anglers, government agencies, and members of the public—raised concerns about the effects that installation of foundations could have on the marine environment. Their concerns included the direct effects on species from disturbance or loss of habitat during installation and operation. Other concerns were alterations of physical processes, like changes in hydrodynamics and water quality, which can affect benthic species (i.e., species living in, on, or near the seabed). While offshore windfarm foundations and associated scour protection can create artificial reef-like structures that support marine life, different foundation types will have differing degrees of environmental impact. BOEM recognized that a comparison of these impacts will help better inform the public.

Our team looked at various foundation types that are currently in use or are likely to be used in the future and compared their likely environmental effects on the marine environment. Each have different shapes, dimensions, footprints, and installation methods.

We identified the key questions lessees must ask themselves before selecting a foundation for their offshore wind energy installations: 

• How deep is the water at the site?
• What is the seabed like? Is it sandy, or are there rocks?
• What is the wind load (i.e., wind pushing against the sides of the installation)?
• What is the hydrodynamic load (i.e., water flowing against and around the installation)?
• What will be the effects on the environment?
  
   

The type of offshore wind foundation utilized is highly dependent on the geological conditions and water depths of the windfarm site. Our white paper compares the potential impacts of different foundation types on benthic species and habitats. We also looked at the impacts on spread of invasive species, wake effects that increase concentration of prey, changes in species’ resting or feeding behaviors, alteration of migration patterns, avoidance effects, the generation of suspended sediment during installation, and underwater noise.

Our analysis shows that the environmental effects of offshore wind turbine foundations are generally limited to the immediate vicinity of the foundations and the windfarm site area. The magnitude of the effects may vary among foundation types, primarily due to each type’s underwater surface areas, volume it occupies in the water column, and its footprint on the seabed.