SUT US – Sediment Mobility, Scour and Seabed Disturbance Consideration for Offshore Wind Development

09 September, 2021



The Offshore Site Investigation and Geotechnics Committee (OSIG) of the Society for Underwater Technology in the US (SUT-US) is pleased to invite you to a webinar session titled “Sediment Mobility, Scour and Seabed Disturbance Consideration for Offshore Wind Development” delivered by industry and academia experts.

SUT Members: $100
SUT Non-Members $125
SUT Student Members: Free
SUT Student Non-Members: $15

Student registrations are only valid using ‘.edu’ or corresponding institutional email domains. Connections are unique and should only be used by one person. Duplicate connection will be forced out of the webinar session by the organizers.

Professional Development Hour Cerficates:
2.5 PDH certicates will be issued a day after the presentation. If you have more than one person viewing these webinars at your location, you can request additional PDH certificates for $10 at the email above.

Webinar Session Program

8:00AM CDT Welcome & Introduction
Tricia Hill, Society for Underwater Technology in the US (SUT-US); Dr. Xiaoyan Long, Fugro
8:10AM CDT Sediments on the move? Understanding the local geology and geomorphodynamics of the US Atlantic coast and continental shelf for offshore wind development
Dr. Nina Stark, Virginia TechLocal seabed geology and geomorphology are key factors for the site assessment and design of offshore wind developments. Both can vary on large or small spatial scales calling for smart designs of site investigation strategy as well as later design of foundations and cable routes. However, special attention should also be given to temporal variations of geomorphodynamics in terms of sediment erosion, deposition, and migration which may change the landscape of an area significantly over time. Particularly climate change including sea level rise, change of storm patterns, intensity, and frequency, may introduce additional uncertainties and importance regarding active geomorphodynamics in areas of interest. This presentation provides an overview of local geology and geomorphology of the US Atlantic continental shelf and relevant geomorphodynamic processes affecting offshore wind development.
8:30AM CDT Overview of Block Island Windfarm’s Cable Shore Crossing Incidents and Solutions to Preventing them in the Future
Mr. David McLaurin, Intecsea Engineering/AdvisianNational Grid’s portion of Block Island Wind Farm’s power transmission export cable (from The substation at Block Island to the mainland) has been experiencing issues since it was installed in 2016.  While there have been no problems with the cable’s landing point on the mainland, in Narragansett, where a horizontal directional drill (HDD) was performed at the shore crossing to bury it deep below the beach area, it’s been a different story on the Block Island side. At Block Island, a less expensive, shallower jet plow method was used to cross the shoreline. The shore crossing location at Block Island ended up more rocky than expected and burial depths for the cable were not sufficient to avoid exposure of the cable at multiple locations. With time, exposed sections of this cable have been exacerbated. In recent months, National Grid started preparing to install the new stretch of cable through its HDD pipe at Block island, when workers discovered unexpected obstructions.  They are working with contractors to clear the blockages, but have decided to halt installation until a solution if found regarding the sand, mud and other obstructions on the seabed. On the other side, Orstead’s inter-array cable (from the wind turbines to the Substation at Block Island) also had similar issues at the shore crossing location on Block island. Recently, Orstead corrected these issues with an HDD and a new cable was installed and spliced into the rest of the system. Seabed scour is widely recognized as a difficult engineering problem which is likely to cause instability of buried cables at the shore crossing. This discussion will address the conditions and design issues that caused these incidents with the goal of preventing similar issues on future projects in offshore wind in the NE USA. This includes discussion on scour, other causes for unburial, prevention, and mitigations.
8:50AM CDT Scour Mitigation at Offshore Wind Foundations
Dr. John Harris, HR Wallingford, UKThere are a range of approaches that can be taken to prevent or mitigate against scour around foundations, either planned for or as a remedial measure if scour is more severe than was expected. Rock armour has been the most commonly used form of scour protection at offshore wind farms using gravel, quarry run stone or blasted rock to cover a particular area of seabed to a specified thickness. In addition, other approaches include monitoring of the seabed around foundations, with the design philosophy for the monopile foundations involving installing them without scour protection. The presentation will provide an overview of scour protection measures, outlining the principle approaches in common use including examples from built wind farms. It will also look at the approaches adopted in a range of seabed soil conditions as well as the effects that can be induced by the placement of scour protection measures including secondary scour. The talk will also touch upon recently discussed issues of cable damage over the placed scour protection.
9:10AM CDT Break
9:20AM CDT Scour Hazard and Implication for Renewable Foundations and Cables
Dr. Joe Tom, University of Illinois Urbana-ChampaignScour is a nearly ubiquitous risk for offshore renewable energy infrastructure, particularly in the relatively shallow waters where most current developments exist. Local scour is the process in which the seabed is transported away from a structure (e.g., the foundation or seabed cables) due to moving water, such as induced by waves and currents. Unless prevented through scour protection, sediment loss caused by scour around foundations can lead not only to reductions in foundation capacity and system stability but also changes in the structural dynamics of wind energy systems, affecting energy harvesting uptime and production. Although many export cables tend to be buried, scour presents complicated risks for unburied cables. These risks include the potential for vortex-induced vibrations and cable fatigue associated with free-span development as well as changes in the burial conditions that can lead to inefficiency in cable thermal design and management. In this presentation, we will first briefly visit the primary mechanics that lead to local scour (a complex interplay between fluid mechanics and soil mechanics) around foundations and cables. This will then lead us to an overview of the impact of scour on monopile foundations in particular. Finally, we will discuss learnings from the oil and gas industry on sediment transport effects for unburied cables and the potential implications of this for renewable energy.
Dr. Sarah Courbis, Advisian
10:10AM CDT Panel Q&A Session
Dr. Xiaoyan Long, Fugro
10:30AM CDT Closing Remarks
Andrew Hill, BP

For more information, to read about the speakers and to register for this event click here.