Subsea Power Cable Risks off Southern Victoria Gippsland Coast - Basslink Lessons for Offshore Wind
Around 20 years ago, AMOG performed pioneering work on subsea power cable route risk assessments to assist the #Basslink?Interconnector Project off the South Gippsland coast in Victoria, Australia. At the time, it was the the longest HVDC cable of its type in the world.
Flash forward, and there are now a number of #offshorewind energy developers planning feasibility projects in this coastal region, and a renewed interest in subsea power cables and the risks associated with them.
Considered less conventional at the time, AMOG used a risk-based methodology for the Basslink studies. Risk-based methodologies have since been adopted as a standard approach in Europe for similar projects.
Two of the key subsea cable issues for the Southern Victoria #Gippsland coast that AMOG identified, and which remain relevant today, were:
Megaripple sand waves.
These sand waves are the result of at least 40,000 m^3 of sediment transport annually along the Ninety Mile Beach in an easterly direction.
Troughs are formed off the beach which mean that shore crossing directional drilling off the coast should extend beyond 450m. Regions of shallow cover, rock dumping and/or trenching to almost one metre depth are required to avoid exposure as megaripple sand waves progress and potentially expose the cable.
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Vessel activity resulting in anchor drag and drop or fishing gear snags on the cable.
With high levels of marine activity, the there are a number of cable hazards in the region; from recreational fishing to commercial fishing, workboats and even construction vessels related to other local offshore energy resources such as oil and gas platforms. This activity can result in anchor drag and drop events causing failure to the cable, and even damage from fishing gear snagging the cable.?
After conducting numerous studies, AMOG developed a best practice for vessels in the vicinity. Vessels were issued with updated navigational charts and new safer anchors that could limit the potential damage to the Basslink interconnector if they were to snag the cable. Vessels were permitted to cut away their anchors and be issued new free anchors if they thought there was a small chance they had snagged the cable.
We are proud to have played such a pivotal role in the region's subsea cable developments and will continue to keep assisting developers today.