Tsunami risk to UK offshore wind: Palaeo evidence and numerical model simulations

Project Description:

Export cables, linking offshore windfarms to the national grid, are the weak link in offshore windfarm development. Sudden offshore windfarm failure can have significant impact on the national grid; for example, lightning strike caused generator failure in August 2019 at Hornsea One resulted in national power cuts and a £4.5M operator liability to Ofgem. Export cables are at risk of damage when exposed, and their performance drops when over buried. Cables are protected by armouring and burial, and thus sediment transport and erosion by currents and waves is key to assessing risk.

Seasonal risks to offshore infrastructure, related to sediment transport by currents and waves, are reasonably well understood. Despite this, cable failures are associated to ~80% of normal offshore windfarm insurance claims. Often failures are caused by poorly buried or exposed cables, damaged by anchors, fishing gear or natural loading. However, infrastructure vulnerability to high-risk low-frequency geohazards are largely unknown, especially in the near-shore zone, i.e. as export cables are brought on-shore.

In particular, the North Sea is periodically subject to tsunami events, generated by deep water slope failure

on the Scandinavian continental shelf [4,5]. Event frequency ranges from 1,000 to 10,000 years. The lower end of this range requires hazards to be included on the UK National Risk register, requiring built infrastructure to include management and mitigation solutions. The last major known significant event, the Storegga slide, is estimated to have occurred ~8,150 years before present. However, with limited research into this area, the real frequency in the palaeo record, and the potential for increased future risk frequency with climate change and other anthropogenic influences, is uncertain.

The aim of this PhD is to better quantify geohazard risk to offshore wind infrastructure, in particular tsunami risk to export cables and related infrastructure.

The PhD will focus on expanding palaeo-records of tsunami deposits from sedimentary cores along the east coast of the UK, in particular the extent of deposits around the south North Sea, to investigate the risk to current and future offshore wind farm developments. The PhD will use proxies such as grain size and XRF analysis (at laboratories at the University of Hull) to identify tsunami deposits and radiocarbon dating to date these events, in order to provide a more accurate estimate of the likely frequency of these hazards in the palaeo record of the south North Sea region.

The PhD will also work with Japanese collaborators on new laboratory scale experiments of tsunami deposits to advance detailed models of the sedimentary record that these events generate. There will be the opportunity for the PhD researcher to visit Japan to work with the collaborators.

By integrating data from the analysis of the cores and from the laboratory scale experiments, the PhD will develop magnitude-frequency risk assessments for offshore wind infrastructure for various scales of tsunami events. These will be used to identify appropriate management and mitigation solutions required in infrastructure that is located both in the North Sea and in the emerging Japanese offshore wind energy sector.