New field-scale calibration for turbidity current impact modelling

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Subsea infrastructure networks underpin our daily lives, providing critical global communication links and supporting our demand for energy supplies. These strategically important networks are vulnerable to fast-moving seafloor flows of sediment, known as turbidity currents. Such flows have previously broken important subsea cable connections; leading to £Ms in lost financial trading and repair costs. The seafloor cable network transfers >95% of all global communications traffic. The International Cable Protection Committee (represented by partner Carter) has a vested interest in understanding the risk of turbidity currents, but there is a paucity of direct field measurements of turbidity currents. Thus, numerical models are largely based on scaled down experimental studies. Here, we show how the first deep-ocean high resolution measurements of turbidity currents can enable improved understanding of the risk posed, through calibration of numerical models for impact analysis. This will directly benefit partners Chevron and Shell, who are responsible for ensuring safe operation of multi-£M seafloor oil and gas pipelines worldwide. Loss of hydrocarbons to the environment can have severe environmental and reputational implications; hence minimising the risk of a pipe rupture is important. Improvements to modelling will be immediately taken up by partner HR Wallingford, who advise a wide range of owners and stakeholders on hazard assessment for seafloor infrastructure. We aim to address the following questions: [1] How can emerging direct monitoring technology lead to a step-change in assessment of turbidity current risk to offshore infrastructure? Until recently, there were no direct measurements of turbidity currents due to the difficulties in deployment in remote and challenging subsea environments. New advances in technology have enabled the first measurements of velocity and concentration in deep-ocean turbidity currents. Techniques developed for, and lessons learned from, the monitoring of flows at a number of sites will be transferred to industry partners. This first aim is thus to help improve how industry assesses turbidity current hazards by using the first ever direct measurements. [2] How appropriate are existing models and how should they be revised based on new field-scale calibrations? As no comparable datasets exist, this new direct monitoring provides a unique opportunity to validate, test and refine numerical models of turbidity current. We will first assess how appropriate existing flows employed by industry are at recreating real flow behaviour. We will then run variants of a depth-resolved model developed by Dorrell. The aim is to provide a modelling approach that is acceptable in terms of computational cost, and that can recreate observations from direct monitoring. Specific guidance will be provided to the partners on how models should be developed to assess impact of turbidity currents on seafloor infrastructure. [3] What impact do real-world turbidity currents have on seafloor infrastructure? We will then quantify turbidity current impact on a range of seafloor infrastructure. This is novel because it will involve the application of new models based on the first deep-sea direct monitoring data. The analysis will transform industry understanding of impacts and mitigation strategies. Deliverables will include: (i) Report outlining industry best practice for turbidity current hazard assessment; (ii) New numerical modelling approach outlined in a workshop; (iii) Summary report detailing the modelled impacts of real-world turbidity currents on a range of seafloor infrastructure, and guidance for design, mitigation measures and future data acquisition strategies. Project cost = £87.2k (at 80% FEC) over 12 months.