Next-generation Forecasting of Hazards Offshore from River Deltas

Lead Research Organisation: University of Southampton
Department Name: School of Ocean and Earth Science

Abstract

"NERC : Lewis Bailey : NE/L002531/1"

Our overarching aims is to better understand the processes that trigger submarine avalanches of sediment, known as turbidity currents, offshore from river mouths. By analysing triggering mechanisms, we aim to build a model that can forecast turbidity current activity, and be applied to river deltas globally. These sediment flows can be exceptionally powerful (velocities of up to 20 m/s) and travel for long (100s km) distances. Therefore, turbidity currents pose a significant hazard to seafloor infrastructure such as oil and gas pipelines and telecommunication cables. We have never been more reliant on the internet in the current world of lockdowns and remote working. Even weaker flows travelling at speeds of ~1-2 m/s can severely damage seafloor equipment making hazard mitigation be re-routing challenging and very expensive ($millions per km). Improving our understanding of the frequency and timing of flows is therefore critical to asses where these extra costs are a necessity.

The destructive nature of turbidity currents means there are very few sites where a significant number of flows have been directly measured. Therefore, the mechanisms that result in flow triggering still remain poorly understood. Recent monitoring has made advances using instruments moored along flow paths to precisely measure turbidity current timing to compare with potential triggers. Analysis in remote fjord-delta settings in British Columbia, Canada, have shown turbidity currents preferentially occur at low tide during periods of elevated river discharge. Novel multivariate statistical methods (i.e. analysing the combined effect of multiple variables) have quantified the relative role of river discharge and water level. Using this relationship, it has been possible to successfully predict almost 90% of turbidity current activity. However, this analysis is based on data acquired over relatively short-time periods (months), and therefore may miss longer (seasonal-yearly) cycles of flow activity. It is also unknown how the relative roles of river discharge and water level vary when upscaled and applied to major rivers where underwater events pose a much greater hazard to coastal communities and critical seafloor infrastructure.

The project will use longer-term monitoring datasets that have been made possible by the pioneering Canadian Government-funded Victoria Experimental Network Under the Sea (VENUS) cabled observatory, which has been recording unusually detailed data offshore the Fraser River Delta, British Columbia, since 2008. Using this dataset combined with previous direct measurements of turbidity currents the project aims are to:

(1) Understand how the roles of discharge and tide for turbidity current triggering vary at different scale river systems.

(2) Develop a predictive model for turbidity current occurrence that could be applied to river delta systems globally.

(3) Understand the potential effects of climate change on the frequency and timing of turbidity currents.

Our results will benefit future geohazard assessments for seafloor infrastructure including oil and gas pipelines, and telecommunication cables. The development of a turbidity current forecasting model will help us understand the frequency and timing of flows and the risk to seafloor infrastructure. Such forecasting can also contribute to future planning of cable or pipeline routing.

Publications

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