Developing the UK national centre of excellence for geohazards through quantification of field-scale turbidity current hazard
Lead Research Organisation:
NATIONAL OCEANOGRAPHY CENTRE
Department Name: Science and Technology
Abstract
Our over-arching aim is to better understand the impact of powerful submarine flows, called turbidity currents, on pipelines and other seabed infrastructure used to recover oil and gas. Turbidity currents pose a serious hazard to expensive seabed installations, especially in deeper-water settings. These sediment flows are particularly hazardous because they can be exceptionally powerful (travelling at speeds of up to 20 m/s), and can flow for long distances (100s km), causing damage over vast areas of seafloor. Even weaker flows travelling at ~1-2 m/s can severely damage seafloor equipment, or break strategically important submarine telecommunication cables, while some flows have maintained speeds in excess of 5 m/s for hundreds of kilometres. This makes hazard mitigation by local re-routing of pipelines difficult. Where seafloor topography is rugged, many operators route pipelines within canyons; however, these are focal points for turbidity current activity. Mitigating against turbidity current geohazards, particularly within canyons, can have very significant cost implications for industry - additional deepwater pipeline routing costs ~ $3 million per km. Mitigation costs of $2 billion are predicted to route pipelines under the Congo Canyon, where turbidity current hazard is deemed to be high. Perhaps just as importantly, pipeline oil spills could lead to major reputational damage. Given concern over accidents to structures used to recover oil and gas, a focus on geohazards is also aligned with NERC's environmental responsibility.
The most remarkable aspect of turbidity currents is how few direct measurements there are from flows, in part because they damage monitoring equipment placed on the seafloor. Several lines of evidence point to the existence of a region of high sediment concentration at the base of turbidity currents. These dense basal layers are of key important because of: (i) their location just above the bed where most submarine infrastructure is located; and (ii) they carry most momentum due to their large density. Yet, sediment concentration has never been measured directly measured in these layers. Physical experiments, numerical modeling and ancient deposits provide valuable insights into these flows; but there is a compelling need to monitor full-scale flows in action. This project is timely because it will develop innovative field-based techniques for imaging near bed flow structure and vertical changes in sediment concentration in situ.
Aims: (1) Our first aim is to develop and field test a novel technique for remote sensing of dense near bed layers. (2) Our second aim is to better understand the nature of near bed dense layers. (3) Our third aim is to embed improved understanding of dense near-bed layers into numerical models used by industry to assess impact of turbidity currents on oil and gas pipelines. (4) The project will also help to establish an international centre of excellence for submarine geohazard research at the UK National Oceanography Centre.
Here we propose to make direct measurements of dense basal layers that form part of the turbidity currents occuring daily during the elevated summer river discharge on the Squamish Delta, located in Howe Sound, Canada. We will use an innovative four-point mooring to hold a vessel and suspended instrumentation payload stable above an active channel system, while we observe the dense basal layer with a Chirp sub-bottom profiler. The low frequency and broad bandwidth (1.5 -13.0 kHz) Chirp source guarantees penetration through dense near-bed layers, resolving layers with ~10 cm resolution. These field observations will help to understand the fundamental character of near bed layers, and the situations in which they form.
The most remarkable aspect of turbidity currents is how few direct measurements there are from flows, in part because they damage monitoring equipment placed on the seafloor. Several lines of evidence point to the existence of a region of high sediment concentration at the base of turbidity currents. These dense basal layers are of key important because of: (i) their location just above the bed where most submarine infrastructure is located; and (ii) they carry most momentum due to their large density. Yet, sediment concentration has never been measured directly measured in these layers. Physical experiments, numerical modeling and ancient deposits provide valuable insights into these flows; but there is a compelling need to monitor full-scale flows in action. This project is timely because it will develop innovative field-based techniques for imaging near bed flow structure and vertical changes in sediment concentration in situ.
Aims: (1) Our first aim is to develop and field test a novel technique for remote sensing of dense near bed layers. (2) Our second aim is to better understand the nature of near bed dense layers. (3) Our third aim is to embed improved understanding of dense near-bed layers into numerical models used by industry to assess impact of turbidity currents on oil and gas pipelines. (4) The project will also help to establish an international centre of excellence for submarine geohazard research at the UK National Oceanography Centre.
Here we propose to make direct measurements of dense basal layers that form part of the turbidity currents occuring daily during the elevated summer river discharge on the Squamish Delta, located in Howe Sound, Canada. We will use an innovative four-point mooring to hold a vessel and suspended instrumentation payload stable above an active channel system, while we observe the dense basal layer with a Chirp sub-bottom profiler. The low frequency and broad bandwidth (1.5 -13.0 kHz) Chirp source guarantees penetration through dense near-bed layers, resolving layers with ~10 cm resolution. These field observations will help to understand the fundamental character of near bed layers, and the situations in which they form.
Publications
Azpiroz-Zabala M
(2017)
A General Model for the Helical Structure of Geophysical Flows in Channel Bends
in Geophysical Research Letters
Clare M
(2018)
Complex and Cascading Triggering of Submarine Landslides and Turbidity Currents at Volcanic Islands Revealed From Integration of High-Resolution Onshore and Offshore Surveys
in Frontiers in Earth Science
Vendettuoli D
(2019)
Daily bathymetric surveys document how stratigraphy is built and its extreme incompleteness in submarine channels
in Earth and Planetary Science Letters
Hage S
(2019)
Direct Monitoring Reveals Initiation of Turbidity Currents From Extremely Dilute River Plumes.
in Geophysical research letters
Hage S
(2020)
Efficient preservation of young terrestrial organic carbon in sandy turbidity-current deposits
in Geology
Chen Y
(2021)
Knickpoints and crescentic bedform interactions in submarine channels
in Sedimentology
Azpiroz-Zabala M
(2017)
Newly recognized turbidity current structure can explain prolonged flushing of submarine canyons.
in Science advances
Clare M
(2015)
Quantification of near-bed dense layers and implications for seafloor structures: New insights into the most hazardous aspects of turbidity currents
in Proceedings of the Annual Offshore Technology Conference
Hage S
(2022)
Turbidity Currents Can Dictate Organic Carbon Fluxes Across River-Fed Fjords: An Example From Bute Inlet (BC, Canada)
in Journal of Geophysical Research: Biogeosciences
Gales J
(2018)
What controls submarine channel development and the morphology of deltas entering deep-water fjords?
in Earth Surface Processes and Landforms
Heerema C
(2020)
What determines the downstream evolution of turbidity currents?
in Earth and Planetary Science Letters
Hizzett J
(2018)
Which Triggers Produce the Most Erosive, Frequent, and Longest Runout Turbidity Currents on Deltas?
in Geophysical Research Letters
Description | We have used a CHIRP system to for the first time image a dense basal layer in a turbidity current. |
Exploitation Route | The CHIRP approach will probably become a standard in monitoring turbidity currents. The results allow us to estimate the thickness and density of the basal layer of turbidity currents. This information is vital to keep sea floor infrastructure protected against turbidity currents. |
Sectors | Energy Environment Transport |
Description | Our findings will be used as input for models that estimate forces that a turbidity current might apply to seafloor infrastructure. |
First Year Of Impact | 2016 |
Sector | Energy,Environment,Transport |
Impact Types | Societal Economic |
Description | Company presentation 2015 |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Industry/Business |
Results and Impact | We have ran presentations on the ongoing work at NOC for the research and development departments of the following oil and gas companies: ExxonMobil, Shell, Chevron, ConocoPhillips, BP, FUGRO. These presentations were given at the companies and have been viewed by up to 100 industry geologists. These presentations have also lead to further funding from ExxonMobil with a value of ~£120k. Additionally, the talks have got us excess to further data with an overall value of over £1M from Chevron. |
Year(s) Of Engagement Activity | 2015,2016 |