Making landfall: the view from the shore
Exploring how data, analysis and insight inform landfall assessment to solve pipeline FEED and installation questions.
Every offshore operation eventually makes landfall in the coastal zone; a unique and dynamic environment with challenges and risks that must be understood if a pipeline is to successfully and safely come ashore.
Landfall assessments used to inform FEED and installation activities are prepared by ABPmer’s geomorphologists and metocean scientists, founded on data and analysis which lead to the insights shared in the final assessment.
Below is an extract from our piece in the October 2020 issue of World Pipelines magazine, outlining how ABPmer solves questions posed by engineers and operators at the FEED stage. The full article also explores the inter-relationship between data, analysis and insight that inform landfall assessments.
Understanding informs action
Depending what a client needs to know, various types of analysis are applied to answer their questions.
What is the submarine topography?
Whilst pipeline technology has advanced to deal with practically any type of topography, pipeliners prefer to not leave an asset vulnerable to the hydrodynamic forces of waves and currents.
We provide clients with measures of the minimum and maximum bed levels and change likely to occur over the assessed intervals. There would also be additional information on the time period associated with the observed variability.
We regularly provide mapped measures of minimum and maximum bed levels with accretion and erosion events matrices.
What is the composition of submarine and shoreline sediments or how deep should the pipeline be buried?
Pipelines are buried for several reasons; the primary reason is for protection.
We recommend pipeline burial depths along the assessed length based on the understanding of likely bed level variability along the route.
If using horizontal directional drilling (HDD), at what point should this begin?
Horizontal directional drilling (HDD) allows for the installation of a cable underneath the beach without disturbing the surface sediments. Considerable control is possible over the drilled route enabling the avoidance of sensitive areas.
We provide an assessment of the likely range of beach variability at the proposed landfall location(s), along with a definition of the beach closure depth.
How long will the trench remain open?
By knowing the types of sediment present, ground condition, estimated rates of sediment transport (which may be intermittent and seasonal in nature) and the anticipated depth and width of the trench to be dug, we can estimate the potential rate and nature of any expected infill arising from naturally occurring sediment transport.
Our report will likely include conditions that might lead to infilling; information as to the best place to deposit displaced material to maximise or minimise time to fill; estimate recovery rate and level of infill at periods of one day, one month, one year, etc., as well as identify residual risks to effective burial of a pipeline.
What are the metocean conditions in the area?
To inform technology and operational decisions, clients usually want to know about shoaling, refraction, waves and currents as the pipeline makes the shore approach.
Informed by our in-house SEASTATES metocean hindcast data product, we can provide metocean reports, describing the requisite set of typical and extreme conditions together with a set of data tables, and/or timeseries allowing further data analysis from the pipeline engineers.
How should dredging be managed to minimise environmental impacts?
When asked to do this our reports usually cover project design and planning, equipment impact, dredging impact, spoil placement and controls.
What changes can be expected at the landfall site that we need to mitigate?
We are often asked to consider whether the evolving coast could damage the pipeline in the short term or during the usual 25-year operational period.
We normally deliver a Technical Report providing a descriptive understanding of the likely changes that might be experienced over the design life of a pipeline asset, and the potential impacts of such change.
Conclusion
Pipeline landfall assessments provide answers to questions at the FEED stage. Such assessments are undertaken by ABPmer’s geomorphological specialists and metocean scientists to develop a conceptual understanding of the local environment from insights gained from integrating data and undertaking analysis.
This understanding is used to provide informed assessments of conditions over an asset design life which are used by pipeline engineers to help define the installation and monitoring plan.
Learn more about our services to the pipeline sector.
Read the full article in October 2020 edition of World Pipelines magazine.
Prepared by Tracey Hewett, Business Development Manager
ABPmer is a recognised authority on the physical and ecological marine environment and is regularly called upon to provide technical input to inform engineering design that satisfies both statutory consenting requirements and the lifetime management of the asset.