Marine environmental modelling for Darwin Pipeline Duplication Project

RPS has delivered an integrated marine modelling program to help Santos understand and manage the potential impact of suspended sediments from the development of its Darwin Pipeline Duplication (DPD) Project.

Integrated modelling support for Santos

The DPD Project involved the installation of a new pipeline, effectively extending the Barossa Gas Export Pipeline (GEP) inshore to the Darwin LNG plant at Wickham Point in Australia’s Northern Territory. Developing the pipeline involved the removal of seafloor sediments and rock within Darwin Harbour using multiple dredge vessels, and disposal of this spoil in nearby Beagle Gulf.

Santos engaged RPS to develop an integrated modelling study to assess the potential impacts of suspended sediment plumes – information that supported regulatory approvals for the project and informed its environmental monitoring and management plans.

Complex modelling for data-informed development

Trenching and spoil disposal can have a significant impact on marine environments if not managed carefully. It’s vital to understand both the environmental context in which work will take place, and how marine conditions and processes are likely to influence sediment dispersion behaviour.

To support Santos to understand this as fully as possible, RPS designed a modelling approach that simulated planned dredging methodologies, sequences and timing in terms of sediment movement (transport), settlement (fate) and resuspension.

Our team utilised RPS’ in-house model SSFATE (Suspended Sediment Fate) to complete long-term simulations of plume behaviour in relation to all construction activities, in combination with multi-source forcing data (information about the external conditions and processes that influence sediment movement).

Forcing data included spatially varying wind fields, and highly detailed models of hydrodynamics (tides and ocean currents) and waves, customised for the Darwin region and benchmarked against in-water observations.

Far from a mere desktop analysis, our approach incorporated geotechnical data collected from around 70 sample sites along the pipeline corridor and within the disposal area, allowing us to align modelling parameters with real conditions during various dredging and disposal scenarios, and at different times of year.

In conjunction with our modelling, RPS also completed comprehensive early-stage environmental surveys within and around Darwin Harbour. These surveys encompassed benthic habitat mapping, sediment and water quality sampling, and infauna assessments across multiple field campaigns.

This data, together with our sediment dispersion modelling outcomes, informed key project management plans for the Darwin Pipeline Duplication Project, including its Trenching and Spoil Disposal Management and Monitoring Plan (TSDMMP).

Monitoring support for pipeline development phase

Following the project’s approval, RPS supported Santos to implement the Darwin Pipeline Duplication Project’s TSDMMP, with a robust monitoring program designed to detect and manage project-related impacts.

Our work included marine condition surveys and deployment of metocean monitoring technologies (telemetered water quality monitoring buoys) within the development area. Such an integrated approach to modelling and monitoring supported rigorous environmental monitoring throughout the pipeline’s development phase, and informed adaptive management of construction activity in line with local environmental conditions and risks.