BMT WBM was commissioned to undertake Computational Fluid Dynamics (CFD) modelling of a proposed deep sea tailings placement (DSTP) project in Papua New Guinea as part of the review of the Woodlark Mine EIS.
These tailings were proposed to be discharged via an open pipe outfall. The use of CFD modelling allowed the effects of ocean density profiles, plume dilution processes and the behaviour of particles to be included in the assessment.
Two models were developed to predict the motion of the tailings: a homogeneous fluid model and a turbidity model.
The homogeneous fluid model showed that dilution of the plume led to reduction of its velocity and density in the near and mid-field. It also showed that at a distance of about 3km from the outfall location, the tailings were effectively diluted to the background density of the ocean at this depth/location.
This modelling approach, however, excluded the effect of the particulates on the flow, specifically their tendency to settle towards the ocean floor, effectively ‘perpetuating’ the density current. Thus, a supplementary turbidity model was created which simulated the tailings as a slurry composed of five discrete particle sizes.
This modelling showed that finer particulates in the slurry discharge were likely to disperse within the water column and spread laterally; coarser particulates were likely to drop out within 100 - 200m of the outfall and mid-sized particles were likely to form a stable plume that should reach the intended tailings placement location.
Based on these outcomes, key recommendations were made with regard to the operation and ongoing monitoring of the discharge.
For general enquiries relating to Woodlark Mine EIS Review - CFD Modelling, please contact Dr Darren Richardson
Dr Darren Richardson
Manager Ecology and Environmental Management