Modeling offshore mining turbidity sources

Abstract

Accurate predictions of the environmental impact remain a major challenge in the licensing phase of offshore mining projects. A significant part of the environmental impact of offshore mining is caused by an increase in turbidity of the oceanic waters. Turbidity levels are increased by the suspension of sediment during the excavation process and due to the discharge of return water and possibly tailings into the ocean. Current consensus prescribes releasing discharges in close proximity of the seafloor to decrease the impact area of the turbidity plume. Main engineering choices remain a challenge. Available engineering models and software are unable to include the interaction between the turbulent slurry mixture and the (deep) seafloor. This introduces an uncertainty into the predictions of the turbidity source. Uncertainties increase as the source is used as input for long-term and far-field environmental impact calculations.
A research program is presented aiming to develop a numerical model which will be able to simulate turbulent turbidity sources and their interaction with a submerged bed. With the use of open source CFD software and a three-dimensional large eddy simulation turbulence model, significant improvements are expected in the prediction of the dominant transport processes. Two numerical validation cases are presented in this paper to demonstrate the possibilities and accuracy of the chosen model for this application. Currently, the introduced model is limited to represent entrained solid particles by weightless tracer particles. In the near-future, the model will be able to include density gradients and particle settling, increasing the application accuracy for higher concentrated discharges.