Near-Field Analysis of Turbidity Flows Generated by Polymetallic Nodule Mining Tools

The interest in polymetallic nodule mining has considerably increased in the last few decades. This has been largely driven by population growth and the need to move towards a green future, which requires strategic raw materials. Deep-Sea Mining (DSM) is a potential source of such key materials. While harvesting the ore from the deep sea by a Polymetallic Nodule Mining Tool (PNMT), some bed sediment is unavoidably collected. Within the PNMT, the ore is separated from the sediment, and the remaining sediment-water mixture is discharged behind the PNMT, forming an environmental concern. This paper begins with surveying the state-of-the-art knowledge of the evolution of the discharge from a PNMT, in which the discharge characteristics and generation of turbidity currents are discussed. Moreover, the existing water entrainment theories and coefficients are analyzed. It is shown how plumes and jets can be classified using the flux balance approach. Following that, the models of Lee et al. (2013) and Parker et al. (1986) are combined and utilized to study the evolution of both the generated sediment plume and the subsequent turbidity current. The results showed that a smaller sediment flux at the impingement point, where the plume is transformed into a turbidity current, results in a shorter run-out distance of the turbidity current, consequently being more favorable from an environmental point of view.