Environmental Study on the Deep-sea Mining of Manganese Nodules in the Northeastern Tropical Pacific - Modeling the sediment-laden negative buoyant flow

Abstract

A 3-D hydrodynamic model for sediment transport has been developed to assess the environmental impact of benthic disturbance during the deep-sea mining activity. The model was applied to the Japan Deep-Sea Impact Experiment (JET) and a series of numerical simulations were carried out in order to reproduce the observed sedimentation profile of resuspended particles. Although the general tendency was reproduced in every simulation run, the observed resedimentation maxima at the northern and the southern ends of disturber towing zone could not be accounted for after all. The' discrepancy seemed to be partly because the model did not take into account the effect of sediment-laden negative buoyant flow which must contribute to the transport of resuspended sediment. Thus the model was modified to include the density effect associated with the resuspension of sediment, and then applied again to JET site to examine how the reproducibility of the resedimentation profile was improved. From the comparison of model results, it turned out that the sediment-laden negative buoyant effect plays an important role in improving the predictive capability of the model, but does not cause the model to reproduce the double-peak phenomenon of resedimentation at the ends of towing zone. This suggests that the complete reproduction of the double-peak phenomenon requires another simulation that takes into account the sediment-laden negative buoyant effect as well as an artificial sediment source involved in recovery operations of the seabed disturber