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.

Introduction

As part of our· environmental study on the exploitation of deep-sea mineral resources, a numerical model capable of evaluating the sediment transport arising from benthic disturbance during the mining activity has been developed since 1992. In 1995 and 1996, aiming at verifying the general applicability and predictive capability, the model was applied to the in situ impact experiments, JET conducted by MMAJ(Metal Mining Agency of Japan) in 1994 and BIE-II by NOAA(U.S. National Oceanic and Atmospheric Administration) in 1993, to simulate the resedimentation profiles during the benthic disturbance (Taguchi et al., 1995 and Nakata et al., 1997).

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