FY 1981

Dispersal and resedimentation of the benthic plume from deep-sea mining: A model with calibration

Lavelle, J.W., E. Ozturgut, S.A. Swift, and B.H. Erickson

Mar. Mining, 3(1/2), 59–93 (1981)

An analytical solution of the time-dependent mass conservation equation is used to describe the passive dispersion of deep-sea particulates resuspended during mining. Data from bottom photographs, deep-sea particulate casts, and moored nephelometers taken during and after North Pacific manganese nodule test mining in March-April 1978 have been used to fix model parameters. Both the in situ settling velocity spectrum of the resuspended particulates and the near-bottom vertical turbulent eddy diffusivity have been estimated by the least-squares method. The settling velocity spectrum shows a mean near 10⁻¹ cm/s, a value higher than expected of clay size particles in a primary particle size mode. The settling velocity distribution is also broad, extending below settling speeds of 10⁻² cm/s. The vertical turbulent eddy diffusivity has a magnitude of approximately 40 cm²/s, a value in agreement with interpretations of North Pacific deep-sea ²²²Rn profiles. Under reasonable extrapolation assumptions for mining systems and patterns, the model and selected parameters are used to predict commercial mining resedimentation and benthic plume scales. Single-track resedimentation thicknesses greater than 1 mm are not expected beyond 400 m from a mining track. During continuous mining operations, a benthic plume with particulate concentrations exceeding ambient levels at the bed (approximately 5 µg/1) may be expected to extend some 160 km downstream, bearing particulates resuspended as much as 45 days earlier.