Appendices 5-13 - Nautilus Cares - Nautilus Minerals

dB re 1uPa @ 1m
200
195
190
185
180
175
170
165
rig tender holding station, Relative azimuth = 0
160
0 500 1000 1500
Frequency (Hz)
Figure 2. Third octave source spectra. Red - measured spectrum of the Pacific Ariki, blue - extrapolated
spectrum for mining vessel.
2.2! Propagation modelling
The location of the proposed mining operation (see Figure 3) is a seamount formed by
volcanic activity. Geological information for the area indicates that the seabed is
primarily a hard massive sulphide material with some basalt, but that at depths greater
than 1650 m this is "covered by an apron of dark gray volcanic sandy silts and silty
sands" (Coffey Natural Systems, personal communication, July 2008). For comparison
purposes propagation modelling was carried out using two seabed models: A. a basalt
seabed at all water depths, and B. a basalt seabed for depths less than 1650 m, and a sandy
silt seabed for greater depths. A basalt seabed is highly reflective to sound, so model A
represents the worst-case situation.
Geoacoustic parameters appropriate for these materials are given in Table 2 (based on
Jensen et. al. 2000). Propagation model runs were carried out using bathymetry profiles
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