Figure 6. Sound pressure level produced by dredge bucket closing as measured over ambient conditions and its attenuation with distance from the point source in Cook Inlet, Alaska

ERDC TN-DOER-E14

August 2001

a. Ambient conditions

b. Attenuation with distance from the point source

Figure 6. Sound pressure level produced by dredge bucket closing as measured over ambient conditions

and its attenuation with distance from the point source in Cook Inlet, Alaska

903.1 Hz) compared with other dredging events (Table 3). Figure 6 illustrates the attenuation of

sound pressure levels measured over distance (150-5,500 m) for this event.

Winch In/Out: Winch noise is produced as the bucket is either lowered through the water column

or raised to the surface in combination with the derrick as it swings over to the barge in preparation

to release material into the hopper barge. SPL generated by the operation of the winch and derrick

movement measured over peak ambient conditions is shown in Figure 7. At the 150-m listening

station SPL was measured at 116.6 dB re 1 Pa-m at a peak frequency of 34.99 Hz, or 43.4 dB re

1 Pa-m above peak ambient conditions. The lowest SPL for winch noise occurred at 1,300 m at

94.7 dB re 1 Pa-m at a peak frequency of 47.1 Hz, a reduction of 21.8 dB re 1 Pa-m. SPL

measurements did increase somewhat from 1,400 m (96.3 dB re 1 Pa-m) to 2,000 m (103.2 dB re

1 Pa-m). This increase at the 2,000-m range was still 13.3 dB re 1 Pa-m lower than readings

taken at the closest listening station. Figure 7 illustrates the attenuation of SPL (dB rms) from the

closest (150 m) to the farthest (2,000 m) ranges. Winch noises produced lowest peak frequencies

compared with other dredging events (33.6 to 56.5 Hz).

Dumping Material into Barge: Sounds associated with this aspect of dredging were dependent

on the volume of material in the barge at the time the measurements were taken. Material placed

into an empty or partially full barge frequently generated audible sounds, whereas material placed

upon existing material sometimes did not, probably due to sounds being buffered as they were

transmitted through the hull. At the 150-m listening station, SPL was 108.6 dB re 1 Pa-m at a peak