Construction & Tool Noise
A wide variety of tools are used underwater by divers. Nedwell et al reports on measurements of the levels of noise generated by various underwater tools. In some cases the sound was measured at the diver's head at a distance of 0.5 metres from the tool; the data has in this case been corrected to give an equivalent Source Level. In some of the measurements the sound was recorded at 1 metre. Two representative sound files can be listened to by clicking the links below:
The authors note that in general, a substantial level of low frequency sound, typically from 100-1000 Hz was found. The spectra were broad however with sound energy up to frequencies of at least 10 kHz. The levels were generally found to be very high by comparison with those which would be recorded for the same tools in air. The Cox's Bolt Gun, which is a tool using an explosive charge to fire a bolt into a substrate such as the steel plate of a ship's hull, was found to generate very high levels of noise, peaking at a Source Level of over 220 dB re 1 µPa. The results presented in the paper were recorded by a hydrophone attached to the head of the diver. They have been corrected for transmission loss to give the effective Source Levels summarised below.
In addition to noise created by diver's tools, significant noise levels are also created by pile driving.
Wursig and Evans report on the noise levels generated by pile driving using a percussive hammerpile driving in Hong Kong harbour. The piling was in shallow (6-8 m) water in Western Hong Kong. The impulsive noise levels were measured on 2 days at distances of 250, 500 and 1000 metres.
The paper reports that Indo-Pacific hump-backed dolphins (Sousa Chinensis) occurred in the area before and during piling, but were less abundant immediately after it.
The data indicated a peak piling level of 80 kPa, equivalent to a SPL of 218 dB re 1 µPa. Fish kill also occurred.
For further information regarding underwater noise levels that occur during piling, consult Subacoustech report 513R0108 on 'Measurements of underwater noise in the Arun River during piling at County Wharf, Littlehampton', available to download. There are also many publications available from the Subacoustech website concerning underwater noise levels during impact piling operations.
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