Maintenance Dredging Noise Levels
Most birds are present within the designated areas of interest during low tide in the winter months. The dredging activities mostly occur around times of high water, and so these birds are not generally present during this time (PLA, 2004).
The dredging activities within this stretch of river are primarily undertaken by water injection dredgers anything up to 4 times a year. The areas being dredged are the jetties and the main navigation channels which are heavily used by many types of vessels, but mainly by the larger ships. These are short-term, infrequent events which will take place during the normal operation of the estuary, and so will be in addition to the noise produced by the passage of the vessel traffic. The birds of the SPA will already be accustomed to such background noise, and the noise levels from the dredging, particularly water injection methods, are comparable to, and often lower than, the ongoing noise from routine ship operations (PLA, 2004).
It is more likely that disturbance to the waterfowl will be caused by the movement and visual presence of such a vessel rather than the noise associated with it (Bureau Veritas-Acoustic Technology, 2003). However, given the slow-moving nature of dredgers (i.e. the lack of fast and sudden movements), it is likely that disturbance arising from their movement and presence would also be low.