Underwater noise measurement of dredging vessels during aggregate extraction operations

Extraction of marine aggregates in UK waters can exceed 20 million tonnes each year, with dredging activity taking place at any given point in time within the licensed areas. There is concern that the noise generated during the extraction of this aggregate has the potential to negatively impact marine species in or around the dredging area. For aggregate extraction, the type of vessel used is a trailing suction hopper dredger, which lowers a drag head and suction pipe to the sea floor to extract the sand or gravel, depositing it in a hopper on the vessel, whilst returning unwanted material and water over the side of the vessel. The potential sound sources during this type of dredging activity are numerous and this paper considers some initial results of a series of systematic noise measurements performed in shallow UK coastal waters of a large dredging vessel, under different operating configurations. The measurements are performed in such a way as to allow propagation loss and the source level to be estimated. The provisional results are compared to background noise measurements performed in the area in the absence of the dredging operations and will ultimately be used to assess the impact of the radiated noise on marine life.