The Port of Rotterdam is expanding to meet the growing demand to accommodate large cargo vessels. The construction of Maasvlakte 2 (MV2) started in September 2008.
One of the licensing conditions is the monitoring of the underwater sound produced during its construction, with an emphasis on the establishment of acoustic source levels of the trailing suction hopper dredgers (TSHDs) during their various activities: dredging, transport and discharge of sediment.
TNO (Netherlands Organisation for Applied Scientific Research) Sonar and Acoustics carried out measurement and analysis activities for this monitoring. During an initial measurement campaign in September 2008, background measurements were performed in the absence of dredging. Source level and background sound measurements were made in the dredging area while MV2 dredging activities were underway in September 2009.
In a final phase of the study, possible effects of underwater sound on marine fauna were considered for scenarios with and without dredgers. In this article, the principal results of the research are described and discussed in the context of the effects predicted in the Environmental Impact Assessment.
Maasvlakte 2 is the Port of Rotterdam Authority’s port extension project west of the existing Maasvlakte. The project area comprises approximately 2,000 hectares gross of which 1,000 hectares is the net infrastructure. The first phase of the project was finished April 2013.
To determine the effects of underwater sound generated by dredgers on fish and marine mammals, model calculations were made for the Environmental Impact Assessment (EIA) on the basis of the best knowledge available at the time. From these calculations it emerged that the sound level below the water in the vicinity of dredgers can exceed the hearing threshold of fish and marine mammals.
However, at a distance of more than a few hundred metres away from the vessel, it was thought that the threshold for avoidance would not be exceeded.
On that basis, it was concluded in the EIA in 2007 that the area affected is negligible in size by comparison with the total space that is used by the animals as feeding grounds and migration areas.
This article focusses on the provision included in the Soil Removal Permit for the construction of Maasvlakte 2 on the monitoring of underwater sound related to the construction activities. The research conducted in the context of the aforementioned provision focussed on finding answers to the following questions:
– What is the source level of the underwater sound of the deployed dredgers during the various phases of the dredging cycle?
– How does the dredger sound relate to the background sound?
– To what extent are the effect contours (determined on the basis of the predicted received levels, weighted on the basis of the hearing sensitivity of the relevant species) related to the contours for a possible impact on marine organisms predicted in the EIA for a possible impact on marine organisms?
The Port of Rotterdam Authority does not have any extensive expertise in the field of the recording of underwater sound levels or processing measurement data and has therefore asked TNO (Netherlands Organisation for Applied Scientific Research) to elaborate a measuring strategy for the monitoring requirements stated in the permit. The strategy has been included in full in the MV2 Construction Monitoring Plan. In this article, the principal results of the research will be described and discussed in the context of the effects predicted in the Environmental Impact Assessment.
Press Release, September 5, 2013