To estimate the environmental risk of offshore projects and determine the potential need for mitigation measures, it is necessary to bring together the knowledge on underwater sound and its effects on the environment. To this aim, a prototype sound risk analysis framework (SORIANT), has been developed, which is aimed at assessing the impact of underwater sound on marine life. A complete risk assessment tool has been implemented in the ‘VUM SORIANT’ project, a project commissioned by Rijkswaterstaat. The tool initially focusses on determining the effects of pile driving sound during construction of offshore wind-farms on the harbour porpoise population. In the assessment process, the effects of accumulation of effects due to multiple windfarms can be accounted for over a period spanning multiple years. The current version makes use of the Interim PCOD model (Population Consequences of Disturbance), developed in the UK, which has been integrated to translate the predicted level of disturbance of construction of multiple farms to the effect on the North Sea harbour porpoise population.
The full risk-assessment chain consists of:
- A module for defining the construction process (e.g. location, duration of piling activities, type of piles).
- A sound mapping module. A source model that has be en developed within VUM for pile driving sound has now been integrated into SORIANT.
- A module for determining effect distances and number of disturbed animals.
- A module for accumulating the disturbance effects due to the construction activities of multiple windfarms (national and international projects).
- Integration with a module for determining the population level consequences for the harbour porpoise, using the Interim PCOD model (developed by SMRU Marine and the University of St. Andrews).
The risk assessment tool has recently been applied during the development of new guidelines for the licensing process for new offshore windfarm developments in the Netherlands (Kader Ecologie en Cumulatie). The effects of planned Dutch as well as surrounding developments have been assessed on the North Sea harbour porpoise population.
The SORIANT risk assessment tool has been set up to be modular and flexible, enabling an easy extension to alternative assessment methodologies for estimating population level consequences, or to different type of sources (e.g. seismic surveys, shipping, dredging, explosions and sonar), or other species (e.g. seals or fishes). Based on the risk assessment framework adopted in SORIANT, key knowledge gaps that have been identified are reported.
This report was presented at a symposium at Naturalis in Leiden on September 8, 2015. A complete report containing brief abstracts of all studies presented at the symposium can be found here.