UNDERWATER ACOUSTICS SURVEYING
UNDERSTANDING POTENTIAL IMPACTS OF NOISE ON SENSITIVE SPECIES
The realistic prediction of the noise propagated from construction of marine renewable devices can be used by the renewable energy industry to understand the potential impacts of noise on sensitive species at their development sites. Moving forward, this will allow project developers to develop effective monitoring and mitigation plans for underwater noise as the UK moves towards the first commercial tidal turbine arrays.
PERFORMANCE PARTNERSHIP
HR Wallingford and Loughborough University have worked in partnership to develop HAMMER, a cutting edge underwater acoustic propagation model that allows the potential impacts of noise on the marine environment to be understood.
HYDRO-ACOUSTIC MODEL FOR MITIGATION AND ECOLOGICAL RESPONSE (HAMMER)
HAMMER builds upon established parabolic equations to produce three dimensional sound maps that take into account water depth, attenuation in seabed sediments, temperature and salinity profiles which affect transmission of sound through water.
A full assessment of underwater noise impacts on sensitive marine receptors required updated modelling tools that integrate the noise propagation into the actual marine environment. Launched in 2012, HAMMER offered this technology for the first time, delivering an underwater acoustic propagation model combined with both a hydrodynamic model and a species behavior model to predict underwater noise impacts on marine life.
HAMMER has been extensively tested and has performed well against existing sound models in bench mark tests. In 2013 HAMMER was validated using pin- piling and ambient noise data collected from a boat-based hydrophone during the construction of the SeaGen tidal turbine in Strangford Lough, Northern Ireland.
Data provided by Marine Current Turbines Ltd, for both discrete frequencies and for broadband sound, i.e. several frequencies at one time, was compared to the transmission loss predicted by HAMMER. The high level of accuracy shown (90%) for all those frequencies tested indicated that the model provided realistic predictions of underwater noise propagation from the pin piling along the measured transects.
PREDICTING TRANSMISSION LOSS The modelling tool can be used to predict the transmission loss from a variety of noise sources for EIA purposes including turbine operation, pile driving, mobile vessels (e.g. dredgers), mechanical components of a device and anchor chains. Three dimensional sound maps of the underwater noise levels are produced and can be interpreted in relation to the hearing sensitivities of the marine mammals in the area to produce ‘zone of influence’ maps for each species.
HAMMER allows underwater noise levels to be mapped
ONGOING DEVELOPMENT Development of the HAMMER tool continues. In particular, research is being carried out that looks into the response of fish to noise and is being undertaken as part of a three year NERC studentship to produce data to drive the ecological response model, allowing greater certainty of the ecological impacts of underwater noise.
HR Wallinford Founding Partners
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www.wavetidalenergynetwork.co.uk
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