Offshore Wind Power Projects in the Great Lakes - Ministry of ...

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Offshore wind power projects in the Great Lakes: Background and science considerations for fish and fish habitat avoidance in fish and other aquatic organisms (e.g. Gerlotto & Freon 1992, Misund et al. 1996), but in conjunction with other noises from construction it could potentially have more significant, cumulative effects on animals. The sound levels produced by motor-powered vessels typically increases with ship size, while the frequency of the emitted sound tends to decrease with increasing vessel size (Richardson et al. 1995). As a result, the low-frequency engine noise from large barges and freighters could pose a greater risk to nearby fish than the running noise produced by smaller boats. Very large vessels will necessarily be required to transport the large turbine components and assembly equipment such as cranes and pile drivers to the project site. While this cannot be avoided, there are some options that might reduce the impacts associated with large vessel traffic. The working components of all construction-related vessels should be routinely inspected and serviced to ensure that they are in good repair and running efficiently, as this can help to cut down on running noise. Propellers and thrusters contribute the most to underwater noise levels, so regular maintenance of these components is particularly important (Spence et al. 2007). These parts can also be modified or designed to further reduce noise levels, although the costs of doing so is often non-trivial. An alternative option is for larger vessels to be towed to the project sites by smaller ships or tug boats that produce less harmful low-frequency sound levels, or to moor large vessels once they are in place so that thrusters aren’t needed for dynamic positioning. In addition, because boat noise increases with increasing speed, vessel operators travelling to and from wind power project sites could limit their running speeds to minimize noise disturbance— particularly in sensitive habitat areas (Evans 2003). Vessels used for wind turbine construction could also be routed along pre-specified transportation corridors that avoid areas known to house critical fish habitat or species of concern. This precautionary approach was employed during construction of both the Horns Rev and Nysted wind power projects, where all transport and construction vessels were routed around nearby nature protection areas (Kjaer et al. 2006). Similar recommendations or requirements could be proposed for proponents involved in offshore wind development in the Great Lakes to avoid unnecessary disturbance to areas of ecological significance or fish species of conservation concern. Aquatic Research and Development Section 28
Offshore wind power projects in the Great Lakes: Background and science considerations for fish and fish habitat Dredging noise Unlike monopile foundation installation, gravity base foundations do not require noisy piledriving operations, and for this reason might be preferable from a noise-reduction perspective. However, extensive sediment dredging and levelling is often required to prepare the lake bed for gravity base foundation installation, and these activities could still generate a significant amount of low-frequency underwater noise. While dredging noise has not been the focus of many environmental impact studies to date, it might be plausible that devices otherwise employed to mitigate dredging-related increases in turbidity—such as air bubble screens or cofferdams (see below) –could also function to reduce noise levels. However, to our knowledge there have been no attempts made to measure or document the potential of these devices to attenuate noise specific to dredging operations. The choice of dredging equipment can also affect the noise levels generated during these operations. Suction hopper dredges create significantly more sound than mechanical or bucket dredges owing to the noise produced by the powerful onboard pumps and generators required to vacuum up the sediment (Spence et al. 2007). Sounds associated with bucket dredges include noise from winches and derrick movement and from the bucket striking and digging the sediment, which are not necessarily high impact sound sources. Thus, if dredging noise is a concern in certain areas, mechanical dredges might be the preferred option although factors like sediment type, efficiency of removal, and turbidity levels would need to be considered as well. Noise from geophysical survey activities required for site selection Another wind power project-related activity recently flagged for underwater noise concerns is the geophysical or geotechnical assessment required for site characterization during the pre- construction phase (Nedwell & Howell 2004). These surveys are typically conducted using seismic techniques or boomers and sparkers, both of which can produce significant amounts of noise. Ramp-up or slow start methods similar to those proposed to warn mobile species of pile driving operations could be adapted to reduce the potential for injury associated with these activities as well. This mitigation strategy is already recommended in guidelines for exploratory air-gun seismic surveys in marine offshore areas (Canada-Newfoundland and Labrador Offshore Petroleum Board 2008). However, it would be best for developers to limit the use of these high- Aquatic Research and Development Section 29
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