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

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Offshore wind power projects in the Great Lakes: Background information and science considerations for fish and fish habitat Table 1. Mitigation strategies for potential impacts of offshore wind power projects to fish and fish habitat in the Great Lakes. This table follows a similar structure to Table 1 in the first report outlining potential effects (Nienhuis & Dunlop 2011). Effect Disturbance or injury to fish from underwater noise during construction Release of contaminants Associated wind power activity Construction (mainly pile driving) Construction (dredging, cable trenching) Predicted magnitude of effect without Mitigation strategy mitigation (uncertainty) High (Low) • Warning or deterring fish from area in advance of pile driving or dredging • Reducing noise transmitted into surrounding aquatic environment • Alternatives to pile driving • Reducing disturbance from boat noise • Type of dredge used High (Low) • Project location Examples of specific mitigation measures • Slow or soft start; Strobe lights • Air bubble curtains; Isolation casings and cofferdams; Noise dampening devices; Reducing number of pile strikes by using pre-drilling or water jetting • Vibropiling; Press in piling • Limit vessel speed and route • Use mechanical dredges instead of suction hopper dredges • Avoidance of areas with high concentration of contaminants Examples of potential limitations for application in the Great Lakes • Strong currents and waves and deep waters might limit applicability of bubble curtains; Cofferdams more difficult to install and dewater in deep water • Not feasible for all substrate types; Vibropiling might increase turbidity; Press in piling currently limited to small monopiles • Mechanical dredges increase turbidity • Sites with low contaminants might have high biodiversity, valuable tourism operations, etc. Aquatic Research and Development Section 10
Offshore wind power projects in the Great Lakes: Background information and science considerations for fish and fish habitat Effect Release of contaminants cont. Disturbance to fish from underwater noise during operation Disruption of fish distribution or migration and harm to sensitive life stages (eggs and fry) from electromagnetic fields Associated wind power activity Construction (dredging, cable trenching) Turbine operation Operation of submarine power cables Predicted magnitude of effect without mitigation (uncertainty) Mitigation strategy High (Low) • Use barriers that minimize spread of contaminated sediments into Medium (High) Medium (High) surrounding aquatic environment • Reduce sounds from gearbox • Reduce rotational speed of turbine blades • Choice of foundation type • Use noise or vibration minimizing materials • Reduce strength of electromagnetic field emitted into aquatic environment • Alter cable route Examples of specific mitigation measures • Silt curtains and other types of turbidity barriers • Direct driven generators (no gearbox needed) • Variable speed turbines; Pitched blades • Concrete gravity instead of steel monopole • Insulate gearbox, below water structures, and foundation (e.g. insert layer of foamed polymer between tower and water) • Cable burial; Cable armouring or sheathing; Core twisting • Avoid areas or habitats with sensitive species or life stages Examples of potential limitations for application in the Great Lakes • Strong currents and waves might limit use • Technology not yet widely available for large turbines • Tradeoffs with other effects of gravity foundations such as increased habitat loss • Cable burial will increase risk for other impacts such as increased turbidity and habitat loss from dredging; Given long cable routes, burial might not be feasible in all cases Aquatic Research and Development Section 11
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Offshore Wind Power Projects in the Great Lakes - Ministry of ...

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