Abstract
This report presents methods, observations, data analyses, results, and conclusions from passive acoustic monitoring (PAM) surveys conducted during the operational phase of Coastal Virginia Offshore Wind Pilot Project (referred to as CVOW in this report). The monitoring was conducted under the United States (U.S.) Department of the Interior (DOI), Bureau of Ocean Energy Management’s (BOEM) Real-Time Opportunity (RODEO) for Development Environmental Observations Program.
PAM data were recorded over approximately 40 days during the operational phase of CVOW to measure underwater sound levels within the water column and seafloor sediment vibrations generated by the revolving turbines. Data were collected using one Geosled; two Ocean Bottom Seismometers; and one RBRconcerto conductivity, temperature, and depth logger deployed approximately 1.3 kilometers from Turbine A01 and 352 meters (m) from Turbine A02.
Underwater noise levels recorded during turbine operations ranged from 120 to 130 decibels referenced to a pressure of 1 micropascal (dB re 1 µPa) except during storms, when the received levels increased to 145 dB re 1 µPa. Recorded particle acceleration levels were compared to published behavioral audiograms of selected fish species (e.g., Atlantic salmon [Salmo salar], dab [Limanda limanda], Atlantic cod [Gadus morhua], and plaice) and were found to be below the respective hearing thresholds for these species. Additionally, all recorded measurements at CVOW were below the temporary threshold shift (TTS) and permanent threshold shift (PTS) onset criteria for marine mammals recommended by the National Marine Fisheries Service1 .
Operational phase sound levels recorded at CVOW were higher (10 to 30 decibels [dB]) than those previously recorded at the Block Island Wind Farm (BIWF) at frequencies below approximately 120 hertz (Hz). It is hypothesized that the higher operational noise recorded at CVOW is due to vibrations in the monopile structures. The BIWF foundations are lattice-jacket structures with four legs and have no detectable structural vibrations. It is possible that the CVOW monopile foundations vibrate when the turbines are operating, and the vibrational energy is transmitted into the water column and seabed. This hypothesis needs additional investigation, both for the structural vibration mechanisms and potential biological effects.
At frequencies above 120 Hz, CVOW’s operational phase monitoring results were broadly consistent with operational phase acoustic monitoring previously conducted at wind farms in the U.S. (BIWF) and Europe. At the BIWF, for example, underwater sound levels recorded at 50 m from operational turbines were near background (ambient) levels, and often not measurable due to other natural and anthropogenic noise (waves or boat sounds). Recorded sound levels at BIWF were also below the underwater TTS and PTS onset criteria for marine mammals. It should also be noted that lattice-jacket foundations were employed at BIWF, whereas monopile foundations were used at CVOW.
The data, results, conclusions, and recommendations presented in this report were generated for the U.S. DOI, BOEM, by the HDR RODEO Program Team under IDIQ Contract M15PC00002, Task Order 140M0118F0006.