Abstract
Construction of fixed foundation offshore wind farms involves the installation of large diameter steel piles using high-energy hammers. These piles are installed via vibratory or impact pile driving or using a combination of these methods to drive the pile to its desired installation depth. This report focuses on impact pile driving, which is when the top of the pile is struck repeatedly by a hammer to force the pile into the sediment (much like a hammer hitting a nail into a wall).
There are few studies that investigated substrate-borne particle motions from offshore wind farm activities. The amplitudes and frequency content of construction (impact pile driving) and operations were measured at select locations, but source models were not developed (e.g., HDR 2019; Potty et al. 2020; Sigray and Andersson 2011; Yang et al. 2018). Importantly, results from recent studies funded by the Bureau of Ocean Energy Management (BOEM) show that, at ranges of 500 m and 1,500 m, particle acceleration levels measured on the seabed during pile driving (up to approximately 300 Hz) were well above the behavioral sensitivities for fishes that primarily detect particle motion, such as Salmo salar (Atlantic salmon), Pleuronextes platessa (plaice), Limanda limanda (dab), and Gadus morhua (Atlantic cod) (HDR 2019; 2020). Such results suggest that economically and environmentally important fish species living close to the bottom can potentially detect such signals.