Assessment of Noise Transmission Mechanisms and Approaches to Mitigate Underwater Noise Associated With Installation of Monopile Foundations for Off-Shore Wind Turbines

This paper reviews our investigation of the underwater noise mitigation technologies applicable to the installation of large monopile foundations. The purpose of this effort is to provide technical background and understanding of the issues surrounding underwater noise generation associated with monopile foundation installation in order to better inform future decisions regarding the need for and effectiveness of proposed mitigation plans and technologies. The paper outlines the fundamental physics basis for the generation and transmission of acoustic energy into the water through three primary paths including airborne-to-water, direct radiation from the wetted structure into the water column, and structure-to-seismic coupling and radiation. Descriptions of the modeling approaches used to assess the significance of each path are presented along with the findings. The models for each path are integrated into a layered-media propagation code that calculates the spreading and distribution from each path, individually and combined, into the water column. The paper then presents the predicted performance for a range of mitigation approaches selected for this study, which focus on the controlling mechanisms of noise transmission. These cases range from highly idealized treatment configurations, intended to bound the performance of any treatment option, to models representing more practical engineering implementations appropriate to the scale of the these structures and the environment. This study was funded by the Department of the Interior Minerals Management Service.