Dredging Sound Levels, Numerical Modelling and EIA

This paper was initially presented at the CEDA Dredging Days in November 2015 and was included in the conference proceedings. It is reprinted here in an adapted version with permission. Underwater sound from anthropogenic sources and its potential adverse effects on the marine environment is a topic of much global interest. In recent years, there is recognition that sound from some shipping and dredging activities could have impact on the marine environment, particularly in deep sea areas where low frequency sound can travel long distances. Dredging activities emit underwater sound in the marine environment. Monitoring of sound from dredging equipment is occasionally carried out for an individual project and usually only to support research. Because of the way in which sound interacts with the marine environment, the propagation of sound from individual dredging vessels will vary depending on the activity and location of the dredging. The level of sound at the dredger, termed the source level, will also vary between dredgers due to a range of different environmental and mechanical factors. Thus, applying this monitoring information to other projects is not always straightforward. The article presents an overview of known sound source levels for various dredging equipment and activities and it describes a method used to extrapolate source levels based on the pump power when a source level has not been directly measured. Furthermore, the article explains how information can be used to predict the propagation of sound from dredging activities using numerical modelling tools for Environmental Impact Assessment (EIA) purposes.