Managing the Impacts of Underwater Sound

Acoustic risk assessments to support your offshore construction project and mitigate environmental impact

Human activity from offshore construction for oil and gas platforms and wind farms, dredging, shipping, and military and other sonar or seismic surveys, generates underwater sound. The resulting effects on marine life can range from very subtle behavioral reactions to physical damage and even death at very high exposure levels. In response, international bodies, such as the UN, stress the need for regulatory control and Europe and the United States require developers to consider (e.g. via an Environmental Impact Assessment) and manage sound-related impacts. This often entails the modelling of the underwater sound and, if a significant impact is discovered, the development of a measurement to minimise the sound exposure to marine life.

The experts at DHI advise industry and policy makers on noise-related issues with systematic risk assessments that uniquely integrate biological expertise with advanced modelling capabilities to enable a more realistic exposure assessment. DHI uses underwater acoustic modelling to calculate sound ranges and sound maps showing the distribution of the sound field in a study area and beyond.

Example of a baseline ABM for bowhead whales in the Chukchi Sea.

Typically, sound maps are used in conjunction with data on the distribution and abundance of fish and marine mammals to provide an estimate of the number affected. The impact is then extrapolated using empirical data on hearing sensitivities and demonstrated effects. However, at DHI, we have moved beyond the above-mentioned static analysis to the use of agent-based models which take into account the movements of mammals before, during, and after noise exposure. This dynamic approach to sound exposure modelling avoids related overestimation of impacts (takes) by, for example, allowing for avoidance behaviour of effected wildlife. 

Visualisation of the Northern Right Whale spring migration with added pile driving noise and assumed avoidance.

Applied early in the project cycle, these tools allow for optimised design of marine structures that reduce sound-related impacts on the marine environment. This strongly supports the consent process by minimising the environmental footprints and benefiting marine inhabitants.
A representative example of DHI’s unique approach is the Mobile Animal Ranging Assessment Model for Biological Studies (MARAMBS). MARAMBS is a web-based integrated modeling tool that simulates the behaviour of seabirds and marine mammals and models their responses to stressors like underwater noise and oil spills. With MARAMBS, environmental issues can be identified early / throughout the project cycle to allow for mitigation solutions that ease environmental approval processes and reduce related scheduling and investment risks. MARAMBS can be applied to oil and gas exploration, offshore wind farm construction, shipping, dredging and other human activities.