Regulating underwater noise during pile-driving
17 July 2018
Pile driving generates some of the most disruptive underwater noise. We asked Mathias Andersson, a Swedish fish ecologist and bio-acoustician with the Swedish Defence Research Agency, about the current state of pile-driving regulation around the world. Andersson has been studying the impact of sound on marine life for a decade and recently published A framework for regulating underwater noise during pile driving, an extensive review of scientific literature on underwater noise from pile driving and its effects on marine life.
Pile driving involves repeatedly pounding long pipes—made of wood, steel or reinforced concrete—into the ocean floor to support other structures, such as bridges, piers or turbines. To drive the piles down, a hydraulic hammer strikes their tops repeatedly at a rate of once per second. Depending on the project, it can take up to 5,000 strikes per pile. The noise can reach levels high enough to disturb, injure or even kill some marine animals.
What is pile driving used for, and why is it necessary?
Pile-driving is a well-established method of building a structure on the sea floor. For example, if you want to build a wind turbine, you can hammer the metal piles down to 30 or 40 metres depth and the structure will be quite stable. Any time you want to attach something to the sea floor, pile driving is the solution. It has probably been used to build most harbours in the Arctic. The downside is it makes a lot of noise in the water.
What sort of regulation is there around pile driving?
It is mixed—some countries are quite progressive, others less so, and there is no single international agreement. Taking Sweden as an example, environmental law here says you should use the precautionary principle: if the effects of an activity are unknown, you shouldn’t do it. As well, steps need to be taken to minimize the impact on species that are on the International Union for Conservation of Nature (IUCN) red list, such as the harbour porpoise. Sweden has signed various international treaties, like the HELCOM (Baltic Marine Environment Protection Commission) treaty and the OSPAR (Convention for the Protection of the Marine Environment of the North-East Atlantic). But there is no single global agreement when it comes to pile-driving noise and animals.
Should we have something more unified among countries?
In my view, no. I think each nation needs to deal with its own issues. Finding a worldwide solution will never happen because there are simply too many regional differences in terms of species and activities. How far and how quickly sound travels in water depends on local conditions as well. A generic threshold wouldn’t be helpful.
One multinational initiative we do have is the International Council for the Exploration of the Seas (ICES) impulsive noise events registry. It’s not regulatory, but it supports HELCOM and OSPAR by collecting data on events like pile driving, controlled explosions and other activities to increase knowledge of trends in underwater noise. It will also be used in the future to evaluate the pressure of impulsive sound on the marine environment, according to the EU’s Marine Strategy Framework Directive (MSFD). In this work, a threshold for noise will be developed, not with regards to individual piling activity but in terms of the cumulative impact on a regional scale.
I would say in terms of mitigation techniques, the leaders are Germany, the UK, the Netherlands, and to a slightly lesser extent, Denmark—and because they’re ahead in mitigation, it’s also natural for them to have more developed regulations. Here in Sweden, we have just one big offshore wind farm and three small ones, so there hasn’t been a big debate, though pile driving also occurs in the construction of harbours here.
Are there new technologies that can make pile driving less disruptive to marine life?
Yes, several. One approach is to use cofferdams, which involves placing the piles inside tubes to help keep the noise from travelling. Or you can have a bubble curtain around the pile driving, which involves a hose at the bottom that releases bubbles into the water, or you can erect nets with plastic bubbles. Another approach is to alter how you hammer: if you hammer more forcefully, the work will go more quickly, but it will be louder. If the maximum sound level is more important than the duration, you can hammer more softly—but it will take more strikes and more time to get it done. The choice depends on what local species you want to protect. That’s a good example of why it’s so difficult to come up with a global or even a national strategy.
If these mitigation strategies exist, why aren’t they used more often?
Mitigation costs money—for example, it can make construction take longer—so there has to be an incentive for industry. We can learn from Germany: it set a very strict threshold for injury of the harbour porpoise, in terms of sound level, and industry was not able to comply right away. But after a few years of research and technical development, companies now have the technology to comply with the set threshold. I think the lesson is that if a government is going to set a high standard, it has to be willing to help pay for some of it.
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