Prevention Measures for Piling Operations used on Offshore Wind Farms
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- Sep 17, 2019 7:08 pm GMT
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Offshore Piling causes strong impulse underwater noise that’s potentially harmful to the marine environment, in particular to marine mammals. The blow rates of a hammer are usually between 15 to 60 per minute and the total of blows may vary from 500 to more than 5000, with frequencies between 100 Hz and 400 Hz depending on the soil properties and on the required penetration dept of the pile.
Underwater sound behaves very differently compared to sound in the air, as sound travels faster in water than in air (~1500 m/s vs. ~340 m/s). Noise is perceived more intensely underwater and can propagate over greater distances. To protect the marine fauna, various prevention methods are employed which are launched prior piling operations.
The FaunaGuard The FaunaGuard is an acoustic deterrent device which creates a noise that positively deters the animals from the work location. The philosophy of the FaunaGuard, which is developed by Van Oord and SEAMARCO, is to make optimal use of the behavioral effects induced by specific sounds with different species or species groups. This causes the area in and around the work location to be (temporarily) unattractive to marine fauna, and so prevents more serious effects related to high peak energy events. As such, the FaunaGuard aims to utilize mild behavioral effects (moving from an area) just before piling, to prevent more serious physiological effects on marine fauna during the piling.
Bubble Curtain A bubble curtain can be described as a screen of bubbles around the working area. Underwater bubbles can inhibit sound transmission through water due to density mismatch and concomitant reflection and absorption of sound waves. A bubble curtain is produced by heavily perforated hoses which are positioned around the construction site as a ring prior to piling operations. An excessive amount bar of oil-free compressed air is pumped into the hoses, which escapes through the holes in the hoses according to a well-defined pattern. The result is a curtain of millions of small bubbles that rise to the water surface, forming a kind of whirlpool around the construction site. The air bubbles change the density of the water and thus break down the sound waves, thereby protecting marine life from piling noise.
Find out more on how offshore wind farms are build from the Building an Offshore Wind Farm: Operational Master Guide: