Environmental Engineering Reference
In-Depth Information
potential impacts on sea turtles of underwater explosives. Although explosives produce
greater sound pressures than pile driving and are unlikely to be used in most ocean
energy installations, studies of their effects provide general information about the peak
pressures and distances that have been used to establish safety zones for turtles.
Wahlberg and Westerberg (2005) compared source level and underwater mea-
surements of sounds from offshore windmills to information about the hearing capa-
bilities of three species of fish: goldfish, Atlantic salmon, and cod. They predicted
that these fish could detect offshore windmills at a maximum distance of about 0.4
to 25 km, depending on wind speed, type and number of windmills, water depth, and
substrate. They could find no evidence that the underwater sounds emitted by wind-
mill operation would cause temporary or permanent hearing loss in these species,
even at a distance of a few meters, although sound intensities might cause permanent
avoidance within ranges of about 4 m. They noted that shipping causes considerably
higher sound intensities than operating windmills (although the noise from shipping
is transient), and noises from installation may have much more significant impacts
on fish than those from operation.
In the Environmental Assessment of the proposed Wave Energy Technology (WET)
Project, the Department of the Navy (2003) considered the sounds made by hydrau-
lic rock drilling to be detectable by humpback whales, bottlenose dolphins, Hawaiian
spinner dolphins, and green sea turtles. Assuming a transmission loss due to spherical
spreading, drilling sound pressure levels of 160 dB re 1 µPa would decrease by about
40 dB at 100 m from the source. They regarded a SPL of 120 dB re 1 µPa to be below
the level that would affect these four species. In fact, they reported that other construc-
tion activities involving similar drilling attracted marine life (fish and sea turtles, in
particular), perhaps because bottom organisms were stirred up by the drilling.
There are considerable information gaps regarding the effects of noise generated
by marine and hydrokinetic energy technologies on cetaceans, pinnipeds, turtles,
and fish. Sound levels from these devices have not been measured, but it is likely
that installation will create more noise than operation, at least for those technolo-
gies that require pile driving. Operational noise from generators, rotating equipment,
and other moving parts may have frequencies and magnitudes comparable to those
measured at offshore wind farms; however, the underwater noise created by a wind
turbine is transmitted down through the pilings, whereas noises from marine and
hydrokinetic devices are likely to be greater because they are at least partially sub-
merged. It is probable that noise from marine energy projects may be less than the
intermittent noises associated with shipping and many other anthropogenic sound
sources (e.g., seismic exploration, explosions, commercial, naval sonar).
The resolution of noise impacts will require information about the device's acous-
tic signature (e.g., sound pressure levels across the full range of frequencies) for both
individual units and multiple-unit arrays, similar characterization of ambient (back-
ground) noise in the vicinity of the project, the hearing sensitivity (e.g., audiograms)
of fish and marine mammals that inhabit the area, and information about the behav-
ioral response to anthropogenic noise (e.g., avoidance, attraction, changes in school-
ing behavior or migration routes). Simmonds et al. (2003) described the types of
in
situ
monitoring that could be carried out to develop information on the effects of
underwater noise arising from a variety of activities. The studies include monitoring
