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“It was in the term and condition of our biological
opinion from NOAA fisheries that we install and utilize these as a
minimization measure,” said Bauman. “We also consulted with U.S. Fish and
Wildlife for bull trout in the McKenzie. So, if there are bull trout in the
area, hopefully these will be beneficial to them as well as any other trout
and non-game species.”
Bauman said this is the first time ODOT is using the
bubble curtain to lessen the impacts of driving pile during a bridge project
and it won’t be the last.
“We expect to see this term and condition more
frequently on future consultations,” said Bauman.
Pile type a factor
The level of impact to fish habitats depends on what
type of pile is being used, in this case ODOT is using steel pile, the type
and hardness of the bedrock, how easy it fractures, and how deep the pile is
driven before resistance.
The pile driving for the Willamette River work
bridge is finished and the contractor has started driving pile for the work
bridge at McKenzie River.
The work bridge is parallel to the detours bridges
that are being constructed. Driving pile into the ground takes a tremendous
amount of force and maintaining separation between the pile and the bubble
curtain is a challenge. Several curtains were smashed or ripped to shreds
during construction of the Willamette River work bridge.
“The contractor had to redesign until they got one
that worked,” said Bauman.
The disastrous effects of underwater shock waves
received attention in California when pile driving activities resulted in
large fish kills. As a result, research has shown that transmission of
acoustic waves from steel pile driving into the water causes expansion and
compression of the swim bladder. This led to either mortality or a change in
the behavior pattern of the fish or adversely impacted the fish.
The bubble curtain information ODOT is using is
based on research from Frasier River Pile and Dredge Ltd., a Canadian outfit
that produced a document called Bubble Curtain Systems For Use During Marine
Pile Driving. The report was in response to fish kills during pile driving
in March 2000 off the coast of Vancouver, British Columbia.
The device is not designed as a containment system.
There are confined bubble curtains and un-confined bubble curtains. A
confined bubble curtain is long with plastic or other material that makes a
solid wall so bubbles don’t get rushed downstream. The one at the McKenzie
and Willamette Bridge project does not extend to the bottom of the stream.
It works to dissipate acoustic energy into the water.
“This is a relatively new development in our realm
of things,” said Bauman. “A problem was identified and in a short amount of
time a solution was developed. We are seeing it implemented and it is a
great minimization technique.”
Dan E. Knoll represents the Oregon
Department of Transportation.
Reprinted from Better Roads Magazine
August 2004 |
