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Environmental considerations

Protecting the environment

Measures have been developed for the construction of Stages 2 and 3 to manage the noxious weed Caulerpa Taxifolia, manage road runoff and water quality via detention basins and to protect the Port River's dolphins.

Port River dolphins

The department has considered the potential impact of construction activities on the Port River's dolphins. Although the likelihood of injuring the dolphins during construction is extremely low, the department has sought the advice of local dolphin expert Dr Mike Bossley to make sure the most current information was incorporated into contract documentation. In addition, the department will ensure that the contractors comply with comprehensive environmental management systems to minimise any possibility of risk or injury to the dolphins.

In addition, Abigroup Contractors researched best management practices to minimise the potential impact on the Port River dolphins during construction of the Port River Expressway Road and Rail Bridges. The comprehensive environmental management systems and controls implemented during construction, especially the installation of a bubble curtain in the river surrounding the work zone, proved effective in reducing maximum noise amplitude which presented the greatest risk to the dolphins.

A PhD student was engaged to review the natural movement patterns, distribution and behaviour of inshore dolphins in relation to percussive piling during bridge construction. This review established that the bubble curtain was effective in reducing maximum noise amplitude by a maximum of 10 Hz; also there was no direct fish kill, dolphin mortality or temporary and/or permanent hearing impairment imposed to dolphins as a direct, or indirect, result of Abigroup's work practices.

In short, the thesis review revealed that the natural movement patterns, distribution and behaviour displayed by inshore dolphins during percussive piling varied to include increased swimming speeds with increased blow rates, decreased surfacing patterns, shielding of young, tail slapping, and departure from the ensonified area during the act of piling; but that these behaviours reverted to normal when percussive piling was not in progress.

Despite the variations from normal behaviours, there was an increase in dolphin sightings observed at both Lipson Street Wharf and Snowden Beach during the percussive piling phase of construction in comparison to a previous thesis study completed pre-construction.

The Port River dolphins continue to be regularly sighted in and around the construction site and within Inner Harbour.

Bubble Curtain

During the construction of the Canada Place Cruise Ship Terminal in Vancouver in 2000, a Bubble Curtain System was developed following observations of considerable ocean fish mortalities attributed to extremely high underwater shock wave overpressures created during pile driving. The bubble curtain method developed consisted of a ring of bubbles placed around the steel pile that dissolved shock waves while the pile was hammered into the sea bed. A pile is a vertical support member for a bridge.

The bubble curtain method developed consisted of a circular or square shaped air distribution manifold made of rubber, plastic, or steel tubing which surrounded the piling at various points below the water surface. An effective bubble curtain system distributes air bubbles around 100% of the perimeter of a pile over the full depth of the water column while it is being driven. The main components include a high-volume air compressor, primary feed line, and a distribution manifold.

The Oregon bubble curtain mode was adapted to suit the Port River Expressway Road and Rail Bridge construction site, with particular regard to the uniqueness of the Port River Dolphins.

During pile driving, each individual pile was encircled by a bubble curtain originating from an air distribution manifold made up of an air hose that was anchored or weighted to the river bed. The compressor was mounted on a barge and connected to the manifold by the air hose.

See below for an outline of the bubble curtain and a photo taken during its use in the Port River.

bubble_curtain_1bubble_curtain_2
Click on image to enlarge

Water Restrictions

The Environmental Protection Agency (EPA) requires that dust mitigation measures (such as the use of water) are in place during construction works associated with Stages 2 and 3 of the Port River Expressway project to prevent air pollution. As such, water will continue to be used in construction works to prevent dust which is a health and safety risk for surrounding residents, businesses and local flora and fauna.

Water use is being carefully monitored to minimise wastage while meeting EPA requirements. Although extremely dry conditions have been experienced to date, there have been minimal complaints regarding dust during construction.