In the Yarra River, works involve the installation of specially designed steel protection plates to go over and protect the Melbourne Water Hobsons Bay Main Sewer, which runs across the Yarra River just south of the West Gate Bridge.
A support frame measuring about 23 m in height has been purpose built to accurately place these protection plates over the sewer pipeline. This support frame, called the ‘Yarra Tree’ is a stable, non-propelled structure that will be securely installed in the riverbed during operations. It will be lifted and placed in position by the project’s existing grab dredge and crane barge. Most of the frame will be underwater and only an upper section will be visible during operations.
It is expected that 44 steel protection plates with an integrated concrete cover (each plate measures 6 m by 3.5 m and weighs about 25 tonnes) will be used to cover the sewer pipeline across the Yarra River. Rock berms will be placed on either side of the sewer in addition to the protection plates. These measures will protect the sewer in the unlikely event of an anchor drop or drag by a vessel.
To date, capital dredging as part of the Channel Deepening Project is 75% complete and is on schedule to have major dredging completed by August31, 2009 and the overall project completed by December 31, 2009.