The “cofferdam” is coming to a river near you

Docklanders will soon have a bird’s eye view of an interesting piece of engineering when Melbourne Water begins replacing Melbourne’s 100-year-old main sewer under the Yarra River.

The 140-metre section of new pipe will lie under the riverbed just upstream of the Charles Grimes Bridge, it is being replaced as part of a $220 million project involving 2.3 kilometres of sewer from Docklands to Port Melbourne.

Yarra’s Edge residents are already aware of the project because of concerns surrounding blocked pedestrian and cycle access to the southern bank of the river.

Melbourne Water and contractor John Holland are holding a public information session to explain the project and address this issue at The Hub, Waterview Walk, on June 29.

The sewer replacement under the river will be done in three stages and will involve a “wet cofferdam” construction method.

A cofferdam uses steel sheets to build an enclosed area in which to work.  Once constructed, specialist divers will work underwater within the structure undertaking the installation of pipe supports, steel pipe, sealing and protection works.

Docklanders will notice a large floating barge with a crane which will be used to install the cofferdam and then service the works within the cofferdam.

A third of the Yarra River will be closed to marine traffic for each of the three stages of work, with each stage expected to take about eight months to complete.

A river traffic management plan will be implemented for each stage to ensure the safety of river users. This plan has been consulted widely with commercial and recreational river users and approved by relevant authorities.

Construction methods for the river crossing have been designed for a one-in-100 year flood and king tide event.

The Melbourne Main Sewer Replacement is being constructed by John Holland on behalf of Melbourne Water and will be completed during 2012. The Yarra crossing will be completed by mid-2011.