The new pipeline and its associated infrastructure and systems will carry the desalinated water from Kurnell, across Botany Bay, to the city’s main water supply, the City Water Tunnel at Erskineville. Water supplied from the desalination plant will increase the total volume of water available to all customers across the whole Sydney Water area, including the Blue Mountains, the Illawarra and Sydney.

The desalination plant will be capable of producing up to 250 megalitres of water per day (ML/d), and will be able to be modified to produce 500 ML/d if required. With a nominal capacity of 500 ML/d, the new pipeline will be able to operate for short periods at up to 550 ML/d, to allow the flow to integrate into Sydney Water’s existing water supply network.

The pipeline and associated infrastructure is under construction by the Water Delivery Alliance, made up of Bovis Lend Lease, McConnell Dowell, Kellogg Brown & Root, WorleyParsons, Environmental Resources Management and Sydney Water Corporation. All of the parties to the alliance are responsible for the works to be designed, constructed and commissioned.

Project scope

The main project works are:

• A drinking water pumping station on the site of the desalination plant in Kurnell.
• Infrastructure from the pumping station to the existing water supply system in Erskineville, via Silver Beach and Kyeemagh, including associated connections and flow and pressure controls.
• Marine works consisting of twin 7.5km long, 1,400 mm diameter steel pipelines across Botany Bay;
• Approximately 6.4 km of 1,800mm diameter mild steel cement-lined (MSCL) onshore pipe, slipped inside 2,100 mm diameter concrete pipes and installed by trenchless microtunnelling; and,
• Approximately 3 km of 1,800 mm diameter MSCL onshore pipeline, installed by dig and lay conventional trenching methods, with sheetpile and trench box shoring as required.

Design and construction

Following the award of the project to the Water Delivery Alliance in June last year, the team spent six months on the design and development phase. In December 2007 the project development report was formally accepted, with completion scheduled for December 2009.

Project design is well advanced and works have commenced with bored piling at the delivery water pump station and sheetpiling at cofferdams for the temporary tunnel shafts. The major items of plant and materials have been procured, including the pipe and lay barge for the Botany Bay crossing and three tunnel boring machines (TBMs). Pipe deliveries have commenced and the first of the TBMs has also been delivered, allowing the driving of the first pipejack tunnel to commence by the middle of this year.

Challenges

Given the size of the project, and the locations it must traverse, considerable pre-planning and consultation has taken place with various regulatory authorities and the many wider stakeholders, including the community that will be affected by construction operations along the pipeline route. The Water Delivery Alliance have in place a structured team of proven community and environmental personnel, providing support to the wider team and ensuring that all approvals have been obtained and that stakeholders are well informed of both the program and methods that the activities that will take place in their vicinity. Community feedback has been encouraged and adjustments to the method or timing of activities have been made to accommodate their concerns, wherever possible.

The pipeline will have various work fronts when in full construction operation. These will be in three main areas of tunnelling, pipelaying from a barge and conventional onshore pipeline trenching. It is anticipated that the workforce will increase considerably over the third and fourth quarters of this year, peaking in the order of 500. Tunnelling and barge operations will work on a number of rostered shifts requiring additional workforce.

This project will be breaking new ground to achieve the distances set for the tunnel drives, while the sizing of the laybarge operations require laying twin 1,400 mm diameter pipe in a pre-dredged trench across the vast Botany Bay waters which is likely to be challenging. Some of the tunnels will be the longest undertaken by pipejack method in Australia and potentially within the Southern Hemisphere. No twin pipeline of this diameter, laid simultaneously from a barge for 8 km, has been executed previously in Australia.

Notwithstanding the considerable challenges that exist, the Water Delivery Alliance team are well skilled and committed to overcome them, utilising innovation and a team culture that is striving for the completion of this project on time, in a safe manner and surmounting technical challenges to break new ground.