There are a number of desalination projects have been constructed or are in planning to secure water supplies for different states following drought that affected many areas of Australia.
As the projects tend to be located in environmentally sensitive coastal areas, Trenchless Technology has been used when installing the pipeline elements of the projects.
Gold Coast Desalination Project The $A1.2 billion Gold Coast Desalination Project is the first large scale water desalination plant on Australia’s eastern seaboard, having the capacity to provide up to 133 ML/d of water to South East Queensland.
Construction of the project involved:Article continues below…
* Separate marine intake and brine outfall tunnels; * Full remediation of a former landfill site; * 300 ML/d dual media gravity filtration pre-treatment process with residuals treatment; * Two stage reverse osmosis desalination; and, * Network integration works that include a 1,085 mm diameter, 25 km mild steel pipeline, a 30 ML storage reservoir and a 2.4 MW pump station.
An intake and outlet tunnel connect the desalination plant to the ocean. The tunnels are located approximately 70 metres below the surface in rock, and extend 1.5 kilometres offshore at Tugun. The intake is located in about 20 metres of water and collects the seawater by a low flow rate intake to ensure marine life is not ‘sucked’ into the tunnels. The outlet uses a diffuser, designed to quickly disperse and diffuse the brine using the energy of the ocean. The diffuser is a 1 m diameter, 287 m pipeline, with 14 dispersion outlets spaced evenly to distribute the brine within a very small mixing zone. The water will be dispersed to normal salinity levels within a 120 x 300 m area.
Trenchless in action Trenchless Technology was used in two of the project areas – specifically-manned tunnel boring machines (TBMs) were used for the construction of the marine intake and outfall tunnels, while microtunnel machines were used for the construction of road and creek crossings on the network pipeline.
In the case of marine tunnels, Trenchless Technology was chosen after a risk assessment process. Several factors, including the reduced impact on the beach zone for both the environment and the community, reduced time impact due to unfavourable weather interruptions, and the removal of potential damage from severe storms and seas, meaning that trenchless was favoured over open cut installation.
The marine tunnel works consisted of two tunnels, both with an outside diameter of 3.2 m lined with concrete segments providing an internal diameter of 2.8 m. The intake tunnel is 2.2 km long while the outlet tunnel is 2 km long. John Holland completed the marine tunnels using Herrenknecht machines and some Herrenknecht personnel.
Construction of the two 70 m deep launch shafts for the intake and outfall tunnels commenced in November 2006. The TBMs began excavation in July 2007, which was completed in June 2008. The tunnels were flooded in October 2008, after completion of the risers and shafts.
For the network integration works, the primary considerations for choosing microtunnelling were the depth of excavation and the reduced impact on the environment – especially in the case of the two creek crossings.
The network microtunnelling works included four separate 1.5 m diameter bores, ranging in length from 135 m to 270 m. Each bore consisted of a 1.5 m steel enveloper pipe jacked into place behind the TBM, followed by the 1,085 mm mild steel concrete lined (MSCL) carrier pipe, which was grouted in place.
Winslow Infrastructure and MacCormick Civil and Tunnelling completed the network microtunnelling works, commencing the first bores in March 2008 with the last completed in September 2008.
Microtunnelling the network pipeline proved a challenge due to the ground conditions of the creek crossings. Marine clay was encountered, which made it challenging to construct shafts and maintain the alignment of the microtunnel bore.
Constructing access roads suitable for heavy machinery through wetland areas on the creek banks also proved to be a challenge. Through consultation with local regulatory authorities, larger and stronger temporary infrastructure was provided, which overcame these challenges.
Sydney Desalination Project
The $A1.9 billion Sydney Desalination Project includes a $A650 million pipeline linking the 250 ML/d desalination plant at Kurnell with the city pressure tunnel at Erskineville – a distance of around 18 kilometres. Approximately 8 km of the pipeline will cross Botany Bay, between Silver Beach at Kurnell and Lady Robinsons Beach at Kyeemagh.
On 25 May 2007, Sydney Water announced that the Connect Alliance had been selected as its preferred partner for the project. A design and construction alliance agreement was executed on 6 June 2007. The private sector parties to the project’s main contract are five non-owner participants: Bovis Lend Lease, McConnell Dowell, Kellogg Brown and Root, WorleyParsons and Environmental Resources Management Australia.
The Connect Alliance will design, construct and commission:
* A drinking water pumping station on the site of the Sydney Desalination Plant, with an initial capacity of 250 ML/d and a capability of expansion to an ultimate nominal capacity of 500 ML/d; * Overland and marine pipelines, with a nominal capacity of 500 ML/d and catering for flows of up to 550 ML/d for short periods, from the pumping station to the existing water supply system in Erskineville via Silver Beach and Kyeemagh, with associated connections and flow and pressure controls; * Service relocations, corrosion protection, monitoring systems, air relief and other valves, surge mitigation systems and other mechanical and electrical systems; and, * Environmental management, OH&S management, community and stakeholder consultation and liaison, quality management, and incident and risk management.
The project is set to flow first water in December this year.
Trenchless in action
To avoid impacting sensitive seagrasses off Silver Beach at Kurnell, a tunnel was dug under Botany Bay from Silver Beach to a point 835 metres offshore. Operating 24-hours a day, the TBM drive under Botany Bay took a month from 8 March 2009 to 8 April 2009 to complete. The drive involved the installation of 271 jacking pipes. The best distance achieved in a 12 hour shift was 36 metres.
Twin 56 inch diameter steel pipes are being laid down across Botany Bay with a tie-in to the pre-driven 1,800 mm diameter tunnel extending 800 metres into the bay.
The TBM, currently parked about 5 metres below the Botany Bay seafloor, will shortly be retrieved and used for other tunnelling in the Kurnell area.
The Easter break provided a four-day window to tunnel under three sets of freight rail tracks. The first 24 m of the 98 m drive was completed in the lead up to Easter. Over Easter, 16 jacking pipes were installed without impact on the rail line. Completion of this section means that there are now over 2 km of continuous tunnelled pipeline under industrial areas and roads in Sydney’s inner west.
This project is another example of Trenchless Technology offering an environmentally friendly alternative to open cut methods when dealing with environmentally sensitive areas.
Adelaide Desalination Project
The Adelaide Desalination Project will have a capacity of 100 GL. First water will be delivered via the plant in December 2010 and the plant is expected to be fully operational in late 2012.
Port Stanvac has been chosen for the development of the plant due to the accessibility of relatively deep seawater, optimal marine dispersion characteristics and better access to the water supply network.
The AdelaideAqua consortium has been named as contractor for the construction of the plant. The companies comprise Spanish firm Acciona Agua, United Utilities, McConnell Dowell and Abigroup Contractors. Together they will design, build, operate and maintain the plant for 20 years.
An associated 1.5 m diameter, 11-12 km transfer pipeline will be located a suitable distance from residential areas, shops, schools and other community facilities to minimise impacts upon community during construction.
It will include a transfer pumping station at Port Stanvac. The pipeline has been designed for an ultimate average flow capacity of 300 ML/d and will connect into storage tanks at the Happy Valley Water Treatment Plant. Trenchless in action
As part of the project, contractors will complete a 405 m microtunnel using a MTS-2000 slurry machine, 1,800 mm outer diameter separator unit. The technique has been chosen to tunnel under roads and rail to ensure minimal disruption to traffic and general public during the completion of the works.
Winslow Infrastructure has been contracted for the microtunnelling works, which are expected to take approximately five months to complete.
An SA Water spokesperson said that the main challenges expected in using Trenchless Technology include avoiding existing services and groundwater. Where practical, the pipeline will be located to avoid underground utility services and, where this is unavoidable, the relocation of services will be arranged with the relevant authority.
A preferred route for the tunnelling works has been selected on the basis of minimising environmental, community and adverse hydraulic design impacts as much as possible. SA Water said that fine detail for the overall pipeline route is still being studied.
Desalination on the drawing board
Other desalination projects in planning include the Southern SeaWater Desalination Project and the Wonthaggi Desalination Project. Although in early stages of planning, the environmentally sensitive locations selected for the projects mean that it is likely trenchless techniques will be employed. Southern SeaWater Desalination Project
The Water Corporation of Western Australia is set to construct a second desalination plant as part of the Southern SeaWater Desalination Project.
The Southern SeaWater Alliance (SSWA), comprising AJ Lucas Group, WorleyParsons, Tecnicas Reunidas and Valoriza Agua, has been chosen to construct the project.
AJ Lucas said that the plant, located near Binningup to the south of Perth, will be constructed in stages, with work to commence in 2009, and operation to begin in 2011. The total construction cost is estimated at approximately $A1 billion, together with a 25 year operations and maintenance contract.
The project scope includes the construction and operation of a 100 GL capacity desalination plant, marine inlet/outlet pipes and a 30 km water supply pipeline of 1.4 m diameter, to transport potable water to the integrated water supply scheme via a proposed storage facility near Harvey.
Wonthaggi Desalination Project Earlier this year, the Wonthaggi Desalination Project, located in Victoria, was given the go-ahead by the Victorian Planning Minister Justin Madden.
The project involves an 85 km water transfer pipeline that will connect the $A3.1 billion plant with Melbourne’s supply network. The pipeline will transport treated water from the plant to the Cardinia and Silvan Reservoirs and augment water supplies at Melbourne, Geelong, Westernport and South Gippsland, with further pipelines being built to give these areas access to the water.
A 4 m diameter, 1.5 km outlet pipe will be used for the plant’s brine discharge.
A shortlist of tenderers for the project has been made, with a final decision to be reached mid-2009. A spokesperson from the Department of Planning and Infrastructure said that a tight evaluation process was currently being completed at the time of writing. He said that tender proposals may involve the use of Trenchless Technology to install the pipeline, but such information would not be released until a contractor for the project has been chosen.
Trenchless terrific for desal pipelines
Trenchless Technology offers an environmentally friendly alternative to open cut methods, especially when dealing with environmentally sensitive areas.
Reduced excavation, reduced reinstatement means that the techniques are becoming an ever more popular component of infrastructure jobs.