Pipelines and power supply

The desalination plant has a series of pipelines and tunnels that connect with a power supply, Victoria’s water grid and Bass Strait.

The transfer pipelines

The 84 kilometre underground pipeline connects to Melbourne's supply network at Berwick. It then flows into Cardinia Reservoir or into the pipe system.

In Cardinia Reservoir, the water mixes with catchment water and transfers into Silvan Reservoir if needed.

It has delivery points from Melbourne's supply system (including desalinated water) for these water corporations when required:

• South East Water
• South Gippsland Water
• Westernport Water.

The 2-way pipeline means that water can be supplied from Cardinia Reservoir if the desalination plant is not running.

Most of the transfer pipeline was manufactured by Victorian-based company Tyco at its Somerton factory.

The pipe is 1.93 metres in diameter, and each section weighs about 13 tonnes. While the plant can make 150 billion litres a year, the pipes can deliver up to 200 billion litres of water a year. If the plant is expanded in the future, the pipes can handle the increased capacity.

A booster pump station maintains pumping pressure between Cardinia Reservoir and Wonthaggi. The site for the booster pump station reflected community views about the initial proposed location exhibited as part of the Environment Effects Statement.

Air vents and scour valves along the pipeline allow air into the pipe when the pipe is draining and out of the pipe when it is filling with desalinated water.

Two surge tanks control the rate of pressure changes in the pumping system. They are located at Kilcunda Ridge and St Heliers Gurdies Road.

The power supply

The power supply line is 87 kilometres long and is a dedicated supply for the desalination plant.

Communities and landowners had concerns about overhead power line ruining the visual amenity. As a result, the power supply is underground within the pipeline easement.

While the cables are in the same easement as the pipeline, they lie in separate trenches. They share the same alignment except for a 9‑kilometre section at Clyde North.

The power supply uses a high voltage alternating current (HVAC). This was a better choice than high-voltage direct current because:

• it's a more reliable supply of power
• it loses less energy
• it's technically less complicated.

The HVAC design uses power-load compensating equipment. This is co-located with the pipeline booster pump station at Clyde North and at a point south of Lang Lang.

Each installation takes up a small area and has landscaping that minimises the visual impacts.

Fibre-optic cables installed with the power supply support operations for the plant, power and pipeline.

Renewable energy

Renewable energy is energy that comes from an unlimited power source. These might include wind, tidal and solar sources.

Using renewable energy sources reduces our reliance on coal-fired power. Burning coal contributes to the production of greenhouse gases.

But we can't directly use renewable energy sources for the desalination plant. Research done for the Environment Effects Statement showed that renewable sources aren't reliable enough to directly power the desalination plant. The plant needs a direct, continuous power supply. So, the plant makes use of renewable energy credits (RECs).

Renewable energy credits are tradeable, non-tangible energy commodities. They represent one megawatt-hour of electricity generated from a renewable energy source.

The funds from RECs purchases have supported AGL's wind farms developments. Such projects include the 63-megawatt Oaklands Hill wind farm and 420-megawatt Macarthur wind farm. These include other wind farms, solar and landfill gas-to-power projects.

This provides more than enough energy to offset the 90 megawatts used by desalination plant and pipelines.

Saltwater intake and outlet structures

Research determined the design and location of the intake and outlet structures. Investigations into the marine environment included:

• Hydrodynamic modelling
• Biological studies
• Water column and bathymetry surveys
• the Construction of a large-scale physical model in a laboratory.

The final design passed a comprehensive approval process. It was reviewed by the Independent Reviewer and Environmental Auditor and the EPA. The EPA did the final assessment for compliance with the EPA works approval.

The intake structures

The intake structures draw in high-quality seawater with as few impurities and particles as possible. This makes it easier to filter and treat the water.

Vertical risers connect the two intake structures to a 1.2 km underground tunnel. They draw water in so slowly that small fish and other species can easily swim in, out and around the structures. Grilles prevent larger sea animals from entering. The intake structures are about 500 metres away from the outlet structures.

The outlet structures

The 2 outlet structures return seawater concentrate to the ocean at the end of the desalination process. Vertical risers connect them to a 1.5 km underground tunnel. The 2 structures are fitted with 9 diffuser nozzles each to ensure rapid dilution of the seawater concentrate.

Due to the open ocean currents of Bass Strait, the salt content in the mixed water will drop back to standard seawater concentrations within a very short distance of the diffuser nozzles.

The seawater concentrate discharge must meet the requirements set by the EPA according to EPA licence conditions.

Evidence from other desalination plants suggests that the small area where the discharge is most concentrated will provide a habitat for salt-tolerant species such as mussels, sponges, and some ascidians.

Page last updated: 08/09/23