Where does our water come from and how do we minimise impact on the ocean?

Q: The Sydney Desalination Plant makes high quality drinking water from seawater. Where does the water come from?

A: The water that is used to make drinking water at the Sydney Desalination Plant comes from the Tasman Sea off the coast of Kurnell, Sydney. A seawater intake system is used to carefully draw seawater from the Tasman Sea to feed the Desalination Plant.

Q: Can you explain how the seawater intake process safely draws water without harming marine life?

A: The intake process carefully draws in seawater from the Tasman Sea via intake risers linked to an intake tunnel approximately 2,500m long and 3.4m in diameter. Seawater is drawn in approximately 300m offshore at a depth of 25m.

The intake risers consist of a circular concrete base, lid and bar screens that surround the top circumference beneath the lid to prevent people or large marine life from entering.

The intake risers are designed with maximum intake velocity of 0.1m per second to minimise the potential for marine life being drawn into the Plant.

At this low velocity, most mobile marine organisms can comfortably swim in and out of the intake structure. Once seawater arrives at the Plant, it passes through screens that remove any large materials such as seawater, shells and general rubbish.

Q: How does the water outfall process safely return water to the ocean?

A: The outfall discharge system collects all water that is to be returned to the ocean that include seawater concentrate (effectively saltier seawater) through an outfall tunnel with high flowrate diffusers. The high flowrate diffusers make sure the water mixes rapidly and returns to normal seawater salinity and temperature within a short distance of its discharge point, so as not have an adverse effect on the local marine environment.

Q: The Sydney Desalination Plant places a high priority on minimising any environmental impacts on land and in the water. What are the key design considerations?

A: The Sydney Desalination Plant was built with a strong focus on the environment. A study led by the University of New South Wales into the marine ecological impacts of operating a large-scale desalination plant was conducted over a six-year period during which the plant was under construction, then operating and then idle.

This study took place at six underwater locations at a depth of about 25m which enabled the team to rigorously monitor for impacts and recovery among marine life from the effects of pumping large volumes of hyper-saline water (saltier seawater) into the ocean.

The study found no significant impacts from the Plant on the local marine environment which is due to the high-pressure diffusers that return the high-concentrate salt water to the ocean at a high velocity that are effective at diluting the brine, so that concentrations were almost at background levels within 100m of the outfall.

This outcome reflects strong engineering and effective modelling in diffuser design, demonstrating that the Plant was thoughtfully designed and constructed with consideration for the marine environment.

Q: What environmental activities are occurring on land in the conservation area?

A: The Plant’s site covers 45 hectares, including a 15-hectare environmental conservation zone that is home to several unique species of native flora and fauna. This area is protected and closely monitored, with programs to survey and protect the number of Grey Headed Flying Foxes and Green and Golden Bell Frogs.

Bush regeneration and the removal of invasive flora from the conservation area is carried out on a regular basis to ensure the animals have a safe place to feed, breed and roost.

The protected Conservation Area was established as part of the approval process for the design and construction of the Plant. With the Green and Golden Bell Frogs translocation project, special tadpole ‘nurseries’ are built on site, with the intention that once the tadpoles mature into frogs, they will use the conservation area and its connection to Kamay – Botany Bay National Park to establish a breeding colony and help repopulate the peninsula.

In another joint project with Symbio Wildlife Park, about 800 eucalyptus trees have been planted in the southern area of the Plant. Leaves are harvested periodically and used to feed orphaned and rescued koalas which are being housed at Symbio Wildlife Park.

The Plant and its operator, Veolia, have also been working with marine scientists from the University of NSW and La Perouse Local Aboriginal Land Council’s Gamay Rangers to establish a special nursery onsite to help to restore seagrass fragments (Posidonia australis) that wash up on the shores of Silver Beach in Kurnell so they can be replanted in areas damaged by storms, anchors, and recreational boating.