An Updated Water Security Program for SE Queensland

An updated Water Security Program (WSP2023) was released by Seqwater and the Queensland Government today. The WSP2023 sets out a 30-year plan to ensure high levels of water security for South East Queensland (SEQ), including Brisbane, the Gold Coast and the Sunshine Coast.

Water supplies in SEQ are highly interconnected via a system known as the SEQ Water Grid. This interconnectivity provides an enhanced degree of flexibility regarding where new water sources can be located.

Some important highlights from WSP2023 include:

• Connection of supplies from the Logan River, including Wyaralong Dam (south-west of Brisbane), and a new water treatment plant to supply this additional drinking water into the SEQ Water Grid.
• Possible upgrade of the existing Gold Coast Desalination Plant at Tugun to increase supply capacity.
• Examining opportunities to use the Western Corridor Recycled Water Scheme to further supply industry and agricultural customers to offset some potable water demand.
• Maintaining the role of the Western Corridor Recycled Water Scheme as an important drought supply asset, to supply drinking water to Lake Wivenhoe when SEQ Water Grid storage levels drop to 40% of their capacity.

The overall drought response triggers are shown in Figure 10 from the WSP2023 (reproduced below). As shown, purified recycled water would be delivered to Lake Wivenhoe when storages drop to 40% of capacity.

However, this is more complicated than it sounds since the Western Corridor Recycled Water Scheme is currently in a partially decommissioned state. It will take considerable time (certainly more than a year, perhaps two) to have that scheme up and running at significant additional capacity. Therefore, a decision to recommission would need to occur well before the 40% trigger is reached, while storages are still up in the "pre-drought" section of the Figure. As is stated in the WSP2023:

“The amount of time for the Western Corridor Recycled Water Scheme to become fully operational will depend on the age and condition of the asset and the level of use by industry and other customers. This will therefore be reviewed when the pre-drought trigger has been reached and the recommissioning plan will be updated and implemented as appropriate. Seqwater will also consider the weather outlook at the time and, in consultation with the Queensland Government, implement recommissioning activities as appropriate to ensure Western Corridor Recycled Water Scheme is fully available before the 40% Grid storage level is passed”.

A further important drought response trigger is the activation of “contingency supplies” at 25% capacity (See Figure 10 above). This is to enable “all contingency infrastructure [to be] available at 10%”. Clearly that doesn’t leave any room for error or construction delay. On this aspect of the plan, the WSP2023 states:

“Seqwater will complete and activate additional contingency water supplies including new climate-resilient infrastructure, prior to reaching this level. Given the scope of this, supply depends on the conditions of the prevailing drought as well as the availability of future Grid infrastructure projects identified within this Program.

Seqwater will use an adaptive strategy to implement contingency supplies. This adaptive strategy will identify and accelerate delivery of suitable infrastructure within Seqwater’s forward works programs to ensure the community’s water needs can continue to be met during extreme drought but also that the infrastructure will have lasting value for the SEQ Water Grid”.

That all sounds a bit vague, which is why a further immediate activity for the WSP2023 is to complete a new detailed business case by the end of 2024 for the next major supply augmentation – a new seawater desalination plant. This business case is to include assessment of potential locations, capacity and timing of delivery.

For whatever reason, it was the longer-term plan for this seawater desalination plant that the Queensland Premier focused on when announcing the release of the WSP2023 today. She said in parliament “This plan firmly focuses on desalination because it goes directly into the water grid and is not lost to evaporation during droughts”.

I think this statement is a bit wrong on two counts. First, its not really correct to suggest there is a particularly heavy focus on seawater desalination, while other supply strategies -including new surface water, water efficiency/restrictions, and recycled water for both potable and non-potable uses- all feature prominently.

Second, it’s not meaningful to suggest that delivering desalinated seawater directly to the water supply distribution system will reduce evaporation from the system as a whole. Any water that goes directly into the distribution system will directly replace water that would otherwise have come from a dam. So less water will be drawn from the dams, meaning more water will be retained in the dams. This water retained in the dams will be subject to the same evaporation as it would if the desalinated seawater (or purified recycled water) were added directly to a dam.

I know, its complicated. But worth thinking that one through.

A more real advantage of delivering water straight to the distribution system (rather than say, into Lake Wivenhoe) is that this source would be unaffected by water quality challenges during major Brisbane floods. Being able to supply some water direct to distribution would relieve pressure from the Mt Crosby Water Filtration plant, enabling a higher overall water supply production rate to be maintained.

This was an important advantage observed in Sydney during 2020 when water quality in Warragamba Dam was severely impacted by bushfires and floods. The ability to supply 15% of Sydney’s drinking water from seawater desalination provided some relief for the Prospect Water Filtration plant, supplying most of Sydney. Thinking about water supply resilience in this way makes a lot of sense.