Potable water for South East Queensland in flood, hail or shine

The Millennium Drought of 2001-09, which almost crippled South East Queensland’s water supply, saw the planning and implementation of the largest water infrastructure project in Australia since the Snowy Mountains Hydro Scheme.

The $7 billion South East Queensland (SEQ) Water Grid, which supplies 3.2 million people in South East Queensland with drinking water, is a connected web of approximately 600 km of new and existing bulk water pipelines, linking a diverse system of water supply infrastructure across 23,000 sq km.

Prior to the construction of the SEQ Water Grid, the region was supplied from eight discreet water supply zones, with no ability to share water. The lack of connection meant water restrictions were frequently applied in some parts of the region while dams in other parts were full or overflowing. Similarly, operational issues often had to be managed on a local basis, without access to supplies in surrounding areas.

A regional approach to water supply planning, management and operation was made possible by institutional reforms and a combination of new infrastructure, including around 250 km of new bulk water pipelines, pump stations and reservoirs managed by LinkWater. This network connects the region from the Sunshine Coast in the north, the Gold Coast in the south and Toowoomba in the west.

Components of the SEQ Water Grid

The 250 km of new bulk water pipelines includes the Southern Regional Water Pipeline (SRWP), the Eastern Pipeline Interconnector (EPI) and the Northern Pipeline Interconnector (NPI).

Completed in 2008, the $900 million, 960-1,290 mm diameter SRWP project was designed to help manage South East Queensland’s existing and long-term water requirements. The reverse flow, 94 km pipeline can move 130 ML/d between the Brisbane, Ipswich, Beaudesert, Logan and Gold Coast regions, ensuring water can be distributed to where it is required. The SRWP helps to manage the demands of residential and industrial growth, and has provision for integrating supplies from new water storage infrastructure proposed for the Logan River catchment (Wyaralong Dam and Cedar Grove Weir).

The pipeline includes a number of microtunnels that were bored under four major river crossings, numerous highways, railways and hilly terrain. Constructed over 12 elevated crossings – including one over the Brisbane River – the pipeline required four pump stations (Bundamba, Swanbank, Chambers Flat and Coomera), two balance tanks (North Beaudesert and Staplyton), and an 8.5 km extension of pipeline between Helensvale and Molendinar. An additional pump station, reservoir and associated works were required at Molendinar.

Also completed in December 2008 at a cost of $39 million, the 8.4 km, 600 mm diameter EPI was built to transport up to 22 ML/d of water in either direction between Redland City and Logan City. It was constructed over
three road crossings, two creek crossings, and required a pump station and water quality facility based at Mt Cotton.

Both the SRWP and EPI were constructed by the Southern Regional Water Pipeline Alliance, consisting of Abigroup, McConnell Dowell and Kellogg, Brown and Root (KBR).

The last link in the SEQ Water Grid pipeline chain is the NPI, connecting water supplies between the Sunshine Coast and Brisbane for the first time.

The Northern Pipeline Interconnector

Completed in two stages, NPI – Stage 1 spans 47 km and has the ability to transfer up to 65 ML/d. The gravity-fed, $315 million 750-1,290 mm diameter pipeline project, which was completed in December 2008, was built to accommodate the reverse-flow capacity installed as part of the nearly complete 1,200 mm diameter NPI – Stage 2. The second stage spans 48 km and includes a balance tank, four pump stations, a new water quality facility, and upgrades to an existing water quality facility.

At the time of writing, completion of Stage 2 was scheduled for the end of 2011, with commissioning to take place in the first quarter of 2012. The Northern Network Alliance – comprised of McConnell Dowell, Abigroup and KBR – was appointed as the construction contractor for both stages of the NPI.

In addition to linking the Sunshine Coast with Brisbane, the NPI will connect the currently segmented water zones of the coastal region, providing greater security and flexibility of water supply. In terms of supporting growth on the Sunshine Coast, the pipeline includes offtakes for future local water distribution at Eumundi, Yandina, Nambour, Pringle Hill and Paynter Creek. Construction of these connections aims to avoid future duplication and disturbance, cost and other impacts upon the community and environment.

Like the SRWP and the EPI, the NPI allows for continuous quality water supply and better management of water quality issues, ensuring that residents from nearly all of South East Queensland will have access to potable water even during events such as the January 2011 floods.

Supplying potable water in times of need

The January floods saw damage to multiple water treatment plants (WTPs) and water and sewage mains, chemical shortages, and widespread access issues contributing to a reduced ability to deliver safe drinking water through conventional water treatment processes.

At the peak of the floods, more than 10 tonnes per second of wreckage, debris and silt flowed past the extraction points for the WTPs in the upper reaches of the Brisbane River. Impacted plants included the Mt Crosby Eastbank and Westbank WTPs, the largest plants in the region and the key sources of supply for Brisbane, Ipswich and Logan. Production from the North Pine WTP was also restricted due to poor raw water quality. These interruptions resulted in treated water storages being depleted to critical levels.

In response, the Gold Coast Desalination Plant increased output to help ensure a continued supply of high-quality drinking water. After being mixed with water from other treatment plants, desalinated water was piped to Brisbane via the SRWP to ensure maximum quality water supply.

In addition to supplies from the desalination plant, water was also piped from the Gold and Sunshine coasts into central South East Queensland.

The response to the flood event involved all elements of the SEQ Water Grid and the combined efforts of the state-owned bulk water entities LinkWater, the SEQ Water Grid Manager and Seqwater.

Seqwater says that the construction of these pipelines mean that water security and supply risks can now be managed on a regional level, rather than on an individual storage or system basis.

Conceived in drought and proven in flood, the SEQ Water Grid enables the centralised management of water supplies, allowing water to be transported to where it is needed most.

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