Coomera Megavault: 3,000,000 litre Detention with Stormwater Harvesting & Treatment

A key upcoming development in Coomera, Queensland, will see a flagship extension to the local Westfield shopping centre – with the additional complex housing a large warehouse retailer, service station and 783-car parking lot. 

Supporting local growth, the large-format site will complement nearby retail establishments and community infrastructure. Close to local creeks and surrounded by the scenic Gold Coast environment, SPEL designed and installed stormwater treatment assets to meet the unique requirements on the expansive 14,000 square-metre site. 

Sustainability outcomes were a key consideration in meeting the development’s environmental goals, with the site characterised by large impervious areas of hardstand and car parks. 

High volumes of stormwater runoff are expected during rainfall events. Subsequently, stormwater assets had to be designed to accommodate these potential flow rates. Four main stormwater management specifications were defined for the multi-purpose site – hydrocarbon capture, tertiary filtration, detention, and stormwater harvesting. 

The versatile stormwater assets supplied will ensure vital water quality, spill containment, flood mitigation and water storage capabilities across the site’s multiple catchments.  

Underground Stormwater Tanks: Maximising Useable Land

Large-scale detention systems were supplied to the site, including an impressive 3,000,000-litre cathedral-style Megavault system. 

The Megavault’s precast, modular design was a perfect fit – providing on-site efficiency, fast 12-day installation, and reduced open excavation times. This key OSD asset (on-site stormwater detention) will ensure that stormwater runoff from the large catchment is slowed, and flood mitigation capabilities are available during heavy rain events. 

Across the site, stormwater assets were installed underground to maximise usable land. This ensured all detention and treatment assets were able to meet the available on-site footprint. Fully trafficable, they will support vehicle use & load ratings for heavy vehicles. 

Stormwater reaching the Megavault will pass through two satellite filtration systems housing SPELFilters. These devices are designed to remove phosphorus, nitrogen, and total suspended solids to help reach the site’s water quality objectives. 

Hydrocarbon Capture for Service Station Catchments

A secondary main catchment area was the service station and its surrounds. A SPEL Triceptor was installed to ensure capture capacity for on-site spills and oil separation – a legal requirement on high-risk sites. 

Discharging into a 100,000-litre Megavault detention system with internal SPELFilter bays, the stormwater that passes through the service station’s catchment will undergo tertiary treatment within this nearby OSD. 

Protecting the local environment, a key benefit of the Triceptor is the ability to treat both high and low-risk areas of the surrounding catchment. Hydrocarbon spill capture helps to protect local waterways and the surrounding environment – with these compounds eliminated from runoff prior to entering downstream devices or surrounding areas. 

Stormwater Harvesting & Sustainability Goals

Capacity for local stormwater harvesting was also part of the long-term sustainability goals of the development. An 80,000-litre SPELVault system will allow this precious resource to be captured for reuse. Minimising cost and environmental impact, this green approach will help to alleviate water use and reliance on local water networks. 

The rectangular precast SPELVault system was installed to complement on-site detention. Similar to other on-site assets, the SPELVault will be fully trafficable and will be located underneath key car park assets. 

In addition to providing climate resilience, the dual systems in this modern development will mitigate the impacts of severe weather events such as flooding and droughts. Futureproofing the site to meet environmental demands, the result is a multi-pronged approach that provides comprehensive stormwater management infrastructure. 

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