Filling the void

Conserving and reusing water will always be a hot topic for facilities managers. This month fmME goes behind the scenes to bring you the lowdown on the simplest, yet most effective method of water drainage, capture and re-use

Something interesting has been going on in Jebel Ali Free Zone for the last five odd years. Something that, in a city state known for its non-permeability, is being manufactured to help drain, capture and re-use rain water with the added ability to support the aesthetically pleasing landscaping that has become the Emirate’s benchmark. That something is the Modular Geo-Void System.

Only 0.3 percent of all water on the earth is freely usable fresh water, and that is being used in a permanent cycle. With that in mind, the capture of run-off storm water is key for FMs’ consumption and reduction key performance indicators. So what is the Modular Geo-Void System, how does it work and what are the benefits to FMs?

Iain Cusick and his team manufacture the system in Jebel Ali and have installed it across Dubai, including the Palm Jumeirah and Meydan Racecourse, the world’s largest, spanning some 76 million square feet. “The drainage system works like this,” says Cusick, holding a light weight porous cube around 50cm squared.

“This high density polypropylene grid structured cube I’m holding here is modular, so it fits together with those over there making it versatile,” he says, pointing to a warehouse full of multiple cubes.

“If you are using the system for a soakaway application, the trench, or void, is lined with geotextile and filled with cubes which act as the drainage system. The subsurface system allows for high infiltration areas to prevent ponding and pest infestation due to stagnant pools of water.”

The cubes are cheaper, more durable, and easily installed and maintained than traditional concrete drains. “Concrete drains crack if either knocked in transit or during installation or through fatigue. You also need heavy lifting equipment to install concrete drains in deep trenches. Then there’s the production costs and the attendant impact on the environment.”

Cusick says ease of maintenance for FM teams is also a plus point. “You have complete linear access, while the low flow channels are designed to prevent the build up of silt.”



Tank modules

Storm water can be recycled by plumbing a filtration unit to the drainage system which passes the treated water into a storage tank. A pump is then used to draw the grey water to the surface to be used for irrigation, for instance.

“Being modular, the advantage is increased performance over aggregate trenches – i.e. the system provides a void space of over 90 percent compared to less than 20 percent in typical aggregate trenches,” Cusick points out. Consequently, the tank leaves a smaller footprint while achieving the same capacity as a traditional aggregate trench.

“This saves time and money in installation and civil works costs. And there’s no sediment build-up so the system doesn’t clog – a characteristic of aggregate approaches.”

High density green buildings  

For outdoor landscaping and green roofs, the Pluvial offshoot AquaDrain is a cell geocomposite for sub-surface drainage with high compressive strength up to 200 t/m2. “It’s made from recycled material, and like the cube it’s lightweight and low cost, giving it a huge advantage over lightweight concrete. 

“I’ll give you an example: we’re involved at the design stage with a developer and its FM team concerning a roof garden on a large facility. Initially the designer specified lightweight concrete to support the weight of the roof – this would still have added two tonnes of structural weight, which hadn’t been calculated.

“In consultation with the developer and FM team, we decided to go with the cell because it is not only lighter, but also removes only excess water. And the water retention cups provide optimal conditions for plant/grass growth. Geotextile functions as a protective membrane for waterproofing and provides ventilation for concrete slabs, which alleviates heat induced stress and cracking.”

During heavy rainfall, roof gardens must be able to infiltrate water quickly to avoid structural stress and water ingress. “The system is designed with horizontal drainage capacity giving storm water the freedom to run off quickly before build-up and flooding,” says Cusick. 

Reduced consumption

The benefits of using these polypropylene grid structured systems for voids and roofs are both environmental and financial, according to Cusick.  “We’ve installed thousands of water recycling, drainage and attenuation tank systems for schools, car parks, retail parks, offices and sports arenas throughout the UK, Europe and the Middle East, and calculate they pay for themselves in three – to four years.” You heard it here first.