Perth is Sucking Up Its Groundwater and Sinking Into a Hole

Not as fast as Mexico City, but fast enough for people to be talking about it.

by Royce Kurmelovs
Nov 4 2015, 12:00am

Image via Flickr user Mark Ireland

According to a recent study by Curtin University Professor Will Featherstone, Perth is sinking. Don't feel too bad, so is Bangkok, Mexico City, and much of California, so at least it's in good company. The city's problems are due to groundwater related subsidence—a process that occurs when people start sucking groundwater from aquifers beneath cities, causing the soil to compact and the ground to sink.

The situation is worsened by climate change, which forces cities to draw on groundwater to make up for a lack of rain and dry rivers. If it's any comfort, it's sinking at a pretty leisurely pace; Professor Featherstone notes, "We're looking at subsidence now of three millimetres per year, whereas others are looking at rates of centimetres per year."

As worrying as the news is, the world's most isolated city has actually stabilised in recent years. At its peak, Perth was sinking at six millimetres a year between 2000 and 2005, with some areas sinking faster than others.

So is Bangkok, Mexico City, and much of California, so at least it's in good company.

While six millimetres may not sound like much—for reference Mexico City has sunk metres in the last century—it adds up to six centimetres over ten years. With enough time the movement can damage roads, bridges, and building's foundations. And with the added stress of climate change, the situation may escalate.

Perth is a thirsty city in a drying climate. Rain used to provide Perth with the bulk of its water; it was collected in a network of dams—which worked well from about 1911 to 1974 when it averaged 338 gigalitres a year. From 1975 this started to change as rainfall dropped 15 percent and the amount of water flowing into the state's dams annually halved to 177 gigalitres.

That decrease isn't expected to abate. Between 2006 and 2010, the state averaged about 57.7 gigalitres a year. Now, as climate change plays with global weather patterns, even less rain is likely to fall. To make matters worse, forecasters have been warning of a Godzilla El Nino event, a prospect that has UN officials warning Australia is thoroughly underprepared for a long-term drought.

Bruce Dawsett, a farmer from a little town called Wandering about 120 kilometres southeast of Perth told VICE it is already happening as farmers in his region have been forced to watch their crops fry in an unusual October heat.

"In 2010, we were classed as having a one in a 100-year-drought," he said. "And now we've turned around and had another one in 100-year-drought in five years. In the past our rain was so consistent. Two droughts in five years? It's unheard of here."

To its credit though, Perth has been doing its best to prepare for a worst case scenario like becoming a waterless "ghost city". Two years ago, Premier Colin Barnett declared the city "basically drought proof" at the opening of a desalination plant in Binningup. Today 41 percent of the city's water supply comes from desalination, 42 percent comes from groundwater, and the rest comes from dams.

Perth has been doing its best to prepare for a worst case scenario like becoming a waterless "ghost city".

The sinking however is a side effect of all that prep, as relying increasingly on groundwater to keep the taps flowing risks making parts of Perth sink faster. Classic damned if you do, damned if you don't situation.

Luckily Perth's options aren't to sink or crumble to dust. There are ways around this, whether it be to draw water from deeper parts of the aquifer or to replace whatever is extracted.

Perth's Water Corporation is already working on a project to do just that using treated wastewater. Wastewater is what's produced every time you run a shower, wash your clothes, or flush a toilet. Perth produces 432 million litres of the stuff a day, which is then treated in one of 106 different plants. In most cities, this water is flushed back out to sea but Perth now wants to filter it to drinking standard and inject some of it back into the aquifer.

Despite the synergy of the plan, the sewerage bit has at times made the project tricky to get up and running. Not that the city has too many options, California is experiencing a similar drying climate and has turned to groundwater to provide 60 percent of the state's water supply. The increased pressure on aquifers has created a situation where subsidence crumbles roads and lowers bridges into the canals they were built over. Data released in 2012 showed the Sao Joaquin valley was sinking at a rate of 30 centimetres a year.

With this grim model Perth started work on its first groundwater replenishment plant last year which will be capable of recharging 14 billion litres back into the aquifer and there are plans to eventually expand it. So look on the brightside, we might lose California, but hopefully Perth will be around for a while longer.

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