Restraint on water not enough

DID you know WA has a chateau d’eau?

Do you know what a chateau d’eau is?

It’s French, for water castle.

Geographers use the term to describe high terrain, particularly regions from where rivers originate.

For example, Switzerland and the alps form Europe’s chateau d’eau because that’s where its three magnificent rivers – Rhine, Rhone and Danube – originate.

South Asia’s chateau d’eau is the Himalayas and Tibetan plateau, from where the mighty Brahmaputra, Indus and Ganges originate.

Southern WA’s far smaller chateau d’eau is the Wickepin district, since it’s from there that WA’s only two river systems worth speaking of – the Avon/Swan and Blackwood/Arthur – originate.

But they’re saline.

However, south-western WA also has a network of shorter westward-flowing sweet water carrying rivers originating from beyond the wooded Darling Scarp, which have been progressively dammed – Mundaring Weir, Serpentine Dam and so on – to help meet water needs.

But what makes the State’s coastal south-west unique is its network of huge aquifers, which hold far more sweet water than those dams.

The reason, a geologist contact says, is that all the land back from the scarp to beyond Kalgoorlie is a craton called the Yilgarn Block – a huge, billion-plus year old geologically stable slab of earth.

As this block eroded at the scarp the scree formed Perth’s sandy coastal plain, which is why Swan River colonists were nicknamed Sandgropers.

Over those eons, water-holding layers formed – some now thousands of metres deep – meaning southern coastal WA has two sweet water sources, the varyingly replenished visible woodland dams and unseen coastal aquifers.

At their peak the dams hold 678 gigalitres (678 x one billion litres). Currently they’re holding 160 gigalitres, so just below quarter capacity, thus the current concerns.

The deepest of the aquifers, called the Yarragadee, extends from Geraldton to Augusta.

The Water Corporation is licensed by the Water and Rivers Commission to draw 159 gigalitres annually from subterranean sources, which are monitored to prevent depletion beyond replenishment rates.

Current total south-western annual consumption stands at around 350 gigalitres.

Complicating matters is the fact that the scarp’s dams are south of Great Eastern Highway, while most currently utilised subterranean water sources lie north of the Swan River estuary.

That has presented the corporation with the major and costly engineering challenge of having to equip itself to pump northern subterranean waters southwards and southern dam water northwards.

Today the corporation, with its trunk pipe network and pumping facilities, can mix both waters, offering a ‘cocktailed’ product.

Water can even be drawn from beneath Perth and pumped into Mundaring Weir for cocktailing.

South-western WA is, consequently, not water deficient. And nor will it be in the foreseeable future.

If it was the corporation would be considering shipping water in to the State, as they do in water-deficient Israel, which announced last month it had contracted to bring 50 gigalitres annually from Turkey until 2022.

Perth’s population, now 1.4 million, is expected to more than double by 2050 and resultant demand will be met from current known sources.

Even so, the desalination of seawater is on a relatively nearby horizon, while piping Kimberley water or bringing it in by tanker are on more distant horizons.

If south-western WA is, therefore, not deficient in sweet water, and won’t be in the foreseeable future, what’s it short of?

The answer is money for dams, piping, pumps, bores, and desalination plants; all costly items.

That, as much as WA’s lack of a European or South Asian-sized chateau d’eau, is good reason to move for greater across-the-board water usage efficiency.

No-one is saying current government media campaigns urging restraint aren’t worthwhile.

But they could be broadened beyond just publicising rainfall and dam levels to embracing the horticultural, town planning, and building – including design – industries.

Government knows that the present lifestyle of Perth residents would be maintained even if each person used an average of 155,000 litres annually. Before last year’s limited restrictions, which didn’t impact harshly, it was 180,000 litres.

So the 25,000-litre saving can be comfortably attained without browning the suburbs.

But the impact of such a reduction upon Perth’s water needs by 2050 would mean an annual requirement of 432 rather than 570 gigalitres, a saving of nearly 140 gigalitres, or the yield of two Serpentine Dams, Mundaring Weir, and Wungong Dam.

In the first 10 years these savings would largely offset the impact of population growth on consumption.

However, there are problems, one being that per capita consumption by higher income earners is demonstrably higher, meaning wealthier people, on average, con-sume more water.

This probably points to the need for more progressive water pricing – like taxing of income.

But there are problems in moving to even slightly ‘dry out’ the rich. The last time the Gallop Government moved to soak the rich – the premium property tax – it was a politically torrid experience.