18/03/2003 - 21:00

State Scence - Dam issue won’t go away

18/03/2003 - 21:00


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THE issue of Western Australia’s freshwater needs persistently rates highly in party political and other local polling. Press reports showing quarter-full dams and constant chatter about the so-called greenhouse effect have had their impact.

THE issue of Western Australia’s freshwater needs persistently rates highly in party political and other local polling.

Press reports showing quarter-full dams and constant chatter about the so-called greenhouse effect have had their impact.

Pollsters’ ‘radar screens’ display public unease. People are worried.

Some even see ensuring water availability as being akin to a war, and fear it’s a fight that won’t be won.

But, just as World War II wasn’t won with one overriding breakthrough, there’s no single answer to WA’s water needs.

It’s worth emphasising that the Western Allies won that war with a range of rarely publicised breakthroughs, including self-sealing aircraft fuel tanks, new and faster welding and riveting techniques, specialist radars and sonars, the Jeep, and drop fuel tanks that dramatically extended the range of fighter aircraft.

Cumulatively these and other developments gradually gave the Allies a crucial edge over the Axis.

A snow-capped mountain range isn’t about to arise in central WA and a Kimberley pipeline is prohibitively expensive.

A series of ongoing smaller and cheaper, but each crucially important, adaptations and modifications are what’s likely to steadily improve matters.

Last week, State Scene spoke to two experts linked to long-time WA coal miner Griffin Coal about one such modest-but-farsighted proposal that has the potential to markedly boost the freshwater stock of WA’s integrated system, so for Perth metropolitan area, the Goldfields and Wheatbelt.

The story they told involves not just Griffin’s water experts but also those at the Water and Rivers Commission (WRC).

The basic problem facing Collie and environs is how to markedly lower salinity of the now brackish Wellington Dam, which holds a third of the current annual dammed water consumed from the integrated system.

Water is classed undrinkable when salinity levels exceed 500-600 parts-per-million (ppm).

Annually these regions consume around 300 gigalitres of above ground-stored water, or the capacity of 300 Subiaco Oval complexes.

Brackish Wellington Dam holds 133 gigalitres with about half-earmarked for open field irrigation.

Wellington Dam, completed in 1933, offered drinkable water until the late 1980s.

But its salinity levels began rising because of clearance of local woodlands, especially to Collie’s south and east, during the 1960s.

Currently Wellington Dam registers, on average, 880ppm, meaning water was withdrawn from the integrated system, although irrigation continues.

The rising salinity level stabilised around 1990 because of the 1976 legislation controlling woodland clearance and private and governmental reafforestation.

Now, one of Wellington’s catchment rivers, Collie River East, which originates from a heavily cleared region, contributes the greatest annual salt load.

Its average salinity is 3318ppm, or nearly 40 per cent of the dam’s salt intake but only 10 per cent of its water inflow. Seawater is 33,000ppm.

It has been around this crucial finding that boffins have begun devising a plan to restore Wellington Dam as a drink-able water source, meaning it would contribute in the order of 15 gigalitres to the integrated scheme.

They noted that, at one point, Collie River East flowed within two kilometres of Griffin Coal’s huge, no longer used, open-cut pits.

The boffins consequently proposed that the east river’s heavily salt laden early winter water be diverted into those pits until that river’s salinity levels fell later in the winter.

Such early winter diversion would mean that most of the saline water from Collie basin’s cleared regions would no longer enter Wellington Dam, thereby lowering its average salinity level.

At a workshop in Darkan last November, the WRC, the Collie Salinity Recovery Team and other stakeholders decided to adopt the plan to divert early winter saline water into Griffin’s huge pits.

WRC salinity expert Tim Sparks said it was an attractive short-term management solution.

The WRC has launched a long-term plan to lower the dam’s salinity to 500ppm by 2015.

“Diverting the river’s most saline flows into mine pits could be done quickly and relatively cheaply, as long as the technical issues can be sorted out,” he said.

Mr Sparks’ qualification refers to confirming that the diverted early winter saline waters don’t contaminate below ground water sources near the pits.

Although Griffin’s studies show this won’t occur, the company is funding a team of hydrologists to double-check that contention.

Once confirmed the diverting can proceed, with the outcome being a rapid fall in Wellington Dam’s salinity levels and the linking of this sizeable source to the integrated system.

And there are other possibilities.

Diverted saline water can be used as a power station coolant or be desalinated and pumped to Wellington Dam.

All up cost for the project would be about $10 million.

That’s remarkably cheap for the dramatic outcome – a revitalised one-time freshwater storage, thus boosting the integrated system’s dammed fresh water stock by about 5 per cent and potentially far more.

So, a little like self-sealing aircraft fuel tanks, which saved thousands of shot-up Allied planes, not to mention their pilots’ lives.


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