A Wizard with Wavelengths

Article excerpt

Philip Kofoed follows the trail of an environmental troubleshooter whose investigative techniques reveal more than the eye can see.

Songs and stories from our past often mention the coolabah tree, its generous shade providing welcome relief for many a weary traveller through Australia's dry interior. It features in the ill-fated trek of Burke and Wills as the famous `dig' tree. Our most renowned swaggy even camped beneath one shortly before temptation got the better of him and -- well, you know the story.

Yet despite its hardiness, the coolabah at times relies on deep groundwater for survival. If that water supply is threatened, the tree can quickly perish. This poses a problem for Hamersley Iron's Marandoo iron ore mine in Karijini National Park in northern Western Australia. The mine is about to steal water from beneath a large stand of a rare coolabah species, Eucalyptus coolabah Aff. Victrix.

The likely effect of Hamersley Iron's mining operations on the coolabah stand is being investigated by Dr Peter Hick of CSIRO Exploration and Mining, a member of CSIRO's Minesite Rehabilitation Research Program.

Hick is an authority on environmental uses of spectral analysis, a science that uses sensitive instruments to analyse the wavelengths of light sources, including light waves we can't see (see story on opposite page). He uses this and other techniques to evaluate the impact of mining on natural ecosystems. His recent work has taken him to Ranger Uranium in the Northern Territory, and to mines in the Pilbara region of northern WA, including Marandoo.

`At Marandoo they may be mining up to 90 metres below the watertable,' Hick says. `And to stay operational they will have to pump out the water that will inevitably flood the mine. The worry is that the nearby coolabahs might be denied their water.'

Hick says there are two watertables at the site, one at 15-20 metres and a deeper one down to 80 m. `It's the 80 m watertable that may be affected by the mine, he says. `The trees probably depend on the shallow one, but if there's a connection between the two, the coolabahs might still be in trouble.'

Members of Hick's research team are looking at tracer isotopes in the bark and leaves of the coolabahs to determine which watertable the trees arc using. Tile mine's environmental manager will then know how best to divert the water: whether to keep it in artificial ponds and allow it to leach gently back into the ground, or pump it directly into groundwater aquifers.

Hick says many mines in the arid Pilbara region are mining below the watertable. `They're pumping out millions of tonnes of groundwater to keep their mines operational,' he says. `And their only choice is to run the water down normally dry creek beds.' This causes other problems downstream.

The fragile ecosystem supports an adapted range of eucalypts, but because of the extra water from the mines, the vegetation along the normally dry creeks will become more consistent with aspects of rainforest found along perennial rivers in the north of Australia.

In anticipation of such changes occurring along the intermittent Robe River at Pannawonica, Hick was invited to survey original vegetation below the Robe River iron ore mine. Spectral analysis of aerial images along the river downstream from the mine has provided an accurate record of the types and density of the natural vegetation. With this record as a guide, plant life along the river below the mine will be returned to its original state after the mine's closure.

Mulgas under threat?

Another problem for Hamersley Iron at Marandoo is that the mine's railway line may be altering water flows. `Mulga is the dominant vegetation and it doesn't have a very deep root system,' Hick says. `It relies on surface sheet-flow in periods of floods and cyclones. If the sheet-flow is impeded, the mulga can die.'

Airborne and satellite spectral sensing techniques are being used to determine whether the mulga, Acacia aneura, has been affected since the railway line opened. …