River Rights: Reliable Ways of Testing Decisions about Environmental Flows Are Needed to Begin Diverting Water Back from Irrigation. (the Wentworth View)

Article excerpt

Australia is the world's driest inhabited continent, yet Australians are the highest users of water per capita in the world. Our demand for water is so great, that more than a quarter of our river systems are close to, or have exceeded, sustainable extraction limits.

Nowhere is this more evident than in the Murray-Darling Basin, where more than 80% of the total flow from the combined river systems is diverted for industry and domestic use. Irrigation accounts for 95% of this.

Dams and weirs have dissociated Murray-Darling floodwaters from the floodplains, and altered the magnitude, frequency, seasonality, duration and variation of flows. Algal blooms, native fish losses and explosions in carp populations are increasing.

If nothing is done, closure of the Murray River mouth and the subsequent death of South Australia's Coorong region and its internationally listed wetlands is imminent.

Adelaide's main water supply is predicted to fail World Health Organization standards for every two days in five, within 20 years. The salinisation of our farmlands (through irrigation water) will increase.

These issues were highlighted in the report, Managing Australia's Inland Waters. Roles for Science and Technology, presented at the Prime Minister's Science and Engineering Council (PMSEIC) meeting in September 1996.

Strategies to address these issues, such as the water market and a cap on extractions from the Murray-Darling, have been in place for some time, but the Wentworth Group says these reforms have not secured the long-term health of the basin.

'It is obvious that environmental flows need to be increased,' the group says. 'Rivers, like the River Murray, are not working. It is time to begin the process of recovering water from irrigation.'

Saving the Murray

In 2002, the Murray-Darling Basin Ministerial Council took steps to address the problem of environmental flows in the Murray system. These included the initiation of a community-wide discussion about environmental flows, and an assessment of the costs and benefits to the environment, industries and communities of returning water to the river.

As part of this 'Living Murray Initiative', a computer software tool was chosen to assess the ecological impacts of a range of environmental flow scenarios.

One of the developers of the Murray Flows Assessment Tool (MFAT), CSIRO Land and Water river scientist Dr Bill Young, says the tool will help the Ministerial Council and others to understand the environmental outcomes of any flow allocation decision.

'Much of the debate over water concerns efficiency, so how do we use water more efficiently in order to save more for the environment?' Young asks.

'Achieving greater water savings may cost millions of dollars, through lining channels, installing pipes or improving delivery. So unless we've got some idea of the environmental gains resulting from that expenditure, we won't be able to make informed or effective decisions. That's where MFAT comes in.'

MFAT is being used to assess the environmental returns from three reference flows established by the Ministerial Council: 350 gigalitres a year, 750 GL/yr and 1500 GL/yr.

These are not actual flow options, but are intended to give all sectors of the community an idea of the costs and benefits involved in transferring various annual volumes of water from current uses, such as irrigation, to the Murray.

Thirteen scenarios--different spatial and temporal hydrology patterns--have been developed around these flows, to investigate the effects of recovering these quantities of water from different parts of the river system, or releasing water at different times.

MFAT is then used by 10 regional evaluation groups (state agency scientists or consultants) to determine the ecological effects of these hydrological changes.

'Each regional group uses MFAT to model different aspects of the ecology at about 10 locations along their zone of the river,' Young says. …