15/06/2004 - 22:00

Growth could pressure water supplies

15/06/2004 - 22:00

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An unlimited supply of cheap water has long been touted as one of the great attractions of the Ord River project, but the reality is not so simple.

Growth could pressure water supplies

Growth could pressure water supplies

 

An unlimited supply of cheap water has long been touted as one of the great attractions of the Ord River project, but the reality is not so simple.

Lake Argyle is the largest freshwater storage in Australia with a capacity of 10,760 million cubic metres, about nine times the water volume of Sydney Harbour.

The ability of Lake Argyle to support expanded agricultural production depends on which commodities lead future growth.

A large expansion of sugar cane production, which is the most water-intensive crop, would push the limits of sustainable water supplies.

Uncertainty about water supplies was one factor (along with low sugar prices) that forced a Wesfarmers Marubeni consortium to abandon plans for a massive $500 million sugar project in 2001.

The State Government’s Waters and Rivers Commission is currently finalising a water allocation plan for the Ord that seeks to balance the competing demands from agriculture, hydro power generation and the environment.

In rough terms, nearly 2,000 gigalitres of water is released each year from Lake Argyle.

About half this amount is allocated for environmental purposes, with the balance available for irrigation.

Ironically, the environmental allocation has nothing to do with the natural environment and everything to do with the man-made environment downstream from the diversion dam (Lake Kununurra).

The steady release of water from the diversion dam has created a freshwater river that flows year round.

The unique wetlands environment that now exists has become a popular playground for locals and tourists and is considered environmentally significant.

Presently, between 300 and 350 gigalitres are used for irrigation, so there is plenty of scope for expansion.

The commission’s program manager, Ian Loh, said the additional allocation for irrigation was likely to be somewhere between 400 and 600 gigalitres. (This is well below the 690 gigalitres the commission had planned to allocate to the Wesfarmers Marubeni project.)

Mr Loh said the commission was likely to license a certain amount of water with a high degree of supply certainty.

Additional water would be available but with a lower degree of certainty.

The task of setting water allocations was complicated by variations during the year, and the need to plan for worst-case scenarios.

For instance, if storage in Lake Argyle is low, more water needs to be released for hydro electricity production.

“It’s not the averages, it’s the dry season and the restrictions [that would be needed] in years of drought that control it,” Mr Loh said.

An added complication is the possibility that Pacific Hydro may install an extra turbine at Lake Kununurra to lift its generation capacity from 30 megawatts to 42 megawatts.

The extra capacity would supply the underground expansion of the Argyle diamond mine, should that proceed.

If water efficiency (not to mention commodity prices) dictate future development on the Ord, the focus is likely to be on cotton, which uses about seven megalitres a hectare each year.

Mango and banana growers use about 15 megalitres while sugar farms use about 22 megalitres.

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