Developing Australia’s tropical water resources – Part 2

Part 2.  Is there a case for major expansion of irrigation in Northern Australia?

Earlier this week in Part 1 I argued that ecologically-sustainable irrigated agriculture is, at least, technically feasible (if politically unrealistic!) …….the remaining fundamental question is this – is Australia’s tropical north the potential agricultural utopia it is claimed by many to be?

The northern regions in question stretch from Broome in Western Australia to Cairns in north Queensland. There is already rangeland grazing through the region, and some irrigated agriculture, for example in Western Australia (Ord River), Queensland (Flinders and Gilbert Rivers) and the Northern Territory (Daly River).

The idea that northern Australia should be a good place to develop agriculture has been pervasive for many decades, in spite of well-documented arguments to the contrary (for example, Davidson, 1965). The region has almost 50 per cent of Australia’s total surface water runoff, a big contrast to the runoff in the Murray Darling Basin of only six per cent, and where there is already billions of dollars-worth of agricultural productivity. It is captivating in a food-hungry world to think we might harness those northern water resources and have more agriculture and more production. Naturally, it is not quite that simple, or development would have proceeded long ago (notwithstanding the initial faltering attempts for the Ord Irrigation scheme).

A relatively recent set of scientific, economic and cultural studies into the development prospects of the north was reported by the Northern Australia Land and Water Taskforce (CSIRO 2009). One key point from that investigation is that, despite the high average rainfall, the north is seasonally water limited. This is not unusual in the tropical latitudes, being also the case in the Philippines, Indonesia and parts of southern India. In all of those countries, a higher than average annual rainfall does not guarantee a year-round water supply.

A further important point noted by the Northern Australian Land and Water Task Force (CSIRO, 2009) is that the most useful rainfall tends to be away from areas where the soils are suitable for irrigation. Also, there are not very many good locations for big dam sites in the north (notwithstanding the major ecological impacts of large dams already discussed). Although Lake Argyle, the second largest dam in Australia, has been built on the Ord River in northern Western Australia, there are not many dam sites like that and, as already noted, it is to be hoped we are wise enough now to know that building large dams like that is not the way of the future.

CSIRO and others acknowledge, however, that there is potential for some new irrigated agricultural development in northern Australia, largely based on complementary use of surface water and groundwater, between wet season and dry season. But the extent of this is nowhere near that suggested by some.

Prior to the 2013 federal election, the Liberal-National opposition (now government) released ‘Coalition 2030 Vision for Developing Northern Australia’, their vision for developing northern Australia. That policy document stated that Australia’s agricultural production could be doubled by 2030 with such northern development.

However, CSIRO and the northern Australian Task Force had already concluded that only about 600 gigalitres (GL) of groundwater is available to sustainably support production, which is a very small amount when compared to the greater than ten thousand gigalitres of water typically used by irrigated agriculture across Australia (in non-drought years). On an area basis this would mean an additional 40,000-60,000 hectares of irrigated farmlands,[i] which is minor compared to that already in Australia of 1.8 million hectares.

It was concluded that achievable extra irrigated agricultural production in Northern Australia is likely to be only around three to four per cent – a long way from the doubling proposed by the (now) Federal Government.

The Flinders and Gilbert catchments in the elbow of the Gulf of Carpentaria feed significant river systems and, during 2013, the Queensland Government released about 94 GL of that surface water for new irrigation developments there. Again, this is not very much water in comparison with the volumes in use for irrigation in southern regions, although it is evidence that some new agricultural development is underway in the north.

From an ecological perspective, there is a pertinent warning by Georges et al. (2002) based on work in the Daly River that overuse of groundwater is likely to interfere with habitat for at least some of the north’s unique freshwater species, especially turtles and other amphibians.

One other important aspect that must be understood and respected in the north, particularly around the Gulf of Carpentaria, is that successful coastal commercial and recreational fisheries for Barramundi and Banana Prawns are highly dependent on the amounts of water that flow down the rivers and out to sea. If too much water is taken out for agriculture upstream, the coastal fisheries are likely to suffer. This point was made recently by Professor Michael Douglas who leads the Tropical Rivers and Coastal Knowledge (TRaCK) research hub based in Darwin (TRaCK 2012):

There is a perception that wet season flows in the north are ‘wasted’, but our research has shown a direct correlation between river flows and the commercial and recreational catches of coastal fish such as barramundi, king threadfin, and prawns…..Large floods that spill over the banks allow fish to move onto the floodplains to feed then move back out to the river as the floodplains dry….This means that much of the meat on barramundi in the upper reaches of river systems may have been ‘grown’ on the floodplains, potentially many months before and hundreds of kilometres downstream, and similarly, freshwater flows into estuaries play a significant role in determining the numbers and sizes of fish that live there….These floods are also necessary to connect the floodplains to the river and allow movement throughout the entire river system, while maintaining dry season flows may be essential for the life cycles of important species such as barramundi and freshwater prawns.”

[i] Currently there are about 34,000 hectares of irrigated lands in northern Australia (CSIRO 2009).

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