The Agricultural Potential of the Pilbara

by David Archibald

17 January 2017

 

The latent agricultural potential of the Kimberley region is well understood. Annual rainfall of in excess of a meter falls on a largely stony, barren plateau and there are plenty of opportunities to build dams which would catch that summer rainfall and distribute it to the fertile plains downstream. Properly managed, the development of the Kimberley could produce in excess of 8 million tonnes of wheat per annum — equivalent to a third of Australia’s wheat crop. Rain falls in the summer monsoon and wheat would be grown in the ideal conditions of the northern winter.

Pibara: Sun going down, Fortesque River, and the spinifex lights up.

The Pilbara region is similarly blessed, and might produce up to about a third what the Kimberley could do.  This map shows the annual average rainfall of the Pilbara region over the period 1990 to 2012:

There are two main centres of rainfall.  These are the area along the coastal plain east of Pardoo and the the elevated ranges from Pannawonica to Newman.  The rain east of Pardoo falls onto mostly unconsolidated sand; there are no streams and no runoff in that region. That is a good thing, because the rain that falls could be retrieved by pumping it back up from the water table. The economics would depend on how deep the water table is.

The Hamersley Ranges have an area 400 km long by 250 km wide receiving more than 350 mls of rain per annum.  To put that it into context, the Wheat Belt of Western Australia gets 350 to 500 mls of rain per annum.  When the summer rains fall in the Pilbara, substantial volumes of water flow. The rivers of the Pilbara and their annual average flow rates are:

Ashburton                952  GL

Cane                          82  GL

Robe                        125  GL

Fortescue                 224  GL

Maitland                    48  GL

Harding                     39  GL

Sherlock                   164  GL

Yule                         363  GL

Turner                        33  GL

De Grey               1,342  GL

Shaw                        221  GL

Coongan                  118  GL

The total is 3,700 GL per annum. A gigalitre is 1,000 megalitres, which is one thousand tonnes of water in turn.  One megalitre, a thousand tonnes of water, is required to grow one tonne of grain.

An Olympic-size swimming pool holds 2.5 ML, enough to grow 2.5 tonnes of wheat, which is enough to feed seven people for a year on an almost completely vegetarian diet.

So, if all the rivers running in the Pilbara had their flow captured and stored with no evaporation, then 3.7 million tonnes of grain could be grown per annum.  The reality is going to be well short of that but there are mitigating factors. Rain falling in summer could be used to grow sorghum, a crop which requires 700 mls if grown by irrigation. Rain of 400 mls would halve the requirement from water storage. There is also a lot of usable water in the unconsolidated sediments on the coastal plain.  This water currently flows underground out to sea, wasted.

The importance of the agricultural potential of the Pilbara was recognised a couple of generations ago, with the first river gauging station installed on the Coongan River at Marble Bar in 1966.  The highest flow recorded at that station was 2,940 cubic metres per second in 1980. On average, the Coongan River flows for 210 days per year.  The gauging station was at Marble Bar because in those days someone had to be able to go down to the river each day to take a measurement. The damsite it was investigating was downstream at Doolena Gorge, a narrow gorge in jaspilite which would be an efficient use of rock and concrete relative to the water that could be stored. Successful irrigation from that dam would then be used as the model for a dam on the much larger De Grey River four km to the east.

Dales Gorge Formation near Pannawonica, Pilbara

Agricultural economics are affected by the distances the inputs and outputs have to travel. That can be offset by upgrading to a higher concentration of protein by feeding sorghum and irrigated pasture to cattle, taking the protein content from 9% (for sorghum) to the 70% in meat.

We don’t have to have imagination to develop the agricultural potential of the Pilbara. It was obvious to our forebears. All we need is the will, and some common sense.

 

David Archibald is the author of Australia’s Defence, Twilight of Abundance, and American Gripen: The Solution to the F-35 Nightmare.