A tale of two great rivers

Engineers have worked the Murray with the same destructive effect as the Americans. In the 1850s snagging parties rowed up from Wellington in South Australia to clear the river for the new paddlewheel steamers. Huge Murray Cod had their homes of a hundred years sawn up and dragged out of the river by horse teams. So much life was pulled out with the logs that the South Australian section of the Murray lost many of its invertebrates.

Animal and vegetable life in rivers depend on woody debris for food and shelter. When a big River Red Gum falls into a river it can dump more than 8000 invertebrates into the water, spiders, bugs, beetles, flies, ants, wasps, scorpions, moths, others in lesser numbers. They are immediate food. Bacteria, fungi and invertebrates then begin work on the leaves and wood providing a feast of organic matter for hundreds of creatures visible and invisible.

The boilers of the paddlewheelers required wood to fire them. An eight-week trip used about 140 tonnes. Since for some 30 busy years a hundred or so steamers plied 6500 km of the Murray-Darling rivers, enormous quantities of timber were burned to power them.

As river traffic gave way to railways, irrigation began. From Blanchetown to the border in South Australia and along the Murray to Mildura and beyond, scores of steam engines set down on the banks to drive big centrifugal pumps with long, crossed, leather belts. Each engine used more than 30 tonnes of wood a day.

All the water pumped was for flood irrigation. Despite the fact that Australian soil began to protest as early as the 1920s that it could not tolerate that method of watering, the Snowy Mountains Hydro-Electric Scheme was completed in 1972, a social and engineering marvel, an environmental disaster. It harvested two beautiful rivers, the Snowy and the Eucumbene, and turned their water into the Murray and the Murrumbidgee to salt thousands of hectares of river flats by unsustainable methods of irrigation. The recently announced increased flow to the Snowy will not change methods of irrigation. The extra water will come from improved methods of delivery to the farmers who are misusing water.

Sixteen dams were constructed as part of the Snowy work. Other dams on other rivers followed, the most stupid of all the Copeton dam on the Gwydir River. Before that dam some of the world's richest land, the Moree watercourse country, was laid out naturally to be flooded every few years. In a high flood an extent of country 80km long and 80km broad received gentle flooding varying in depth from a few centimetres to a metre. The growth of pasture after such a flood was prodigious.

Dams and weirs are an offence to native fish accustomed to ranging hundreds of kilometres. Even when fish ladders were put in they were built to a Canadian design for salmon. The engineers forgot to teach Murray Cod and Yellowbelly to jump. All water is released from the bottom of the dams. Such water has little oxygen, it is ten degrees Celsius colder than river water and the temperature holds for 300km, putting native fish off feeding and breeding. If top water only were taken, not a difficult engineering feat, dams would not be nearly so destructive.

It is fair to say that irrigation in Australia has been a failure. Not all the electricity, not all the vegetables, not all the grapes, not all the rice, not all the cotton, can compensate for the damage already done by flood irrigation. If methods do not improve, if all flood irrigation does not stop, 4 million hectares will be salted in the Murray-Darling Basin. That is sufficient land to grow one quarter of Australia's wheat and barley.

Irrigation is essential, we can not produce enough food without it. But it has to be drip irrigation or well-managed sprays. Not a drop more must go onto the ground than the crop can use.

Temporarily, because of salt interception schemes and the calculated release of flushing water from the Menindee Lakes and Lake Victoria, the quality of Murray water is improving, though the Darling and its tributaries are rapidly deteriorating. The Namoi is in special trouble. While the salty watertable is rising on the Liverpool Plains, so much water is being drawn out of deep freshwater bores to supplement the river water that trees are dying. The water has receded below their roots.

There are government attempts, still too weak, to reduce the water taken from rivers and bores. In numbers of areas in the Basin, State Forests are carrying out trials with trees, principally River Red Gum (Eucalyptus camaldulensis), to lower watertables while producing timber and charcoal. Water Resources are also working to maintain River Red Gum forests on the Murray.

Most importantly, it has been realised that lakes should be allowed to function naturally. In Australia a full lake is not a natural lake. In March 1998 Moira Lake was drained, a big lake on the outskirts of the Barmah-Millewah Forest. In 1855 a commercial fishery was established there, taking 150 tonnes of Murray Cod annually. Sometimes the lake dried up, to be stocked naturally with fish again on the next Murray flood. When the lake was held full of water after the dams went in, European Carp took over. Hundreds of thousands, many a metre long, died when the lake was drained. Grass grew in the bed for a few months, then the lake was filled again and native fish introduced.

Like the American Indians, Aboriginal Australians demonstrated that humans can live on a river without destroying it. Before smallpox, the Murray population was high, many thousands. There is hope for the Murray-Darling Basin under our management but it will require years of determined work and courageous government leadership to rectify the damage.