FLOODS OF LAKE EYRE
Dr Vincent Kotwicki
Aspirations to populate the inland of Australia have had a long history. Marshall (1977) divides the development of Australian primary industry into four periods: recognised ignorance, learning the hard way, incautious optimism and informed adjustment. Once, the aridity was regarded as somewhat non-existent, and any mention to the contrary was considered unpatriotic. Then, great inland watering schemes were postulated and even debated by Parliament of the day. Marshall notes that with climatology being a relatively new science, the meteorologically based proposals for watering of the interior were often both simplistic and naive, as shown by the following quotation (Bradfield, 1941):
The evaporation from a water surface of 50 000 km² (proposed inland reservoirs) at 2500 mm a year could cause a fall of rain of 100 mm over 1 250 000 km² of the dry inland. That rain after refreshing the vegetation would evaporate and fall again as rain.
In other words it would be a sort of meteorological perpetuurn mobile. It is worth noting that with such a philosophy, reservoirs are not.necessary. One very wet year in the catchment - for example 1974 - would generate an unlimited sequence of wet years. Unfortunately, this is not the case.
The existence of Lake Eyre fires the imagination. Various schemes have been brought forward for filling the Lake and improving this desert region. Towner (1955) reviews a number of these schemes. Chronologically, the oldest is that of letting sea water into Lake Eyre by means of a channel cut from Spencer Gulf. This was considered by the Government in 1883 and rejected. The length o a canal would be 400 km, its slope 3 x 10-5 and required bottom width 1.5 km. With estimated 10 km³ of excavations, the magnitude of earthworks would be without precedent in the world, with the possible exception of Plato's canals of Atlantis. The cost of such an enterprise - using conventional methods and 1986 prices would be in the order of 10 billion dollars.
Another scheme, by Dr Bradfield, was to transport the waters of the Burdekin River across the Great Dividing Range by tunnel from the Queensland coast and discharge them into Cooper Creek with a constant rate of 160 m³/s. Annual import of some 5 km³ of water would allow huge areas to be irrigated. However, as Towner points out, this idea lies in a category of wishful thinking, not supported by any calculations.
One part of the another scheme proposed by Dr Bradfield was the construction of four reservoirs at the headwaters of the Finke, Georgina, Diamantina and Cooper Creek. Each dam was to be 200 km long and hold some 80 km³ of water spread over an area of 12 000 km². As a subsidiary scheme he recommended the damming of the Mulligan River and taking its water to the Hay River that traverses the Simpson Desert.
Considering our present needs, and technology, such schemes although appealing, could be only born from ignorance of hydrology in general and the hydrology the Lake Eyre Basin in particular. Their weak points can be seen a glance:
Filling of the Lake with sea water is impractical. From evaporation, after say 100 years, the Lake would contain 30 km³ salt instead of water. Benefits having such an amount of salt are doubtful, and the relevant desalination techniques are not available.
There are no technologies presently available for increasing the rainfall over large areas. Thus, until such methods are developed, it is pointless to construct reservoirs with holding capacities some hundred times more than mean annual flows. In the meantime, smaller reservoirs on the Cooper and Diamantina can be given some consideration.
Generally, the diversion of rivers is impractical before the fullest use has been made of their waters in their own basins.
As already mentioned, filling of the Lake will not increase the rainfall in central Australia. Spencer Gulf and the Red Sea, for example, have little if any effect on rainfall in the surrounding country.
Great water schemes of the world are usually built for the purpose of power generation, flood protection, irrigation and water supply. In our century, a filled Lake Eyre could merely serve as a major tourist attraction.
So, is the man-made inland sea feasible?
Probably the most correct answer is: not now.
Above: Satellite image of Lake Eyre partially filled, taken 22 February 1984.
Question: Is Lake Eyre wet or dry?
Answer: It depends. Most of the time it contains some quantity of water, and on average, almost all of its surface area is covered with water once in eight years.
Question: Say, we fill Lake Eyre with water. Would it change the climate of central Australia?
Answer: Not likely.
Dr Vincent Kotwicki
An idea of the Trans-Australia channel surfaces from time to time. I remember discussing it in great detail in 1986 with Mr Norman of Port Lincoln.
In principle, it would require an enormous channel, and the benefits of such an undertaking are vague.