FLOODS OF LAKE EYRE
Diamantina River rises in Kirbys Nob, east of Selwyn in Queensland. Through the majority of the 720 km distance to Birdsville it runs as a braided channel with a mean slope of 2.7 x 10-4. At Birdsville, where the catchment area is 115 000 km², there is only one site along the central reach where the Diamantina is sufficiently confined for accurate measurement.
The Water Resources Commission of Queensland has kept records of water levels at this point or nearby since 1948. Extensive flood gaugings to determine stage/discharge relationship have been undertaken by the South Australia and Engineering and Water Supply Department in 1977 and 1981 (Aeuckens, 1980; Marks, 1981). The mean annual flow for the period 1950-83 was 1.42 km³/year with a standard deviation of 2.29 km³. The highest annual flow was 10.6 km³ in 1974 and the highest monthly flow 6.84 km³ in February of that year with the highest instantaneous flow of 4680 m³/s.
Diamantina floods reach Birdsville relatively frequently, and having done so, most likely flow to Lake Eyre. Bonython (1963) and Graetz (1980) give an estimate of past floods and comparisons on progress of floods in Cooper Creek and the Diamantina River.
Leaving Birdsville, the Diamantina River runs 80 km south to Goyder Lagoon, a 1300 km² swamp on the junction with Eyre Creek. Twidale (1972) classes the so-called 'lagoons' in the channel country of south-west Queensland and in the lower reaches of Eyre Creek and the Diamantina River in South Australia as another type of playa. They are receptacles for overflow waters from major rivers and develop in major distributary areas. They receive sediment from the catchment, mostly fine silt and sand, and are gradually being filled. Their surfaces are black or grey due to their cover of desiccated organic slime, and are interrupted by innumerable channels, most of which are sinuous and clearly of riverine origin.
The Georgina River system covers an area of 205 000 km². In the upper reaches the Georgina River is joined by the Sandover River, then by the Burke and the Hamilton rivers, becoming known in its lower reaches as Eyre Creek.
The length of the main channel is 1130 km with a mean slope of 1.9 x 10-4. A good indication of flows is available at GS 001203 Roxborough Downs. The annual flow in 1974 was 5.71 km³ with a highest discharge of 3 530 m³/s. Higher flows have been recorded in 1977 with values of 6.27 km³ and 3 830 m³/s respectively. Mean flow for 1967-83 was 1.23 km³ with a standard deviation of 1.96 km³. David Brooks of Birdsville states that major floodings of Eyre Creek occurred in 1933, 1944, 1950, 1953, 1971-74 and 1976-77 (personal communication, 1985). The major part of runoff probably originates from northeastern tributaries of the Georgina River. Here, at GS 001202 - Burke River at Boil, 2.60 km³ has been recorded in 1974 from a catchment of only 15 540 km², giving a peak discharge of 2890 m³/s. Consistently high annual flows at this location give a mean annual flow of 0.58 km³ with a standard deviation of 0.65 km³.
The combined waters of the Diamantina and the Georgina rivers fill Goyder Lagoon which drains to Lake Eyre by the Warburton. During floods, the area to the north of the Lake is a maze of channels and lakes, but the main flow paths are discernible along the Warburton and the Kallakoopah, which branch and then rejoin near the Lake. Another branch, the Kalaweerina, enters the Lake independently.
The total catchment area of the Diamantina system entering the Lake via the Warburton and its branches is 365 000 km².
Above: Most of Lake Eyre Basin is seen on this satellite photo. The Diamantina River is flowing to Lake Eyre.
Rising as the Barcoo on the northern slopes of the Warrego Range, Queensland, the Cooper Creek flows north-west to Blackall. Joined by the Alice River, it continues south-west past Isisford and receives its principal tributary, the Thompson. At Currareva, with the catchment area of 150 220 km², the mean annual flow is 3.35 km³ with a standard deviation of 3.45 km³ for 33 full climatic years between 1939 and 1984.
Crossing the South Australian border near Innamincka, Cooper Creek cuts through a range of hills and these, in a similar manner to the slight constriction of the Diamantina at Birdsville, offer the only chance of accurately measuring the flow anywhere within the 500 km of its central reach. The location also provides a potential major dam site, a feature almost entirely missing on the other rivers of the Lake Eyre Basin.
The catchment area at Innamincka is 236 700 km², and the mean annual flow for the period 1973-83 is 2.06 km³ with a standard deviation of 3.63 km3. The highest annual flow was 11.47 km³ in 1974; the highest monthly flow 6.49 km³ in February 1974; and the highest instantaneous flow 3 740 m 3/s on 18 February 1974.
Immediately downstream of Innamincka in periods of high flows, water is diverted through a natural control into the Strzelecki Creek, which also has a catchment of its own and can flow due to the effect of heavy localised storms. Flow in Strzelecki Creek fills Lake Blanche, Lake Callabonna and Lake Frome in that order. In 1974, overflow from Lake Blanche also reached Lake Gregory. It appears possible - and on some occasions probably inevitable - that Lake Gregory may overflow in a northwestern direction to Cooper Creek. If this is the case, then Strzelecki water can re-enter Cooper Creek in the vicinity of Lake Killamperpunna. This did not happen, however, in 1974-76.
Once Cooper Creek leaves the hills of Innamincka, it emerges on to a very wide floodplain in the Sturt Stony Desert, interlaced with channels, billabongs and lakes, and intersected by lines of north-south dunes. These floodplains of its central reach are highly complicated.
Above: The Cooper Creek, November 1989.
The Neales originates at Mount Brougham, 430 km from the western shore of the Lake. Joined by Arckaringa Creek and Lora Creek, creating in their lower reach the Peake Creek, it runs across the broad floodplain to the Dividing Bluff and then branches, entering the Lake by three channels.
The Neales has a catchment area of 35 000 km² . Major floods have been recorded in the area in 1885, 1908, 1950, 1953, 1967 1974, 1976 and 1984. However, the majority of floods must have gone unnoticed due to the lack of permanent observation. Nothing quantitative is known about these floods, but on occasions they were heavy, as described by Hunt (1918):
10 March 1908, - Oodnadatta. - There was no telegraphic communication between Oodnadatta and the south, from noon on 6 March until the evening of 9 March, owing to the water rising high above the wires at Peake Creek; and the train from Warrina was detained for five days. The flood water at the Peake Creek (about 10 miles from Warrina) rose 12 feet above the bridge, and the rapidity with which it subsided was remarkable. Between Dalhousie and Macumba stations a plain about 40 miles long was under water.
Above: The Neales in flood at the old railway crossing.
The Macumba, which joins the Kallakoopah in discharging its waters into the Warburton Groove, consists of four rivers. Its longest potential tributary, the Finke, which rises in the MacDonnell Ranges 825 km NW from Lake Eyre, is ephemeral and there is no hard evidence that its waters ever reached the lake, being absorbed by the sands of the Simpson Desert (Williams, 1970). However, there is some information that the Finke did reach Lake Eyre in 1909, 1938 and 1945 (Bonython, 1963). Irrespective of this the Finke catchment area of 63 000 km² contributes little water to the Lake.
River stages are measured by the Northern Territory Department of Transport and Works at:
GS 005136 — Horseshoe Bend
GS 005137 — Idracowra
GS 005138 — Finke Siding.
However, the stations are not instrumented, are not connected to Australian Height Datum, and the stages have not been converted to flow figures.
In 1967, one of the most devastating floods in central Australia caused the Finke to rise to 6.98 m in Hermannsburg, 3.36 m at ldracowra and 2.84 m at Finke. Highest velocities in the western Lake Eyre Basin were estimated at 3.5-3.7 m/s which corresponds to a discharge of 1200 m³/s at Idracowra (Williams, 1970, 1971). However, the Finke did not reach the Lake. Being 11 km wide with an average depth of 0.8 m southwest of Andado homestead, and farther downstream 3 km wide with depths of up to 1.4 m at McDills Well, the distributary stream ran north-east into the sand dunes filling interdune corridors to a depth of 6 m. Water remained in some of the corridors for nineteen months (Williams, 1970).
The duration of recession flows of the Finke is probably very short. Some indication is given by the adjacent Todd River, where a pre-1973 maximum of only five days has been noted. It has risen to sixty-seven days after rain in May 1974 and to in excess of sixty days after rain in March 1976 (Verhoeven, 1977).
The Alberga, the Hamilton and the Stevenson rise on the eastern foothills of the Musgrave Ranges, some 500 km WNW from the Lake and join their courses more or less in the middle of this distance. If the floodwaters enter the Lake via the Macumba, they originate almost certainly from the catchments of these rivers which have a total area of 39 000 km². The Engineering and Water Supply Department has good photographic aerial coverage of the extent of the 1984 flood.
The length of the Finke to the Macumba is 725 km with a mean slope of 6.7 x 10-4. The Hamilton to the Stevenson is 260 km with a mean slope of 1.7 x 10-3. The Stevenson and the Alberga are 230 and 380 km to their confluence respectively, with similar slopes of 1.3 x 10-3.
Above: The Neales in flood at the old railway crossing.
The Frome rises at Mount Rose in the northern Flinders Ranges. Joined by Taylor, Mundy and Leigh creeks, it passes Marree and Muloorina and enters the southeastern part of Lake Eyre North, known as Lake Clayton.
The length of the Frome is 245 km and its catchment area is 18 200 km2 . The highest floods in living memory occurred in 1938, 1974 and 1984. The river ran 1.5 km wide in 1885.
Many smaller ephemeral rivers enter the Lake from the western side. A number of them originate on the range of hills peaking with Mt Margaret at 412 m and Mt Anna at 265 m, 80 km west of the Lake. The longest of them, Douglas Creek, which empties into Halligan Bay, has a length of 93 km with a mean slope of 2.8 x 10-3. The 65 km long Sunny Creek which empties into the southern branch of the Neales has a mean slope of 3.8 x 10-3. Named watercourses include the 34 km long Cooinchina Creek discharging into Belt Bay, and Koorakarina and Anchor creeks which flow into Lewis Bay and have a length of 49 and 25 km respectively. Nothing quantitative is known of flows in these creeks although on occasions of heavy rains, runoff to the Lake can be significant due to their proximity and therefore lower transmission losses.
In arid central Australia, 15 to 20 mm of rain of moderate intensity can cause flow in such minor streams which lasts for only an hour or two. Such a flow may occur as often as five times each year. However, about 50 mm is needed for full channel flow and these rainfalls can be expected less frequently than once per year.