Flood History

Flood History

"Wetter than you may think!"

Click on the thumbprint above to see a graph of Lake floods and water source compiled from satellite images from September 1979 and measured depths from 1973-1978 that may illustrate the 25-35 year flood cycle. See below for an explanation of both graphs.

Most Flood Level Reports are Wildly Innaccurate

Lake Eyre has some water in it more often than many would lead you to believe. When Halligan flew over the Lake in the 1920's and reported it as being about one third full he was ridiculed by seasoned explorers.
Today we have similar situations where land based observers can't believe the dry Lake they are looking at contains water and airborne observers are claiming that the "Lake is the fullest it's been in years". Quite often they are both wrong!
Why:

Most people who travel over land to view the Lake arrive at a point on the Lake where it is shallow and often dry, for example William Creek to ABC bay, or arrive at a basin that is not currently flooded, for example Madigan Gulf in a Warburton flood.
Aerial observers, especially in a floods initial stages, see the sky reflected across the entire wet surface of the Lake and claim it is "full". Most of this water is very shallow, say 10mm deep, and still FLOWING to deeper parts of the Lake.

Of course the tourist industry would prefer the Lake to be full for only the second time this century every year. The possibility of any water being in the Lake generally causes a flurry of exagerated claims to reach an ignorant city based media. Roll out some file footage and you've got a story.

Reliable Information From Satellite Images

In the early days the Commodore was faced with the difficulty of deciding if the 3000km round trip would result in a successfull sailing adventure. Phone calls to locals, rangers, policemen, publicans and pilots gave wildly conflicting reports. Their report was based on limited personal observation and heresay - a more reliable method was required.
Landsat satellite images available from the Auslig web site http://www.auslig.gov.au were proven to be the most reliable way of determining these parameters. Of course the images were first "calibrated" using published depth diagrams checked by actual depth measurements on sailing trips. Experience has shown depths can be estimated within 100mm in the navigation critical 1 to 3metre depth range.
With experience water proximity to certain features in the Lake can quickly indicate depth.

The colour of an area on the image provides the information required:

White The highly reflective surface of a dry salt crust

Brown Dry mud on the Lake edge

Red Browns Algae living in wet mud

Pale Blue Wet salt crust

Mid Blue Shallow water (<50mm)

Dark Blue Deeper Salty Still Water mostly navigable (>450mm)

Blue-Green Turbid fresh water containing algae

Red Fresh vegetation growing in creek beds

Green Established vegetation growing on dunes

Blue/Purple-Black Dead vegetation in creek beds

Browns and Oranges on land Arid landscape

Darker Browns and Blacks on land Rocky hills or Gibber desert

Lighter browns and yellows Dunefields

Recent local rain, however, can make the whole Lake appear dark and give a misleading indication of depth. A more accurate reading can only be made when the Lake is either white(or light blue) salt where dry and dark blue where the depth is greater than 50mm. Consideration must also be given to wind direction and strength which is discussed in the yachting guide.

Water Source

Water inflow is crudely, but interestingly, represented in the lower graph by assigning the units 1-3 for each source. 1 = minor flood, 2 = moderate and 3 = overflowing the bank. The units (Floodges) add to produce the coloured bar graph. The colours indicate the source - reds the Warburton, yellow the Cooper, blues flow into LES and the greens the western creeks into LEN. An observation being that local rains comtribute to navigable floods more than may have been previously thought.

Scoping the rivers - typical floods

These are "back of an envelope calculations" only!

Warburton flood

In a typical Warburton flood 10 cubic kilometres of water crosses the Queensland/Souith Australia border.
At the Cowarie/Kalamurina boundary The Warburton is typically 50m wide x 7m deep flowing at 5km/hr = 1,750,000 cubic m/hour = 1.75glt/hr = 42gl/day = 3.78 cubic kilometres over 3 months

Cooper Flood (at Birdsville Punt)

200m wide x 4m deep flowing at 3km/hr = 2,400,000 cubic m/hr = 2.4glt/hr = 57.6 gl/day = 5.184 cubic kilometres over three months

The Murray

Averages 3-10gl/day but in flood can exceed 100gl/day.

White	The highly reflective surface of a dry salt crust
Brown	Dry mud on the Lake edge
Red Browns	Algae living in wet mud
Pale Blue	Wet salt crust
Mid Blue	Shallow water (<50mm)
Dark Blue	Deeper Salty Still Water mostly navigable (>450mm)
Blue-Green	Turbid fresh water containing algae
Red	Fresh vegetation growing in creek beds
Green	Established vegetation growing on dunes
Blue/Purple-Black	Dead vegetation in creek beds
Browns and Oranges on land	Arid landscape
Darker Browns and Blacks on land	Rocky hills or Gibber desert
Lighter browns and yellows	Dunefields