We can’t write appropriate black letter law to deal with a highly variable environment. The reality of Dorothea Mackellar’s “droughts and flooding rains” and you could add ‘not much in the middle’, cries out for adaptive management.
The water sharing plans for each of the main water courses in the Basin, need to be expressed in general terms. Single figure Sustainable Diversion Limits (SDL’s) are nonsense. As difficult as it may be, we need to calculate broadly expressed % of flows to guide flexible decision making. The event nature of our rivers (particularly northern) needs to be recognised. As does the dynamic nature of water flows. They don’t wait around for you. If they go into downstream storage’s they can quite quickly evaporate or they can flow to the sea. Extractions for irrigation from big events can be a quite small percentage of the flow. The average (with all the weaknesses of relying on averages), of extractions in the Mungindi/Menindee reach of the Barwon/Darling is about 6% of the average annual flow. A small price to pay for the economic benefit.
A visitor to say, Wilcannia, may find a dry Darling River. If they then go upstream to Bourke and find full off-river water storage’s (those were the days), they conclude that that was obviously where the water went. However,when you recognise the event nature of the river and learn that there have been no subsequent high flow events when extractions were allowed and consider the dynamic nature of water flows, it should dawn that this is a false conclusion. The flow from which the Bourke off-river storage’s were topped up, would have long since passed by Wilcannia and the river would be exactly as they found it.
“Drought proofing” is a pipe dream. Rather like dealing with climate change we need to adapt. As I continually argue two words should dominate our thinking-conserve and flexibility. We can’t have too many water storages, but like the big, pipes in the bed of the river on the Warrego River thru’ Toorale, we need to be able to allow flows to pass when downstream circumstances demand it.