All licenses/entitlements in the Murray Darling Basin are subject to seasonal allocations, or on the "unregulated" rivers, the attainment of minimal river heights. I believe it was the late Professor Peter Cullen who made the statement that "in a dry country like Australia we shouldn't be growing thirsty crops like rice and cotton". Both Australian industries lead the world in their use of science and technology. By every measure they lead their respective world "competitors"-yields, water use efficiency, etc..
The Peter Cullen statement was "parroted" by the "chattering classes" over their chardonnays in Paddington. Cullen was subsequently convinced by the likes of fellow Water Commissioner Peter Corish, that annual crops like rice and cotton are in fact ideal for our highly variable rainfall and river flows. No or little water, no crop. He recanted before he died and withdrew the comment, but the chattering classes never caught up and the statement is still frequently quoted.
Likewise I still hear references to "rights to permanently extract water which need to be withdrawn". There are no such things! For some reason people seem to resist thinking about it sequentially. It rains or it doesn't. Dams fill or they don't and water is allocated or it is not. The defined requirments of the environment, critical human needs and stock and domestic needs are all given priority before allocations for irrigation are granted. This process is all set out in the much debated Water Sharing Plans applicable to each river. And this is why it is just plain wrong to blame extractions for irrigation for low water flows. The simple cause of low river flows is lack of natural run-off! Dorothea Mackellar understood this so well,hence "droughts and flooding rains". See Clive James wonderful essay.