In discussions about water allocation in the Murray Darling Basin it is generally assumed that runoff now is equivalent to what it was at the time of European settlement. Consider, for example, the following table from a Murray Darling Basin Commission Facts Sheet.
At the same time there is a perception that there are a lot fewer trees now than there were at the time of European settlement. As Ian Mott points out in the following comment, first posted at 'Banking in the Macquarie Marshes', if there are fewer trees now, then there is more water now:
"If you really want to correct the misconceptions that threaten you water allocations then you should correct the fallacy that the pre-irrigation runoff into the marshes was 460,000 megalitres which has since been reduced to 395,000ml by irrigation.
The pre-settlement runoff into the marshes would have been much less than 460,000ml and most likely less than 395,000ml because much of the upper catchment has been cleared for pasture. And this has substantially increased the catchment yield.
But don't expect the MDB Mafia or the Land and Water audit people to concede this willingly. The work of Robert Vertessy and the CRC for Catchment Hydrology makes it very clear that the switch from forest to pasture increases water yield.
So your group has to determine the exact amount of clearing that has taken place in your catchment and overlay the rainfall data so you can find out the real historical water footprint for the marshes.
There is not the slightest room for doubt that the volume of water taken out of the system by irrigators, given that extractions are only 14% of current runoff, is less than the improvement in yield produced by clearing.
My understanding is that the upper Macquarie is not subject to widespread thickenning like the mulga and brigalow country so cleared land has been more likely to stay cleared."
Sorry Michael, I took it the other way. But you are right, it is most likely this fetish for maintaining artificial water flows during times when rivers would have been bone dry, that has played the major part in habitat destruction.
For this 'landscaping water', (you couldn't correctly label it as 'environmental flow') play a key role in concentrating ferals and excessive native animals, especially 'roos, in the very places where they will do the most damage.
This water does not act as a sustaining refugia in drought but merely operates to prolong the suffering of populations that routinely undergo up to 90% declines in populations in drought.
These natural population declines are the flip side of the enhanced reproductive capacity of natives and ferals in good years. But the bimboscenti do not carry out any culling of these species when circumstances demand so large populations are left long after farmers have either destocked their herds or have switched to suplementary feeding.
The evidence is very clear, especially in the mulga lands where 'roos don't eat mulga that is pulled for grazing stock, that the critical damage that is being inflicted on overgrazed pastures, and public reserves, is being done by the public's negligently managed native and feral animal herds.
Access to artificial water supplies, at stock watering points and by non-seasonal creek flows from regulated sources, plays a critical role in keeping animals alive and overgrazing when nature would have killed most of them off much earlier.
But that is par for the course in the brave new green utopia.
"Marshes do have only a dribble of water through them in droughts, Michael. Thats why they call them droughts."
-------------------------------------------------
These are a semi-arid, lower floodplain wetland system right? I was surprised by the presence of any water at all in the middle of the drought, that was my point. I presume river regulation upstream was to blame.
I was extremely dissappointed by the Macquarie marshes and kept on driving when I went to visit the area back in 2002. They looked like a pig infested, shit mess of cumbungi, dead trees, weeds and stagnant permanent water. Looked awfully stressed and unhealthy, but certainly not because of lack of water!
Geoff, these people are fully capable of quietly capturing every benefit that is produced by farmers and then assigning every cost onto those same farmers. That is the nature of parasites, they will take, and take, and take until the host is dead. They will just go looking for another host while chanting some mantra about "partnerships for intergenerational equity".
By their deeds shall ye know them.
I thought that the available data was insufficient to make any other than a general assessment relating to the Macquarie Marshes.
Irrigators may well be the most efficient users of water, and irrigators can also be graziers (albeit intensive).
Extensive tree planting may also take valuable water away from the marshes.
Thanks,Rog and Ian, for the references to various reports/papers on water use and runoff.
Assuming other factors such as rainfall intensity remain constant, current and future land use does point to lesser runoff.
I cannot see where anybody has had a stab at predicting the magnitude of this other then in the case of hypothetical reforestation.
I think this is important because figures show 31.5% of runoff north of the Murrumbidgee/Murray is presently used. If runoff decreases by say 15% and environmental flows increased, what is the future for the irrigators and indeed much of west of the Dividing Range [Well named isn’t it] in central/northern NSW and Q’Land.?