Monday, October 03, 2011

Still water flowing down the Murray Darling and out the mouth

The perceived wisdom that drought and a closed Murray Darling system is the new normal continues to be challenged by reality. From my reckoning and the following graph of the Murray river flow rate at lock one, the closest proxy of what is flowing to the sea from the system, 15,000 GigaLitres (or 30 Sydney Harbours) of fresh water has flowed to the sea since September 2010.

This link to see more live river data flows if you are interested.

I had predicted at around January that more water would flow out of the mouth than the total official storage of the whole of the Murray Darling before it stopped again. The total official storage is around 22,000 GL so I could yet be right. I figure that one more year of this kind of thing and we will be wanting to redact our thinking and declare that (the 10 years from 2000 to 2010) was just a freak drought the likes of which we would never see again in our lifetime. It is plausible that we may want to keep strategic dams along the Murray at half capacity to hedge our bets with catastrophic lower Murray floods now possible if we get a repeat of the inflows of last year. Namely the Menindee lakes, Hume and Lake Victoria could moderate catastrophic inflows to just the major flood mark at Renmark and below if they are pre-emptively emptied.


Dr Clam said...

Have you found a site with year by year Murray mouth data? I can only find them with the 1891-2010 flows ranked from highest to lowest ... This is practically an exponential curve which makes the current management plan discussions centred on 'average' flows faintly ridiculous.

Marco said...

No. The few bits of data that I know are that there was no flow out of the mouth for 10 years, that the MD dams were at 20% capacity up to 2009, and are now near 90%. There is a particularly thorough research called the water availability project which gives fine grained data and seems to be good science but a work in progress.
I think you are right about planning around average flows being rediculous. We really need a "flood mode" and a "drought mode" set of policies. Just predicting whether it is La Nina or el Nino year can make the policy that much more sensible. If it is a La Nina year and your dams are full, we are in flood mode - Give everyone their full allocation, and free water for any excess usage at that. Dams need to have preemptive releases before a rainfall event which is predicted by better models 1 to 2 weeks in advance.
Drought mode will kick in when an el Nino year is predicted, and/or dam levels are depleted back below a threshold of say 50%. The combination of wet/dry risk factor and storage levels should determine the mode.
In drought mode, irrigators (and environmental flows) are cut back to a lowish percentage of their allocations, discretionary water will be charged foretc.

Marco said...

Having these "modes" takes away pressure from having to reduce irrigation allocations. During floods, even excessive allocations won't deplete the environment. In droughts, they are progressively being reduced anyway independently of their permanent allocation. Having a more stringent reduction during marginal droughts is fairer than denying the purchased allocation altogether.

Chris Fellows said...

Crummy subconscious - I had that t-shirt you wouldn't make for me all ready for double ten day, but I had to leave the ute at the servo and ride in, and I *left my change of clothes in it* :/

So not only do I not get to make a political statement, I get to hang around looking sweaty and athletic all day :(