The lack of a three day forecast track map for this system from the BOM seems to have confused everybody, especially since it is likely to cross the NQ coast within the next three days! There is method to this madness and this system is more chaotic than normal, so they don't want to send even more mixed messages than that.
This link shows the best guess of what rainfall and barometric pressure will ensue in the following few days, so I suggest it is the more useful "warning".
Friday, January 28, 2011
Monday, January 17, 2011
Lessons from flooding
I fear that lessons from the Brisbane catchment flooding may not be heeded for the Murray Darling basin at the moment.
The main thing I have seen is that, for the Brisbane River at least, it is enough to refine procedures (or the rule book, as I have heard it called in the media) to have made the catastrophic major flood of the lower Brisbane river a moderate flood (albeit a longer lived moderate flood). The rule book seems to have been written at the time the Wivenhoe was built, and it essentially awaits for upstream data of inflows to enable releases in advance to allow room for incoming floods. This was fine when weather predictions days in advance were highly unreliable (as they were in the eighties) or for inflows of a volume that is not several times the capacity of the dam, nor when "La Nina" conditions point to aggressive early releases being more "conservative", than a wait and see what runoffs eventuate policy.
This lesson, which I am sure will be heeded for the Brisbane River catchment because catastrophic floods make it obvious, seems to be being ignored for the Murray-Darling. At the moment, the calculations are quite similar - with the Menindee lakes at over 100% and three major floods on their way in the next few months.
In 1956, another La Nina year, catastrophic floods hit the lower Murray when floods of the Darling and Upper Murray converged at the same time - Similarly a reaction was to build flood mitigation storages (in that case the Menindee lakes). They really should be emptied at a much faster rate right now, not just to absorb the peaks coming down already, but to have enough capacity to hold back the flood such that it doesn't coincide with possible autumn upper murray floods. The analogy with the Brisbane catchment is that the Wivenhoe may have been able to actually slow down the outflow as the Bremer and Lockyer floods peaked through, mitigating them rather than exacerbating them (If enough pre-emptive releases were made).
Of course, the bigger the flood, the less dams can feasibly hold them back, regardless of strategy.
The main thing I have seen is that, for the Brisbane River at least, it is enough to refine procedures (or the rule book, as I have heard it called in the media) to have made the catastrophic major flood of the lower Brisbane river a moderate flood (albeit a longer lived moderate flood). The rule book seems to have been written at the time the Wivenhoe was built, and it essentially awaits for upstream data of inflows to enable releases in advance to allow room for incoming floods. This was fine when weather predictions days in advance were highly unreliable (as they were in the eighties) or for inflows of a volume that is not several times the capacity of the dam, nor when "La Nina" conditions point to aggressive early releases being more "conservative", than a wait and see what runoffs eventuate policy.
This lesson, which I am sure will be heeded for the Brisbane River catchment because catastrophic floods make it obvious, seems to be being ignored for the Murray-Darling. At the moment, the calculations are quite similar - with the Menindee lakes at over 100% and three major floods on their way in the next few months.
In 1956, another La Nina year, catastrophic floods hit the lower Murray when floods of the Darling and Upper Murray converged at the same time - Similarly a reaction was to build flood mitigation storages (in that case the Menindee lakes). They really should be emptied at a much faster rate right now, not just to absorb the peaks coming down already, but to have enough capacity to hold back the flood such that it doesn't coincide with possible autumn upper murray floods. The analogy with the Brisbane catchment is that the Wivenhoe may have been able to actually slow down the outflow as the Bremer and Lockyer floods peaked through, mitigating them rather than exacerbating them (If enough pre-emptive releases were made).
Of course, the bigger the flood, the less dams can feasibly hold them back, regardless of strategy.
Saturday, January 08, 2011
Two non-rhetorical questions
Given the current flood on the Mary River I have two serious questions:
1: Would the Traveston Dam have been ableto mitigate this flood in a meaningful way?
2: Is a major flood any LESS a threat than a dam is to the lungfish or any other endangered species of the river?
I suspect the answer to the first is possibly yes, even though the premise of it needing to be built was predicated on mitigating drought, the shallow nature of the valley it would have flooded would tend to at the absolute least flatten the peak of floods, and with a bit of luck and timing could have absorbed most of it.
With the second question, I suspect the flood would have done the lung fish little damage, but I am not aware of how it copes with floods. Most fish use it as an opportunity to spread. Endangered land animals already marginalised by drought and the encroaching humanity might have been better off with a mitigated flood, however.
1: Would the Traveston Dam have been ableto mitigate this flood in a meaningful way?
2: Is a major flood any LESS a threat than a dam is to the lungfish or any other endangered species of the river?
I suspect the answer to the first is possibly yes, even though the premise of it needing to be built was predicated on mitigating drought, the shallow nature of the valley it would have flooded would tend to at the absolute least flatten the peak of floods, and with a bit of luck and timing could have absorbed most of it.
With the second question, I suspect the flood would have done the lung fish little damage, but I am not aware of how it copes with floods. Most fish use it as an opportunity to spread. Endangered land animals already marginalised by drought and the encroaching humanity might have been better off with a mitigated flood, however.
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