As advised by SEQ Water just a moment ago regarding WIvenhoe & Somerset:

Minor releases from Somerset are continuing at a slightly increased rate of 408m3/s.

Minor releases from Wivenhoe are continuing at a slightly increased rate of 370m3/s.

Current strategies would be in violation of the 2010 Manual for dam operation, or at least my reading of it.
- At levels between 0.5m and 0.75m above the FSL limiting release from Wivenhoe is 380m^3/s, current release is 420m^3/s.
- If strategy S2 is invoked (Wivenhoe & Somerset above FSL), water cannot be released from Somerset until it reaches 100.45m (approximately). Perhaps they are claiming S1 (Wivenhoe below FSL).

Perhaps some things have changed in the manual, and/or there is a lot of sensitivity about retaining water in the dam. I wish they'd have been this aggressive in 2011.

Well its been a week since that post and Toowoombas dams are now at a combined level of 99.8%. Cooby dam only got about 20mm over the week, therefore it didnt fill.

Cooby dam - 97.1% (19,129 ML)
Cressbrook dam - 100% (79,058 ML)
Perseverance dam - 100% (26,967 ML)

I've been going back over some of the dat from the event and picked up on something quite interesting.

At midday on Monday 10th January, the total outflow from the dam was 2,053m3. Allowing 12 hours for this to get to the Moggill gauge, combined with existing flow from the Bremer and Lockyer catchments this generated a 6.5m river level at Moggill at midnight on the Monday.

Roughly 12 hours later (midday Tuesday) this water was reaching the city reaches of the Brisbane River. I was at the rivers edge around midday and observed Regatta Ferry terminal starting to go under. 5 hours later I was down at the drift restaurant watching pontoons and other peices of flotsam float past.

Any one who believes they could have released 2500m3 on the Saturday and Sunday without an expectation of significant urban impact by Monday/Tuesday clearly has no real comprehension of what was occurring. I have the video proof of the damage and mayhem even a 2000m3 release caused in the Brisbane area.

So what release limit should be imposed?
If we could rewind to January 2011, and we had collective control of Wivenhoe/Somerset, what could have been done differently to minimise the flood impact?

I don't think it should be less than 4000cumecs in W3. I would even question the concept of measuring this at Moggill, other than on a "best endeavour" basis. In 2011, this flow rate was exceeded at 11am on 11 Jan, 3 hours after W4 was invoked. I do not believe this is due to the increase in outflow from 8am. So an argument can be made that this level of flow was in breach of the manual. Such a thing should not open up public liability for damage.

My suggestion for the limit of discharge in W3 is the greater of:
4000 - Current Bremer&Lockyer flows
4000 - Predicted Bremer&Lockyer flows

That way there is no danger of a flash flood event causing a breach of the manual, as still applies in the Sep2011 version, which gives the engineers certainty.

I hope the commission can find a way to make a finding which doesn't make the state make significant payouts for this event.

So you would have allowed a 4,000m3 flow at Moggill in October and January 2010 and flooded hundreds if not thousands of homes 3 times in the space of 4 months?

Study the flows a little more. You can measure the impacts of the flows at various times also by going back through the event thread.

Perhaps one approach look at whether the W4 strategy should be implemented a little earlier.

The target should be just under 4000cumecs @ Moggill, but it should not be a hard "limit", opening up liability, for that as it is too easy for such a limit to be breached in circumstances beyond the engineers' control. This resulted in Jan 2011 in them having a fairly wide buffer which still proved insufficient.


Absolutely not! In fact, I would be happy for it to be implemented later, and without the concept of avoiding eroding the first fuse plug like the plague. Problem is that the current strategy/dam doesn't allow compliance with the Australian standard so arguing that it can be relaxed isn't going to hold up unless you can argue that you can improve Somerset safety while doing so.

In case anyone is interested, the Sep2011 manual is available here: http://www.seqwater.com.au/public/sites/...8%20Sep2011.pdf

In case anyone is interested.

Irks me that this water is to be released.

I think it irks most people on this forum that water security is being jeopardised just because armchair experts/flood victims think it should be done.

Did you mean with a more slowly graduated increase in releases here?

Well currently W4 is implemented when the dam level can't be kept below 74m whilst maintaining a maximum 4,000m3 flow at Moggill.

I guess this approach takes into account how much inflow is coming into the dam. A 73.5m dam level which is rising at 25cm an hour is going to hit 74m as surely as a 73.8m dam level rising at 10cm.

I really don't think there is a right or wrong answer. You can start releasing earlier and achieve a final flood level assuming the rain keeps falling. Or you might release a greater amount than you really needed to if it doesnt.

When you get into that type of situation you need sound principles ahead of hard fast rules albeit with the exception that you dont want to put the dam at risk.

I think to a certain extent the current guideline allows this. In some cases it will not achieve the optimal result in other cases it will.

Its easy to sit down afterwards knowing the inflow on an hour by hour basis and plot a release strategy that achieves the optimal result. Dam operators who do not have a crystal ball don't have that luxury.

I'd disagree. If you don't have the hard and fast rules, how are you going to model the risks of various low lying areas going under?

Also, the dam is always at risk. It's just the degree of risk which should be accepted which is at issue.

Wel said LLocke. Alll those who continually bash the dam operators do so with the benifit of hindsight and believe they are the wisest peope on the planet. Given the dynamic and uncertain situation facing those making the descisions I reckon they did a fantastic job and all the whingers should bugger off and be thankfull that far worse did not eventuate. This was a potentail 1890's event that was turned into a sub '74 event. Deal with it.

Let me rephrase then Somebody.

In a scenario where conditions can change quickly, strict guidelines and processes which allow for no degree of flexibility are a recipe for disaster. You can paralyse a person into taking no action at all at a time when taking no action is the wrong action.

In some cases, it is simply not possible to provide a set of guidelines that are suited for every scenario. In the field of risk management in which I work this is certainly the case.

Whilst there are some absolutes in terms of the guidelines I follow, in the more complex situations I am expected to exercise my judgement based on years of experience in order to acheive the best result. It is simply not possible to formally document a rule for every possible scenario.

What worries me about this whole witchhunt is that SEQWater might be pressured in to changes that will result in the likelihood of dam operators in future opening the flood gates at the drop of a hat for fear of being sued because they "didnt release early enough".

I want trigger happy dam operators about as much as I want trigger happy cops.

I'm going to waigh in on this descussion

one thing we need to remember is and i quote from the flood comissions own inderpendant hydrologist "flooding of Brisbane in January was inevitable and engineers had done a good job"

also dont forget why the dam was origianlly build (and this is taken from seq waters own website "It is anticipated that during a large flood similar in magnitude to that experienced in 1974, by using mitigation facility within Wivenhoe Dam, flood levels will be reduced downstream by an estimated 2 metres.

a 1974 event... jan 2011 far excded a 1974 event infact rain rates were closer to a 1893 event. in 2011 the flood peaking at 4.46 metres (14.6 ft) in Brisbane City, the flood level was about the 10th highest in the city's history, several metres below the 1890 flood and the two major floods in 1893 (WIKI). so in my opinion that a "job well done boys"
how in saying that i'm not saying more could be done to further decrease these values in future events extensive training for junier dam engneeres in the area of risk managemnt and decision making and continued training for existing engneeres.

a revew of the dam operating manual after every sigfigicant event. what worked? what didn't work? what could we have done better? and how can we improve for next time? and this really is a P&P at the seqwater level that need to be constantly reviewed

and a blackout on future development in low lying areas on the Brisbane vally flood plain (what the actual figure for this is not for me to say and left to experts). 4.46m in not a large flood and the fact so many homes built after 1974 were allowed to built in this zone is ludicrus boarding on incompitant

I personally feel that the provisions of "reasonable discretion" in the manual cover this point, where the Chief Executive/delegate's approval can be sought to deviate from the manual in any way desired.

I'm interested to hear why you think that it doesn't.

Oh, and by the way, does anyone know at what flow the Moggill Ferry needs to stop running?

What you ignore is that while it might be 4.46m at the city, it was 12m at Jindalee. To black-out future development on properties below a 4.5m peak at the City is silly, especially given that this is a 1 in 100 flood (or so). This was two 1974 events in terms of rainfall. Had we had half of the rainfall we received, Brisbane would have escaped unscathed.

Instead, we should buy-back properties below the 2.5m flood mark, and prevent future development there. The raising of Colleges Crossing might be an idea as well. Not only is that more realistic, but it allows (in future events) for the Wivenhoe Dam operators to release a fair amount of water without causing damage to property.

4.45 meters might not sound big, but everything is relative.

Q: Should Colleges Crossing have been closed in recent days, until Sunday apparently?

Are they working on the basis they have 7 days to reduce the dam level back down to 75%?