Wivenhoe role in Brisbane floods

Spillway at Wivenhoe

An article in The Australian today highlights the role of the Wivenhoe Dam in the flooding that affected Brisbane:

The official records from SEQWater show that, at 6am on Friday, January 7, Wivenhoe Dam, Brisbane’s insurance policy to protect the city and surrounding suburbs from a massive rainfall and flood event, was at about 106 per cent capacity. This means that Wivenhoe had filled to 100 per cent of its capacity for water supply with a total 1.15 million megalitres, and it was 6 per cent into its additional 1.45ML of storage for flood mitigation.

On Saturday, January 8, it is understood to have let about 100,000ML go; on Sunday, when Mr Goodwin’s family was there, a further 116,000ML were released.

By 9am on Monday, the levels in the dam had soared to just over 148 per cent, and it was reported that managers at the dam had “scrambled”.

That afternoon, the extreme rainfall over Toowoomba and the Lockyer Valley unleashed a maelstrom that the Bureau of Meteorology had not predicted. While the run-off from this event did not fall into Wivenhoe’s catchment of about 7000 sq km, the dam’s operators were caught by surprise and released 172,000ML as the capacity went past 150 per cent.

Through Tuesday, as Wivenhoe continued to rise past 175 per cent and then 190 per cent, the situation was becoming critical as the available buffer for more rain had been almost fully taken up. Nobody wanted the dam to go to 200 per cent, and the theoretical maximum of 225 per cent needed to be avoided at all costs.

One of the crucial questions that will be asked in a commission of inquiry, called late yesterday by Premier Anna Bligh, is whether the releases from the flood storage compartment of a little over 200,000ML on the weekend were too little, too late, necessitating a huge outpouring to get levels down quickly.

The operators of the dam gave the order on Tuesday, cranking up the release to a staggering peak rate of 645,000ML a day. At that point the Brisbane River flood was not a case of if but when: the computer modelling showed major flooding from this Wivenhoe discharge was inevitable and would peak in the 36 hours the water would take to reach the city gauge.

The release from Wivenhoe at a peak rate of 645,000ML a day represented up to 30 per cent of the dam’s total capacity. Nobody was under any misapprehension about the consequences. It was this release from Wivenhoe that represented about 80 per cent and perhaps more of the volume in the Brisbane River.

A rainfall event that could have been comfortably managed by the dam if its flood compartment had been lower had turned into a major flood that would devastate thousands of homes. (source)

So the question to be asked is, was it an oversight not to release water earlier, and at a more controlled rate, in anticipation of the floods, or was it to preserve water in the dam due to some diktat from the climate change department? Hopefully the inquiry will answer that question.

Comments

  1. I didn’t say anything when Bruce suggested “SEQWater are to
    be commended with the way they handled this” but I think that as
    each new item of data becomes available (and quite a lot was
    released yesterday, just before the inquiry was announced) it
    becomes more and more obvious that they messed up. They may have
    followed the procedures in the play-book, but that was clearly
    insufficient and they should have known that. It doesn’t change the
    loss of life, or the devastation of the Lockyer valley, but it
    would have made a huge difference to the losses in Brisbane. People
    were saying that Wivenhoe didn’t work as expected, but now they’re
    realising it would have; if it had been used as designed.

    • Russell (I’m assuming you’re talking about me) – obviously more data has come to light and opinions are running thick and fast, but at the moment I’ll still stand by my point that they should be commended for the way they handled it. Anything could come out which reverses my opinion on this, but they were following the operating rules of the Dam to the book. This is evident in the BOM plots of dam heights. The rules (as I understand them) state bringing the Dam back to 100% within a week of a peak, so that’s what they were doing when caught with very high flows. Many rivers and streams were close to the minor flood level going into the weekend. The Bruce Highway was very nearly flooded at Caboolture late on Friday night as I drove past. Perhaps they took their eye off the ball with regards to forecasts and were concentrating too much on the here and now going into the weekend.

      I guess my main point would be to say that it was no time for inventive strategies and they appeared to be not under any political influence. So they did their job well. The Dam was kept very close to maximum capacity during the flood peaks, which is similar to trying to keep a balloon with a hole in it inflated when you’re not entirely sure how much air is coming in the other end.

      I’ll reserve the right to completely backflip on my position if information comes to light that they were under the influence of ministers to not flood low lying areas, or any other such pressure.

      My expectation is that an operating review of the dam will probably incorporate BOM predictions for rainfall in the catchment, and that future flood peak releases will be done more aggressively. People with property at or around the minor flood level will probably be told to expect more flooding with more aggressive releases.

  2. “Hopefully the inquiry will answer that question.”

    I am not overly optimistic that this inquiry will answer any pressing questions or produce anything of any substance.
    Readers’ attention is drawn to three fundamental facts:

    1) Anna Bligh’s husband is Greg Withers.
    2) Greg Withers was the principal author of “ClimateSmart 2050: Queensland’s Climate Change Strategy 2007” (i.e. the “strategy” that has spectacularly failed in this instance).
    3) Greg Withers was appointed to head the Office of Climate Change, an office that Anna Bligh created for him when she became Premier.
    http://www.couriermail.com.au/news/queensland/blighs-husband-gets-top-post/story-e6freoof-1111114682554

    That is – Anna Bligh’s husband bears a primary responsibility for the comprehensive failure of Queensland’s response to the evident climate change that is being loudly proclaimed by Will Steffen, Bob Brown and others.

    For this inquiry to produce anything like sensible or realistic findings, Anna Bligh will need to throw her husband under a bus (or at least stand by while others do it for her).

    Odds on that happening?

    • Distressing news indeed, Eloi. So much for the almost universally effusive praise on her performance during the crisis. Tarred with the alarmist brush after all.

  3. Would it not have been better to release 300,000ml/day over 3 days then 600.000ml over one day.And what was going on between Jan4-8.
    Seems a bit like the Pearl Harbour scenario everybody who could make a decision had gone home for the weekend.

  4. About Toowoomba’s flash flood mitigation did they have any and was it in a good state of repair.

  5. bruce askin says:

    Its very easy to lay blame after an event, Did anyone really know how mush rain was due, had they released more water earlier & then copped another drought they would have been under fire for wasting water. I previously wondered why levies werent built along the brisbane river as in many NSW towns. The reason is the richies dont want to spoil their water views. The rest of brisbane has to suffer because of the financial influence of the few. I would guess the cost to these select few is not going to burden them to much anyway

  6. “Did anyone really know how much rain was due..?”

    Apparently, yes.
    “In the days before the flood, the BOM warned of an upper level low pressure system dumping a large amount of rain over southeast Queensland.”

    http://www.theaustralian.com.au/news/opinion/far-too-much-water-left-in-the-dam/story-e6frg6zo-1225990589929

  7. It is very easy to be clever in hindsight.

    I was watching this situation develop from the Christmas Day event and called a 74 event in Brisbane on the Saturday based off weather modelling. This was obviously a well calculated guess at that point in time.

    Sunday panned out exactly as the models suggested and I then started tracking the water through BOM’s guages from the areas of Gregor Ck, Linville, The Stanley etc into our wonderful flood mitigation catchment.

    The peaks recorded on the Sunday were extremley high in the upper brisbane and both dams responded far faster than anyone had predicted. Gates were further opened to try and manage the inflows and were pushed to the minor flood limit at Mt Crosby.

    At this stage the models were saying the rain would continue but WHAT REALLY HAPPENED is on tuesday morning when dam managers were preparing for another thrashing the band spread and dumped HUGE falls over the un mitigated lockyer and bremer catchments at the WORST possible time.

    The reason I say this is Wivenhoe had been performing its job PERFECTLY and SEQ Water played it very well. They pushed the dam to its absoloute limit holding back as much water as they could. When the region wide fall occured it produced similar inflows to Sunday’s deluge and the dam started rising incredibly fast – some 15cm per hour. It came within about 1/2m of the dreaded 75.3m which is when the first spillway is designed to fail. If that happened the 650ml release would have looked like a council water fountain.

    And here is where the remarkable actions occured. SEQ Water CLOSED the gates to 200 or so ml in the middle of the crisis to try and off sync the unexpected peak from lockyer and bremer. When they did this the headwaters of Wivenhoe once again started rising DRAMATICALLY and it was VERY apparent that the dam would fail. They were then forced to increase flows back to 300ml to stop this from happening.

    What they effectivley did is throw the water out of sync by utilizing one of our largest pieces of infrastructure to its maximum potential.

    There is really only 1 vaild point here in terms of Wivenhoe ‘causing’ what is mother nature’s intention (the sheer arogance and ignorance of human’s believing they ’caused’ this is insane) and that is the dam could have been emptied more before the crisis. But this is in hindsight. and we dont have enough water as it is. Secondly the dam has been doing releases since October and was releasing right through the weekend starting at 150ml per day and ramping up as the event unfolded.

    People seem to think that the dam can withstand anything. This is rubbish. In fact the dam doesnt have bucklies chance of holding back a true 1 in a 100 event and it is completley nieve to think that it will. The fact is we experienced falls of around 300-400mm catchement wide over the course of our ‘flood’ which is NOTHING in comparison to a 1974 (think 500-750mm) or 1893 (750mm+) amount over the same period of time.

    In short process can always be improved upon but this blame game is ridiculous. The gate operation on Tuesday night from 650ml to 300ml was a calculated mitigation strategy that was carried out without error. To say the dam could have been operated more effectivley is a very hasty opinion at this stage. What people have to realize is that the inflows were HUGE. When they were releasing 500mL the dam was still rising FAST. They had no choice and to be honest – it was only just steady at 650ml. What that means is that they were spitting out 1.2 or so Sydney harbours per day and at the same time there was about 1.1 Sydney harbors flowing IN to the dam at the same time. To expect a man made piece of infrastructure to be able to hold all that back is insane. There were something like 5 sydney harbors which either went through the gates or were held in the dam over the course of the event. Thats a pretty large bucket of water!

    If you look at the rainfall comparison above and apply the lack of storm surge due to the lack of a cyclone in the most recent event you will see that Brisbane is well and truely F@#@ed WHEN (note that it is not if) it really does happen. We could EMPTY Wivenhoe which would leave us with about 5 sydney harbors of mitigation and it would go from empty to 225% from a ‘small’ flood event. Its like expecting a straw hut to withstand a cyclone. Just not going to happen.

    I guess my point is – blame isnt going to achieve anything. I think the biggest failure in this whole disaster has been not the mitigation but more the total lack of warning the Brisbane recieved. This should have been called on Sunday with the CBD shutdown from at the very latest COB Monday. All the data was there to make it a near certain decision and yet the govmt failed to act. All of those people could have removed nearly everything in that time. Shops would have had more time to deal with emergency supplies. The total road chaos from people going to work on Tuesday would have been avoided and there would be a whole heap less people whinging about an event that has happened nearly every 20 years on average over the last 200.

    With that statistic in mind why are people so surprised?

  8. Electrical Engineer says:

    Jeff Wehl said:

    The peaks recorded on the Sunday were extremley high in the upper brisbane and both dams responded far faster than anyone had predicted.

    They may have responded faster than anyone predicted but everyone should have predicted by 9 pm Sunday night that the rain that had already fallen (more than 700 GL since 9 am), let alone forecast rain, would fill up the dams unless releases were greatly increased.

    Gates were further opened to try and manage the inflows and were pushed to the minor flood limit at Mt Crosby.

    They were still trying to keep those bridges open even though they should have known the dams were going to fill up. Even when those bridges eventually were flooded they still didn’t increase releases to anywhere near what they were allowed until Wivenhoe hit 73.5 m.

    Also, those last two bridges (Fernvale and Mt Crosby) had already cost 15% of the flood reserve or 175 GL by Saturday morning to keep them open. Compare that 175 GL with the 280 GL that flowed past Savages crossing in excess of 3,500 m3/s (maximum non-damaging flow) during the flood. That’s a lot of floodwater just to have saved building higher bridges.

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