Unable to wait for the outcomes of the Queensland floods royal commission all sorts of people have been quick out of the blocks to criticise the management of the Wivenhoe Dam. An early one suggested outright that the flood peak was man-made. That bloke has a bit of form in that he’s never wrong. A royal commission which disagreed would merely demonstrate their stupidity in his book.
Another line of argument suggests that the balance between water storage and flood mitigation should be altered in favour of flood mitigation. Quiggin suggested ( Kim’s Quick link post here) that the water storage compartment could be reduced to 75% of the present.
Legal eagles are circling, waiting to see whether the royal commission provides the basis for a class action.
I won’t link to all the other experts who have come out of the woodwork, giving opinions that a bit of work on the back of an envelope together with information publicly available, but not heretofore collected in one place, would have shown them to be foolish.
The situation is fairly simple, but first you need to understand some basic metrics about the dam.
The Wivenhoe Dam when full to the top of the wall has a storage capacity of 2.6 million megalitres (ML). (ML is by convention the basic unit of measurement in this discourse. Get used to it!) This is divided into two sections. There is a water storage compartment of 1.15 million ML (more on the adequacy of this later). On top of that sits a flood mitigation compartment of 1.45 million ML.
By convention the dam is deemed 100% full when the level is 1.15 million ML. At 2.6 million ML it is therefore 225% full. You will hear that these compartments are split 40:60. The simple application of a calculator will tell you that should be 44:56.
At 225% full the dam wall is threatened, so the managers try to keep the levels below 200%, at which time the sluice gates are ineffective and they have to open a series of valves which leads to an uncontrolled release. During the latest event the level peaked at 191%, I think, which is as close as they’d want to go for orderly operation. At that point they were pretty much obliged to release an amount equivalent to what was coming in. Hence we had a flood but we would have had a flood anyway, because the Wivenhoe only controls 40% of the Brisbane River catchment. There was plenty coming down the Lockyer Creek, which joins the Brisbane about 5km below the Wivenhoe wall, and the Bremer River, which enters further down via Ipswich.
There have been allegations that too much water was held back and then had to be released when the rain was pissing down. Any dolt could see it was going to rain.
Well I watch the weather pretty closely and I can tell you that any dolt can’t see that it’s going to rain. Often they say it’s going to rain and you wake to find that the weather influence is 50km out to sea, or has migrated north or south. There are plenty of instances where you get a significant downpour and then practically nothing for six months.
The Wivenhoe operates to strict rules, with rule number one that no politician should interfere. These rules have now been released. The highest priority is dam wall safety. The second is that you don’t release water that will flood urban areas.
The Brisbane CBD gauge is in a tidal area, and I understand zero is effectively sea level, which is an average midpoint between low and high tide. A fairly normal tide is 1.6m, a king tide is 2.6m. the flood peaked at 4.45m, so you can see there’s not a lot of leeway. The one riverside area I know well sees a highish tide with the river out of what a normal person would call its channel, spilling onto a low-lying grassy area. I’m not sure at what point the level becomes a minor flood.
Another rule is that the flood compartment must be emptied within seven days, all thing being equal.
From this site you can see the recent historic water levels of the dam:
Historic water levels of lake Wivenhoe
From this you can see that the Wivenhoe probably knocked out three instances of perhaps minor flooding before the big one. The Oz, which is on a campaign about this, have latched on to some engineer’s emails and are making much of them. Just remember that when the levels hit 190% they had a dam wall to protect, a flood entering downstream from the dam wall, which in the event was close to 50% of the whole flood water, flooding already occurring in Brisbane, the prospect of king tides coming up, and water entering the dam at the rate of 2.6 million ML per day, with a forecast that the rain would break but not for some very long hours. The flood was being monitored with 200 gauges and constant reference being made to the BOM.
I’d be more than happy to cut them some slack, pending the inquiry.
Had they gone into the event with the dam at 75% capacity instead of 100% how much difference would it have made? They would have been 287,000ML better placed, that’s what. And that would have filled in about two and a half hours.
In a Courier Mail article of 18 January I can’t find on the net, we were told that the Brisbane River would have been flooding at the rate of 13,000 cubic metres per second, if Wivenhoe did not exist, compared to 9,500 in 1974. I came to the rough conclusion that Quiggin’s idea might have shaved centimetres off the flood.
Yesterday on local radio I heard an expert hydrologist say exactly the same thing. I thought his name was Professor Ackenasy, but google doesn’t call him into being. I listened to this guy, because as a younger man working for the relevant authority, he set up the operating rules for the Wivenhoe Dam. This is some of what he said.
The rules were set up on the basis of flood behaviour according to models. Now that we have an actual instance, of course they will be changed on review.
This flood, without the Wivenhoe, would have been about 1.5 metres higher, that is 6m instead of the actual 4.45 and 5.5 for 1974. The difference in using different release rates would have been trivial, a matter of a few centimetres.
The Wivehoe is useful for flood mitigation, but there are limits to what it can do. On the positive side it has completely knocked off two significant floods since it was built.
The Brisbane River according to the 160 years of records available, floods every 20 years on the average. This one was roughly one in 40 years, not the one in 100 typically quoted. Much of the rest of what he said I’ve already included in the above.
So settle down everyone, but that 1 in 40 figure is a bit alarming.
This post is already long, but I want to say a bit about storage, before we go cutting bits off it.
Anyone contemplating such ideas should read and learn by heart this SEQ Water Strategy document (large pdf) which you can (download from here). One of the more interesting figures is this one:
Partitioning SEQ water storage
The idea is that we have a 1% probability of being reduced to the T1 trigger (40% capacity) in the next 10 years. Knocking off 25% of storage from the top would compromise this safety margin and make water much more expensive.
At T2 (30% capacity), you should be building climate-independent extra capacity and have another 30 months to complete it.
Under this planning regime, which takes into account population projections, we should have medium level restrictions no more than once in 25 years, those restrictions should not last more than six months and should amount to no more than a reduction of 15% of normal entitlement.
Sounds rational to me.
While we are at it here are the SEQ dam capacities. There are no more sites available, other than building the Wolfdene at huge cost of resumptions.
This map shows the rivers and dams in the area:
SEQ dams
The Somerset is below Kilcoy and above the Wivenhoe at Esk. These together with the North Pine Dam to the east constitute the main Brisbane storage. The Locker Creek flows in from near Toowoomba. The next river system down is the Bremer which is shown as flowing to Bundamba, a suburb of Ipswich. The Lockyer Creek catchment is actually about 50% bigger than the Bremer and was one of the driest catchments in Qld during the drought. Neither has major dam sites.
The Woldene dam was to be on the Albert River just north of the Gold Coast.
This map shows the rivers more clearly:
SEQ water resource areas
A point of interest here is that the now-abandoned Traveston Dam was to be on the Mary River approximately west of Noosa, I think. It was a case of stuffing over one community to serve the needs of another, and about as popular with the locals as raiding the water resources of the Clarence to the south would have been.
Brian, a major factor in the ’74 flood was that the water coming down the river (again, much of it from the Bremer and Lockyer catchments) peaked at the same time as the Brisbane suburban creeks were peaking. A lot of the flooding around Brisbane was from the creeks backing up – e.g. Moggill Ck at Kenmore, Norman Ck at East Brisbane and Kedron Brook at Nundah. On this occasion, the Wivenhoe engineers were able to hold the upper Brisbane and Stanley peaks back for enough time to allow the peaks from Lockyer, Bremer and suburban creek flash flooding to subside before opening the sluices. There is no doubt in my mind that this substantially reduced the flooding in metropolitan Brisbane. Moreover, in 2010 most of the flooding in metro Brisbane occurred after the rain had subsided, making relief and rescue efforts more effective and less dangerous. Again, in ’74 the main river inundation occurred as the rain bucketed down.
IMHO the Wivenhoe engineers deserve medals, but in all likelihood the OO campaign will mean they’ll get nothing.
Hal9000, in ’74 I was living in Kenmore Road and we had an operation in the old Red Comb House. During the night in question I drove in there via the back roads of Chapel Hill to check out the ground floor. Thence across via Wardell St, Banks St and Kelvin Grove Road, from memory. Red Comb was well above flood level but water was coming down the inside of the back wall and moving across the floor. I worked about 3 hours in there with a wild wind blowing and doors banging elsewhere in the building, by myself. It was spooky.
My memory accords with yours. The catchment was saturated, Somerset Dam was full, and I think cyclone Wanda cut inland to the north and then came back out to sea as a rain depression moving through from the west. Most of the evacuation occurred at night with wind and driving rain. Altogether more scary.
So, all the “experts” coming out of the woodwork don’t need to wait until all the information is in, collated and the inquiry held, Brian?
And all are no doubt experienced flood mitigaters and could have imparted this 20/20 hindsight at the height of the floods? I’m astonished they didn’t come forward with all this sage advice when it was so desperately needed.
Is, perhaps, Professor Hubert Chanson the “expert hydrologist” you refer to?
http://www.abc.net.au/news/stories/2011/01/21/3118379.htm?
Brian: Good one. Of course there is nothing like hard facts to stuff up arguments.
To my mind the idea of Brisbane running out of water is more frightening than floods – Where the hell would the Brisbane refugees go to, particularly given that the drought would not be restricted to the Brisbane area.
Have you any feel for how long the various stages would last under current consumptions and the various stage restrictions.
My feeling would be that we should kick in desal and recycling much sooner than the current politically timid policy allows for. In addition the trigger point for a sudden boost in desal construction should be sooner than the policy suggests.
I sense the OO’s basic agenda here is to discredit the BOM and anything to do with climate mitigation planning. If they can pin the blame for the floods on any form of planning process even vaguely related to the BOM and climate-related mitigation, they’ll be reminding us of how this is all “too difficult to trust to government” for years to come, as a fatalistic and cynical argument against AGW mitigation/prevention.
John D, they say that we should get to T3, which is a slightly moveable feast but roughly 20% capacity, once in 100 years and to 10% capacity once in 1000 years.
That’s pretty good, I think.
The only thing about leaving recycling to 40% is that it’s expensive water if you use it earlier, but we should probably max up recycling as a higher priority than using desal.
There’s stuff in there about tanks, which I think are mandatory with new construction, and storm-water harvesting, that I didn’t have time to look at properly.
On the whole, though, it seems to me a very rational piece of work.
Refugees shouldn’t be necessary, but when we were down to less than 17% a few years ago (about mid 2007, from memory) and 18 months away from the SE Water grid and associated works from being completed, things didn’t look good.
Jane @ 3, quite so.
sg @ 5, they are evil, cynical bastards, I think, and don’t need any motivation beyond that. But you could be right.
Me too. But the tricky part, as you know, is that any scenario will be a counterfactual. We’ll never know what might have been done.
Interestingly, decision makers under extreme pressure use a highly instinctive decision making process that does not resemble the process taught in decision theory. For a full (and very interesting) discussion, see Sources of Power: How People Make Decisions by Gary Klein.
The arm chair critics are really giving me the irits. People should wait for the evidence. I also think the guys from SEQWater deserve medals. Not only did they manage the dam, but they kept the water supply on to most of SEQ, with only small areas having boil water alerts.
One of the impressive factors of the crisis was the way assets developed to protect us from drought were deployed to save us in a flood – desal water into the drinking water supply, and recycled water used for the clean-up all took pressure off a struggling, but still functioning, Mt Crosby water treatment plant.
Of course, the role of certain elements of the MSM will be beating this up for all it’s worth. But I wish the ABC would behave better.
Jacques, in this case the counter-factuals are clear – we have exact information on what was happening at the dam and what would have happened if things were done differently. The media just don’t want to look at that information because a) scary numbers omfg and b) pack of fucking arseholes.
It’s not exactly “what would have happened if hitler was admitted to art school,” is it?
I wouldn’t be so quick to assume it wasn’t offered in a timely fashion.
Just as a heads up on storage, there had been talk for a while about damming the top-most reaches of Clarence in northern NSW, just 50km south of the border. That would have secured SEQ’s water supply, specifically the Gold Coast’s way better than the Wivenhoe could, therefore allowing the Wivenhoe to divert even more storage to flood mitigation. (Not that it would mattered much in this case)
From what I’ve heard the NSW Govt apparently got the shits even thou QLD would have paid for both the Dam & the water, specifically because NSW wouldn’t get much benefit out of it. Long story short, the discussion was canned.
When you think about it, it makes you wonder why some issues aren’t taken directly out of the hands of State politicians & handled directly by Canberra.
Brian @6: What I really wanted to know was how much time is left after T3 is reached?
sg @10 (“the counter-factuals are clear”)and Brian @7(“[the Australian] are evil cynical bastards.”)
I thought we were waiting for the inquiry and the evidence? You can’t have it both ways. Unless of course you really mean “people who disagree with my view need to wait for the inquiry and the evidence”.
To be clear, my post didn’t criticise the decisions made by the dam managers, but made suggestions for the future based on the experience of the flood. So, some responses:
1. Taking all your data as given, I don’t find your analysis convincing. As you show early on, the fact that the dam reached 191 per cent necessitated a qualitative change in the management strategy, which greatly increased the required outflow from the dam. Given an extra 25 per cent buffer, there would have significantly more flexibility. Without having access to the operating rules I can’t say how much, but neither, I assume can you.
2. You nowhere give any basis for your repeated assertion of “a few centimetres”, or even any range to cover this. Linear interpolation would suggest substantially more than a few.
3. Flood damage is not a linear function of peak river height. A 4.45 metres flood submerged houses that would be safely above water level in a king tide of 2.6meters
4. The extra cost of using recycling/desal more of the time is trivial in relation to either the cost of flooding or the social cost of water restrictions – rough guess would be around $100/household/year, or maybe $100 million a year, as opposed to many billions in damage from the Brisbane floods. On any plausible rate of return, this is a mistake reflecting an excessive focus on the internal accounts of the water business.
5. An obvious modification to the proposal would be to adjust the target seasonally, aiming to go into the wet season with less than 75 per cent capacity and end the wet season with more. History suggests that flood risk is greatest in January, although of course climate change implies that we should not rely too closely on history.
Argh! Argh! You cause me pain and I cannot finish this article!
2.6 million ML, not 2.6 million MLs. You can’t pluralise these metric abbreviations! (That said, it should be 2.6 TL, just because the prefix “tera-” isn’t in the popular mind yet, and it is appropriate here.)
Excellent post Brian. Wonderful job of pulling all this information together.
Mott does seem wrong about one thing. He seems to insinuate that that there was no date for the weekend before flood and that SEQ took the weekend off. Of course he wrote his post on the 13th but today’s article in The Australian reveals emails that show the situation was being monitored over that weekend.
In the end I have no issue with the management of Wivenhoe Dam being examined but it does seem to have strangely become an idealogical battle.
Great post, lots of great information.
Note that while no dam sites available Wivenhoe’s dam wall could be increased by 4m at the cost of about $138m. That would deliver around 481,000 ML of extra contingency
See here http://www.qwc.qld.gov.au/planning/pdf/support-docs/provision-of-contingency-storage-in-wivenhoe-and-somerset-da.pdf
On a separate note, why does almost every post on this site have to attack the Oz?
I see nothing wrong in their articles, it’s not turning into a political game, no one is blaming Anna Bligh. But investigative journalism should ask these questions so they start the debate.
You probably would not have written this article without theirs.
The Royal Commission hearings on this will be worth reading.
Much to comment on here. Unfortunately I have some stuff to do in the next few days, so not sure how far I’ll get tonight. I’ll leave John Quiggin’s to last, because if I start there the odds are I’ll get no further.
Meanwhile on the dam rules I was going on this Courier Mail article. Tonight I did end up finding the real thing after rummaging around.
John D @ 6:
John, I only read bits of the SEQ Water Strategy document, but I recall them saying that the level of T3 would be decided according to the conditions at the time, but it would be in the region of 20% storage.
All I can say is that in mid-2007, when Armageddon loomed, we were below 17% and with usage down to just over 120 litres per person per day, we were losing ground (or water!) at the rate of about 1% a month. That was when the Government actually called tenders for emergency supply. There was talk of bringing water down from FNQ in bladders, tankers from NZ, towing icebergs, setting up floating recycling plants in the Brisbane River etc. Not sure how much of that was silly talk, but the situation was desperate with the major works not scheduled to be finished until December 2008.
I think you’ll find that we got one small burst of rain in June and another in August, which took us over 20% and we went on from there. Along the way they cancelled the tendering process for emergency supply.
But if they make the right moves at T3 we shouldn’t get into that situation.
Wozza @ 15, the main thing I’m objecting to is the notion that the dam authorities stuffed up as a fact.
Alexander @ 17, I’m sorry for pluralising the abbreviations. I stand chastised. Didn’t know it was a sin.
I think the public mind is always going to be confused about how many noughts there are in a gig or a tera. I’ve noticed that the CM, the ABC and just about everyone else talks about dam storage for domestic purposes in terms of megalitres. I was chastised on an earlier thread, but remain unrepentant, for reasons similar to why I suspect Bob Katter will always say a “thousand million” instead of a “billion”. No-one should be confused or misunderstand him.
Matt C @ 19, yes someone did accuse Bligh. Look here.
At that stage I’m not sure that hydrology engineers en masse or whether it was the likes of Ian Mott and Joanne Nova.
The Oz has done much and very consistently to earn the ire of people on this site. Whole posts were devoted to the issue, but I’d instance their consistent war on science, as documented at Deltoid.
Also the BER where they published a negative story on the front page every day for months. The official inquiry showed that the incidence of complaints was from memory between 2 and 3% of some 24,000 projects. The picture they built up was one of an incompetent government, when a fair minded approach would have come to the opposite conclusion. We’ve had whole posts on that too.
Plus more, much more.
Thanks for the link to the possibility of raising the Wivenhoe and the Somerset dams. I had heard it mentioned but didn’t know whether it had any substance.
John Quiggin, thankyou for a detailed response. I’ll have to take a longer run at it later. A couple of things.
I’d place more store on what Professor Ackenasy(?) said rather than my own estimations.
Secondly, I’m well aware of a lack of linearity in statistics around flood heights etc.
Thirdly, the weather event that did us in was quite unusual. It was a long cigar-shaped strip from Tewantin through to Warwick and beyond. The forecast had been for rain in SEQ but there would have been places that got very little that day. It was smack over the North Pine dam catchment, the Wivenhoe and the Lockyer, I think less so the Somerset and the Bremer.
It just sat in one place, whereas every other system over those days moved during the course of a day.
Perhaps the rules were too rigid to respond optimally in those few hours. Hopefully the inquiry will tell. But Prof Ackenasy(?) seemed to think it wouldn’t have made much difference. He said he’d be more than willing to put his case to the inquiry, so I hope that happens.
Right now I’d still favour keeping the balance between storage and mitigation roughly where it is, but more of that anon.
JQ, your point 2.
Given the high non-linearity of dam capacity with stage (height), you should not try to infer what you did using linear interpolation.
Grace @ 4, as a first timer(?) your comment was auto-moderated, now released. The link you provide about what Prof Chanson said is interesting. Don’t have time now as I’m on the fly.
The one Madonna King interviewed I heard first as Askenasy, but when she signed off she said something like Ackenasy. Definitely not Chanson.
JQ said:
I find this an appealing idea. The link I provided in the open floods thread allows us to to look at flood events in QLD going back a fair way (I started browsing from the 1940s). There was a very definite cluster between October and April and within that, between November and February.
As I’ve said elsewhere, the inflows to Wivenhoe were so large that it’s hard to see how even a bone dry Wivenhoe would have foreclosed flooding by very much this time around. The event itself was huge and of course it came on top of previously good rains. With Climate Change, we will probably get more such events more frequently, which does suggest a change in built development patterns in low(ish) areas near the rivers.
Brian @ 28, it’s Professor Neal Ashkanasy. He’s cited in this article by Tony Koch in The Australian:
http://www.theaustralian.com.au/national-affairs/brisbane-saved-from-ruin-by-dam/story-fn59niix-1225992598096
The link @30 has some very quotable quotes from Prof Neal Ashkanasy, a water resources engineer and psychologist who now works at the University of Queensland and a former national president of the Hydrology and Water Resources Institution of Engineers.:
The real danger with this inquiry is that the focus will be on flood mitigation. It is crucial that the inquiry is an integrated one that looks at both floods and water shortages as well as making the city less vulnerable to the effects of both.
One thing is for sure. Brisbane will have to face worse droughts and worse floods than we have experienced recently at some time in the future. We need to be ready to deal with both.
Brian @22: The diagram says that construction of drought resistant supplies would start at T2 which looks as though it would be around 30%. I am not sure that 30 months would be enough if construction of a desal plant was to start from scratch. There should be a very clear plan with conservative construction times and possibly stages that would allow the job to be stopped if the dam level rose.
It is worth keeping in mind that the city would be in crisis once business has to start shutting down.
I always love sentences like this. It’s up there with Captain Cook discovering Australia and Blaxland, Lawson & Wentworth discovering the route over the Blue Mountains.
Discover in this sentence calls a whole paradigm.
There is movement underway ! See -
http://www.wivenhoedamclassaction.com
After lotsa searching I’m unable to find the first instance of 225% being quoted. I’d always had it in the back of my mind that the original design parameters were to be one third for water supply & two thirds for flood mitigation.
The reason I’m searching is that before the drought broke a friend of mine was working for Tyco Water on the water grid. He mentioned an international dam expert had been called in because the dam wall was moving downstream at a rate of 10-20mm pa iirc. They were investigating ways of adding more anchorages into the rock either side & downstream to arrest this drift.
How many mm below overflow did it peak? Could it be they’ve reduced the original Safe Working Level of the dam wall as an increased safety factor?
Whose fault is it that Wolffdene dam was never built? A case of the Labor Party machine putting their electoral interests over the common good. If Wolffdene had been built I suspect we wouldn’t have had the water crisis of 2007, and SEQW would be under less pressure to maintain Wivenhoe’s “supply water” capacity.
Fran, I can’t help reading that as “when … discovered the thriving community at …” Much as Oprah recently discovered Australia and one day Brian might discover the metric system.
Fran: I have been married to a language teacher whose current specialty is teaching ESL and writing books for very very low level students. she has been trying to fix up my language skills since before we got married – So I think you are wasting your time.
Moz said:
Too charitable. Oxley must have assumed when he went to the land on which Brisbane now stands that there would be indigenes there. The first community he met (“discovered”) would not have seen themselves as living in the Brisbane area and would have been only one of quite a few whom Oxley had yet to “discover”. Discovery of a community here was revelation to Europeans and their incorporation into what came, through European policy, to be Brisbane. In short, Oxley “discovered” (i.e revealed) a piece of land that Europeans could usefully appropriate, sought data from the local indigenes that might be useful to the project and defined objective reality in terms that suited him. As the European narrative advanced, the indigenes were made a footnote and ultimately disappeared altogether, as they were when Blaxland et al. crossed the Great Dividing Range in 1813.
I wasn’t having a go at your syntax John D. I was exploring the cultural specificity of discovered.
Until Oxley was directed by a shipwrecked timbergetter to the location of a broad, long river which enters Moreton Bay, the wider world did not know of that river’s existence. So one could say that Oxley did “discover” the Brisbane River (although I believe that credit should go to Richard Parsons, Thomas Pamphlett and John Finnegan).
Yes, the river was there for a long time prior to Oxley. And yes, there were people living there for a long time before Oxley was born.
But to the world in general, that river was unknown to and undiscovered by the wider world until.
And commenting on to whom the credit is due is rather a distraction from the subject, isn’t it?
Thanks for an excellent article. However I don’t think it will make any difference to the LNP astroturf mob who are denigrating the great work by the people who manage the dams. And let’s not forget that in October 2010, the LNP wanted Wivenhoe to be filled up completely in case of another drought, despite the fact that this would have made it useless for flood mitigation. Appallingly bad judgement, and they got smacked down fast; but that won’t stop them from going after the government now – they have no shame at all. The line “anyone could have seen it was going to rain well ahead of time” is in full flight.
Chris G @ 42, to be fair, I think the LNP were suggesting that the flood mitigation compartment be reduced without specifying by how much. But you’re right, they were saying that as recently as October.
Colette @ 36, Paul Norton knows the story of Wolfdene. I think the National Party virtually made the decision by rezoning parts of the catchment to “rural residential”. By the time Labor came along the cost of buying up the real estate would have been prohibitive.
There are many people who seem to think SEQ Water should have released drinking water storage, the 1.15 million ML component, to a lower level, or to have prevented the dam from reaching 100% by releasing enough water to hold it at a lower percentage as a “La Nina” strategy.
Looking at the Wivenhoe dam, it does not have an obvious capability to do such a thing in a rainy season. Does anybody know the dam’s actually release capability form 100% full, the drinking water component (1.15 million ML, to a significantly lower level during the rainy season? There appear to be no large feeder tubes to a lower level hydro station. There is a single mini-turbine below one of the floodgate spillways. Versus 1.15 million ML in a rainy season, that’s an enlarged prostate. It has water supply tube(s). Again, these are probably small for the job of keeping the dam at a low level when water from a saturated basin is continually flowing into the dam.
I think is likely the lower portion of the dam cannot be quickly evacuated. Does anybody know the actual numbers on it.
I love being fair. What I don’t love is when the LNP come up with these wonderful ideas which are totally bereft of thought and detail. Like the Rabbit’s latest idea – let’s build lots more dams! Um….. where Tony? But the clear implication is that the LNP would have prevented the flood, and their faithful will spread the meme far and wide.
IMO, I think the Wivenhoe was managed extremely well with people under great pressure to make proper, and very difficult decisions. But for the most part, the Wivenhoe couldn’t have prevented the tidal wave through the lower Brisbane valley and the Lockyer, which directly contributed to the floods. They aren’t part of any dam catchment system – and no proposed dam’s catchment to date includes these areas.
I braved the trip to Esk last weekend to visit an elderly relative who was affected by the flooding on the same day as the Toowoomba flooding, and was astounded at the absolute destruction that has barely been reported on, due to the larger stories of Toowoomba, Brisbane, Ipswich and the upper Lockyer. I don’t think they’ve been intentionally overlooked, I just think the scale of the disaster through the mountain ranges out from Toowomba and the valleys is largely unreported and difficult to appreciate.
Yankb2T @ 44,I believe most of the volume of Wivenhoe is held by the gates,so releases down to the lip of the main spillway can be quite fast if needed. That takes you down to 40%. Below that things slow down with narrow pipe outlets via the small hydro unit and another outlet.
Once again we have the ghost of Wolffdene dam summoned to remind us of the path we could have taken. Everybody knows that the ghost talks politics,but does it have a file or three so we can see the bloody specifics? No,never.
Recently ,I have seen people claim that Wolffdene would have been as big as/bigger than Wivenhoe,and implicitly with a yield to match.They’ve even claimed it was meant to be Brisbane’s primary water source,never mind Wivenhoe.
Simply getting to know the Albert River catchment completely destroys the technical claims. Wolffdene would have had a catchment one tenth the size of Wivanhoe’s,so getting anywhere near the sustainable yield of the latter is impossible. As broad and shallow as Wivenhoe,Wollfdene would have been worse. Fillable only in a flood,it would have had massive evaporative losses,and destroyed a lot of valuable land. The idea was crap,and the real estate story commented on by Brian is very much what I have heard as well.
The actual idea developed for the Albert was abandoned ,too.Glendower was the site,upstream past the biggest horse studs,and east of Beaudesert,but still shallow. An 86GL dam with a yield after environmental flows of around 20GL/annum,similar to Wyaralong,with which it was to be paired as part of the south-eastern water strategy. Chicken feed.
Brian,
excellent post. As comprehensive as one can get without digging into the technical side of things.
Nick – I read that it is “law” that any water above the lip of the floodgate spillways has to be released within 7 days. I’m certain there are situational exceptions: flooding downstream, but it appears to me their intention is to never store water above the lip of the floodgate spillways.
The dam fills to 100%, and no further storage is allowed. That component is left empty for flood mitigation. I cannot imagine a PM would interfere with that. Here in the states it would take a legislative act. In any seven-day period, all flood water is gone if downstream conditions allow the release.
At issue, is the cry that they should have lowered the dam as a La Nina strategy. I do not think the dam has that sort of capability in a rainy season. They would have to have outlets in the lower portion of the dam, that part below the lip of the floodgate spillways, that could release water much faster than rainwater flowing in from the basin. It’s an earthen dam. Best not to tease it with lots of big openings. Earthen dams seep water. More than a little Dutch boy’s thumbs can stop.
@12, I feel pretty confident that wouldn’t be the case, or these “experts” would have been trumpeting “I told you so”, instead of “If they’d just asked me!”
Yank@ 49,the dam can lower quickly below 100%,policy aside,so the dam does have the capability you wonder about in your third para.
This is the breakdown of levels: the foot of dam at riverbed EL23m to concrete bottom lip of spillway at EL57m is the first 40% of storage.Removing water below EL57 IS slow. The gates,16m high,sit on the lip and take the elevation to 73m [57+16].The next 60% of storage is EL57 to EL67,making up the 100%/1165Gl of full water supply component. This leaves 6m from water line at EL67 to the top of the gate at EL73 as the flood buffer,which rises to around EL75 in extremes. IOW in attaining the highest possible surface elevations[above EL73],the gates must be partially open,with inflows being sufficient to balance or exceed outflows and push up elevation.
So the intention is to retain water at 100%,which means to never store water above the 67m line,6m below the top of the fully lowered gates. So,if there is mechanical failure and gates are compromised,at least there are 6 vertical metres [about 750GL] to fill while desperate repairs are made,and evacuation warnings sent!
In flood mode the intention is to never store/impede water above 75m,because the fuse plugged secondary spillway soon comes into play after that,and that means uncontrolled release,and may threaten structural integrity. So the gates are opened further to keep all release directed through the main spillway. At full stretch the spillway can pass 13400cusecs,which is an almighty flood.
This event saw a peak release of 7465cusecs from the gates for a short period.Downstream,this translates to a considerably lower peak flow,given the lower gradient,higher drag,broader river profile than the spillway.I’m not sure how much,but I think well more than 1000 cusecs lower peak at the next gauge,excluding tributaries.
Unfortunately at the time of the peak releases,Lockyer Creek,entering just below the dam, was in major flood.I believe operators were trying to avoid a coincidence of peaks[this is operational policy],but the rapidly developing situation forced their hands.Holding on any longer meant perhaps reaching secondary spillway activation. However ,even with the addition of the major Lockyer flood,peak flow below the dam was still 500 cusecs below that peak at the dam gate.
30% of peak period volume was from the Lockyer,and another unconsidered factor is the contribution of 500km2 of unregulated side catchments[such as England Creek and Lake Manchester] between the dam wall and the Bremer River junction. This 500km2 was absolutely deluged in the last 36 hours of the rain event.
By the time the peak was approaching the city,I’d estimate the non-Wivenhoe[non-controllable] component at around 40% of volume,possibly more,but I’m an amateur.
re our recent qld floods, there are many articles mentioning “greedy developers” and “inept local councils”, etc.
however, the real causes of the over-development of our cities (s.e. qld. in particular) are two-fold:
1. the current tax system. it rewards property speculation through negative gearing, reduced capital gains tax (thanks john howard), and generous allowances for expenses. property development, therefore, is a great way to get rich, and is encouraged by our banks, tax laws, and governments. we have too many buildings now, and the so-called ‘shortage’ of housing is highly debatable. the oz. bureau of statistics shows that we currently have an excess of residential housing.
the community (us) pays for the infrastructure and the services which add value to land. a private individual can buy this land cheaply, leave it vacant until the community builds up the area, then sell it at huge profit – the latter mostly goes back into the seller’s pocket even though the community has paid for the increases in land value. big developers are notorious for what is called ‘land banking’. (This is a very incomplete summary.)
it could be very different with a reformed, more efficient and much less expensive tax system which did not reward property speculation. http://www.prosper.org.au
2. overpopulation. australia’s birth rate is higher than most of the rest of asia, and the highest of any of the OECD countries. we still give out baby bonuses. we then bring in hundreds of thousands of immigrants, all of whom require more resources, services, and produce more waste and pollution – and lots more buildings – which are often built on flood-prone land. http://www.population.org.au
get the picture?
Tia @ 30, you are right, Neal Ashkanasy it was. Everything reported by Tony Koch he said word for word to Madonna King, plus more.
Importantly, he said the difference would have been measured in centimeters if we had started from 75% full.
In response to John Quiggin @ 16, John my recall was that he said a “few” centimetres, but I wouldn’t trust my memory absolutely on that. If you figure it in linear terms, according to Ashkenasy 90% capacity took 1.5 metres off the flood. Proportionately an extra 25% should take 42 centimetres off it. But the top part of the flood for a given depth always contains more water. My guestimate from other figuring is that you could perhaps knock a third off for that factor to get 28cm, but of course I don’t know.
How much damage that would have saved and whether that is worth the potential loss of storage, I don’t know either. It’s a fair point that the authorities may well ask themselves the question.
Put it this way. The worst thing that could happen is that the dam wall fails. The second worst is that Brisbane runs out of water. We came close. The Wivenhoe is our major water storage. The SEQ Water Strategy has been a major planning exercise to give us peace of mind on that score. Desalination plants are part of the future strategy, but the plan takes into account a 50 year time frame and a considerable population increase.
I think it unlikely that sacrificing 25% of the Wivenhoe storage can reasonably be accommodated, but if it can, so be it.
My preference is not to try to second guess the weather, or more specifically the catchment runoff, which is quite a different thing.
In November 2004, according to my records in Ashgrove, we had 196mm. In Dec 2004 we had 225mm. The prospects for the summer looked good. After that there were only four occasions to August 2007 when water would have run into the Wivenhoe if they had had the rain we had in Ashgrove, and then not much. My memory is that they didn’t. The Wivenhoe’s average is perhaps 25% down on ours and the rain seemed to actively avoid it. The common parlance was that you never needed rain insurance if you had an outside event at the Wivenhoe.
The basic problem is that we are repeatedly told that it takes 50mm to wet the Wivenhoe catchment before water runs. Leave it a week in summer or two in winter and you have to start over unless you have had major rain.
I wouldn’t like to be in charge of second guessing the weather, which is erratic enough and we are told is likely to become more so.
On the question of increased flexibility with a 25% buffer, 25% as such is likely to have filled up in less than a day. I think the biggest gain would have been an early release to cause minor flooding in order to save major flooding later. This again is second guessing and my understanding is that causing minor strategic flooding would have been verboten by the rules.
If that last rain band had been 50km eastwards, which it could easily have been, the flooding would likely have been minor.
But it will all come out in the wash, I’m sure.
I can see that people have moved on from this issue and I have to also. I was going to give you some back of the envelope calculations and find I had forgotten that the basis is already in the post. I said this:
And this:
If you take 1974 as your base, then 9,500 cubic metres per second produced a flood of 5.5m. Had the Wivenhoe not existed then 13,000 cubic metres per second would have produced a flood of 6m.
So for an increased flow of 37% you get an increased flood height of only 9%.
On the basis that a cubic metre of water is 1,000 litres, I did some calculations on how much water would flow past a given point in 24 hours. You have a one-off saving of 287,000 ML from your 25% of dam storage. The flood lasts a number of days, several at a high level.
The total amounts of water in these floods is phenomenal, which is ironic, because 25% of storage can be very hard won in normal times.
Anyway I’m neither a mathematician, nor a hydrologist, but that, roughly, was the basis of my “few Centimetres” guestimate.
Brian said:
Between 7:30 am Tuesday the 11th and 1:00 am Thursday the 13th, the flow at Savages Crossing (below Lockyer Creek) exceeded 3,500 m3/s, the limit allowed by the manual for non-damaging floods at Lowood. The volume of water in excess of 3,500 m3/s flowing past Savages Crossing during that period was 280 GL.
Compare this floodwater volume of 280 GL with 25% of Wivenhoe FSL, 290 GL.
Quite clearly, the volume of floodwater above 3,500 m3/s could have been absorbed by 25% of Wivenhoe. There would have been no major flood in Brisbane if the flow at Savages Crossing had been limited to 3,500 m3/s.
Also, I should point out that Wivenhoe started at 115% on the morning of Sunday the 9th because the manual requires the dam to hold back 15% if necessary to keep Fernvale and Mt Crosby bridges open. That 15% caused a lot of damage in Brisbane, far more than the cost of two high-level bridges.
Electrical Engineer, I might be a bit thick, but I’m scratching my head over the information you provide. The basic bit of information I provided is that we were told that
At 13,000 per second you have 1.123 million ML per day, or 287,000 ML takes 6 hrs, 53 mins.
We were also told that at one stage water was entering the dam at the rate of 2.6 million ML per day, but I don’t know for how many hours. (Actually I query that figure. I heard on the radio it was two Sydney Harbours, or 1 million ML pd for a time.)
You cite a flow rate for Savages Crossing for a time when I think the flood was peaking around the CBD. It was certainly in retreat by Friday 14. If Ian Mott is right it takes 36 hours for the water to flow from the Wivenhoe to the CBD. I think the Toowoomba/Lockyer deluge happened on Monday 10, didn’t it?
For a time early that week the Wivenhoe dam authorities were dealing with humungous quantities of water coming into the Wivenhoe, into the Lockyer and the Bremer and already in the Brisbane below the dam. I think it’s time to wait for the true narrative which should come out during the royal commission.
Brian, you asked:
The Lockyer Creek gauge at Rifle Range Road peaked sometime between 10 am Tuesday morning and 10 am Wednesday morning. We don’t know exactly when because the gauge stopped working in that period. At a guess I’d say between 9 pm and 10 pm Tuesday night which, given that it takes a few hours to flow from Rifle Range Road to Savages Crossing, more or less coincided with the maximum release rate from Wivenhoe. It was certainly in the period when they were forced to release most of the inflow.
I’m a bit dubious that there was 13,000 cubic metres per second inflow to the dam for any significant period of time. The reason is that the fastest rate of rise of Wivenhoe was 0.2 metres/hour between midday and 1 pm on Monday. This was about 28 GL or 7,800 cubic metres per second. It was also rising about 1/6 metre per hour for a much longer period than one hour which is equivalent to 6,500 cubic metres/hour. I’m going by the gauge on the dam and the gauge at Savages Crossing for my earlier figures. You may have encountered a case of “don’t believe everything you read in the papers”.
Brian also said:
This flood was actually two floods, one occurring centred on Sunday night which the dam absorbed and the second occurring centred on Tuesday night which they had to let through because they had a full dam.
The dam rose from 68.71 m at 5:40 pm Sunday to 72.93 m at about 6 pm on Monday, which is around 550,000 ML. During that time they released 170,000 ML past Savages Crossing which includes Lockyer Creek water so the inflow to the dam in that time was about 720,000 ML minus the Lockyer flow, i.e. nothing like 2.6 million ML per day.
I haven’t been through the figures in detail for Tuesday night but the figure I checked suggests a similar inflow rate on Tuesday evening as on Sunday night/Monday morning. So talk about a rate of 2.6 million ML per day just looks like exaggeration to me.
They certainly took the front off the flood by absorbing the flood on Sunday evening/Monday morning but as for how much they took off the Tuesday night flood, I’m not sure they took much off it because they already had a full dam so were forced to more or less let the whole flow through.
You might have noticed I mentioned that they let 170 GL past Savages Crossing from 6 pm Sunday to 6 pm Monday during which the dam was rising rapidly. The dam operators were allowed by the manual to release 300 GL/day past Savages Crossing so they released 130 GL less than allowed just during that single 24 hour period. They could have had a lot less water in the dam on Tuesday when the second flood arrived but their response was very slow until the dam fuses were in danger.
There’s not much information easily available at the moment. I hope this issue get the factual publicity it deserves because I don’t know why they didn’t do a lot better on Sunday and Monday.
Sorry Brian, you have confused the levels used to forecast tides with AHD levels when you quote tide levels at Brisbane City. This puts your tidal data at about a metre too high (at 2.6 metres AHD, the river is already flooding). Unfortunately, this means your assessment of the impact of reducing the level of Wivenhoe to 75% is based on wrong assumptions. Further, your assessment of the statistical likelihood of floods occurring in the river is so broad that it is meaningless to use them in your discussion. I know you are just ‘shooting the breeze’, and why not, but I thought I should let you and the readers of your ‘blog’ know.
Robbie