I wanted to start this thread, as we now watch in anticipation of potential events 22-29th January, and questions start being raised in regards to the performance, levels and possible mitigation by our dams in Qld (esp WIvenhoe and Somerset, but also the Hinze Dam).





Currently we have the following (as @ 22.01):
SOMERSET - @ 1205 - 99.04m (0.4cm above FS)- steady
WIVENHOE - @ 1229 - 64.00m (3.0m below FS) - steady

HINZE - @ 1304 - -13.22 (m below spillway) - falling

Locke - do you have the figures handy for what Somerset and Wivenhoe were going into last January's flood event?

Locke may have exact figures, but if I remember correctly it was around the 130% mark going into the weekend of January 8-9. They did very minor releases during that weekend and then the floodwater poured in on Monday and Tuesday, jumping it up as high as 191%.

The fact it's around 80% now means we'd need even more inflows into the catchment than last year to cause similar flooding. However, the risk is of course heavy rainflow below Wivenhoe or into the Bremer/Lockyer Creeks again.

It will be very interesting to watch dam levels and inflows over the coming days though.

Wivenhoe was at 101% going into last years floods. Not sure about Somerset but probably at 100%.

The total inflows for last years event were arount 2.7 million megalitres. The 25% reduction in capacity leading into the wet season has given them an additional 370,000 megalitres to play with.

Yeah somerset was constantly over the 100%. It was 102.9% on the 4 Jan and then it peaked at 189.7% on the 13 Jan. On the same dates wivenhoe was 102.1% (4 Jan) and 186.5% (13 Jan.

Just for interests sake Toowoombas dams are at 98.6%

Cooby dam - 96.5% (19,015 ML)
Cressbrook dam - 99.3% (78,333 ML)
Perseverance dam - 97.8% (26,304 ML)

Hopefully we can snag around 100mm over the next week to push all the dams over 100% again

These figures are quoted in the report for DERM/inquiry.
7:42am Thu 6 Jan 2011:
Wivenhoe: 67.31m
Somerset: 99.34m

3pm Fri 7 Jan 2011:
Wivenhoe: 68.03m
Somerset: 99.94m

1am Sun 9 Jan 2011:
Wivenhoe: 68.63m
Somerset: 100.32m

So it depends on when you consider the "start" of the flood event actually is. To my knowledge it hadn't touched 100%/67m at Wivenhoe for like a month, but it wasn't significantly above it.

More info is in the report.

I presume posters here are dismissive of the suspiciously timed article in yesterday's Australian.

SEQ rivers and Dams seem to be coping quite well. Some steady increases though.
http://www.bom.gov.au/qld/flood/seast.shtml

I think the rain over the last 24 hours would've served to prime the catchments in most cases. Very interesting to see how the river levels look if the forecast totals for the next 24-36 hours come off.

No significant inflows yet. That will change in the coming 24-48 hours if GFS is accurate.

300+ mm in the space of 24 hours would be very similar now to one of the 2 big inflow events that occurred last year. Wivenhoe should comfortably handle that with releases in the 1500m3 sec range. What impact this has down stream will depend on how much of the projected rainfalls below wivenhoe as well.

Thanks somebody - thats exactly what I was after

So looking at the current obs compared to last year and yesterday:

SOMERSET
6 Jan @ 0742 99.34m
7 Jan @ 1500 99.94m
9 Jan @ 0100 100.32m

22 Jan @ 1205 99.04m (4cm above FS) steady
22 Jan @ 1328 99.06 m (6cm above FS) rising

23 Jan @ 1008 99.00m (at FS) rising

WIVENHOE
6 Jan @ 0742 67.31m
7 Jan @ 1500 68.03m
9 Jan @ 0100 68.63m

22 Jan @ 1229 64.00m (3.0m below FS) steady
23 Jan @ 0950 64.04m (2.96m below FS) falling

HINZE
22 Jan @ 1304 -13.22 (below spillway) falling
23 Jan @ 1002 -12.88 rising

Hinze is the only one with any real increases (as would be expected), although i think we will see that change over the coming days.

I still don't think releasing water from Wivenhoe to keep it at the 75% is a good idea right now! With potentially anywhere from 200mm up to 700mm forecast for the next week, if it falls above the dams thats fine... but anything falling below the dams is already going to cause flooding, and would only be exacerbated by any releases now. If the dam cant mitigate flooding with the flood mitigation supply PLUS the extra 25% from last year, then its just not meant to be!!

And looking at the radar currently, quite a lot is falling on or below the dam. If that rain continues in the lower Brisbane catchment it'd be pretty silly to add releases to it. But can they afford to wait?

Personally - yes I think they can. Anyone who especially after last year still thinks Wivenhoe is there to "save" Brisbane from floods is mistaken. Wivenhoe was not built to stop floods, it was built to (a) store water and (b) mitigate floods - I can't understand why the powers that be won't let it function as its supposed to rather than bowing to the pressure of the public.

Not to mention, I've stopped reading the comments on the Courier Mail page about the floods today... full of people saying "let the water out of the dams" without realising the ramifications. I swear, many people still think that water let out now will be out to sea within a few hours.

But they can pull the plug out of their bath and it goes very quickly!
Gotta love the Courier Mail (and it's readers)!

You would've thought with last year that the flood peak came after 2 days of relatively rain-free weather that the time lag from release from Wivenhoe to appearing at the lower reaches would give them a clue, hey?

Conversely I have friends who are dismissive of the threat altogether. "It's not going to flood". After 1 rainy day primarily on the coast? No. But if we were to have 3-4 consecutive days like this, including catchment rain, the risk would be there.

I don't understand people panicking. And I don't understand people completely dismissing the chance of a flood at all.

This is the link that I posted in another thread.
http://www.seqwater.com.au/public/dam-levels
Its only updated once a day but shows if they are releasing water & where from.
Yesterday it showed a lower dam level but they were releasing as they are today.

They have a policy in action of keeping it at 75%. So they will continue releasing small amounts to keep it at that level. I don't necessarily agree with that given the current rainfall situation (as more water being released into the lower Brisbane river combined with runoff from the rain means higher levels, especially with current high tides)...but it is what it is.

I think thats what Locke was referring to above too Coxy, which will be interesting to see - the 75% is the new FSL essentially, so do they keep it at that, or use the manual procedures of comparing inflows and outflows etc and let the dam mitigation to a certain event take over? they couldn't possibly let it stay at 75% and keep releasing if there was the prospect of severe flooding downstream from rain fall below the dam? Locke - you know more about the damn than I do - whats your thoughts?

Sorry, i noticed my dates above were wrong too lol:
23 Jan @ 1229 64.00m (3.0m below FS) steady
24 Jan @ 0950 64.04m (2.96m below FS) falling
24 Jan @ 1433 64.06m (2.94m below FS) rising

It appears there are in fact releases happening from Wivenhoe:
24/01 0405 27.31
0419 27.35
0421 27.41
0426 27.50
0434 27.54
0453 27.57

24/01 1253 27.56
1302 27.62
1310 27.67
1456 27.69

(Refer here:http://www.bom.gov.au/fwo/IDQ65389/IDQ65389.540178.tbl.shtml)
Looked like they ceased around 5am this morning, and then began releasing again from 1300-1500. It seems to have stayed steady since then.

Yes, when they said there were no planned releases I think they meant in excess of the current small releases to keep it around 75%. Fairly misleading message they sent anyway.

The problem is the W1 strategy outlined in the manual is for use when the dam level is between 67 and 68m. I'm not too sure whether they will commence gate operations until the dam reaches 67m. I know they have started flood operations which means they are staffing for the event and preparing for action if needed but I also saw on an earlier post they have no plans for gate releases in the next 24 hours.

Its also worth noting that inflow into the dam has been minimal to this point and if the rainfall continues to remain coastal we may not see a release at all.

There would be a certain irony to having a significant rainfall event for SE QLD with no dam release and then have the dam run dry in 5 years if no follow up rain occurs.

I'm curious though, what level of rain would be needed below Wivenhoe to cause the Lower Brisbane/Bremer to break its banks? I would've thought apocalyptic levels of rainfall...but wondering if apocalyptic can be numerically defined.

Several years ago Ipswich got about 200mm or so in an overnight storm which pushed the Bremer up to moderate flood level.

This had very little impact downstream on the Brisbane River. I think the Moggill guage peaked at about 3m for that event and the guages downstream saw no effect.

Ta. Good to know.

Bremer can flood and Brisbane not, but if heavy falls occur south of Wivenhoe Dam into Brisbane river it can still have major flood, and rain falling in Lockyer Valley will hit Brisbane river south of dam, so even without the dam can have major flood in Brisbane river.

Historically Brisbane river has flooded due to above Wivenhoe or even above Somerset.

Somerset was built to first stop flooding, enough rain in Stanely river above Somerset dam can also trigger flood if to much to hold back once it gets to Wivenhoe.

It is complicated it is not a science rocket but can appear that way at times.

Big floods in the Bremer have never caused significant flooding of the Lower Brisbane river. The flow rate generated is simply not high enough. You get flows through the upper Brisbane of far greater magnitude purely because the catchment is so much bigger.

I still think I could've made my first million doing that :-)

I'm sorry re tomorrow.... If I could get out of work I would!!! At this stage best I could do is Sat....

I cant see even a remote possibility of 2011 at this stage. the falls have to push a lot further inland and the longer the event fails to do that the ever increasing chance that it wont do so early enough to cause the epic issues we saw last year. By this time last year places such as Gregor Ck were already in Major. This year its all about the sunny coast and the gold coast. My brother pumped out 1200l from his bottom floor this morning!

I think they've now started to open the gates at Wivenhoe. The flow just below the dam has certainly increased in the past couple of hours.

You don't think its local Heavy rain /runoff , I think from Memory they've had 50mm in the last few hrs ?

Nope. Its the Wivenhoe gauge just below the dam. You can always tell when they've upped the release by the way the gauge responds. It doesnt surprise me though as the dam level is now starting to rise and they're going to get major inflow from Somerset overflow shortly.

From what your seeing in those Wivenhoe DS figures do you think they are going to try and match the imminent Somerset release figures ? Or is this just a step increase ( we'll call W0.5 ) ........

I'm really not sure. I do expect the level at Somerset to start to rise quickly by morning. Somerset does have 8 radial gates and they can hold the dam above 100% (they did during last years floods) so I'm not sure whether they will let the inflow straight through to Wivenhoe or not.

My theory it seems they have already open couple of gates at Wivenhoe which suggests to me that SEQ Water is concerned this so called event going to happen this Friday onwards which we'll have a better idea by tomorrow model runs....

right now the gates are closed, just checked the camera. The small power generating gate is open however that is a very low flow rate.

Does anyone know where to get 'current up to date' dam levels data. Wivenhoe is receiving big falls now.
I have now found the wivenhoe level here http://www.bom.gov.au/fwo/IDQ65389/IDQ65389.540177.plt.shtml

Go to the river level section on the BOM site.

http://www.bom.gov.au/cgi-bin/wrap_fwo.pl?IDQ60286.html

Latest levels are Somerset at 99.36m (36cm over full supply) and Wivenhoe at 64.10 (2.9m below full supply). At this point in time no real cause for concern. Doesnt look like any releases occurring at the moment from Somerset and only minimal releases from Wivenhoe.

My understanding is that the crest gates were never closed. The report shows that Somerset outflow never stopped, it was just slowed by closing the sluice gates, which are different from the crest gates.

FWIW.

Thanks Somebody. I couldn't find a lot of information on how the gates are operated at Somerset. Do you know where we can find what the current outflow at Somerset is?

Can't find out what it's currently doing but the info on what happened is in the report.

There's a plot of Wivenhoe vs Somerset on P219 (Adobe), and a graph of the whole event on P111 (Adobe).

I think it's bizarre that the operating target line for Somerset targets retaining 1.45m of flood water at low levels of Wivenhoe. That water should be released into Wivenhoe so that it can be considered in setting Wivenhoe releases. The Somerset level has to be actively managed anyway so I can't see that the fixed crest level is the reason for this.

Hinze Dam has made some impressive gains in the past 24-48hrs:

23 Jan @ 1304 -13.22 (m below spillway) falling
24 Jan @ 1002 -12.88 rising
25 Jan @ 0908 -9.80 rising
Thats 3.5m in 36hrs!

Wivy and Sommie have had only small increases in the past 24hrs:

Somerset:
24 Jan @ 1008 99.00m (at FS) rising
24 Jan @ 1411 99.02m (2cm above FS) rising
25 Jan @ 0904 99.40 (40cm above FS) steady
Wivenhoe:
24 Jan @ 0950 64.04m (2.96m below FS) falling
24 Jan @ 1433 64.06m (2.94m below FS) rising
25 Jan @ 0855 61.10 (2.90 below FS) rising

And Wivenhoe TW hasn't moved since 1430 yesterday (steady at 27.68).

Minor releases at Wivenhoe:
This shows Wivenhoe TW:
25/01/2012 09:30 27.68
25/01/2012 09:49 27.69
**Releases begin**
25/01/2012 10:02 27.72
25/01/2012 10:04 27.93
25/01/2012 10:05 27.97
25/01/2012 10:06 28.00
25/01/2012 10:07 27.99
25/01/2012 10:08 27.95
25/01/2012 10:09 27.93
25/01/2012 10:10 27.92
25/01/2012 10:11 27.89

Update at SEQ Water

"Somerset/Wivenhoe dams
Drainage operation releases will commence from Wivenhoe Dam at 10.00 am, at a rate of up to 350 cubic metres per second.

Releases from Somerset Dam into Wivenhoe are expected to commence later today.

These releases will control inflows to both Somerset and Wivenhoe dams and ensure that Wivenhoe Dam is drained back to near full supply levels (75%) in the next seven days.

These releases are expected to impact Twin Bridges, Savages Crossing and Colleges Crossing.

If further heavy rainfall occurs during the next 24 hours, it may be necessary to increase releases from Wivenhoe Dam.

At this stage, no urban flooding is expected.

Operational releases continue."

The reading at Wivenhoe TW is now at 28.42m

And your thoughts Locke on the releases? Good idea, bad idea, probably about what they should be doing?

It should be kept at 100%. No more or less.

75% is the new 100%. Without these releases it would have been pointless to lower the dam in the first place.

SEQWater obviously believe this will be sufficient to keep the dam at 75% based on current flows. They undoubtedly have much more data than we have access to. The release itself will have neglible impact downstream unless your close to the dam so I don't think its a bad move.

I agree. Therefore they should reset the full supply level to 873,298ML. Thus the current 75% mark becomes 100%.
Flood mitigation capacity is therefore 1,741,940 ML.

If it's decided SE Qld needs more than 873,298 ML (plus other dams) for water supply then investigate other dam locations. Start with Wolfdene.

No. The original 100% should be how it stands. I know damn well that if the 75% mark becoms the full time full storage capacity then everyone that is whinging about the fact that Brisbane flooded will be the first to jump up and down when the next drought rolls around and you have no water. Deal with the fact that occasionally nature will deal a crap hand and you will be flooded. Stop building in flood areas and there won't be a problem. If you do then accept the consequencess. I know it is a harsh thing to say but people really do need to face reality.

Wivenhoe was built primarily as flood mitigation. Not water supply. That should be its primary purpose.
If we don't have enough other infrastructure for supplying water, build another dam somewhere else. Would've been money much better spent than the recycled water plant we don't use and the desalination plant we CAN'T use.

it was built for both actually, its not that easy to say, lets build a dam here, it costs money and will leave 1000's of people homeless from the actual artificial lake.

wivenhoe has done its job since it was built, it saved us from running out of water in 2007 and mitigated last years floods. if it was only used for flood mitigation we would have run out of water a lot earlier than 2007 and gone a lot longer without water....

Wivenhoe was built to have the original 100% water storage level and the 140%(I am pretty sure that is the figure)) flood mitigation.

Building new dams is very costly and nearly always controversial. Wivenhoe dam was never just about flood mitigation. It was always a dual purpose dam designed to be both for flood mitigation and for water supply. The flood mitigation capacity is the additional amount above the 100% FSL which amounts to 1.45 million gL.

A knee jerk reaction to what was for all intents and purposes a 1 in 100 year (potentially 1 in 200 year) is not a smart move. The provision of water storage and protection of the water supply is horrendously expensive with the cost far outwieghing the damage incurred from last years floods.

A 75% FSL given our current water storage capacities is incredibly dangerous given that it provides no more than 4-5 years supply in an area which historically can go up to 14 years without an inflow event.

One would of thought they'd be smart about this , start the season at 75% ,
and let it build incrementally to say 80-85 % roughly at this point . Then probably let it incrementally rise to 100 % one month or month and a half from the end of the wet season . this could also be judged on a two week soi running mean and even a Noni or Nino 3.4 . Surely if an amateur can work his way through this mentally that professionals could get it half right .
Along with others , I'm actually of the Opinion that their Flood mitigation work was well done . It was the lead up that was half Cocked Up . Again they need to look at this as a evolving figure . But no that would involve the Government perhaps being Liable . And we all know that anytime legalities become involved then Conservative roads paths turn into multi lane highways ...... So tp speak , Ie : no one is going to afford to live when we over Govern , or become a Nanny State . The beginnniong of the End is Nigh .

I said primarily, not solely. Big difference.

In any case, building a new dam would've been far less expensive than the combined cost of the recycled water and desalination plants, neither of which are in use, and one which is basically a lemon.

They can't build a new dam. Everyone that says we need more water then turns around and says 'not in my backyard'. Don't you remember Taveston. It would have filled a couple of times over in the last couple of years. They have to work with what they have and that is Wivenhoe.

Wolfdene. Wayne Goss. Killed it. Would've been handy in the drought. Would've prevented the waste of money on the other measures.
Just saying.

It's always "not in my backyard" for any major infrastructure. Governments need to show some balls and just go through with it. And stop pandering to the Greens.

People just don't think that way, hence they buy insurance with a risk-adjusted value (AIUI) approximately half the premium. They are willing to pay extra for the predictability of the outcome.

Like you, I don't like the 75% level, but what concerns me most is the date that it is revised up and I also have concerns about what lake level the W2 strategy is invoked from. If it isn't 65.6m-66m then why are we bothering? Has the revised manual been released? I can't find it easily.

Seqwater began minor releases from Somerset Dam into Wivenhoe Dam at 6.30am at a rate of 205m3/s.

As advised by SEQWater this morning

The Wyaralong Dam on wed/25/2012

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%?

Not sure, but that only applies from the peak. At 100m3/s they would drop the dam by 5.19% in a week. Not fast enough by the time Somerset outflow is taken into account, but increase it to 150m3/s, and it probably is. Just.