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Queensland Floods

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Whiskers said:
I doubt the Traverston dam would totally mitigate Gympie and Maryborough on the Mary River from flood damage any more than the Wivenhoe dam will totally mitigate Brisbane form flood damage.
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I don't think anyone is suggesting that the Traverston dam would totally solve the flooding issues of Gympie and Maryborough, however it is deceptive and dishonest to indicate that it would have had no impact. Government modelling suggests that the river peak could have been up to 4 metres lower with the dam and using controlled release. Environmental issues are another story.

Try telling the people of Theodore who at the moment are currently cleaning dead animals, rotten food, sludge and broken memories out of their homes, that a Nathan Dam (with a capacity of 1,000,000 megalitres) would have been no assistance to them on the Dawson River a fortnight ago. This dam has been "in the pipeline" for over 25 years and has been delayed because of Boggomoss Snails, sacred aboriginal sites, rare frogs and the latest was the potential impact on the Great Barrier Reef. Ironically I see on the TV one of the conservationists that fought against the dam was saying last week what a disaster the Fitzroy flood has been for tourism, commercial fishing and the marine life on the reef.

Duckman
 
The Brisbane river broke it's banks a couple of hours ago - Wivenhoe is up to capacity. Have family living in Cooparoo so will be watching closely.

And to think we call this the sunshine state...
 
I just had a phone call from my son who lives in Brisbane. They have taken in friends who have had to evacuate their house at Fig Tree Pocket. They are keeping in contact with other friends who may need assistance.
 
Anyone know where to find info on road closures on the Sydney to gold coast run?
The wife and kids drove up to the gold coast last week to visit relations, so now I am thinking of flying up and driving them all back. Don't want to get stuck somewhere along the way though.
 
It just gets worse, Queensland are in all sorts.

The Premier announced this afternoon that the flood level through Brisbane CBD is likely now to exceed the 1974 levels. And the BOM say a wet few months are ahead.

QLD appears to consist of people being winched into helicopters from the roofs of their houses, or floating along on the roofs of their cars.
 
Logique said:
The Premier announced this afternoon that the flood level through Brisbane CBD is likely now to exceed the 1974 levels. And the BOM say a wet few months are ahead.
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What sort of area are we talking about relative to Brisbane as a whole?

Are we talking about only the CBD and a few nearby suburbs being flooded or are we talking about a large part of Brisbane going under water?
 
sails said:
Building dams is often an unpopular decision at the time. However, those whose lives have been spared ravaging flood waters by the dams would possibly far out number the few that were initially affected. It would be politically a tough thing to do - that is until the floods come.
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Ironically, the dam operators are going to flood the Brisbane River. Hope the good people of Brizzy aren't affected greatly.
 
You would think walking down the street in Towoomba would be safe, hoping the toll doesn't get to much bigger

Predictions of further events through to April likely more heart break to come Australia will need to throw its support behind the flood victims for some time I think.
 
Wysiwyg said:
Ironically, the dam operators are going to flood the Brisbane River. Hope the good people of Brizzy aren't affected greatly.
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Ironic may be an understatement!

'Catastrophic'
Professor Chanson says the dam operators have been progressively releasing water from the dam to prevent it filling.

"If the Wivenhoe become full up to the stage where the water in the reservoir is very close to the crest of the dam, it would mean a situation where the operators of the dam would have to open fully the gate of the spillway," he said.

"Anything coming into the reservoir would have to be immediately discharged."

He says it would be catastrophic if water made it over the top of the dam wall.

"The Wivenhoe Dam is not designed to be overtopped, it is what we call an embankment dam. And if water was to flow over the top of the crest of the dam, there would be a very high risk of erosion of the dam wall and ultimately failure of the dam," he said.

"If the water was to spill over the top of the crest of the dam we would look at the failure of the dam on the possible complete emptying of the reservoir into the Brisbane River with deadly consequences for the people living downstream."

But he says there are a number of safeguards to prevent such an event.

"The first one is the primary spillway, the main spillway you have seen on the TV news," he said.

"That is the location where they are currently controlling the downstream release of water into the Brisbane River.

"But they also have a secondary emergency spillway where if the water were to reach dangerous levels it would start to provide further release from the dam wall."

The Bureau of Meteorology says major flood levels in Brisbane are likely to be reached on Wednesday afternoon.
http://www.abc.net.au/news/stories/2011/01/11/3110758.htm
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Duckman#72 said:
I don't think anyone is suggesting that the Traverston dam would totally solve the flooding issues of Gympie and Maryborough, however it is deceptive and dishonest to indicate that it would have had no impact. Government modelling suggests that the river peak could have been up to 4 metres lower with the dam and using controlled release. Environmental issues are another story.

Try telling the people of Theodore who at the moment are currently cleaning dead animals, rotten food, sludge and broken memories out of their homes, that a Nathan Dam (with a capacity of 1,000,000 megalitres) would have been no assistance to them on the Dawson River a fortnight ago. This dam has been "in the pipeline" for over 25 years and has been delayed because of Boggomoss Snails, sacred aboriginal sites, rare frogs and the latest was the potential impact on the Great Barrier Reef. Ironically I see on the TV one of the conservationists that fought against the dam was saying last week what a disaster the Fitzroy flood has been for tourism, commercial fishing and the marine life on the reef.

Duckman
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I understand your point Duckman, but the Wivenhoe principle is to minimise or negate many low level flood events. The problem is that how big is big enough to be safe.

Flood Mitigation During a flood situation, Wivenhoe Dam is designed to hold back a further 1.45 million megalitres as well as its normal storage capacity of 1.15 million megalitres. Floods may still occur in the Ipswich and Brisbane areas but they will be rarer in occurrence. Wivenhoe’s flood control facility, together with the existing flood mitigation effect of Somerset Dam, will substantially reduce the heights of relatively small floods.

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.

Full supply level or 100 percent capacity (in the water level analysis) is indicative of the optimum level intended for town water supply, and does not take flood mitigation levels into account. http://www.seqwater.com.au/public/catch-store-treat/dams/wivenhoe-dam
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The authorities underestimated the intensity of this rain event.

If the catchment gets follow up events like the cloud burst near Toowoomba, the risk of the Wivenhoe wall failing increases dramatically... then we will have a flood and disaster of unprecedented proportions and then some.

PS: Is the premier worried about a possible dam burst? She looks grim saying (on the TV news) these releases are not optional, they are necessary to operate the dam as it was designed and to protect the people down stream.
 
moXJO said:
Anyone know where to find info on road closures on the Sydney to gold coast run?
The wife and kids drove up to the gold coast last week to visit relations, so now I am thinking of flying up and driving them all back. Don't want to get stuck somewhere along the way though.
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As a resident on the northern end of the run. I suggest "leave them there this week" as the area now only needs another good storm and the roads will be cut in a few places. Even last Friday it took me half an hour before I got out of sight of my home with water over the Pacific highway backed up by a high tide.:2twocents
 
This is the rainfall chart for Brisbane to 9.00 yesterday, 10th Jan.

The heavy falls couldn't have fallen more plump over the Brisbane River catchment if you tried.
 

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Whiskers said:
I understand your point Duckman, but the Wivenhoe principle is to minimise or negate many low level flood events. The problem is that how big is big enough to be safe.

...

PS: Is the premier worried about a possible dam burst? She looks grim saying (on the TV news) these releases are not optional, they are necessary to operate the dam as it was designed and to protect the people down stream.
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It is a fact that the water stored in Wivenhoe dam is water that would otherwise have flowed downstream.

It could be expected that capturing some water upstream, would reduce the frequency of flooding downstream although it may be of little benefit in an extreme event. That is, the presence of a flood control dam will avoid a lot of smaller floods but will not avoid a catastrophic flood event.

That scenario is very common to virtually all safety devices and systems. For example, A seatbelt and air bag will reduce the risk of injury in most motor vehicle accidents but is of no real benefit in a head-on collision between a car and a large truck at highway speed.

Aircraft safety systems and the life jackets we are all told can be found under the seats may well help under a moderate emergency scenario. But if a wing falls off the plane then no amount of oxygen masks and life jackets fitted with whistles and lights is going to save you.

It's basically the same with most safety-related systems. Your chances of avoiding a moderate incident, or surviving it, are greatly improved. But in a worst case scenario the safety systems are basically useless. Same with flood control dams.

Looking at another flood where I have some figures, the Hobart floods of 1960, it is a fact that Hydro dams retained about 30% of the water upstream in the Derwent catchment. Likewise Hobart City Council dams retained significant amounts of water upstream in the Hobart Rivulet (Mt Wellington) catchment. Had this water not been retained, flooding in the CBD and at towns in the Derwent Valley would have been far worse than it was.

Likewise the frequency of flooding in the Huonville area has decreased since Lake Pedder was dammed in 1972. Prior to that, floods were more frequent in the Huon.

But all that said, if a truly major rainfall event occurs then Brisbane, Hobart, Huonville and everywhere else near a river are going to be flooded no matter how many dams (within practical limits...) have been built upstream. Flood control dams will avoid 95% of floods, but they won't stop the really big one.

As for a dam burst, rockfill dams in general are not designed to cope with water flowing directly over the top of the dam structure. There are exceptions which do have spillways on the downstream face of a rockfill dam, but Wivenhoe is not such an exception. If the dam were to overflow as such, as distinct from simply being on spill, then serious erosion and consequent collapse would be a real possibility.

In reality however I would not be overly concerned about the risk of a flood resulting in structural failure of Wivenhoe dam. It is not totally impossible, but if there is to be a flood of that magnitude then there isn't going to be much left of Brisbane with or without Wivenhoe bursting. Wivenhoe was built for flood control and has huge spillways, indeed the gates are amongs the largest in the world. It's not as though it's doesn't have a spillway or anything like that (actually, there are some pretty large dams around that don't have spillways but there is sound engineering behind that - it comes down to catchment area versus storage capacity).

As of 9am this morning, there were 2050 GL in Wivenhoe versus full supply level (flood control) of 2615 GL and normal FSL (for water supply purposes) of 1165 GL. Information from SEQ Water.

In layman's terms, that means the dam is normally allowed to fill up to 1165 GL, with any surplus water being released via the spillway. However, the actual capacity of the dam is 2615 GL. The reason for normally keeping the level lower is to enable the additional storage of flood waters in an emergency such as the one we have now.

So why are they letting water out if the dam is not likely to burst? The basic aim is to hold back as much as possible when it matters most given that capacity of the dam is limited. That is, someone has done the maths (hopefully) and worked out that flooding will be less if some water is let out now, such that more can be held back around the time when river levels are expected to peak. Obviously there's a bit of estimation being done there, but that is the theory. Trying to lessen the overall severity of flooding through manipulation of water release rates.

If I were in Brisbane right now then Wivenhoe dam bursting would be the least of my worries. I would be more concerned about whether or not the water coming out of it (Brisbane's water supply) will remain safe to drink. Likewise I would be more concerned about all the other consequences of the flood.

A dam could burst yes. And a bridge could collapse and you could be struck by lightning. Assuming that nobody does anything silly, like trying to operate outside the dam's safe operating criteria (let the engineers make the decisions on water release, not politicians), then I wouldn't be worried about the dam itself.
 
folks

I am sure we all are very much concerned on the outcome (and reasons) of the flood to the people of Qld directly and the ripple effect on the whole nation.
On a macro economic level it will affect our GDP as well.

Without any rhetoric, may I urge if you please consider ;

to donate at least $50 per person in your family or 2% of your net profits in the next 10 days from stock transaction whichever is more to a suitable fund for the flood victims. I am sure many have already done it.

Money comes and goes.

I am sure whatever small it is the kindness will be a great boost up for the affected people.

Submitted for your kind consideration

Regards

Miner
 
Smurf1976 said:
Trying to lessen the overall severity of flooding through manipulation of water release rates.
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Given the Bureau of Meteorology rainfall outlook (Jan-Mar), a decision could have been made to let some of the normal storage go in anticipation of higher than normal rainfall.

This would have been a brave call though, in light of the preceeding drought.
 

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Wivenhoe is at 190% now, and we are all worried about what will happen if it overflows.

I live in ipswich and have just finished helping a few friends clear out there houses as they are about to go under. Even though I live in a high area, will certainly sleep with one eye open tonite. I wish all my fellow ipswich and Brisbane residents a safe night
 
pedalofogus said:
Wivenhoe is at 190% now, and we are all worried about what will happen if it overflows.

I live in ipswich and have just finished helping a few friends clear out there houses as they are about to go under. Even though I live in a high area, will certainly sleep with one eye open tonite. I wish all my fellow ipswich and Brisbane residents a safe night
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All the best, pedalofogus. My sympathies are with you. Lying awake and listening to that incessant thundering of torrential rain is a sound I could live without for the rest of my life. Hope it turns out to be less serious than it's looking for Ipswich at present.
 
Smurf, thanks for the detailed explanation re the Wivenhoe. With family not too far from the Brisbane river, it's somewhat re-assuring to know the unlikely event of the dam collapsing...:)

That said, it looks like the family will be coming tomorrow to stay with us for a few days while the danger passes. Hopefully the Gold Coast remains clear of this disaster - it's getting a bit close for comfort...:eek:

And all the best to you, pedalofogus, and trust your friends are OK. It will be a tense couple of days ahead.
 
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