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If this is not a reasonal trade off, the logical extension is to burst the Wivenhoe Dam and let the whole lot down in one hit.
Queensland Floods
- Thread starter Julia
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Whiskers
It's a small world
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If this is not a reasonal trade off, the logical extension is to burst the Wivenhoe Dam and let the whole lot down in one hit.
Oh no... don't talk about bursting the dam on purpose now!
I suppose those at higher levels would consider it a reasonable trade-off, but I wonder what those at lower levels think if they stayed soaked for days longer than they would ordinarily. I suspect if there was no flood mitigation they most likely would have invested in higher ground.
I understand one of the reasons why Rocklea Markets recovered and expanded on the same site and other food distribution facilities developed there since is because of the flood mitigation plan and they are part of the lower level that may be under water for longer. That's Qld's main fresh food distribution centre a casualty, a trade-off of the flood mitigation probably closed down again and again for longer (in total) before the wet season is over..
I hope it all works as planned, but I just can't help considering the worst case scenerio.
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Wysiwyg
Everyone wants money
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Pollution from tonnes upon tonnes of stuff is being dumped in the ocean via rivers along the coast. Scourge of the planet, styrofoam, is seen on this video.
And I just can't help feeling that this is what you would like
Have a think about that post. then apologise.
Whiskers
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And I just can't help feeling that this is what you would like
Well, from my experience, people who never think about bad or worst case scenerios are doomed to be victims of every minor hickup in lifes journey.
It's not about beeing gloomy or pessimestic, but prepared.
I just happen to have been a boy scout and leader in my hey day... and you know what their motto is... Be Prepared!
I'm just highlighting that I hope someone has a contingency plan for the Wivenhoe overflowing the wall, cos regardless of the recent downfall considered a bit unusual, because the Wivenhoe was already well over full and releasing water for weeks, it's probably not going to buff the effects much other than cutting the peak off a bit as I say at the expense of longer lower level flows which I'm curious to see the final analysis come June or so when the wet is over and the costs are weighed up.
Garpal Gumnut
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Let's hope that the folk in Brisbane, the Lockyer, Ipswich and Toowoomba have a safe night.
I've been through one major flood where a family member's house was severely flooded, and I can understand the dread and despair of some of the folk down there.
gg
I've been through one major flood where a family member's house was severely flooded, and I can understand the dread and despair of some of the folk down there.
gg
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Good work maintaining a level and rational conversation whiskers in the face of consistent trolling.
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Full Supply Level (FSL) is 67m AHD (metres above sea level - dam levels are commonly measured this way).
FSL for Wivenhoe is taken as FSL for water supply purposes which is an arbitrary level in terms of the dam's engineering - someone just decided (hopefully backed with proper calculation) to normally store only a certain amount of water, leaving the rest of the dam's capacity available for flood control. There may also have been other influences in this decision - amount of land normally flooded (versus that occasionally flooded when normal level is exceeded), recreational use and so on.
The dam isn't full, in an engineering sense, until it reaches its true FSL which is well above normal "maximum" levels.
Wivenhoe is a bit unusual from an Australian perspective since most dams in this country have only one defined FSL since the aim is to store as much water as possible, with flood control not being an objective. The practice of releasing water when the dam is not actually full, in order to be able to hold back water in the event of flood, is not common in Australia (though this mode of operation is not unique to Wivenhoe, it is relatively uncommon in Australia).
What happens if Wivenhoe does reach maximum level? No different to any other dam - water goes down the spillway (Wivenhoe actually has two spillways) in order to ensure the safety of the dam. This is normal operation.
Whilst FSL is the "maximum" level, dams are designed to allow some water storage above this level during a flood event. Wivenhoe dam shouldn't collapse just because it gets to full capacity, or even a bit over it. Nor should any other dam. It's only if water starts literally running straight over the top of the dam itself that there will be a problem - and that shouldn't happen given that there's two rather large spillways to let the water out at a lower level.
In some cases, for example Lake Gordon in Tasmania (far larger than Wivenhoe), there isn't any kind of spillway at all and that certainly isn't the only dam like that. We've had big dams without spillways in Tas since 1922 and we've got a whole lot of other dams (which do have spillways) in the lower sections of cacade generation systems (most notably the Derwent and Mersey-Forth catchments) that are almost always filled right to the top.
In short, it all works fine as long as the engineering and operation are right. Depending on the purpose, dams "should" be full, empty or somewhere in between. For long term water storage obviously it's "good" if it's full. For a small storage (relative to catchment size) hydro-electric system you want it never full (since that would lead to spill if it rained) and never empty. And for a flood control dam the ideal level is, of course, empty whenever there isn't actually a flood.
So why is water being released from Wivenhoe? The storage (as distinct from the physical dam wall itself) is not large enough to hold back the full volume of water entering it during this flood event. Consequently, some water must be released. From the perspective of the dam itself, they could let the level rise further - the only reason to not do so is that if they did this, peak release volumes would need to be higher, since the dam would not then be storing any additional water at all, and that would cause greater flooding downstream.
If I were in Brisbane right now then there are plenty of things I would be worried about. The structural safety of Wivenhoe would be well down the list unless there's an earthquake or something like that.
Petrol - I hear that Caltex has had to stop production at their refinery (in Brisbane) due to the floods. There are only two oil refineries in Qld - I'm not sure how the other one is doing but it too is in Brisbane so may be affected. Given that the floods may have contaiminated stocks at service stations etc, a petrol shortage is a possible outcome.
Food - Lots of panic buying at the shops according to the media. And of course lots of crops wiped out too, farm machinery damaged etc.
Water supply - Ironic though it may seem, but lack of drinkable water will quite likely be a problem in the days and weeks ahead.
Electricity - Some areas have been switched off for safety but the upstream supply of electricity is OK at least in the short term. Reduced production from Qld power stations is presently being offset by increased production in other states (primarily Vic and Tas although there is some effect in SA and NSW too).
And then there's the immediate effect of the floods to worry about...
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I'll suggest that smoothing the peak is preferrable to an unrestrained flood.
Rings my bell, when after bringing up some possible scenarios I got the tag of bringing bad luck, because sometimes things happened as I assumed they could.
If in 1974 there was similar event and people did not gradually move away from 100 YEARS EVENT AREA, well they could build some better facilities upstream.
Not to mention that 100 YEARS EVENT will not necessarily happen 100 years from now.
(It is only statistical expression of usually rare events, but it is not set in stone)
Julia
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Smurf, thank you for - as always - a coherent explanation of how the dam works.
Re food and water: already some regional Qld towns are out of drinking water as at news bulletin I heard at 6pm. Other towns were being told they must use water only for drinking and showers. Nothing else. Even with such measures, they anticipated having no water available for drinking within a further day.
Supermarkets and fruit/veg shops in the regional centre in which I live have no food available, not even any tinned products or packets of rice/pasta. No petrol left as of this morning.
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Agreed that people should be prepared.
But my point is that food, drinking water, sanitation (disease...) and the like are immediate, real problems. Likewise accommodation, transport (and fuel to run it) and so on are also real problems that are here right now whereas a dam burst is an unlikely (though admittedly not impossible) event.
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If you are forced to drink potentially contaminated water then boil it first as this should kill the bacteria. Not ideal but better than nothing.
I know that boiling it could be a bit of a problem given the circumstances - just have to improvise whatever means can be found to do it.
If the mains water is still working but is contaminated with mud etc then you should get clearer water from the hot tap if you have a storage (tank) hot water system. Just be aware that the mud will be collecting at the bottom of the tank since the water heater is effectively acting as a settling tank (the water to the taps is drawn off the top, whilst cold water enters at the bottom). So you should flush the tank once life gets back to normal (otherwise the accumulated silt will cause it to rust) but it's a potential source of clearer water during the emergency.
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God is giving us a message that he is angry with our commodities exports and their contribution to Global Warming.
First stop coal industry in QLD, next stop will be something major happening in the WA.
First stop coal industry in QLD, next stop will be something major happening in the WA.
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If He is so powerful, almighty and omnipotent, why doesn't He just send us a text message?
Sheesh!
::
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Unprecedented commodities export growth, comes with unprecedented environmental natural disaster.
The planet is just doing what it has always done.
The reason why it takes a while is that there is man made infracture preventing it from flowing out.
I reckon the dam plan worked. People will be relieved in Brisbane this morning.
Prosperine in Nth. Qld. got flooded every big wet. They built a dam years back and the year it was finished it was filled to 6 inches from the top by a cyclone. The dam now supply's irrigation to the agriculture area.
Its the first time I have seen a labour politican in control since 2007. Go Anna!
Cheers.
The reason why it takes a while is that there is man made infracture preventing it from flowing out.
I reckon the dam plan worked. People will be relieved in Brisbane this morning.
Prosperine in Nth. Qld. got flooded every big wet. They built a dam years back and the year it was finished it was filled to 6 inches from the top by a cyclone. The dam now supply's irrigation to the agriculture area.
Its the first time I have seen a labour politican in control since 2007. Go Anna!
Cheers.
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The river peaked in the city at 4.46 metres which is almost a metre less than the peak of 5.45 metres in 1974. Wivenhoe flood mitigation prevented a major flood from becoming a disastrous flood.
No doubt we will find out in the washup, but without the management of the water flow, the flood would have been several metres higher.
No doubt we will find out in the washup, but without the management of the water flow, the flood would have been several metres higher.
I reckon you are correct. I think the rail for coal transport will be a priority.