brissybee

I am sure I was not alone in being alarmed by a recent article in the Australain newspaper in which it was written... "THE Wivenhoe Dam's ability to provide expansive flood protection to the city of Brisbane and surrounding districts was failing yesterday."

A lot has been said about what was done to ensure the dam didn't fail... but, as yet, I don't know if anyone has said what would happen if Wivenhoe Dam did fail.

Does anyone know?

DadAgain

We'd all be f*&ked (not just people wealthy enough to live beside the river )! Or at least we would've been last week.

DeadVim

I don't think it meant structually failing, just didn't have enough capacity for recent events.

I read today that the dam was back to 106% capacity so that's almost all the flood mitigation restored ... maybe they'll release the water differently next time, all down to the inquiry ...

cresta57

Damned if they did & damned if they didn't
If they released to much & the rain didn't come it would have been incompetent management, ditto not releasing enough to cope with the run-off from out West

bcworld

It's amazing all the armchair experts that are popping up on the news sites saying how they could've handled the situation better!

I did read that inflows into the dam were something like 2.5 times what they were into the catchment during the 1974 flood. The flood level in the city was 1m lower than '74, so maybe they got something right!

As Vim suggested the dam effectively did fail, it didn't have enough flood mitigation to be able to really control releases. People say the rain was predicted, but I don't remember seeing it being predicted as bad as it was, Xmas week it was but not last week.

ABCDiamond

That article also went on to say:

The dam has so far been credited with extensively minimising flooding with releases being timed to avoid clashing with high tides that can back up the Brisbane River.

But the worry is this:
"We are seeing 1 million megalitres, or two Sydney Harbours, flow into the Wivenhoe catchment every day."

brissybee

Exactly. And I haven't (yet!) seen anyone in the media ask the hard question. What happens if the dam fails? Who/where gets flooded? I have heard reports say it would be a "catastrophe", but frankly, that's a bit loose in terminology and short on fact.

Will anyone ask the question? Does anyone know where to get the facts?

Pollyana

There are plans that show what properties are affected if Wivenhoe were to "fail" - they were used in exercises several years ago. From memory its a very extensive area, but depends naturally on where the failure is, how catastrophic, and how full the dam is at the time. I honestly can't remember the details - its 6 years ago and I was very new in Brisbane at the time so most of the mapping didn't mean much to me. Today I probably would've kept the maps, but as it is, sorry don't have them.

I would imagine the Emergency Plans for Wivenhoe should be a matter of public record though, if not the detailed mapping - maybe raise the question with your local councillor or even your MP? Failing that, I'm sure they will emerge during the Enquiry.

spalen

I researched this heavily ( 7 minutes on google )

"Failure" of the damn would mean water flowing over the top and destroying the dam wall because its not designed to have water flow over the top it would likely fail (according to an expert).

They have capacity to go up to 225% , it hit 191% at its peak in this incident. At 200% the emergency second release system kicks in and it unleashes a load of water down a second release zone (who is in that zone and how much those poor buggers will get wacked with is unclear) but its an event you dont want to happen. They came within 60cm of that happening in terms of depth of water. But really they came within 5% (191/200) - which is scarily close but still they were managing it, clearly.

Pollyana

Exactly. I remember seeing the maps of the inundation zone for North Pine Dam wall failing, and its a huge area even at only 70% (which is what one exercise was based on). If I can dig out more info I will but it'll be on my old laptop so I'm nto promising.........

spalen

Probably just safe to say - if you can see the river, you'd be in it.

Dams dont fail - thankfully << I typed that and then did more "extensive" research to find that 7 failed since 2000 alone ! Argh!

Including comedy errors such as : Poor design, use of dynamite to remedy structural problems. ( using dynamite to remedy a structural problem...er..)

Pollyana

Yep, they do sometimes fail, we have a cupboard full of plans and info just in case..........

Alfresco

I think anyone, no matter how low their IQ (generally speaking), would be able to say with a great deal of confidence this summer, that the rain will defo come...


Just listening to tipping it down outside now.

lesleys

Start by reading the part headed 'Flood Mitigation'. It's designed bring a secondary spillway into action before the whole thing gets too full and can't hold back the weight. It wouldn't be the best of times but it should stop the whole thing collapsing.

http://en.wikipedia.org/wiki/Wivenhoe_Dam

DeadVim

She'll be right mate.