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Thar she blows! New Cotter Dam overspilled

By johnboy - 1 March 2012 76

The Cotter Dam Expansion Dam Cam is showing the worst case scenario of flood waters rising over the under-construction wall as the capacity of the river diversion is comprehensively overwhelmed.

Let’s hope the raging torrent doesn’t undermine the wall or this will become a disaster of 2003 bushfires proportion.

We certainly hope that doesn’t happen, but it’s not like this was meant to happen either.

UPDATE 01/03/12 09:10: Thanks to dpm for pointing us at the above video compression of the overspill

cotter dam overspill

[Photo by Androo]

UPDATE 02/03/12 8:18: And she’s still going very strong this morning:

cotter dam

UPDATE 02/03/12 09:31: This in from ACTEW supremo Mark Sullivan:

MarkS
2012/03/02 at 8:21 am

This morning observations are that the dam structure is sound. Heavy machinery has remained safe and cranes are fine. Have lost some forms and scaffolding and some light equipment. Biggest concern is the washing out of earthwork on the downstream side (looking at damcam it is on the left abutment or the right hand side looking at the dam). Possibly be a week before we get back on the dam and looks like a three week clean up. Flood is a one in one hunred year event so top marks to the engineers. Now we wait till tomorrows renewed assault.

What’s Your opinion?


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76 Responses to
Thar she blows! New Cotter Dam overspilled
31
Jivrashia 9:25 pm
01 Mar 12
#

32
rohbo 9:26 pm
01 Mar 12
#

Mr Evil said :

Umm, maybe the same way they got them up there in the first place?

The machinery including vehicles rise with the dam wall. They were put there when it was at the valley floor and they go up with it. I assume the only way they come off is when the wall peaks and they can be driven off the top onto the neighbouring hillside.

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33
caf 9:28 pm
01 Mar 12
#

Interestingly the same thing happened during the construction of Googong Dam – http://www.engineer.org.au/images/4-11.jpg – and that’s a rock-fill dam.

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34
EvanJames 9:53 pm
01 Mar 12
#

OpenYourMind said :

Let me just say how cool it is to have the local expert tell us how it is on RiotACT. Thanks MarkS

Seconded. Excellent work, great to see.

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35
MarkS 10:04 pm
01 Mar 12
#

I am leaving reception area and then heading home. Will update early tomorrow as we understand extent of damage. Right now it is not good but not as bad as it could be. Structure secure. Lots of water and debris. Please can the rain stop

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36
toriness 10:06 pm
01 Mar 12
#

way cool video! and thanks to JB for pointing us to the damcam, it has entertained me all night!

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37
BerraBoy68 10:15 pm
01 Mar 12
#

It may be nothing or just something on top of the Dam wall effecting the water flow, but the smooth flat lines that were at the top of the wall up till now don’t look all that smooth anymore, (ref: ACTEW Dam Cam 10:12:57) particularly toward the right hand side as you look at it. It almost looks like something’s given way. I hope not. Ever been so riveted watching a live cam before.

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38
androo 10:27 pm
01 Mar 12
#

I grabbed a short video of the overtopping shortly after it began. Sorry for the quality, using a flipcam but the audio gives you an idea of how loud it was.

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39
7captains 10:28 pm
01 Mar 12
#

Thank you MarkS, what an absolute treat to be given on-site updates.

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40
pandaman 10:33 pm
01 Mar 12
#

Mr Evil said :

rohbo said :

Mr Evil said :

A couple of questions.

Why were vehicles left parked on the topside of the dam when there had been pretty ample warning that NSW/ACT was going to receive a lot of rain in the next few days, and numerous flood warnings had been publicly issued?

If you know how to get some very heavy machinery off a 40m high wall i’m sure ACTEW would love to hear from you. Mark S from ACTEW said they got off everything they could with the cranes and the rest was too heavy so had to stay.

Umm, maybe the same way they got them up there in the first place?

Anyway, maybe I should have expressed myself better – the really heavy stuff isn’t the problem, as obviously if a 40 or 60 tonne object is going to be swept off the wall by the overflow, then I would suggest that there’d be bigger issues to worry about with the dam itself at that point. It’s some of the other smaller vehicles that appeared to be still on the dam in the photo that Mark submitted earlier this morning.

The point I was making is that we have had several days warning that the rainfall was going to be high, but some people seem to have been caught slightly ill-prepared by it all.

And as to my comments about objects seen floating down the river; yes, I understand that there will always be plenty of stuff that is washed down a river in flood, as witnessed on LBG last time we had a flood like this – but isn’t it a good idea to try and ensure that if at all possible that we don’t add to the debris pile unnecessarily?

I could crap on about the capacity of those tower cranes, the likely weight of the equipment left on top and the likely difficulty in getting a big mobile crane anywhere near enough to be of any use, but with the know it all layman such as yourself it will never be of any use.

Suffice it to say, don’t give up your day job. Or if your day job is construction related, consider giving up.

On topic, damn that is some serious water. It’ll be interesting afterwards to see if any of the gear on top has moved. In any case, there’s going to be some damage to clean up and repair. Poor bastards. I saw photos from the first time they got flooded out and the place was a serious mess.

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41
mr_volts 10:51 pm
01 Mar 12
#

Another timelapse from the DamCam: http://www.youtube.com/watch?v=cvZwferhuTo

This one was started at 11:30am and covers footage up until about 10:10pm. You get to watch the last minute preparations, and the rain!

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42
posscakes 11:00 pm
01 Mar 12
#

BerraBoy68 said :

It may be nothing or just something on top of the Dam wall effecting the water flow, but the smooth flat lines that were at the top of the wall up till now don’t look all that smooth anymore, (ref: ACTEW Dam Cam 10:12:57) particularly toward the right hand side as you look at it. It almost looks like something’s given way. I hope not. Ever been so riveted watching a live cam before.

Looks like the forms starting to detach you can see them more clearly on the most recent shots. The forms being the black pieces of ply that hold in the most recent layers of concrete. Still they are pinned into the concrete with steel rods maybe 1.5 metres long so must take a far bit of force to bust them off.

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43
Funky Claude 11:04 pm
01 Mar 12
#

The point I was making is that we have had several days warning that the rainfall was going to be high, but some people seem to have been caught slightly ill-prepared by it all.

And as to my comments about objects seen floating down the river; yes, I understand that there will always be plenty of stuff that is washed down a river in flood, as witnessed on LBG last time we had a flood like this – but isn’t it a good idea to try and ensure that if at all possible that we don’t add to the debris pile unnecessarily?

I would dear say that they had better access to forecasts and warnings than what you and I are privy to, and and as the equipment involved in the construction is worth thousands I doubt that they have adopt a reckless attitude to “add to the debris pile unnecessarily” as you suggest.

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44
posscakes 12:17 am
02 Mar 12
#

Funky Claude said :

The point I was making is that we have had several days warning that the rainfall was going to be high, but some people seem to have been caught slightly ill-prepared by it all.

And as to my comments about objects seen floating down the river; yes, I understand that there will always be plenty of stuff that is washed down a river in flood, as witnessed on LBG last time we had a flood like this – but isn’t it a good idea to try and ensure that if at all possible that we don’t add to the debris pile unnecessarily?

I would dear say that they had better access to forecasts and warnings than what you and I are privy to, and and as the equipment involved in the construction is worth thousands I doubt that they have adopt a reckless attitude to “add to the debris pile unnecessarily” as you suggest.

I think in fairness Actew have been preparing for a rain event for the last month or so, as they have been dropping the level in the dam considerably. You may or may not have noticed also the campgrounds on cotter rd have been shut for a while and i think this your answer why they do that. As much as you might like to think otherwise its a weather event its out of anyone’s hands really. Bulk water would of moved what ever machines they could, but its a wall so the access is restricted, and cranes have limitations too.

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45
OzChick 12:29 am
02 Mar 12
#

Thanks for posting the time lapse videos. Amazing.

Do they always keep the lights on at night at this site?

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