1 December 2011

Works on Scrivener Dam

| johnboy
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The National Capital Authority has announced their plans to make some major renovations to Scrivener Dam:

The National Capital Authority (NCA) today announced that major engineering works at Scrivener Dam will commence in the new year. It is anticipated the works will cost in the order of $15 to $20 million.

The works involve progressively replacing 120 anchor bolts, which are part of the flap gate mechanism. The flap gates are opened in flood events to regulate the water level of Lake Burley Griffin.

NCA Chief Executive said the works were identified during an annual safety audit and surveillance inspection of Scrivener Dam.

[Photo by Martin]

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Disinformation7:30 pm 08 Dec 11

AAMC said :

Let’s not forget that these bolts are holding up a few million tonnes of water, work like this is never going to be cheap.

Holding UP a few million tonnes? How did you work that one out?
The calculation to rough estimates is relatively simple. Height of the water head over relative area of the doors. It would absolutely nowhere near millions of tonnes and would be lucky to be within hundreds.

creative_canberran said :

To service the dam gates according to the technical specs for the dam, a specialist “service gate” is floated to behind the gate requiring work. Ballast tanks are flooded, sinking the special gate and placing it against the wall and the lake bed to create a seal. The fish belly flap is then open and water emptied. Still not sure where the lowering of the total lake level comes into this?

Could it be that each time they empty the big chunk of water between the dam and the “special gate”, there is a correspondingly smaller amount of water remaining in the dam?

It is also possible that the “special gate” does not form a perfect seal when sunk, and that while it is in place there is a constant leaking of water…

creative_canberran4:28 pm 08 Dec 11

Some more news about the lake levels and a sudden increase in dead carp around the foreshores which the NCA is claiming not to be linked to the water levels: http://www.abc.net.au/news/2011-12-08/low-lake-levels-described-as-safety-concern/3720702

To service the dam gates according to the technical specs for the dam, a specialist “service gate” is floated to behind the gate requiring work. Ballast tanks are flooded, sinking the special gate and placing it against the wall and the lake bed to create a seal. The fish belly flap is then open and water emptied. Still not sure where the lowering of the total lake level comes into this?

Classified said :

johnboy said :

shirty_bear said :

Heard talk on the wireless that the lake level will need to be lowered. Not clear how far, but “drained” was not the word used. Would be an interesting (if unsightly) exercise.

500mm, half a metre.

So which is it?

I live in a part of the universe where the laws of physics still require that 500mm equals half a metre, so I’m not currently having any problems with this clarification.

creative_canberran said :

Lowering the lake level is the most suspicious part of this whole thing. I’ve actually read the master technical documents for scrivener dam, they go into remarkable detail about every aspect of the dam’s design, operation and maintenance. Everything from how to enter the water tight gallery and use the internal communications and “dead man” system to how to fit the temporary service gate to allow for repairs to the fish belly flaps. documents I’m waiting on.

Lacking any further context, I can only say that that is one of the weirdest things I’ve ever heard of. I’m hoping against hope that you’re a civil engineer with a pressing need to read dam construction documents…:-)

dungfungus said :

AAMC said :

Let’s not forget that these bolts are holding up a few million tonnes of water, work like this is never going to be cheap. I would love to see them drain the lake for the works, then we could see all of the hidden “treasures” and clear them out.

Maybe the missing Ruger .22 will be found?

There’s be lots of very interesting things to be found, for sure. Lots of crap, too.

dungfungus said :

AAMC said :

Let’s not forget that these bolts are holding up a few million tonnes of water, work like this is never going to be cheap. I would love to see them drain the lake for the works, then we could see all of the hidden “treasures” and clear them out.

Maybe the missing Ruger .22 will be found?

I think i need more context dungfungus, i don’t get it.

creative_canberran3:21 pm 02 Dec 11

Lowering the lake level is the most suspicious part of this whole thing. I’ve actually read the master technical documents for scrivener dam, they go into remarkable detail about every aspect of the dam’s design, operation and maintenance. Everything from how to enter the water tight gallery and use the internal communications and “dead man” system to how to fit the temporary service gate to allow for repairs to the fish belly flaps. Given what I know, there doesn’t seem to be any reason to lower the level, except to reduce the pressure on the dam and gates.

On a side note, this isn’t an isolated incident for a dam in the ACT. I’ll be posting something more comprehensive though about that when the National Archives has checked and released some documents I’m waiting on.

AAMC said :

Let’s not forget that these bolts are holding up a few million tonnes of water, work like this is never going to be cheap. I would love to see them drain the lake for the works, then we could see all of the hidden “treasures” and clear them out.

Maybe the missing Ruger .22 will be found?

dpm said :

Yikes!! Let’s see…. if we reserved $5M to buy the 120 bolts and to pay for associated replacement of encasing ‘steel and concrete structures’, the remainder of that $20M figure could employ 120 people (each at a rate of $125,000) to replace one bolt each! Maybe they should get a second quote? 😉

Better still, I am sure the community minded Bunnings would supply the necessary Made in China nuts and bolts at a good discount (provided single units are not required) and the local Lions Clubs could organize a weekend working bee to knock the job over. ABC 666 could organise an OB and Pedal Power could run a sausage sizzle there to raise money for the Bowen Drive freeway. It could be a real fun event. Would save millions.
I wonder how the bolts were sabotaged by extremists who hate dams – has the security video been checked to see if a couple of people with brush cutters were in the vicinity on a certain date?

johnboy said :

shirty_bear said :

Heard talk on the wireless that the lake level will need to be lowered. Not clear how far, but “drained” was not the word used. Would be an interesting (if unsightly) exercise.

500mm, half a metre.

So which is it?

Gungahlin Al2:20 pm 02 Dec 11

creative_canberran said :

Interestingly, Scrivener Dam is not covered by the ACT Dam Code which mandates certain plans and surveillance requirements. In fact the code doesn’t even require flood mapping downstream of Scrivener Dam based on outflows from the Googong. The fact that these faults were only found by non-standard checks and had the contractor not been changed, would likely have continued to be ignored by the previous one leaves much to be desired particularly as suburbs never envisaged in the past are now being built downstream in Molonglo.

And apart from the questions hanging over the performance of the previous subcontractor, there is the NCA’s own apparently lax accounting practices.

Surely maintenance work such as this would have been provided for in accumulated depreciation provisions in budgets over every year since accrual accounting was adopted?

Dam managers know that they have infrequent but very expensive maintenance works. I put it that not providing for such works progressively over the life of the asset to be maintained is bordering on mismanagement?

When I was on board for the water authority that owned the Sunshine Coast’s main water supply dam and treatment plant, such depreciation provisions were a thoroughly normal part of annual budgeting.

To see what seems to be management-by-crisis from the NCA on this really makes me wonder about a) the staff practices and b) the performance of the NCA Board.

shirty_bear said :

Heard talk on the wireless that the lake level will need to be lowered. Not clear how far, but “drained” was not the word used. Would be an interesting (if unsightly) exercise.

500mm, half a metre.

Heard talk on the wireless that the lake level will need to be lowered. Not clear how far, but “drained” was not the word used. Would be an interesting (if unsightly) exercise.

Let’s not forget that these bolts are holding up a few million tonnes of water, work like this is never going to be cheap. I would love to see them drain the lake for the works, then we could see all of the hidden “treasures” and clear them out.

wow – thats $125k per bolt. And to think I grumble about the $500 ones in my ankle being expensive…

creative_canberran7:42 pm 01 Dec 11

Interestingly, Scrivener Dam is not covered by the ACT Dam Code which mandates certain plans and surveillance requirements. In fact the code doesn’t even require flood mapping downstream of Scrivener Dam based on outflows from the Googong. The fact that these faults were only found by non-standard checks and had the contractor not been changed, would likely have continued to be ignored by the previous one leaves much to be desired particularly as suburbs never envisaged in the past are now being built downstream in Molonglo.

Yikes!! Let’s see…. if we reserved $5M to buy the 120 bolts and to pay for associated replacement of encasing ‘steel and concrete structures’, the remainder of that $20M figure could employ 120 people (each at a rate of $125,000) to replace one bolt each! Maybe they should get a second quote? 😉

Didn’t they do work on the gates a year or two ago?

The NCA took over a decade to get moving on the currently dangerous Bowen Place Crossing, and now it has been delayed. Groan.

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