You obviously have never worked in government. Politics is all about vote-buying and surviving to the following election. For example, the Redcliffe Railway link, 40 years on and still not built.

I think raising the wall of Wivenhoe Dam is warranted, and keeping the dam at 100% FSL. I've said this many times - humans need to learn that there's nothing you can do to stop mother nature. It seems that blaming others for one's own shortcomings is fashionable these days.

And connecting/raising Bourumba is a good idea as well - given the fact quite a few of our rain events are coastal, while the dam might drain quickly, it will get a top-up quite often.

Actually I've worked in government in both NSW and QLD.

Redcliffe railway has been promised for 100 years hasn't it?

What's the point in raising the dam wall with the FSL in the same place. I presume the fuse plugs would still be triggered at the same point. Somerset is the weak point in the system at the moment so no improvement in very large flood readiness either.

Perhaps we do away with Somerset dam. It's getting on a bit.

We then raise Wivenhoe significantly - no need to worry about the impact on Somerset 'cause we have demolished it.

I'm sure the fuse plugs get re-located to a higher level - in fact I think we might even get rid of the fuse plugs and the gates. Then there is just a spillway at full flood mitigation level and a more modest sluice to draw off water supply as required. (No future flood engineers before an inquiry 'cause nature will just take its course. In fact, who would want to be a flood engineer given what those poor sods have had to go through.)

During construction (over 10 + years) we may have to drop the dams levels - but that's ok. We use the water grid to pump the water to other dams and fire up Tugun desal plant if we get a bit short.

Only a couple of billion $$.

Pity the desal plant doesn't work

Just thinking out loud here, but given that there is already a perfectly good narrow natural gorge/dam site at Somerset, then this may not be as odd an idea as it first sounds. By my reading of our written history, there has never been a significant flood in Brisbane city without a massive flood in the Stanley River. This stream alone, because of the position of it's catchment, is by far the most likely cause of truly disastrous flooding of the nature of say, 1893.

There may indeed by merit in revising the existing dam or building a completely new one just downstream of the present dam. I believe that, with new data and knowledge gained from the 1999 and 2011 floods, that it would be possible to create a dam that could go some way to meeting our water needs as well as providing significantly greater flood protection downstream. The restiction of course would be the flood time land inundation upstream around Kilcoy. Maybe someone who knows could tell us close to the town of Kilcoy the dam's water came in the 2011 event. If it was very close then I'm probably just talking a load of guff.

Keep safe all
Neil

The upper reaches of Somerset Dam is very close to the Kilcoy township, and the 2011 flood did result in the D'Aguilar highway being cut close to Kilcoy. There really isn't any scope to increase the capacity of Somerset dam due to the proximity to Kilcoy. There also isn't much scope to have an effective dam on the Stanley above Kilcoy.

My extra 5c:
The Wivenhoe 75% FSL really needs to stay indefinitely primarily due to the fuse plugs lowering the original flood mitigation capacity of Wivenhoe. The water grid will provide security of the water supply to alleviate the loss of the 25% supply. It is better to have a diverse range of smaller water sources, rather than rely on 1 large one. I think the 75% restriction will eventually become a permanent feature rather than a temporary wet season restriction and this will be likely to change as the water grid is enhanced.

Rather than raising Wivenhoe or Somerset, build higher river crossings downstream of Wivenhoe. If higher dam releases can be safely made without undue effect to the local communities, then a larger proportion of Wivenhoe's flood mitigation capacity can be used to safely absorb any peak inflows without fear of triggering the fuse plugs.

The fuse plugs may need to be redesigned slightly so that the first fuse plug can be triggered without increasing the risk of further flooding. Too much media and political emphasis was made on avoiding the fuse plug trigger. There are 3 fuse plugs at different dam levels, and once a fuse plug is triggered, the gate releases can then be reduced to account for the increased flow.

But why bother? If you want a higher level why can't you raise the existing dam, unless the cracking prevents it.

I'd wonder if there was merit in reviewing it's operational strategies. I'm not sure if the 99m FSL has been reviewed since the dam's opening. Given that the dam is now the weak link in the chain, there may be a reason to review this level.

Re: Wivenhoe. I wonder if there is merit in reviewing the W4 level of 74m (upwards)? If the centre fuse plug had gone in the 2011 flood I don't reckon that would have been the end of the world, exactly. Less than 2000cumecs would have been passing it, an amount easily compensated with gate openings/closings. A bigger concern is triggering strategy W4B(2) which requires opening the gates clear of the dam outflow if fuse plug initiation cannot be avoided.

Similarly, the vulnerability of Wivenhoe would not be much different as it is largely subject to Somerset staying upright within a large flood.

People need to get past this idea that higher release rates (above 2000m3) can be done under the W3 strategy without incurring a significant risk of urban inundation.

Releases as low as 2000m3 from Wivenhoe when combined with Bremer and Lockyer flows can cause significant damage in the lower reaches of the Brisbane River (around Brisbane itself).

This was made very clear in last January floods when we saw areas around Brisbane already going underwater by midday on Tuesday coinciding with a 2000m3 release rate from Wivenhoe 24 hours earlier. (24-36 hours from time of release to when the water reaches the city reach).

Had dam operators made this type of release in October 2010 when the dam level exceeded 69m they would have been slammed for causing unnecessary damage.

The fuse plugs really don't change much as gate operations can be reduced once a fuse plug has been triggered if inflows fall. They are a safety valve in case inflows come in so rapidly they outpace/overwhelm the gate opening capacity. They came close to fulfilling that role this time round when the inflow rose rapidly to 11,000m3.

Any advantage gained from a 75% FSL are very situational. There are plenty of possible scenarios where it would make absolutely no difference whatsoever to the end result.

You don't think that city gauge would be affected by the rates of increase in the Wivenhoe outflow which occurred <24 hours before those times? I can see that most of the water is delayed by 24+ hours, but I have little doubt that some of the water travels faster due to the slope on the river.

From about 1am 14/1/2011 Wivenhoe was releasing 3400cumecs+ and the city gauge never got above about 2.1m. Into the BoM's minor flood level range, I guess, but tides on 6/1/2011 were causing it to touch the minor flood level. There really needed and needs to be an understood "tough luck - you shouldn't have built there" level, and I can't accept that is around the 2000 cumecs mark.


Correct. The gates can only get completely clear of the water, after that you can't increase outflow any more. I would add that they also provide a level of protection in the case of a total gate failure.

The real issue is: When should we go into a "protect the dam" strategy? As I posted on above. It seems like there was and is a culture of "never trigger the fuse plugs".


Absolutely. It would make little difference if an 1841 level flood re-occurred, but would make a worthy difference for a 2011 or 1893 level flood. Not too sure about a 1974 level flood - Wivenhoe could stop that dead as in 1999.

'Significant' damage, I agree with somebody, the fact is, in an event such as this, there almost needs to be a level at which we 'accept' the Brisbane River to rise to due to Wivenhoe Damn releases in exchange for saving more of Brisbane. As in, release less water over a longer period of time.

I think all councils along the Brisbane River need to offer a buyback of all properties which are inundated by a minor flood peak (2.5m, for example). The fact is, if we flood-proof Brisbane for a minor flood, the operators of Wivenhoe could send down up to 3000m^3/sec and not fear the NIMBI/concerned mothers/armchair expert panels going after them. (The properties along Norman/Breakfast Creeks come to mind).

And reducing Wivenhoe to 75% FSL is silly. Each and every flood event is different, and this does jeopardise water security.

In fact, the damage from various discharges was studied in 2007: http://www.floodcommission.qld.gov.au/__data/assets/file/0020/3881/Morris_Kenneth_BCC_KJM-03.PDF

Damage from different flow rates:
1000: $232 060
2000: $720 000
3000: $2.21 mil
4000: $13.49 mil
5000: $70 mil
6000: $227 mil
8000: $915 mil

Seems like 4000m^3/s is close to the sweet spot really. I don't see how they can be slammed releasing at this rate if people below the dam have been forewarned.

I've read through the relevant chapter in the Commission's interim report and parts of the new dam manual, and I must say that I object to strategy S3. This allows an unspecified amount of water to be retained in Somerset below the target line to attempt to protect a fuse plug. This seems to endanger what is the weak link in the flood chain for little reason. If a fuse plug lets go the outflow can be compensated by closings of the main spillway gates. Surely it should be managed in this way.