WITH respect to what has happened in this major flood disaster in Brisbane, the role played by the huge Wivenhoe Dam in this flood will be called into question, and as the cleanup is starting now, many more questions will be asked in the wash up, if you’ll excuse the lame pun, and a lot of those questions will have political ramifications.
There is absolutely no doubt whatsoever that this monster dam played an absolutely crucial role in preventing what could have been an even worse disaster. I have mentioned earlier that this huge dam held back water that would have made this flood something not worth even contemplating.
Water was flowing into Wivenhoe at a greater rate than could be released with all five spillway gates open at their maximum. At one stage, water was pouring down those spillways at a rate of around 650,000 megalitres per day, and that is what caused the initial flood devastation in Brisbane. Had they not released that water at that rate, there was the very real probability that the flood would have been even more devastating, only a few days later, perhaps right in the middle of those King tides.
That initial huge release was due to the fact that releases of water from an already filled Somerset Dam, (directly upstream, and itself at 175% capacity and rising, and also filling faster than it too could release, and with all its flood mitigation compartments full) were rapidly filling those flood mitigation compartments in Wivenhoe itself.
Wivenhoe was also filling from runoff in its own catchment as well as what it was receiving from Somerset, and at one stage water was flowing into Wivenhoe at a greater rate than what they were releasing at that maximum I mentioned above.
That initial outflow was eased back after 24 hours, and that initial huge release is what caused the flood damage in Brisbane. The release was eased back to a rate of around 215,000 megalitres a day and stayed at that rate for 2 days.
Now that the major flood peak has passed in Brisbane with the advent of the two king tides, that release from Wivenhoe has increased again to around 320,000 megalitres a day. With the river in Brisbane dropping from its major peak, that release will keep the river (relatively) high, but at a controlled level.
Those current releases from Wivenhoe just have to be kept at that level so they can empty the flood mitigation compartments of this monster dam, now sitting at a level around 192% of capacity. Those releases will continue for days until those flood mitigation compartments are empty.
The reason for this is that if there is another major rain event, and there have been some forecasts for a Cyclone that could move back towards the Coast around the Brisbane to NSW border area late next week, then those compartments will have room in them to actually fill again.
If all that water from that earlier rain event of such huge proportions was kept in Wivenhoe, then any subsequent rain event will see Wivenhoe, already topped out at its maximum holding of around 225% totally full, and then Wivenhoe, and its engineers already performing a huge juggling act will have nothing left to do but let monumentally huge amounts of water flow down the river and into Brisbane, causing an unspeakable tragedy of a far greater proportion than it has already caused now, something that is not worth even contemplating.
UPDATE 18TH JANUARY
Now that the inquiry has been called, I suspect that, (and please don’t think of me as a conspiracy theorist) some aspects of that SEQWater website might be removed from public access.
What I am referring to here is not the home page information, or even the dam levels page, but a small part of that latter page that not many people might even refer to.
If you visit that Dam level page, at the bottom, you’ll see a small interactive chart detailing the current water levels across the whole storage. If you go there, you can navigate around, so there’s no real need for me to explain how to use it.
The default setting shows the tick in the right column set to grid three, but you can add individual dam levels so that the level for that dam overlays the main image of total level.
Tick the square alongside Wivenhoe, and the level for that dam appears on the chart.
Now, untick the default Grid three so only the Wivenhoe level shows there.
Now, scroll your mouse slowly along the line and the levels for each day show up as a percentage.
Get close to where the upwards spike starts and carefully roll the mouse up the spike.
At the bottom is the level for Friday at 106.3%.
No entries for Saturday and Sunday as has always been the case, and I can understand that it’s the weekend and the person tasked with updating the website is away, naturally.
The next reading is for Monday at 148.4%
Then Tuesday 11 Jan (9AM) it is at 175.9%
Wednesday (9AM) it is at 188.5%
Thursday (9AM) it is at 186.5%
Friday (9AM) it is at 179%
Then nothing more until Monday and Tuesday, (today) as levels spike back downwards as those flood mitigation compartments are emptied back out.
The huge rain event in the catchment started Monday PM, and went until Tuesday PM, and I watched it on and off for most of the day on the BOM Mt Stapylton map set to 128Km.
Look at the levels from Friday until Monday, and it rose steeply, and on Tuesday AM was close to its maximum.
The releases obviously started on the Monday, accelerated on the Tuesday to that 645,000 ML rate, and the peak in Brisbane arrived 36 hours later and was then added to by the high tide.
However, it would ‘seem’ (term used very carefully here) that from Friday to Monday, not very much was released, until the levels had become alarmingly high.
For more information:
Link to article on Fed Govt releasing flood maps:
Link to flood maps. This is local SEQ, and above that there are maps for all major cities in Australia. The maps take you to further maps and you can click on individual areas and get three scanarios for each area. (pdf document maps)
Tony is a Rockhampton-based blogger who mostly writes for a US-based audience.
To read more from Tony you can find links to main posts and updates here: http://papundits.wordpress.com/2011/01/13/brisbane-and-queensland-flood-crisis-with-updates/
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