Wivenhoe Dam Levels – Background – After the 1974 Flood

Posted on Thu 01/20/2011 by


After the 1974 major flood in Brisbane, the incumbent Government in Queensland finally decided to construct Wivenhoe Dam.
The dam had earlier been proposed twice, in the 1890’s and then again in the 1930’s. It wasn’t constructed at those times, mainly because of the cost involved was too great for what was effectively still a developing State in a still developing Country.

That major flood of 1974 was the disaster that finally triggered construction. That flood was due in the main to a huge rain event triggered by a tropical cyclone. That huge rain event backed up behind the existing dam near the headwaters of the Brisbane River, Somerset Dam.
That dam was adequate for the water supply of Brisbane, but if filled rapidly with this huge rain event in its catchment. Once full, it had nothing to do but release vast amounts of water from it, and this flow down the river and straight into Brisbane, was further exacerbated by the backing up of King tides into the river from Moreton Bay, open to the Pacific Ocean.

That huge flood provided the political driver that got Wivenhoe constructed, and at the same time also spurred the construction of many other dams in the State, and proposals for new dams flowed in. Some of those dam proposals were not proceeded with at the time, and later, with the advent of a new Government of the opposite political persuasion in late 1989, those proposals were canned, probably because this new Government thought that the money could be better spent on things more in line with their political agenda, and that with Wivenhoe on stream, then there could even have been a sense of complacency that enough had been done to secure water supply, and to protect Brisbane from further major flooding.

The original intent of Wivenhoe was to provide security of a large volume of water for the South East corner of the State.
The other purpose of the dam was to have flood mitigation compartments that would help store excess water in the event of a future flood of similar proportions to that flood of 1974.

The word to stress here is mitigation.

People will confuse this with the word prevent.

Mitigation effectively means that it will store huge amounts of water that will lessen the effect of a major flood ….. not to prevent that flooding, but to lessen its effect.

Wivenhoe can store at its nominal 100% capacity a huge amount of water, 1.1 million Megalitres. (ML) That 100% level is the best case scenario for the water supply for the South East corner.

Now, on top of that 100%, Wivenhoe’s flood mitigation compartments can hold back a further 1.45 Million ML, effectively meaning the dam can hold up to around 230% of its nominal capacity, and I understand that sounds a little odd.

This excess is to lessen the effect of a major flood by holding back that huge amount of water, which will then be released at a later date, after the flood event, into the river at a rate that will not cause major flooding, or to exacerbate any major flooding that is already happening.

At the same time Wivenhoe was being constructed, work was also undertaken at Somerset dam to increase its flood mitigation capability, increasing its ability to hold back further water in the event of a major flood, and this was increase so it could hold back up to around 200% of its nominal 100% water supply maximum holdings.

Here what needs to be realised is that Somerset Dam is directly upstream for Wivenhoe, so any releases from Somerset flow directly into Wivenhoe.

Wivenhoe was finally completed and opened in 1984. It filled slowly, as you might expect of a monster dam, and all proceeded as it should. There was never an occasion when that capacity for flood mitigation was tested, because any significant rainfall events were not of the scale of that event in 1974 when all that was in place was the one dam, Somerset.

Water supply for every contingency in the South East corner was secured, and even though it was always there, Wivenhoe faded from the forefront of people’s minds.

Enter the long years of drought.

The two images shown here of the History of Wivenhoe Dam are taken from the Government site at this link. If you scroll down the page you will see a chart above the image at the bottom of the page. This chart is interactive. Under the chart is a small scrolling bar and you can extend that bar back along its small chart, and the image fro the relevant period will show in the main chart above it. Also as you hover your mouse over the line indicating the level, dates will show indicating the percentage level for that day.

With each image, if you click on the image, it will open on a new and larger page.

Wivenhoe Dam History 01

Click here Wivenhoe Dam History 01 for a larger image.

At the left of the image is the huge rain dump over the New Year period of 1999. The dam level spiked above 100%, and after the event, that level was drawn back down to 100% as the flood mitigation compartments were emptied. The date the dam was back at 100% was the 22nd February 1999.

What followed next were the long years of a major drought when below average rain fell. However, water was still used for any and every contingency, with no restrictions, mainly because there was so much water always in that huge dam.

The low point on this chart is August 19th 2007 when the level reached 15%.

Now, why I have included this particular snapshot of the Dam’s history is to show that even during a major drought, there were still couple of major rain dumps in the catchments of both Wivenhoe and Somerset. Even so, when all that water was being used for every use and with no restrictions, that amount of water in this monster dam still lasted for eight and a half years.

As that water supply gradually diminished, it got to a stage where water usage restrictions had to be imposed so that the water supply could be adequate for an ever increasing population in that South east corner of the State.

Those restrictions were not enough and further levels of restrictions were imposed. It got to the stage where home owners could not use sprinklers to water their lawns and gardens, and then not use hand held hoses, and then time restrictions on hand held hoses, and then even no hosing at all, for any purpose.

Enter the Global Warming scare which later morphed into Climate Change.

Governments were assailed with scary talk that global warming meant that drought became the normal situation, and that huge dams like Wivenhoe were a throwback to times when older Governments (of the opposite political beliefs) constructed dams to give the impression that they were doing something.

These huge dinosaur dams were never going to be full again, and in fact, were probably never even going to be part full.

What this prompted was for the current State Government to further increase restrictions to almost draconian levels.

Then, (to give the impression that they were doing something) they legislated wide ranging plans to ‘secure’ the water supply for that South East Corner.

The plan called for a vast construction of water infrastructure. It entailed masses of pipelines joining dams together so all the water could be available for the one ‘grid’. They constructed water treatment plants to convert effluent back to drinking water. Two new dams were also proposed, not major dams the size of Wivenhoe, or even Somerset, but added to augment the water supply for South East Queensland. One of those dams was vehemently opposed, and in fact, the plans were finally dumped, as an excuse was found to not proceed with it, which provided a nice little convenient political ‘out’ for a Government rapidly losing popularity.

Also, at the same time, water costs being levied on consumers rose three times and each increase almost doubled the previous increase, so people were now being charged what effectively amounted to an exorbitant cost for water.

They also spent $3 Billion to construct a desalination plant. The plant has really never come on line fully to supply its maximum amount of water, and was beset by problems right from the start. To recover this cost, water costs to consumers were further increased. It has been said that a desalination plant provides water no one can afford and uses electricity that the already stretched power grid cannot afford to lose, a double blow, for a plant now closed down. The Government, seeing nothing but bad press for this relented and actually gave back some of that increased water cost to consumers, however barely the tiniest fraction of what was originally imposed in the first place. What this means is that consumers are still paying for something that is not even working, and most certainly not delivering one drop of water. The irony of all this is if the plant was turned on and delivering water at its maximum, that water would be piped into an already full dam with water pouring down the spillway.

What this effectively means is that, (at enormous expense) sea water is converted to fresh, and then pumped (at enormous expense) through pipelines (at enormous expense) to a dam where that water is then released back into the river to flow back out into the salt water ocean where it came from in the first place.

Now that the dams in South East Queensland are back at full levels, all of them, that desalination plant has been placed back in mothballs, turned off, an incredible waste of money for no result whatsoever.

Around the time the legislation came into being, the first thing that was done was to construct a pipeline from Hinze Dam on the Gold Coast to the other major dams in the area. Hinze Dam was owned by the Gold Coast, and they resisted as hard as they could when it became obvious that the State Government wanted to divert their Water supply to be in the mix for everybody now.
This was done because it was now patently obvious that Hinze Dam was indeed a water supply that was excellent at what it did, with its wonderful catchment always keeping it close to full.
Hence, on the Gold Coast, water restrictions were not as harsh as those in Brisbane and other areas.
This was the cause of many arguments as different Authorities sought to make the playing field level.

During this process, I listened to a radio interview with the Government Minister responsible for this water security legislation and the implementation of a vast construction effort. (To be seen to be doing something)

The timing of that interview was when Wivenhoe Dam was at, or around that low mark of 15% in late 2007. The interview was between an on air announcer on a Gold Coast ABC FM radio station and the Government Minister who was on his phone from his Government car.
The Minister stressed the need for maximum restrictions for all south east Queenslanders because of the low level of Wivenhoe, and that everybody needed to pull together as one in a combined effort to make water security something vital, and something that everybody did as second nature, without thinking. The had introduced shower timers for all residences, hoping people would limit showering to three minutes, and had even mailed out these timers to every household. The Minister went on and on with platitudinous monotony about how this was absolutely vital that all these things needed to be done, or else we would get to the stage where there was no water at all. He mentioned that drought was now the normal state of affairs and that we would never see large dams even approach the full stage ever again. Global Warming/Climate Change also got a mention as he went on and on, stressing the Government line.
In closing, the on air announcer asked what percentage level for Wivenhoe would see the easing of water restrictions. (not the cancellation, but just the easing)

In an almost offhanded manner the Minister replied with an off the cuff quote of 85%, and you could actually hear the sneer in his voice as he said this, the intent being that this level would never be reached, ever again, so confident in the belief that Climate Change followers had told him about drought being the new normal situation.
Then there was the thank you’s etc.

Wivenhoe Dam History 02

Click here Wivenhoe Dam History 02 for a larger image.

This image shows the history of Wivenhoe Dam from that low point of 15% to the current date. The drought still persisted and the level rose only by a small amount over the next year, reaching 20% in February of 2008, and then 30% almost a year later. Then, from April 2009, the dam level started to rise significantly, in fact almost all the way to 100% in less than 12 months, and it has stayed at or around that 100% mark for 10 months now, fed by good rains in its own and in Somerset’s catchment areas.

That Minister who gave the interview moved on from that Ministry and another party member parliamentarian has that position now. His offhanded sneering comment that restrictions would be eased when the dam level was back at 85% was reached during the large rain dump in late February of 2010, barely two and a half years after that comment, time enough for people to have forgotten what he said, and his thinking probably along the lines that no one was listening anyway.

I even contacted that radio station by telephone, and asked them if they kept recorded copies of interviews, especially this one, as I discussed the content of that interview with the person on the phone. I was told that they didn’t keep copies, which is wonderful really, especially of you’re the Government Minister in question, because now he can effectively deny he said anything like this at all. I wonder really, because these days when you phone most places like this, the first thing you are told is that the call will be taped and monitored for content.

That Minister is now the Deputy premier for the State.

That dam level of 15% was the lowest level reached. It took nearly 9 years during a drought to reach that level from 100% with no restrictions. That level passed through the Minister’s quoted figure of 85% in March of 2010, when it reached 92%.

Restrictions have not been eased. Costs to consumers have not been lowered.

People still use considerably less water than they once did. The consistent rain is now relied upon to water lawns and gardens, and now with people being charged an exorbitant amount of money (virtually a tax really) for the water they use, then it only stands to reason people will use less.

Wivenhoe has been at 100% for quite a while now, and with people using (a lot) less water, then that level will stay at a higher level for longer.

Here’s the rub.

Refer back to that first image above . That 100% level for Wivenhoe means that the water supply for the South East corner is secure for at least 8 years ….. if it never rains again.

Enter the flood of 2011.