Flood Inquiry

Author : J. V. Hodgkinson F. C. A. Chartered Accountant : Aug 2006 to November 2013    

The principal thrust of this website is
FLOOD PROOFING BRISBANE from damaging floods to the point of extinction. MITIGATING flooding in Ipswich and Gympie. Putting REAL MEANING into "Drought proofing SEQ" and ensuring our water supplies by natural means well into the future

This is my review based on official statistics and documents. It is done in conjunction with Ron McMah, grazier of Imbil and Trevor Herse, retired of the Gold Coast




Flood Inquiry Final Report 15/03/12: The Flood Inquiry did not review my 120 page submission related to this website information. Their Terms Of Reference "did not permit examination of topics such as changes to Infrastructure whether by way of new dams or upgrades to existing dams" Page 438. This was a  short term view restricting the Inquiry by the Government (Bligh) that merely left the Inquiry to clean up the mess of the 2011 flood in Brisbane and Ipswich without the benefit of showing how to avoid it altogether. 
It would have also provided the means to thoroughly drought proof SEQ without costly desalination and recycled effluent.

Flood Inquiry 25th January 2012
The Commissioner has reconvened the Inquiry to cover 9 more sitting days.2011 Major Minor 2011_0001.jpg (138740 bytes) (25th January 2012).
 At the heart of this unusual occurrence is how the minor flood was dealt with prior to the two major events following. The yellow labels have been added by me for clarity. 

The minor flood has a clear demarcation of 34 hours for the period 3pm on Friday the 7th to 1 am on Sunday the 9th of January 2011. In that period the Engineers' log shows only 11mm of rain in the Wivenhoe catchment and 23mm in the Somerset catchment. However these figures do not seem to fully match the rainfall stations. Comparison is difficult as rainfall every hour is required in the matching process. View rainfall stations

The rainfall station information was used to examine the veracity of the Seqwater claim that the 2011 flood was 190 per cent greater than 1974. Even with the minor flood added in to the 2011 flood and the weeks of draining afterwards also claimed, the percentage quoted is fanciful. 

Seqwater claim that it was the spread of rainfall that made the difference is also under severe pressure as a credible statement. Excluding the minor flood, of the 11 rainfall stations in the Wivenhoe catchments in 1974 only 3 were marginally less than 2011. Of the 5 rainfall stations in the Somerset catchments, all registered more rainfall than 2011. Both floods were on saturated catchments which means conversion to inflow conditions were similar.

How the minor flood was dealt with is becoming clear as the evidence and cross examination progresses. 

Depending on the evidence, this Seqwater graph may change but not sufficient to alter one's overall view of the problem.


Notes on Interim report of the Flood Inquiry (2nd August 2011)

As expected, this interim report deals with the aftermath of this 2011 flood. It was designed to observe and recommend changes necessary to deal with the next "wet season". It does not review the 120 page submission made that relates to this website for permanent relief from floods and droughts.

However, I will be raising three interrelated matters that I have observed (Confirmed by letter to the Flood Commission 5th August 2011). They are

"The Queensland wet season extends from October to April" (1.1 Page 24). That is seven months "wet" with five months "dry". This is contrary to recorded rainfall data in this website. Since records were kept, more than 50 per cent of all rainfall fell in the four summer months December to March for all rainfall stations in catchments of the Wivenhoe and Somerset. Refer Summer v Non Sum tab. It is also contrary to Mr Robert Drury advice of 2007 that the "wet" season is four months December to March. That advice is at the head of every page in this website.

However, if they meant to imply that our water supply came from "low pressure systems" they would be close to the mark. Summer storms cannot compete with low pressure systems which are by far our main water supply. As you would see at the top of this page, low pressure systems average 3.7 years. They are oblivious to the time of year.

They are correct in stating that the very large majors, of which there are four recorded, confine themselves to January and February.

Deputy Premier Bligh and Minister Hinchcliffe were alerted to this possibly that with full dams, a major situation could arise with heavy rainfall. Click to observe


"South-east Queensland was affected by drought from 2001 to 2009" (Page 44  2.4.2) This statement emanates from the Queensland Water Commission's Water Strategy.

Australian Bureau of Meteorology records prove that no drought existed in 2007 to 2009, in fact the rainfall was above average. The Summer rainfall for the years 2001 to 2006 was 91.4% in the Somerset and 99.1% in the Wivenhoe of the long term average. The Bureau confirmed that rainfall in the catchments had never been less than 80% of the long term average. The 20% deficiency was in the low inflow months which made little difference to inflow.

This subject has been addressed fully in section "D" in my submission to the Inquiry and has been the subject of further addition to the submission.

The reason for the low water levels is expressed in the heading to this page. It was simply the random nature of "low pressure systems" that are our main water supply. They average 3.7 years with most below the average. Those above are therefore longer in duration and we saw this in 2001 to 2006. The dam level chart in the above heading with the red lines tells the visual story. The approaching problem was not recognized by those in charge. 

If the importance of "low pressure systems" is not understood, we will be forever dealing with the consequences of floods, "drought" and severe water restrictions rather than getting to the heart of the matter of providing a continuous and relatively cheap water supply.

"Apart from the limited flood mitigation capacity of the Wivenhoe and Somerset Dams. it is important to note that approximately 50 per cent of the Brisbane River catchment is below the dams (note 58)" .....( Page 39  2.2.8. third paragraph)

This is a direct take from the submission lodged by Seqwater.
Note 58 is referenced to them. It is based on catchment area without any hydrological evidence of rainfall in those catchments.

The hard evidence is that for the 111 years 1890 to 2000 the pre-development flows (no dams and no people) calculated by the official computer model is that 56.5 percent of all water that reached the Brisbane River mouth came from above the dams. This Computer model has the force of Law in the Water Resource (Moreton) Plan 2007

In addition, Seqwater's own evidence, coupled with a staff member's evidence, shows that water above the dams was 65% of the 2011 flood.

I have drawn the Inquiry's attention to this matter. However, it would have reached the Commission after the interim report was compiled.

End of notes on interim flood Inquiry report   

Additional observation to Flood Inquiry notes (my observations 24/05/2011)

* It is generally accepted in evidence that the water above the Wivenhoe/Somerset dams represents 50% of the water that reaches the Brisbane River mouth.

This sweeping statement does not stand up to close scrutiny and, as a consequence, wrong decisions are drawn. In this 2011 flood, using Seqwater information, the above dam Flow volumes all tributaries_0001.jpg (80606 bytes)Wivenhoe/Somerset catchments recorded flows of 2,650,000ML. Modelled flows accepted by the Flood Inquiry in evidence had the Lockyer Creek flow at 701,858ML and the Bremer River flow at 426,541ML. I have estimated the Mid and Lower Brisbane River and Oxley creek on the basis of catchment areas and rainfall to be approximately 426,541ML. The "below dam" flows total 1,591,043ML. Click to expand graph

The "above dam" contribution was therefore 62.5 percent of the total flood. That means that the "above dams" water contribution was 60.0 percent more than the "below dams" contribution.

Apart from putting true meaning into "drought proofing SEQ" the principal objective of this website is to contain the flow of the Wivenhoe/Somerset until after the flood peak has passed thereby eliminating the "above dam" water from the flood. 

The releases from the Wivenhoe combining with the "below dam" Flow Wiv Brem Lock 2011.jpg (83033 bytes) flows of the Bremer River and Lockyer Creek are shown on this graph. It reveals that, with the Wivenhoe/Somerset contained until after the flood, the velocity and volume of the flood would have been halved. The top half does the damage.

Official confirmation of the resulting percentages above the dams of all floods follows-

* The Principal Hydrologist Water Planning Sciences DERM confirmed to me in writing on the 3rd March 2010 that the percentage is 56.5 percent above the dam and 43.5 percent below the dam. This means that the water above dam provides 29.8 percent more water than water below the dam. 

Downstream of Mt Crosby the percentage of 56.5 rises to 58.0 percent.

This "above dams water " percentage is calculated by their IQQM computer model which has the force of Law. For this calculation it calculates all the flows in the Brisbane River and its tributaries that have occurred in the period 1889 to 2000. It includes all floods without exception. The flows are pre-development flows (No dams, no people).

Evidence at the Inquiry confirms that there is no official modelling. Therefore this calculation is the only authoritative percentage calculation. It should be kept in mind when viewing sweeping statements on the influence of the Bremer River and Lockyer Creek on Brisbane.

Water below the dam is principally from the Bremer River, Lockyer Creek and other creeks that enter the main Brisbane River. The hydrologists seem to agree that very large enforced releases from the Wivehoe dam (no space left in flood compartments) acted as normal in creating a barrier to these tributaries. 

in addition it forced water back up these tributaries in this 2011 flood. In the Bremer River it raised the level at One Mile Bridge by 7 metres according to the hydrologists. That bridge is 47klm from the Bremer River mouth.

The flood waters combined at speed and descended on Brisbane. Approximately 50% of the water above the dams was "mitigated" (held back) by the Dams' flood compartments.

* The requirement that the ecology must receive 66% of all water that passes through the dams has not been mentioned. Also not mentioned is that, due to a drafting error, this percentage has been raised to 78% costing us 160,000ML annually, seems to have escaped attention. This error will cost us the price of three desalination plants plus ongoing costs and interfere with our water security.

* Our main water supply being "low pressure systems" or "Uncommon events" as described by Mr Drury of SEQWater have not been recognized in the Inquiry. As we have seen they have the ability to fill our dams from 20% to 300% of capacity. They account for 90% of our water and a large number did not adhere to the now recognized "wet season" December to March. They can come at any time. 

* Permanent reduction of the FSL (water held for us and the Ecology) by 25% will most likely bring on recycled water and require the proposed desalination plants earlier than planned.

* There is heavy concentration on Dam and Flood management. This is the main objective of the Inquiry.

* Solutions may occupy the second half of the Inquiry. With over 600 submissions, absorption of them will be a major undertaking for the Inquiry. Revision 27th May 2011. An extension of the Inquiry to the 24th February 2012 has been announced.


Flood Inquiry submission

A submission has been made to the Flood Inquiry. It encompasses 120 pages and three additional addendums. Its direction is the permanent solution to damaging flooding and extended drought conditions in SEQ.

The provision of water in South East Queensland is a complex Wivenhoe dam levels red line.jpg (112485 bytes) issue. There is ample evidence that it is not fully understood since the instillation of the Wivenhoe Dam. Reading of the evidence of the Flood Inquiry reveals that it continues. 

There seems to be no understanding that our main water supply is random "low pressure systems" which, apart from filling our dams, creates extremes of flood and the appearance of "drought". Their control through further storage is essential.

While the new Seqwater dam level site is very good, it does not start early enough (1996), nor is the gradient high enough, to view these "low pressure systems" in operation. SEQWater's previous graph from year 1990, and accompanying this sentence, shows their operations and confirms that Summer "wet season" rainfall has been inadequate since 1992. We rely almost entirely on "low pressure systems" which pay little heed to the time of year.

The submission therefore deals with the root cause and its solution in what we have seen in the last 10 years, the shrinking of of our water supply to 18% of capacity and the recent overflows of 285% of capacity. Both had, and are having, a traumatic effect on our citizens.

A brief outline of the 2011 flood. In my view, the 2011 flood was similar to the "little referred to" second major flood 2011 Major Minor 2011_0001.jpg (138740 bytes)1893 Floods chart.jpg (106195 bytes)in February 1893 which concatenated (piggy-backed) on the back of a minor flood. It came to within 0.28 metres of topping the first flood in 1893.

The 2011 flood also concatenated on the back of a minor flood 2011 Rainfall Minor Major 2011 plus 1974.jpg (131308 bytes) assisting in creating maximum height and damage. In my view, the delayed release of the minor flood is at the heart of a major section of the Flood Inquiry. This compilation from Seqwater flood event information shows the demarcation of 34 hours between the minor and major flood.

The three major Hydrology firms engaged by the Insurance Council of Australia in their study of Ipswich seemed to agree. They ignored the minor flood altogether.