AN OBSERVATION OF THE CONFLUENCE OF STATISTICAL ABERRATIONS, DAM RATIOS, TIMING AND UNCOMMON RAINFALL EVENTS THAT COMBINED TO HAVE OUR LEADERS DRAW INCORRECT CONCLUSIONS. THEIR INFLUENCE ON ACTIONS TAKEN.

Author : J. V. Hodgkinson F. C. A. Chartered Accountant : August 2006 to May 2010    

The relationship of the Wivenhoe/Somerset dam system to its rainfall in the catchments has been quite different from the way it has been presented to us since the joint dams’ inception in 1986. The main rainfall supplying our water is the, season ignoring, rain depressions in the form of Cyclones, Monsoons and large scale rain depressions. They generally cover the whole of South East Queensland at the same time. They provide much more water than our December to March “wet season” which is well known to us.

Mr Rob Drury of SEQWater drew our attention to this in his Courier Mail article of the 10th February 2007. Output from the Government IQQM computer model, covering the 111 years 1890 to 2000, has proven Mr Drury correct. In essence 300mm of rain in the catchments in a few days is a flood and, in the right circumstances, can fill the dams from scratch. On the other hand 3 months of 100mm a month is a comparative trickle. These facts can be buried in official overall rainfall statistics the use of which in dam performance can and did throw up statistical aberrations.

Mr Drury called these rainfall events “uncommon events”. Bureau of Meteorology flood records from 1841 reveal that they occur on average every 3.7 years with most below that average. Therefore those above can extend well above that average such as the recent period of 2001 to 2007.

Mr Drury also provided dam level charts which were not published by the Courier Mail. They provided clear evidence of the importance of "uncommon events" and the inability of the "Summer wet season" to provide sufficient water from as far back as 1992. We will examine them.

This is my review based on official statistics and documents. These statistics and documents are presented to you so that you can arrive at your own conclusions.

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This page considers other thoughts of Minister Hinchcliffe.

Following on the bottom of page 2

Consideration of "uncommon events"

"QWC refute any inference that large uncommon meteorological events have not been correctly considered"

Life of the Wivenhoe

A glace of an unpracticed eye tells the story of the Wivenhoe from its inception. Our main water supply, being those described by SEQWater as "uncommon events", not only filled the Wivenhoe from scratch but refilled it 4 more times to overflow. 
Photo : Evidence that random "uncommon events" are our main water supply and dam failure was inevitable.

Our depleted dams were caused by the random nature of these events with some gaps up to 14 years. The QWC from the very top down still believes that a "drought" was the cause of this depletion.

Computer modeling

They specifically refer to their daily time step model. Large scale rain depressions, our main water supply, generally cover a period of a few days but deliver a huge amount of water. In this short time frame hourly would seem to be more appropriate. 

I have asked for the instruction manual of the modeling to satisfy myself that the construction is reasonable in the circumstances. We have proof to some degree in the dam level of the Wivenhoe/Somerset being a known quantity.

QWC recommends that you seek the advice of a qualified Hydrologist to assist etc

Our main thrust is the determination of how much water is available for the Ecology and our consumption. 

From the beginning we have sought an independent review of our material and the QWC material on the basis that "if there is something in it then a more detailed review be undertaken." 

This would automatically occur as an Environmental Impact Study is required for the 80,000ML additional water identified by Engineers GHD when considering raising the Wivenhoe Dam Wall. 

This will also expose to public view the advice received and mentioned by Minister Hinchcliffe when determining the selection of the 66% to the River.

This approach has the support of the Senior advisor to the Prime Minister who has conveyed his support to the Minister. The Prime Minister is my local member and has been kept informed for the past two years.

We would welcome the appointment of a senior and independent Hydrologist to make these observations at the Government's cost.

The QWC should bear in mind :

* That they (or the departments that preceded them) allowed the situation to develop in our dam system that dam failure, due to the inevitable departure of "uncommon events", was obvious even to the untrained eye.

* They still believe from the top down, and confirmed by correspondence, that the cause of depleted dams was a "drought". 

* Permitted on page 2 of the 1500 page EIS report, one of the chief justification of the EIS of the Traveston being comparing the Mary Valley rainfall with the Upper Brisbane River. The upper Brisbane River is the "Wivenhoe" catchment and being further west is the minor player in our water supply.

Dynamics of the Moreton region
Other development considerations drawing water from the Brisbane River

The Minister contends that the Tugun Desalination plant, recycled water and raising the Hinze dam wall has not changed the Dynamics of the Moreton Region. I will leave it for others to judge

Toowoomba water will be transferred out of General reserve and was planned. We agreed but noted that water was being withdrawn

The desalination barges on the Brisbane River was a necessary requirement due to poor past judgments not related to any "drought" and had our support in these circumstances. Our point was that it affected the availability of water in the Moreton system. The press release is attached so that a judgment can be made. My view is that the Barges were on the Brisbane River and there is no mention of the mouth or near the mouth of the River. Photo : Press release on barges on the Brisbane River with desalination plants.

Perhaps it was poor drafting of the press release.