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 January 2012    

FLOOD PROOFING BRISBANE from damaging floods to the point of extinction. MITIGATING flooding in Ipswich and Gympie. Putting REAL MEANING into "Drought proofing SEQ"

Preliminary view of our main water supply. To emphasize its importance it appears at the heading in all pages in this web site 

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. 

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.
 
WEB address: wivenhoesomersetrainfall.com
All comments welcome : hodgkin@powerup.com.au

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May 2009: No change since August 2007

The QCCCE report shown compares the rainfall in the Catchments for the six years 2001 to 2006 with the Federation drought era from 1898 to 1903. The Era followed a major flood in 1898. It is interesting to compare the rainfall for both periods in both dams catchments. 

They qualified their report to the extent  that they do not have the Hydrology for the Federation period and concentrated on Rainfall comparisons. If it were present, they may well have arrived at a different conclusion. 

May 2010. It should be noted that the Water Resource (Moreton) plan 2007 requires the IQQM model to calculate all flows from 1890 to 2000 at pre-development levels to arrive at the "Mean Annual Flow". Therefore there was ample evidence to compare the inflows of the "Federation drought" with this last "dry" period 2001 to 2007. Click to view inflow chart supplied by the Department of Environment and Resource Management (DERM). While the Federation period was calculated, the IQQM model was quite capable of recording 2001 to 2007 inflows as well. End  

You may have read the "Summer V Non-Summer" information at this button. The items of interest are the stable relationship of the Summer months 1893 to 1960. The Summer months were around 50% of the annual totals and this was consistent with all rainfall stations in both the Wivenhoe and Somerset Dams.

This summary of Bureau of Meteorology rainfall data shows that that they are correct on an overall rainfall basis as the Federation period received slightly more rainfall. 

However there are two telling points of difference. 

The first is the complete reversal of the Summer and Non-Summer rains in the Federation period. 

The second is that an examination of the Federation period shows that the months that were likely to create inflow were decidedly less in volume and count than the current period 2001 to 2006.

In addition, they overwhelmingly occurred in the non-summer months in both Dams.

Various other points in this web-site confirm that the Summer Rainfall in the 6 years 2001 to 2006 were quite normal and the balance of the reported 23.8 percent that did not fall was in the non-summer months that provide little inflow.

Further, there was an unrelated suggestion confronting Long Range Forecasters and reported in the C/Mail 9/06/2007 page 5. That the Dams would fill if this period followed the weather patterns of 1903. It bears comparison.     (C/Mail 9/06/2007 Page 5) . 

In the Somerset, the four months of December 2003 to March 2004 saw rainfall of 673mm compared to the four months in 1903 May to August was 486mm being the period that the Federation drought broke. ( the article said May to July. August added for balance.) 

In the 2003/04 period we saw the rise in dam levels of 10 percent in the Wivenhoe and 27 percent in the Somerset. Hardly "drought" breaking rainfall and certainly not acknowledged as such by any Authority.

The suggestion does not stand up.

The Wivenhoe comparison for the same periods as above is 578mm 2003/04 to 392mm in 1903.

Conclusion

The Federation drought has been raised by the Climate Change Centre of Excellence. The hard data of the Bureau of Meteorology rainfall stations seems to dispute their conclusions and has been presented for your own observation. I am apparently reading the same data as the Centre. You will see from my original review of August 2006 under the "Initial Statistics" button that I concluded the period had received close to 80 percent of average rainfall. Their conclusion was 76.2 percent. 

My understanding of Scientists engaged in research is they discipline themselves to keep an open mind. The Climate Change Centre of Excellence may well find that the Federation Drought may reveal more about changing weather patterns than the last 6 years of Rainfall.

The inclusion of this section has little to do with the overall conclusions.

My main point of disagreement is that they are classifying the 2001 to 2006 as a drought in the Catchments. To this end they are currently in good company.