AN OBSERVATION OF THE CONFLUENCE OF STATISTICAL ABERRATIONS, DAM RATIOS, TIMING AND UNCOMMON RAINFALL EVENTS THAT COMBINED TO PRESENT OUR DAMS AS VICTIMS OF A SEVERE DROUGHT. THIS IS NOT THE CASE. THEIR INFLUENCE ON CONCLUSIONS REACHED AND ACTIONS TAKEN.

Author : J. V. Hodgkinson F. C. A. Chartered Accountant : August 2006 to December 2009

The Underlying cause of our depleted dams had the appearance of "drought". However most people would not class 80 percent of rainfall compared with the Bureau of Meteorology long term average 1961 to 1990 as a "drought". This is the case in the catchments. Even less people would class it as a "drought" when closer examination of the rainfall shows that the inflow producing four Summer months had been quite normal with 99.7% in the Wivenhoe and 91.3% in the Somerset catchments. The 20% deficiency was in the low inflow producing eight non-summer months.

This incorrect conclusion of "drought" has clouded the real underlying cause of our depleted dams. It is the random nature of large scale rain depressions and they are our main water supply. They occur on average every 4 years and have the capacity to fill our dams in a few days. The last gap was six years 2001 to 2007 and caused a major and expensive panic. Further evidence is available in the tab DEPLETED DAMS or Click here

Dealing with those large scale events that extend beyond the 4 year average requires a very different approach than dealing with a "drought". The current water resource strategy has ignored the short history of the Wivenhoe dam.

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.

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.