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 : Retained largely as it was in August 2007.

WHAT OUR LEADERS AND DECISION MAKERS BELIEVE THE SITUATION TO BE.

Our Premier has recently resigned and has been replaced by the Deputy Premier. However their comments at the time are relevant.

Our chief decision makers were firmly of the opinion that a major drought is the cause of our depleted dams. This was followed by the Water Commission with similar views and expressed in their advertisements.

This brochure insert appeared in the Courier Mail on the 3rd February 2007. It confirmed that our two chief decision makers at that time were attributing our depleted dams to " the worst drought on record". They also introduced the influence of a rapidly expanding population and its water requirements. The map is 6 year map and important to these observations. It is now expanded for clarity. 

The map shown is clearly a decile map. A decile map grades the rainfall in decimal categories of 1 to 10 with 1 being "the lowest on record". The last 6 years may not be the lowest but they are in the lowest 10%.

I retrieved from the Bureau of Meteorology a "percentage" map of the same rainfall for the same 6 years. It shows 80%.

The stability of district 40 in which the catchments reside permits this 80% to be classified in the lowest on record category because the catchments have never received less than 80%.

It should be recognized at this point that the Qld Govt sponsored "Climate Change Centre of Excellence" reported the catchments as receiving 76.2% and defended it as a "Drought" rivalling the "Federation drought". There was no indication that they were aware that the balance of 23.8% occurred in the low to nil inflow non-summer months which have little impact on dam levels. Refer to "Rainfall deficiency" and the " Federation drought" buttons.

Decile evidence of 6 year periods for both the Wivenhoe and Somerset dams will provide more clarity on that statement. In the Wivenhoe there are 7 periods of 6 years in the last 100 years that are within 66mm ( 693 to 759 mm) mm of the last 6 years. With one exception, there were no "Uncommon event" within those periods.

The 80% of long term average rainfall does not fit within the Bureau of Meteorology definition of a drought being "acute shortage of water" in the context of rainfall. 

Press release on recycled water 28th January 2007

Relevant comments on rainfall were made by our leaders when announcing the cancellation of the vote on recycled water. They are contained in "Rainfall 2001-06" button.

Of particular interest is the comment that it may take 5 to 10 years to fill the Wivenhoe to 40 percent. It was made in the context of "below average" rainfall which has been examined in detail in this web-site.