Rainfall 2001-06

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




May 2009 : No change from August 2007

Comparing apples with apples

In February 2007 our Leaders presented to us all a copy Brochure Expanded.jpg (100575 bytes)of the Bureau of Meteorology decile map for the period 1st January 2001 to 31stDam levels Graph.jpg (130699 bytes) December 2006. The calculations that follow are made on the basis of 1st July 2000 to 30th June 2006 in order to compare with the published dam levels in the Annual 30th June Reports of SEQWater. As the overlap is one summer month and five non-summer months with modest rainfall, the overlap has little influence on these conclusions.

Overall comparison of the six years with previous six year periods.

The attached charts of the Somerset and Wivenhoe dams show the rainfall for the six year period.

They show the comparison of the four Summer months Somerset 65 06 Sum and Non.jpg (317322 bytes)December to March to the eightWivenhoe 65 06 Sum Non Sum.jpg (267816 bytes) non-summer months. This has also been confirmed under the "Summer V Non Sum" button as 50% each. The non- summer months create little inflow into the Dams compared to the summer months.

Both charts show close to normal rainfall in the important summer months. The deficiency of rainfall occurred in  the non-summer months with diminished inflow opportunities.

Rainfall and comparison to Dam levels.

The whole of the monthly rainfall covering every month of the six years is attached for your own viewing and conclusions.

Page 1 of 2 shows the percentage drop in dam levels Meg per day dam drop and rainfall page 1.jpg (212201 bytes) together with the summer and non-summer rainfall for the six years. OfMeg per day dam drop and rainfall page 2.jpg (201808 bytes) particular interest are years 2002 and 2005. You will see in the comments section of page 2 that because of the low rainfall, the requirements of the people who rely on the dams, could be gauged. This is in excess of 1000ML per day. Year 2004
is also of interest as it almost supplied our normal requirements for a full year.

Page 2 of 2 highlights the rainfall above the 100mm mark that are likely to cause inflow. Comments are added on each year. They are my assessments and it is available to all to make their own.

This area forms the base of the "Requirements" button. You will see in that section that the drop in Dam levels together with the estimated rainfall in the "low" and "high" rainfall years match the "business as usual" estimates per person as calculated by the South East Qld Regional plan Part B and multiplied by the Population. The population estimates are also drawn from the Plan and Web based advices of SEQWater areas serviced. 

A visual graph is added for assistance. The years 2002 Drop in Dams Megalitres to rain.jpg (205378 bytes) and 2005 highlight the requirements of our water supply with low rainfall and year 2004 with high rainfall. 2006 saw us heavily into water restrictions.


Recycled water. Comments by our Leaders accompanying press release of 28th January 2007

The following are extracts from our Leaders press release of the 28th January 2007, the main purpose of which was to advise that there would be no vote on recycled water. 

The Premier: "The inflow into our Dams between April 2006 and December 2006 are almost 20% lower, at 38,923ML, than the same period for the worst year on record ( 48,430ML between April and December 2004), he said."

My comment :You will have reviewed the 4 Summer months December to March and the 8 non summer months April to November in the "Summer V Non Sum" button. Rainfall in the 8 non summer months in both Dams has been less than 50% for the life of the Bureau of Meteorology records dating back to the 1880's. Because they are spread over 8 months there is , with rare exceptions, no high impact rainfall and therefore little inflow. The comparison reduces to "almost nothing as usual" to "almost nothing as usual"

The Premier " inflows in the month of December were 80 percent less than those recorded for the same month in our worst ever year in 2004.

My comment : The dam levels are at the front of this section and drawn from the SEQWater annual reports. They show that the Dam level drop in the year to 30th June 2004 was the lowest at 2.2% recording the highest rainfall for a year of this 6 year period. It was well above average rainfall. Average rainfall is totally inadequate for our current needs, hence the water grid.

The Deputy Premier : " It would take between 100-200mm in a single rain event to boost the Wivenhoe Dam back up to 40 percent." 

My comment : There were 11 months over 100mm and 1 month over 200mm in the 72 months of the 6 years. The Wivenhoe rose by 10% after the sustained December to March rainfall of 2004 amounting to 578mm. The individual months each recorded between 109mm to 222mm. See the rainfall figures above for confirmation. The 10 percent rise in the Wivenhoe is recorded in the "Wivenhoe" button.

The SEQWater professionals verified this in their public statements of the 10th February 2007( "uncommon events" button). They stated that the Wivenhoe required 300 to 350mm over a few days to create a major fill. There is no record of this happening in the whole of the catchment back until 1974 and none for many years prior to that. 

Several years to fill :The Deputy Premier commenting on the Wivenhoe Dam. : On the plus side is the recognition that it may take several years to begin to refill the Dams. The Uncommon events were not mentioned.

Our Leaders rely on advice. SEQWater is a very professional body and I find it difficult to believe that their expertise has been used. It seems that the PR department may have misconstrued data.

You have all the records in this section and I leave you to draw your own conclusion on the above statements and comments.


The foregoing is a study of normal Summer Rainfall in the catchments and the implication of a period without those rare "Uncommon events". Summer Rainfall provides the high impact rainfall necessary to create inflow into the Dams.