Dam Statistics.
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 : 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

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May 2009: With the exception of a note it remains as it was in August 2009

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Dam catchments in Sq Klm Graph.jpg (91197 bytes)
A few of the principal statistics have been graphed for visual comprehension. This graph shows the Sq Klm of the catchments.

Dam capacities Graph.jpg (87889 bytes)Dam capacities highlight the enormous capacities of our Dams. The Somerset was our mainstay until 1986 when the Wivenhoe was commissioned.

 

Dam levels Graph.jpg (130699 bytes)Again the deterioration in our Dam levels. Of minor note is that the annual report of SEQWater for the year 2005 was incorrect. The Dam levels at 30th June 2005 were deducted from the 30th June 2003 levels instead of 30th June 2004. It has been adjusted in these figures.

Dam features from SEQWater Web.jpg (215540 bytes)The SEQWater web-site provides the overall statistics of the dams. Of particular note is the completion dates of the Wivenhoe in 1985 and the Somerset in 1959.

The expected annual rainfall in the Wivenhoe at 940mm and the Somerset at 1,230mm is puzzling. You will see from the charts in the "rainfall stats" section that they both appear too high and would place them Graph  Wivenhoe 6 year 1961 to 2006.jpg (114116 bytes) permanently in a position Graph Somerset 6 year 1961 to 2006.jpg (119361 bytes) of "below average" rainfall. I have requested an explanation in writing but it has understandably been ignored. They are currently busy people and have been most helpful in their public pronouncements. The attached graphs further highlight this minor puzzle.

Yields Annual SEQWater web.jpg (114473 bytes)The other aspect of note is that the Annual water supply is currently under review. This attachment was their previous assessment. It suggests that the annual flow into the Wivenhoe and Somerset dams is 446,900 megalitres. That is 1,224 ML per day. Quite adequate for our unrestricted use as compared to the restrictions now in place. If you examine the "Key features" above, you will see that it currently under review. Reference is SEQWater Environment report 2001-2002 page 2.

Note : May 2009 : QWC has considerable disagreement with these calculations. They have changed their approach from HYNF to Stochastic being "best guess under the circumstances". To me it seems that they are having difficulty coming to grips with "uncommon events" which are the major supplier of our water. Their quite normal but temporary departure has caused them some concern. SEQWater had the benefit of 6 "uncommon events" in their calculations. Of course storage is the answer in the expanded Borumba Dam when they are plentiful.

Catchment map with contours.jpg (249481 bytes)For those readers who are unfamiliar with the Location of the Dams and their catchments, I have included a contour map available from the SEQWater web-site. I have overlaid the town names and catchment boundaries for readability.