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 : Since August 2007 the QWC has applied restriction measures and the requirements are now generally available to the public. This section is now redundant in favour of the updated requirements that we must adhere to.

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Now redundant but retained for interest

Our normal water requirements

The final calculation is slightly in excess of 1000ML per day. The SEQ Regional Plan part B uses the expression " business as usual "term which to my understanding means - without restrictions of any kind and before the "Emergency measures" as described and Legislated in the Water Commission's web-site. The Requirements are measured on that basis.

In the first instance, the Population serviced by the Wivenhoe and Somerset Dams were determined. Examination of the SEQ Plan part B indicated the percentages of the areas described as SEQ. The SEQWater web site describes the areas covered by the 3 Dams which includes the North Pine. The calculation comes to 85% of the 2.8 million population. The North Pine population is excised on the basis of Dam capacities. The result is a Population serviced by the two Dams at 2,113,983 or around 2.1 million.

The second requirement was to adopt the SEQ RP Part B method being "per person including Commercial and Industrial at 450 litres per day each". There are adjustments made by me to cater for the Commercial and Industrial from the main Dams. The revision is 474 litres per person per day. The break-up is 300 litres Domestic and 174 Commercial and Industrial.

The third aspect of the Requirements was to measure the calculation with annual depletion of the Dams together with minor estimates of rainfall. These estimates are fully covered in " Rainfall 2001-06" button. You will see from the attached document that the requirement calculations are within tolerance of the annual totals of the depleted Dams together with rainfall in both "low" and "high" yield years.

It was interesting and understandable that in a high rainfall year as 2004, the requirements dip by as much as 6% of capacity. This could well have been the situation in the years 1986 to 2000 covering up to 5 uncommon events. The year 2004 has an accurate assessment of the Megalitres that inflow created. See "Wivenhoe Dam" button.

Confirmation from the South East Queensland Regional Water Supply

The SEQRWSS stage 2 interim report attached confirms the water allocation from the Wivenhoe/Somerset Dams is 374,000 ML per annum. This is the volume allocated and required but as we have seen, not capable of being supplied without "uncommon events". It confirms the calculations made above. If reading of the small print is difficult, it is on their web-site page 8 of the SEQRWSS stage 2 interim report. They do qualify their calculations to the extent that effects of a "drought" are not taken into account.

This 374,000ML a year converts to 1024ML per day which agrees with my calculated requirements. The supply from these Dams in normal times without "uncommon events" is 481ML per day or 176,000ML annually. Uncommon events we have seen are rare and unpredictable. The South East Queensland regional Water Supply report is based on this 374,000ML. From my reading of copious other reports, particularly of the Mary Valley Traveston Dam proposal, they are all based on this calculation. It may be correct over a great many years but is irrelevant for around 20 year periods.

This amounts to a shortfall of 198,000ML each year until uncommon events. Those who follow the "drought" mantra, without thought, will have their calculations severely distorted.

300 Litres Domestic. Further considerations.

Attached is an extract from a water tank supplier's brochure. They have been in operation for 14 years and service an area from Bundaberg to the Victorian border principally to Country clients. The relevant part is the normal household requirements to be calculated when determining the size of your water tank.

It reveals to us that the normal requirements per person is more than twice the current allowance of 140 litres per day. This is not a revelation to us all. It supports the selection of the SEQ RP part B. However, their main sales are Country and Country people are practiced in water conservation.

The calculations are also available for those who aspire to self sufficiency. There has been a recent move by our Brisbane Lord Mayor to limit the rebate on water tanks to those who link them into household use ( June 2007 ). This is entirely compatible with these conclusions.

Water Commission

The public stated aim of the Water Commission is to reduce the level of water use to 700ML per day. They are achieving this through tough water restrictions in operation since May 2005. The Dam releases by SEQWater indicate that they have been reduced to around 50% of normal. It further indicates that the normal requirement is in the region of 1400ML per day and my calculation of our needs may be conservative.

I have not studied the surrounding aspects of water releases but it obviously plays a part. The calculated 1003ML per day requirement is maintained.

Conclusion

The current water requirements from the Wivenhoe and Somerset Dams to resume normal living is a conservative 1003ML per day.