Author : J. V. Hodgkinson F. C. A. Chartered
Accountant : Aug 2006 to November 2013
The principal thrust of this
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 : Left basically as it was some 18 months ago
T0 simplify the use of this website, the Home page has two sections. This is the second of these sections.
WEBSITE SET UP
I have set up this web-site for the benefit of my friends, clients, business associates and people who I think will thoughtfully examine the situation. While the answer to this puzzle is straight-forward, the underlying base is complex and varied. It requires time and patience to explain the situation and a web-site is the ideal solution. I am wary of prophets of doom and gloom and their motives. However, the message is that the problem is much more severe and complex than any drought and we need to be self-sufficient in every way possible where water is concerned. This will be for a much longer period than we imagined. Recognition of the problem will provide the answer to the long term permanent solution for the better part of this century. It will require significant leadership in the widest sense.
I am not a Climatologist, Engineer or Hydrologist. As a Chartered Accountant I am trained to examine the construction and interpretation of data. If we encroach on specialist areas we seek guidance.
If others find their way to this web-site then they are welcome but it is their responsibility to assess the evidence and draw their own conclusions.
This is not a normal web-site. I have set it up for the "buttons" to return to the Home Page. The tread of the logic is then maintained.
There are three phases in this web-site :
1. What happened in our Dams to cause
them to fill and then drop rapidly.
1. What happened in our Dams to cause
them to fill and then drop rapidly.
The answer to this puzzle contains several matters that now follow in logical order they are :
2. Interim measures taken
8. Shortfall in providing for them and comparison to
3. Long term solution
First of all a fore note : SEQWater has advised that the North Pine Dam is a completely separate system. It has been excluded from these calculations. Its Dam levels are included in SEQWater's overall total provided, however its influence is minor and insufficient to cause distortion to the percentage holdings of the Wivenhoe and Somerset Dams. See "Initial Statistics" button. This web-site is directed to the total system of the Somerset and Wivenhoe Dams.
1. What happened in our Dams to cause them to
fill and then drop rapidly.
In this section I am referring to years 2001 to 2006.
They are documented in the "Rainfall 2001-06" button. For continuity, some of the relevant sections follow.
Summer months December to March.
The adjacent Mary River catchment also records 54% in the Summer months with Bureau of Meteorology records dating back to 1903.
Both the Summer months and non-summer months are examined in more detail in the "Rainfall deficiency" button.
External confirmation of rainfall 2001 to 2006.
The Qld Govt "Centre for climate change excellence"
advised in March 2007 that the Catchments had received 76.2% of long
term average rainfall. This confirmed my initial calculations
contained in the "Initial
Stats" button. Close observation reveals that the loss of
rainfall of 23.8% was in the "Low to Nil" impact non-summer
months April to November. They rarely provide inflow into the dams.
Population growth ( Part 1 )
( 2. ) Population growth is in two parts :
Part 2 follows later in logical order.
Population growth is obvious to all. However, in ( Part 1 ) we are looking for a sudden uplift in this growth of considerable proportions. Enough to influence six years of severe drop in the dam levels compared to a rise from zero to full in the previous 15 years. The Qld Govt web-site shows the population growth steady and predictable. It shows no sudden uplift. The web address appears on the graph. It has been recently updated but has no effect to year 2006. The population quoted is for South East Queensland. A study of this web address reveals that approximately 85% of that population is serviced by the Wivenhoe, Somerset and North Pine Dams. The Westpac economic indicator supports this section for the whole of Queensland.
Sudden Population growth in the last six years has no part in this puzzle.
The Wivenhoe Dam and its purpose
( 3. ). The Dam has multiple facets :-
These items have been expanded in the "Wivenhoe Dam" button.
Long term rainfall
This long term associated chart is compiled from Bureau of Meteorology records and shows rainfall in this Dam back to 1910. At that point there were insufficient Rainfall Stations to be reliable. You will see in the next section that the year 2004 was confirmed by SEQWater inflow charts at 10 percent of the Dam's capacity.
In addition to the long term chart, I have included a chart of falls in single months that exceeded 200mm. While the Dam manager has indicated that falls of over 300mm are required to provide a major fill, there are no such falls with the exception of 1974. Some did approach this figure in 1988,89 and 96.The graph shows three of the years already identified in the long term graph. It also shows four non-summer months in this category. Two are mentioned later as they accompanied similar rare events, but with much higher falls, in the Somerset.
You will see from the underneath chart that on a rare occasion the Wivenhoe received as much rainfall as the Somerset. It occurred in the Summer months December 2003 to March 2004 with the rain falling at the same consistent basis. The associated sheet verifies that while the Somerset catchment is one third the size of the Wivenhoe it is three times more efficient. They produced similar inflow results. This is fully dealt with in the next section and inserted here for continuity.
Minor partner to the Somerset Dam
This particular chart verifies that the Somerset receives 30 percent more rainfall than the Wivenhoe and this particularly so in the "uncommon events". From the other associated charts it can be deduced that if the dam was isolated from the Somerset dam and if no water was drawn from it nor any evaporation, the dam would be only 75 to 100 percent full after 21 years of existence. That provides around 100 to 150 megalitres a day addition to the water supply from this Dam's resources. (Capacity 1,165,240ML X 75% / 21 years/365 days = 114 ML per day or ,if 100%, 152 ML per day). SEQWater have the records to confirm these calculations. They are not publicly available and in any event, the Dam is a minor partner in contribution to our water supply.
The associated chart also shows that on only 10 occasions in the 75 years, 1910 to 1986, did rainfall exceed or approach the 10% inflow mark.
You have seen that the Dam is the minor contributor to the water supply. As we progress, you will see that it did its job as the Engineers and Hydrologists intended. It acted as a flood mitigation Dam for its own catchment and the Somerset and a Storage Dam for the retention of these flood waters and Somerset overflow.
The Dam's role is part of the puzzle. This massive dam is mainly on standby for uncommon events ( floods) via the Somerset Dam and its catchment. At present it happens to be very nearly empty with no recent uncommon events. The likelihood of further uncommon events is evaluated below and you will see that dependence on them makes for an unstable water supply.
Relationship of The Wivenhoe and Somerset Dams and the year 2004.
( 4. ) The Somerset and Wivenhoe dams are located at the Junction of the Stanley and Brisbane rivers. The Somerset sits atop of the Wivenhoe. They have separate catchments. The Somerset catchment is the Stanley River and the Brisbane River is the Wivenhoe catchment. The Somerset releases its water into the Wivenhoe which then releases into the Brisbane River. See contour map attached.
The Wivenhoe Dam catchment is 3.69 times the size of the Somerset, see the "Dam statistics" button. However, the Somerset provides, per Sq Klm, 3.01 times the flow into the dams for every millimetre of high impact rain. This was demonstrated in year 2004 by the SEQWater web-site graph when a rare occurrence of approximately the same rainfall with the same monthly pace, fell in the two dams. The Wivenhoe rising 10% and the Somerset 27%. In addition the "Dam Statistics" shows that the Somerset receives on average 30.8 per cent more rainfall than the Wivenhoe.
The Somerset is therefore still the major provider of inflow into our two dams. It has been the major provider and, for practical purposes, the only worthwhile provider for the last 47 years. The positioning of the Dam increased the retention of the Somerset water as well as its own, some of which was previously lost.
Uncommon Rainfall events
( 5. ) This important matter is discussed under the "Uncommon Events" button. I now list the final conclusion of that section.
A review of some of the matters considered by the "uncommon events" button now follow for continuity.
Long term and current statistics
SEQWater in its public pronouncements point to uncommon events required to fill the dams. Examination of the Somerset Summer rains shows two such very uncommon events. Having determined the importance of the Somerset rainfall in (1) above, the Summer rains of 1992 and 1999 approached the level of the 1974 flood. The third last and second last paragraphs of the Dam Manager's comments confirm both the 1992 and 1999 events and the single months of April 1988 (440mm) and April 1989 (564mm).
The 1992 inflow was ably supported by these two non-summer months. The months of April 1988 and April 1989 with very high Rainfall do not appear on the graph being rare non-summer months. They filled the Dams to overflow. The 1992 event was followed by a local event which again almost filled the Dams. The 1999 inflow and top-up in 2001 was described by SEQWater as a flood (Annual report 2001). It filled the dams to overflow. You will see from the accompanying graph of the last 96 years that, apart from 1974, the 1992 and 1999 Summer rains were the highest since 1927.
SEQWater nominated Rainfall recording Stations ( C/M 10/02/ 2007)
In further support of the last paragraph I have added more information. It includes a summary of the Rainfall Stations used as examples in the SEQWater press release of the 10th February 2007. The Bureau of Meteorology data, dating back to 1893 in most cases, are included for your own examination and assessment.
Probability of an "Event"
The odds of two such major rainfall events coupled with three single month high inflows in the space of 12 years are are very long in the Twentieth Century. The second half of the Nineteenth Century saw them as common occurrences. ( See "uncommon events" probability). However I am reminded that Nature takes no account of odds or time. In the month of February 1893 rainfall of 107.6 inches, about 2,690mm, was recorded at Crohamhurst in district 40 in which we reside. Three floods occurred in Brisbane on the 4th, 13th and again on the 17th of February 1893. (Mr Alan Murrell, A HISTORY OF THE BANK OF QUEENSLAND Page 54 and B.O.M. History of floods.)
If the 1999 event had not occurred, the problem I am placing before you would have been identified much sooner.
Uncommon events that fill the dams are just that - uncommon. We saw four major events occur in the years 1988 to 1999. There are just three tight groups stretching back to 1927. With this came the distortion of our view on rainfall and the, now emerging, realisation that we depend on them when they are definitely not dependable or predictable.
The Wivenhoe Dam worked perfectly as a flood mitigation dam. It took the overflow from the Somerset with little assistance from its own catchment. Only a few of us have recollections of 1992 and 1999 being standout rainfall years.
Population growth ( Part 2 )
Our water requirements
( 7. )
Our normal water requirements
This is fully discussed in the "Requirements" button. It 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.
You will see that these calculations are within tolerance of the annual totals of the depleted Dams together with rainfall in both "low" and "high" yield years.
The final calculation is that our requirements as described is 366,044ML per year which calculates to 1,003ML per day.
2. Interim measures taken
( 8. ) Shortfall ( if any) in providing for Requirements and comparison to action taken.
Calculation of shortfall of our normal requirements without water restrictions
This calculation is relatively straight forward.
The Capacity of the Wivenhoe and Somerset are known and over a period of 6 years with 365 days per year the shortfall is 480ML per day.
After adjustments for water restrictions in 2006 and minor rainfall adjustments, the "business as usual" requirement from these two Dams is short by 522ML per day.
Rainfall provided 481ML per day to make up the overall requirement of 1003ML per day. This is calculated in "Requirements" button.
The title of these projects is listed on the Water Commission's web-site as " Water Supply Emergency Projects" together with the date of the updated assessment.
As a starting point I have attached my assessment of new water as at April 2007. It shows a new water total of 372ML per day.
Shortfall ( if any) to achieve normal status
The above requirements show a shortfall of 522ML per day. The water grid at present summarises as 372ML per day. The balance to be met is 150ML per day. It excludes the Traveston Dam.
With the Wyaralong Dam and other relatively minor projects, it appears that the Grid System will provide a stable water supply when coupled with normal and average Summer rainfall without uncommon events. It will not cater for increasing population which is the subject of the next section including the proposed Traveston Dam.
Final assessment of "what happened in our dams" and "interim measures".
( 9. ) The totality of these observations condenses to answer the puzzle of why our dam levels rose from zero in 1986 to full in 1989/1992/1999/2000/2001 and dropped like a stone for the last 6 years with year 2004 being the exception.
The events of 1988/1989/1992/1999/2000/2001 in the Wivenhoe/Somerset combined to put from view the increasing needs of our growing population. The years 2001 to 2006 saw close to average Summer rainfall. What we see in the Dams is absence of these rare uncommon rainfall events and the emergence of the real requirements of our population measured against average rainfall. Our planners were aware that they could not rely on uncommon events and had the Wolfdene Dam well in hand. The cancellation of that Dam at an advanced stage has created the Legislated Emergency measures of the water grid, now in train, scrambling to make up the shortfall. It has caused widespread pain and considerable expense to the Population and this is especially so in the Mary Valley. It is ongoing.
The Dam depletion was and is presented as the "worst drought in 100 years" when the rainfall of the high inflow Summer months was almost average. Climate Change is occasionally thrown in for good measure. It was neither. The evidence points to the central kernel of today's problem being lack of understanding of uncommon events.
The Wolfdene Dam cancellation was the first major causality and it is now laid out for you to make a judgement. It left our recent past Premier and the current Premier scrambling with second class options such as recycled effluent and costly desalination. He had little room to move and advisors with the 'worst drought' contention deeply entrenched. We will see in Phase 3 that lack of understanding is about to force a similar situation.
The forward planning of the South East Queensland Regional Water Supply and copious other reports, particularly of the Mary valley Traveston Dam proposal, are based on a supply allocation from these Dams which includes "uncommon events". From their qualification of their assessments they believe that the current situation is a "drought". It is not. It is the absence of uncommon events and an annually occurs when "uncommon events" do not appear. They are 15 to 30 years apart and this will severely distort forward projections.
Those who still prefer to use the term "worst drought in 100 years" may find the "worst drought" button useful. It is much more serious than that. A drought eventually breaks but the underlying problem is not a drought and will take some years to fix.
3. Long term solution
Having arrived at this point it was inescapable that further supplies of water were needed. The Traveston Dam was the remaining item in the Emergency Legislation.
It was therefore necessary to examine the Mary Valley where the Traveston Crossing Dam was to be located. To this end I extracted all the rainfall data of all the Rainfall Stations in the Catchment area. These are Bureau of Meteorology records.
First of all these records showed that the Summer rainfall of December to March received over 50 percent of the total rainfall. Exactly the same as the Somerset and Wivenhoe catchments.
Second, and most importantly, the rainfall had almost the same rainfall pattern of timing and intensity as the Somerset and Wivenhoe catchments. The Mary Valley has slightly higher rainfall in uncommon events. This is not surprising when one considers that they are adjacent catchments.
This meant that inevitably the Mary Valley would operate in exactly the same way as the Somerset/Wivenhoe System with the same result that we are currently witnessing.
The "Save the Mary Valley" people have voiced strong opposition to the Dam pointing out among other things evaporation and seepage difficulties.
In spite of these objections, our Leaders apparently felt that they no alternative but to proceed. I too was of the same opinion until I read Mr Ron McMah's submission to the Senate Enquiry.
His proposal is listed in this web site. In essence he proposes that the Borumba Dam be expanded to 2,000,000ML. The water of the Mary Valley and the surplus water of the Wivenhoe/Somerset System be pumped to and from this Dam as required. In a public meeting in the Mary Valley, he was given an "Iron clad guarantee" by the then Deputy Premier Hon Ms A. Bligh that this would be adopted if it stood up.
I recognized that this was the opportunity to harness the surplus water of the uncommon events of the Wivenhoe/Somerset system without any further requirement of the Mary Valley. I contacted Mr McMah and traversed the area with him while he again outlined his proposal. The Dam was 12 kilometres from Jimna and from there it was gravity feed into the Wivenhoe/Somerset System.
The feasibility is now explored.
Traveston Crossing Dam
North Pine Dam
The combination of the Surpluses in the Wivenhoe/Somerset system plus the Borumba surpluses match the Traveston proposal
The yield to match all three stages of the Traveston Dam is 150,000ML annually. It does not match this figure and The Harnessing of the uncommon events in the Wivenhoe/Somerset follow after further examination of the Borumba Dam. Hydrology by the Department of Natural Resources and Water in December 2005 indicated that this volume was in excess of 80,000ML on an annualised basis. The total of the Borumba and the Wivenhoe/Somerset contributions exceed the the whole of the Traveston three stages.
The storage implications of the "Grid" system
The Government has done well with the grid system. It will mostly take the place of the absence of "uncommon events". In combination with average Summer rain our needs are taken care of. However, after the first uncommon event " refills the Dams, there is no storage space for those that follows. The draw down will be minimal with the operation of the Grid and Summer Rains. The use of the Borumba as a storage dam will add an additional 125,000ML on an annualised basis. The Traveston will lock up the Borumba Dam to a yield of 40,000ML and that yield is part of the total of 150,000ML from the Traveston proposal.
Hydrology of the Mary Valley in flood
The Borumba Dam
Calculations and Calculation/Base
These were my early calculations to assess the feasibility of my proposal. Since then official statistics and Engineers reports show that the 80,000ML retrieved from the Wivenhoe/Somerset and returned in lean times has been confirmed.
The Borumba Calculations are based on official information of surpluses over the dam wall for the entire period of the Dam's operations.
These calculations remain in the website as they provide interesting supporting information that gives the reader a wider grounding.
In this section we extract uncommon events from normal average rainfall. We then proceed to examine the current population requirement against normal rainfall and the uncommon events that occurred, and when they occurred, in the last 108 years. This is done on the basis that all three Dams were operational for the whole of the period and the current population was in place all of that time. The requirement of the proposed Traveston Dam was also taken into account for the whole period.
The previous 60 years at the end of the Nineteenth Century requires no calculations as it was pitted with major events.
The use of the expanded Borumba Dam had to survive the first 70 years of the Twentieth Century to be considered. This period was quite short on major events. It passed it easily with the full Dams in 1898 and also passed with the Dams at 14 percent in 1898, being a little lower than current levels.
There is no guarantee that the Traveston proposal would have survived this period.
Finally there is a flow schedule that covers from 2007 onwards over the period of all stages of the Traveston Dam.
The "Calculations/Base" button contains the method of preparation of the water flow schedules. It also contains copious supporting data that ensures a reasonably accurate estimate of timing and volume of the uncommon events. It also covers all aspects of items that make up the calculation.
Examination of the GHD engineering desk top report on "The augmentation of the Wivenhoe Dam" confirmed by DNR & W hydrology, the surplus water available from events that usually go over the spillways was 80,000ML on an annualised basis. It cross checks all the previous information.
The same report permits me to draw on extended time for the transfer of water.
Both matters are fully dealt with in my "EIS alternative proposal to the Traveston Crossing Dam" lodged in December 2007.
The Solution is contained from page 9 onwards in the Final solution and EIS tab.
All of the previous information points to the fact that the expanded Borumba Dam to 2,000,000ML is the superior decision. It will supply the needs of the people of South East Queensland for many decades and most probably beyond.
The most fatal flaw in the decision making process was the lack of understanding of uncommon events. It is almost entirely responsible for the situation in which we now find ourselves. In retrospect it has created errors of judgement that are most difficult to rectify. As an example I have added a "Wolfdene dam" button for further observation.
I find it difficult to understand how in a few minutes with two clicks on a computer a statistical aberration can be exposed and not examined. See " Initial research" and "Initial statistics" buttons. Even today, our leaders include the drought in all their pronouncements. They were followed by our opinion leaders of Business and those responsible for our Social structure. Some are now of a different view.
The "Climate change centre for excellence" is said to be made up of many scientists. Its report of March 2007 was headed " The south east Queensland drought to 2007" while dealing with our catchment rainfall. My understanding of men of science is that that they push back the boundaries of mankind by Search and Research always with an open mind. The heading itself is puzzling. It seems to indicate that they have started with the answer rather than " In the context of rainfall, what happened in the catchments to raise our Dams from scratch to overflow in 15 short years and then drop 80% in the last six". They then proceeded to compare the last 6 years with the "Federation drought".
I have added a "Federation Drought" button for those readers who wish to draw their own conclusion. The Bureau of Meteorology actual monthly rainfall for both periods are present and it clears up any misconceptions. The comparison has been useful in determining that a severe drought in the Catchments did not exist in the years 2001-2006.
Climate change and Rainfall patterns
The then Deputy Premier had this to say in her joint
press release of the 28th January 2007.
The matters about to be raised are the collective Rainfall for both Summer and non-Summer rainfall. The deficiency shown in the graphs for years 2001 to 2006 relate to the non-summer months. Bear in mind that the deficiency only exists in the non productive non summer months.
The expected overall rainfall average in the Wivenhoe is listed in SEQWater "Dam statistics" as 940mm. The long term average of the Bureau of Meteorology rainfall stations which is measured against their entire life is collectively 842mm. The average of the 30 years 1961 to 1990 against which the Bureau measures averages was 872mm. That 30 years included the 1974 flood and a look back into the previous 70 years shows little uncommon event activity in comparison. This places the Wivenhoe permanently in "below average" category. For confirmation see "Initial Statistics" button.
This places the expected rainfall permanently in the "below average" category. I have sought confirmation of these figures from SEQWater but my correspondence has not been answered. It is not surprising as they are busy people who must deal with a myriad of opinion leaders.
Having all the past records for over 100 years, we are in an ideal position to judge any effect of climate change. The "Climate Change" button is added to collect various matters of interest. I believe that an assessment by yourself will leave you in no doubt as to the position based on "hard data". Climate Change is leaving the ephemeral regions and moving into the area of "hard data" for clinical observation.
The most interesting observation in the climate change area is the extremely high uncommon events of the last 60 years of the Nineteenth Century followed by the first 70 years of the Twentieth century with very little uncommon event activity. It resumed in 1974.
It is obviously Nature at work. It cares little for the passage of time.
In view of the foregoing I realised that initially I held a different view to 2.8 million people. There are now many thoughtful people who realise that matters are not what they seem to be at the Dams. This gives me added responsibility to be accurate with any information in my possession and fair in its presentation. In this regard I appreciate the assistance of a few close friends whose opinions I value. They provided constructive criticism.
I am not a member of any political party nor am I associated with any members of those parties. I have not been engaged by anyone to produce this report. The use of the "drought" in the catchments has been consistently applied by all sections of the Community over a long period. I felt an obligation to present this view and chose this web-site because of the base complexity of the problem. It requires time and thought and cannot be conveyed by a few minutes face to face or a quick e-mail. My only conflict of interest is that I hold a modest number of Nylex Limited shares who, among other things, manufacture water tanks.
I am an optimist. I avoid the bearers of doom and gloom. Once the facts of a problem are known, someone puts his or her hand up and, with the full support of the people, rectifies the situation. Mr McMah has one of his hands up and I believe that this information may raise his other hand. Once he is understood, it is my estimation that our current Leader has the capacity to follow it through. It is a question as to whether she has the will or will take the current options.
END OF SUMMARY
SURROUNDING MATTERS, NOT PREVIOUSLY FULLY DISCUSSED, THAT COMBINED TO DECEIVE THE PEOPLE OF SOUTH EAST QUEENSLAND
The first aberration was observed by me last August 2006 while examining the rainfall maps on the Bureau of Meteorology web-site. The Decile map was recording "lowest on record" and the percentage map for the same three year period and same rainfall was showing 80%. A Bureau of Meteorology Climatologist confirmed by e-mail that close to 80% of the long term average rainfall had occurred in the catchment and it was the lowest on record. I retrieved all the records from recording stations within the catchments and confirmed this percentage for the last 6 years to 2006. It also gave me the same data that, all who comment on the dam, are reading.
The records go back to the 1880's. A sample of these records is attached. They are available to the general public. A more detailed account of how to identify the recording Stations in the Dam catchments and retrieve these records is provided in the "Find BOM Info" button. The data is in the form of Excel spreadsheet and makes it convenient to analyse data from all angles.
The "close to 80 per cent" was confirmed by the newly created Qld Government "Climate Change Centre for excellence" at 76.2 per cent for the last 6 years. This does not fit the Bureau of Meteorology definition of a drought being "acute shortage of water" in the context of rainfall. The Centre's report is discussed under the "Federation drought" button
This aberration was brought about by the stability of District 40 in which the catchments reside.( BOM information twice sought). The "Climate change" button also provides further evidence of stability over long periods.
The second aberration is related to Summer and Non-Summer months. The Dam Managers have publicly drawn our attention to this occurrence. Later you will see that in both the Wivenhoe and Somerset Dams, the Summer 4 months December to March receive 50% or more of the annual rainfall. The remaining 8 months, April to November, receive the balance. These non-summer months, being spread over 8 months, are "low to nil" impact and have difficulty in making the creeks flow. This is particularly so in the Wivenhoe. More on this aspect in "Summer V Non Sum" button.
Understanding the much produced decile map
As explained, a decile map grades the rainfall in units from 1 to 10 with 1 the lowest. The rainfall may not be the lowest but it is in that category. Having the Bureau of Meteorology source data of every Rainfall Station in the dams from as far back past the 1893 flood, leaves me in an ideal position to examine, among other things, the decile compilation from 1899 to 2006. The physical numbers and the graph are attached. They relate to Wivenhoe Dam. It is similar story in the Somerset Dam.
You will observe that the 6 years to 2006 were the lowest on record but in very good company with the lowest 7 sections of 6 years. Apart from the section including the 1974 flood, all 6 year sections confirm the Bureau of Meteorology observation that District 40 in which the catchment reside is a stable rainfall area.
SUPPORTING EVIDENCE NOT PREVIOUSLY DEALT WITH
The Bureau of Meteorology compares rainfall against the average of 30 years 1961 to 1990. You will see in the "Initial Stats" button that I have used Rainfall Stations that have been in operation before 1961 and still in continuous operation. I have also examined the rainfall Stations not used for any statistical aberrations. This ensures that I am comparing like with like.
Having then produced the information, a review of the Stations total results over the period from 1961 to 2006 showed that all the rainfall stations in the Dams achieved the same results within reasonable limits. There was one exception, Mt Mee, which I will discuss later.
The 6 year comparison starts at 1964 in order to compare 6 year totals as 6 does not divide into 46 years
My overall comparison of Summer months( "Summer V Non Sum" button) rainfall of the 4 months December to March compared to the remaining 8 non Summer months showed the same result as the period 1964 to 2006. This overall comparison reached back into the 1880's. The 50 percent split has been maintained throughout the last 100 years.
Mt Mee Rainfall Station requires some consideration. The Somerset dam analysis shows the total rainfall from this Station to be a little over 50 percent more rainfall than the other four stations in the Dam selected. I confirmed with the Bureau of Meteorology Hydrology Department that this Station was located on the border of the Somerset and North Pine Dams and was precisely on top of the range which divides the two Dams. The Hydrology Department further added that because the North Pine Dam was on the Eastern side and the Somerset on the Western side, the rainfall indicated by the Station would be significantly downgraded in the Somerset dam.
Comparisons of rainfall back to 1909 at the commencement of the Mt Mee Stations would remain intact however comparisons between Somerset and Wivenhoe are slightly affected and adjusted where necessary. The adjustment adopted is to return the Station to the level of the other four stations used. It also had a minor effect in the micro situation of the last 6 years and has been shown adjusted and not adjusted.
SEQWater public announcement Courier Mail 10th February 2007.
The operations manager for the Dams has been most helpful with his public announcements and is to be commended. Of special importance was the article appearing in the Courier Mail 10th February 2007. The official dam level graph was provided but not published. I have added relevant data for ease of viewing.
He made several important points enabling us to gauge the situation in the Dams : -
Point 1. Having retrieved all the data from rainfall stations in the dams, I was in an excellent position to review this statement. The data goes back to past 1893 in some cases. The Summer months December to March received 50% or more of the annual rainfall and the balance received by the 8 non-summer months. It was the case in both the Somerset and Wivenhoe Dams. ("Summer V Non Sum) button.
Point 2. There are four main rainfall events in the last 15-16 years when viewing my Summer rains in graph form. I have a slight disagreement with the exclusion of year 2004. To the graph we add the high rainfall non-summer months of April 1988 and April 1989 which then make up the four events. A partial event in May 1996 also assisted and in my view is the fifth event.
Point 3. Again the rainfall chart of the Summer months shows that the dams received High inflows in the 1992 and 1999 years that rivalled the 1974 flood. As they were largely full in the first place, a considerable amount of water went over the spillway into Moreton Bay. The official graph above, shows water over the spillway in 1989/2000 and after the topup in February 2001.
Point 4. Having nominated specific rainfall stations, I have enclosed a summary of these Stations and the actual data for the lives of the Stations so that you can examine the frequency of these rainfalls. It also confirmed that the rainfall statistics used are the Bureau of Meteorology data. I am reading the same data. " Initial Statistics button.
Point 5. Recently I received an official chart of the dam levels in the Wivenhoe Dam. It was provided by the same Lady who wrote the article we are reviewing. It was provided to the Courier Mail and not published. Viewing of the chart hardly requires comment as to what happened in our dam system. It is obvious to all.
Point 6. This largely confirms this exercise. The rainfall chart of the Summer months particularly in the Somerset show they are around 25 years apart and we received two in 8 years 1992 to 1999 accompanied by two lesser events. If you follow the law of averages then it will tell you that it will another 20 years from 1999 before another such event occurs.
END OF WEB-SITE. Thank you for you patience.