Brisbane River 66%
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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This section deals with calculations of the flow requirements at the mouth on the Brisbane River. Since then I have had a meeting with five senior directors of the Department of Environment and Natural resources and the Queensland Water Commission. 

Subsequent to the meeting they provided me with the following :

* Mean annual flow from all tributaries of the Brisbane River at its mouth was 1,641.331ML/a.
* The contribution to this flow of the Wivehoe/Somerset was 58.2%
* Graph of the pre-development flows of the Wivenhoe/Somerset.

 

 

 * The 66% requirement at the Brisbane River mouth and how it applies to the Wivenhoe/Somerset system

Followed by -

 * An examination of matters that have the ability to affect that calculation

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 * The 66% requirement at the Brisbane River mouth and how it applies to the Wivenhoe/Somerset system

The Water Resource (Moreton) 2007 plan was enacted by Parliament in March 2007. It contained various flow percentages that must be maintained. 

Its most important determination is that 66% of all water that flows into the Brisbane River must reach its mouth. It is calculated without the obstructions created by human intervention such as dams and weirs.

Not all the water of the Brisbane River flows through the Wivenhoe/Somerset dams. We will examine all water that does not feed through these dams to see if there is possible variation from this 66% requirement. We will find that there is little to no effect.

They have divided all the catchments of the Moreton Sub catchments.jpg (123240 bytes) region in sub-catchments. One can see from the plan that the sub-catchments that we are interested in are numbers 1 to 7. Those numbered 8 to 11 do not flow into the Brisbane River.


It is clear from the diagrams in the Water Resource (Moreton) Plan 2007 that the following sub-catchments feed directly into the Wivenhoe/Somerset system and are incorporated in the 66% requirement for the Brisbane River mouth.

Sub-catchment 1. Upper Brisbane River
Sub-catchment 2. Cressbrook Creek
Sub-catchment 3. Stanley River
Sub-catchment 4. Central Brisbane River

The following sub-catchments have their own separate requirements to the point that they enter the Brisbane River.

Sub-catchment 6. Lockyer Creek - 68%  NODE F
Sub-catchment 7. Bremer River    - 81%  NODE G  

WRPM Sub catch Names.jpg (91580 bytes)WRPM Node names.jpg (70389 bytes)WRPM Node percentages.jpg (95954 bytes)

 

 

 

 

The colour coding is mine for ease of recognition.

Possible influences that may affect of the 66% requirement on all water that passes through the Wivenhoe/Somerset system 

Sub-catchment 6 will have no effect as its requirement is similar.

Sub-catchment 7, Bremer River, may have some small effect being 15% higher than the 66%. Its catchment area, using Bureau of Meteorology information, is 15% of the total Brisbane River catchment area. This method produces a small possible variation of 1 per cent and therefore has no real effect on the 66% requirement.

 

The lower part of sub-catchment 4 and all of sub-catchment 5 do not feed into the Wivenhoe/Somerset system. They have no main tributaries and some reservoirs, and as such, the flows into the Brisbane River are unlikely to cause little, if any, variation from the 66% requirement

It is an inescapable conclusion  is that 66% of all the water flowing through the Wivenhoe/Somerset dams has to reach the River mouth and the balance of 34% is for use by SEQ residents and guests.  

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For the technically minded, the 66 percent requirement is of the "mean annual flow".

The method

We will see that currently this method would place us in a Definitions mean annual flow.jpg (110089 bytes) more serious situation with virtually all of the water in the Wivenhoe/Somerset dams destined for the Brisbane River.

Photo : Definitions including "mean annual flow"

The method is that the flow at each "node" is determined by the total flow volume of the period from 1889 to 2000 and divided by the number of years. We have seen above that there is three "nodes" in the Brisbane River System.

The requirement is 66% of that flow in the case of the Wivenhoe/Somerset dams. The dam catchments are incorporated in "node E" being the Brisbane River at its mouth.

How much water is  required on an annual basis?

In order to have some concept of how much water is involved in the Wivenhoe/Somerset system, the following calculation sheds some light.

The yield from the dams has been set at 360,000ML by the Queensland Water Commission. That represents our 34 per cent.

To manage both the 34% to us and 66% to the River, 100% is required or 1,059,853ML each year. (360,000ML / 34 X 100 = 1,059,853).

NOTE : Subsequent to these calculations, the Department of Environment and Natural Resources provided me with figures produced by their IQQM computer model. Their calulation of all pre-development flows at the mouth of the Brisbane River averaged for the 111 years 1898 to 2000 was 1,641,331ML with the Wivehoe/Somerset providing 58.2% or 955,254ML on an annual basis 

By way of comparison, the Wivenhoe dam has a capacity of 1,165,000ML

It takes summer rain about 7 years, without any water use, to provide the flow required in 1 year . 

The importance of "uncommon events" to our water supply

This highlights the importance of "uncommon events" which are our main water supply. They can fill the dams from scratch in a few days but are random. However the storage facilities to cover their random nature are totally inadequate. 

They occurred every 3.7 years on average over the past 169 years
Uncommon events.jpg (133366 bytes)

 

 

 

Photo : Large rainfall events of the last 169 years

The Borumba Dam expanded to 2,000,000ML would more than double the storage capacity of the Wivenhoe/Somerset system. The current storage system is not matched to the manner in which the rain falls.

In a much smaller way, most farmers would tell you that the capacity of their rainwater tanks and dams have to match the rainfall when it happens and be sufficient to carry them through all seasons.

This method would cater comfortably for us and the environmental requirements during long periods of their absence. Their absence is generally misunderstood as a "drought" when viewing depleted dams even though the surrounding districts may have been green for some years.

* An examination of matters that have the ability to affect that calculation

Computer modelling

The Water Resource (Moreton) Plan 2007 relies on heavily computer modelling. In fact computer models and their out-put are written into the Act. A sample of such a model appears on page 36 of "Water for South East Queensland - a long term solution" and was drawn up by the Department of Natural Resources Mines and Water. The model covered the Wivenhoe and Somerset dam catchments.

Examination of the model reveals a great deal of what happened in inflow to our dams during the recent period February 2001 to May 2006.

In addition we have available the actual dam levels from January 1990 to 2006 compiled by SEQWater the dam managers. 

The Acting Principal Executive Director of the QWC has been good enough to provide the basis of the graph. "The HYNF 2001 to 2006.jpg (48255 bytes) graph assumes that the full HYNF has been extracted in this period (February 2001 to May 2006) when, in practice, lesser extractions have been made from the dams. One would therefore expect the actual recorded dam levels to be appreciably higher than those indicated in the graph"
Photo: Draw-down from dams plus inflow both theoretical HYNF and actual

His comments are very much appreciated. It provides us with the ability to calculate the inflow into the dams for the period February 2001 to May 2006. The arithmetic of his observation follows the published graphs.

The variation of actual to HYNF theoretical results appear below. Of particular interest is the decline in the model from being full in February 2001 to 10% of capacity in May 2006.

The actual dam  levels at May 2006 were 30% in the Wivenhoe and 33% in the Somerset. The computer model showed a joint 10% at that date using the theoretical HYNF calculation. 

It will be recalled that it was not until late 2005 that Releases from dam.jpg (61075 bytes) "drought" was mentioned with a full scale media blitz in 2006. For most of the period here was no deliberate attempt to reduce consumption.

Photo : SEQWater dam releases showing the timing of the marked reduction

Photos: 1. Government graph of dam levels 1890-2006 using the HYNF as outlined by the QWC.
             2. Actual dam levels
             3. Variation calculations

HYNF No1.jpg (71083 bytes)HYNF No 2.jpg (48221 bytes)HYNF No 3.jpg (49929 bytes)

 

 

 

 

Calculation of inflow during the period February 2001 to May 2006 using the QWC graph information

* Period from February to May 2006 = 5.25 years
* Yield in QWC literature = 360,000ML annually
* Water withdrawn from the graph theoretically = 360,000ML X 5.25 years = 1,890,000ML
* Dam level drop = 100% in February 2001 to 10.0% at May 2006 = 90.0% drop.
* Total capacity of Wivenhoe/Somerset = 1,541,000ML
* 90.0% of that capacity = 1,386,900.ML reduction.
* The volume of rainfall required to agree the 360,000ML annually = 1,890,000ML - 1,386,900ML = 503,100ML
* Inflow from rainfall required in 5.25 years = 503,100ML.
* Annual inflow required = 503,100 divided by 5.25 years = 95,828ML each year.

Summer rainfall in the catchments have been quite normal Percent_Som_with_40145.jpg (278710 bytes)Percent_Wivenhoe.jpg (254083 bytes)in the 5.25 year period with 99.7% in the Wivenhoe and 91.3% in the Somerset.

Photos: Wivenhoe and Somerset catchment rainfall for both Summer and non-summer months

With normal Summer rainfall providing 95,828ML annually and the dam yield required is 360,000ML it is evidence that large scale rain depressions are our main water supply.

This highlights the inability of Summer Rainfall to service SEQ needs. It supports the Wivenhoe dam level graph that shows that this inability was evident as far back as 1992. 

It is further concrete evidence that large scale rain depressions are our main water supply. It is the control and management of them that is required for the benefit of the ecology and us.

Government sources went to great lengths to convince us that here was a "drought" in the catchments and it certainly appeared that way. For a while, that included me. The evidence points to the random nature of our main water supply designated by SEQWater as "Uncommon events". 

My view is that if one does not correctly identify the problem, one may be well significantly astray in the solution.

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Author of the ecology model

Sandra O. Brizga is the author of the model. She does not answer questions direct from me and that is understandable. I have requested a copy of her model from the QWC. It is held by another Department and at the present, it is not forthcoming. Her address to the 5th Australian Stream Conference, available on the internet, is enlightening.

New model :

It appears that the tried and tested models were unsuitable for the Moreton region. 

A new methodology specifically tailored to the needs of the WRP processes - the Benchmarking Methodology- was developed.

There is nothing wrong with developing a new model. However we should be cautious. There are no 30 dayWolfdene_dam_drips.jpg (272794 bytes) money back guarantees with such models. What we do know is that it took 15 years for the acknowledged error of the cancellation of the Wolfdene dam to become obvious to all.
Photo: Decision makers in cancellation of Wolfdene Dam

With a wide variation of rainfall over a long period of time and a preponderance of "uncommon events", it is reasonable to assume that it will be decades before full judgment can be made from proven records on the hydrological decisions made. We will see that those hydrological decisions are required of politicians by the implicit design of her model.

It is worthy of note that the legislation to monitor and implement this regime the "Resource Operations Plan Moreton", will be at least three years late in the making. The draft has been in the public arena since January 2009.

The Water Resource (Moreton) Plan incorporated this regime in an Act of Parliament on the 17th March 2007.

Reliance on computer model calculating flows :

The Water Resource (Moreton) Plan utilises studies using daily time-step modelling (results of daily rainfall inputs to the model) covering a period of 111 years 1890 to 2000. They quantify flow regimes at network nodes throughout each basin.

What that means is they measure the flow through the tributaries of, and the Brisbane River itself, as outlined above in the first section.

Old hydrological method to calculate the annual flow requirements.

Mean annual flow

We will see that currently this method would place us in a Definitions mean annual flow.jpg (110089 bytes) more serious situation with virtually all of the water in the Wivenhoe/Somerset dams destined for the Brisbane River.

Photo : Definitions including "mean annual flow"

The method is that the flow at each "node" is determined by the total flow volume of the period from 1889 to 2000 and divided by the number of years. We have seen above that there is three "nodes" in the Brisbane River System.

The requirement is 66% of that flow in the case of the Wivenhoe/Somerset dams. The dam catchments are incorporated in "node E" being the Brisbane River at its mouth.

The establishment of that volume of water has little to do with the conditions of the time.

We have seen the departure by the QWC from the tried and tested HYNF method when establishing a yield of a dam to the "stochastic" approach that the cynics in Wikipedia describe as "best guess under the circumstances". In my view, they have yet to come to grips with the root cause and are dealing with the "consequences" of a "drought".

Perhaps the QWC should consider a departure from the method of calculation of the 66% when reviewing the following observations.

The "mean annual flow" method encompasses 3 very major events in 1890, 1893 and 1974. The 1890 event is only slightly lower that the 1974 event which a lot of us remember. The 1893 event is special. The Cromhurst Laboratory at the headwaters recorded 107 inches of rain in 22 days. That converts to approximately 2,655mm or 2.6 metres of rain. 

One rainfall station in the Stanley river catchment recorded 416mm in 1974 and 1,422 in 1893. This would indicate that the flow would be approximately 4 times greater that 1974. 

Anyone dealing with numbers would realise that the inclusion of these events in the calculation of the 66% makes it extraordinary difficult to maintain the 66% in normal times. However, it is the Law.

I have requested the mean annual flows recorded by their computer model for each year back to 1890 which may prove the point depending on the reliability of the computer model. (September 2009).

Government is the decision maker

Ms Brizga does not make the decision on the Brisbane River flows being the 66%. 

She presents to the Government a range of alternative water resource management scenarios which include imbedded assumptions regarding flow environment provisions

She had this to say on the Government as a decision maker:

"Environmental flows may restrict the availability for consumptive users. The Government ultimately makes decisions regarding water resource allocation, and the role of science is to provide the best available information to inform these decisions"

In other words, the Government decides how much water is for us and how much for the River.  

Public knowledge of the decision requiring 66% of flows to reach the Brisbane River mouth

The Draft Water Resource (Moreton) plan had been on public view for some time before becoming Law. With the description of the Brisbane River being "Node E" on page 64 and the 66% requirement of "Node E" being on page 72, it is little wonder that a straw poll tells me that very few, if any, people in South East Queensland realised that we are limited to 34% of the flow through the Wivenhoe/Somerset dams.