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.
*********
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 
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).
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
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
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 
"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
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 
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.
**********
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 day
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 100 years back to 1890. 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 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.
